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The inner structure of haloes in Cold+Warm dark matter models
Abstract
We analyze the properties of dark matter halos in the cold-plus-warm dark
matter cosmologies (CWDM). We study their dependence on the fraction and
velocity dispersion of the warm particle, keeping the free-streaming scale
fixed. To this end we consider three models with the same free-streaming: (1) a
mixture of 90% of CDM and 10% of WDM with the mass 1 keV; (2) a mixture of 50%
of CDM and 50% of WDM with the mass 5 keV; and (3) pure WDM with the mass 10
keV. "Warm" particles have rescaled Fermi-Dirac spectrum of primordial
velocities (as non-resonantly produced sterile neutrinos would have). We
compare the properties of halos among these models and with a LCDM with the
same cosmological parameters. We demonstrate, that although these models have
the same free-streaming length and the suppression of matter spectra are
similar at scales probed by the Lyman-alpha forest comoving wave-numbers k<3-5
h/Mpc), the resulting properties of halos with masses below 1e11 Msun are
different due to the different behaviour of matter power spectra at smaller
scales. In particular, we find that while the number of galaxies remains the
same as in LCDM case, their density profiles become much less concentrated, and
hence in better agreement with current observational constraints. Our results
imply that a single parameter (e.g. free streaming length) description of these
models is not enough to fully capture their effects on the structure formation
process.
... A common approximation used to implement the effects of thermal velocities in N-body simulations consists of adding the physical thermal velocities to the peculiar velocities of the simulation particles in the N-body initial conditions (ICs) [38,[45][46][47][48][49][50][51][52]. The subsequent evolution of structure will then follow both sources of the velocity field 2 . ...
... 2LPTic can generate the ICs for thermal WDM models, taking as input the thermal WDM mass m WDM and computing the corresponding T (k) from eq. (2.3). The code also contains a module for adding thermal velocities, following the approximation used in [38,[45][46][47][48][49][50][51][52]. The thermal velocities for simulation particles are randomly picked such that their magnitudes obey a Fermi-Dirac distribution with a dispersion given by eq. ...
... As studied in [49][50][51], imprinting primordial thermal velocities on the particles ensures a "phase-packing" limit, which prevents the density in the central region of the haloes from increasing arbitrarily, producing a central core. However, for values of WDM candidate masses compatible with the upper limits from Ly-α [36,37], the cores are only a few parsecs in size and not astrophysically relevant [50,51]. ...
We investigate the role of thermal velocities in N-body simulations of structure formation in warm dark matter models. Starting from the commonly used approach of adding thermal velocities, randomly selected from a Fermi-Dirac distribution, to the gravitationally-induced (peculiar) velocities of the simulation particles, we compare the matter and velocity power spectra measured from CDM and WDM simulations with and without thermal velocities. This prescription for adding thermal velocities results in deviations in the velocity field in the initial conditions away from the linear theory predictions, which affects the evolution of structure at later times. We show that this is entirely due to numerical noise. For a warm candidate with mass $3.3$ keV, the matter and velocity power spectra measured from simulations with thermal velocities starting at $z=199$ deviate from the linear prediction at $k \gtrsim10$ $h/$Mpc, with an enhancement of the matter power spectrum $\sim \mathcal{O}(10)$ and of the velocity power spectrum $\sim \mathcal{O}(10^2)$ at wavenumbers $k \sim 64$ $h/$Mpc with respect to the case without thermal velocities. At late times, these effects tend to be less pronounced. Indeed, at $z=0$ the deviations do not exceed $6\%$ (in the velocity spectrum) and $1\%$ (in the matter spectrum) for scales $10 <k< 64$ $h/$Mpc. Increasing the resolution of the N-body simulations shifts these deviations to higher wavenumbers. The noise introduces more spurious structures in WDM simulations with thermal velocities and modifies the radial density profiles of dark matter haloes. We find that spurious haloes start to appear in simulations which include thermal velocities at a mass that is $\sim$3 times larger than in simulations without thermal velocities.
... For WDM, this is not true: its maximal phase-space density f max is finite at early times and does not increase during halo formation [17]. Usually, density distri-butions with finite f max are derived either from analytical studies of self-gravitating Fermi-Dirac dark matter (see, e.g., [18][19][20][21][22][23][24][25][26][27]) or from N -body simulations imitating initial dark matter velocities (see, e.g., [28][29][30][31][32]). ...
... Fig. 1 shows that tNFW profiles match the corresponding WDM distributions at the 30% level. Also, we do not observe any systematic disagreement between the tNFW profile and other WDM profiles from N -body simulations [28,29,31]. ...
In this paper, we formulate a new model of density distribution for halos made of warm dark matter (WDM) particles. The model is described by a single microphysics parameter - the mass (or, equivalently, the maximal value of the initial phase-space density distribution) of dark matter particles. Given the WDM particle mass and the parameters of a dark matter density profile at the halo periphery, this model predicts the inner density profile. In case of initial Fermi-Dirac distribution, we successfully reproduce cored dark matter profiles from N-body simulations. Also, we calculate the core radii of warm dark matter halos of dwarf spheroidal galaxies for particle masses $m_\text{FD}=$100, 200, 300 and 400 eV.
... One extension of WDM is to assume that DM comes in two components, a cold one and a warm one, which can be produced via two co-existing mechanisms. These models are called mixed dark matter (MDM) (Maccio et al. 2013;Diamanti et al. 2017;Parimbelli et al. 2021). In this paper, we decided to investigate the case that dark matter consists of only one component, but its behavior depends on k-scale such that in small k it behaves like cold DM, and in large k it shows the properties of warm DM. ...
With the emersion of precise cosmology and the emergence of cosmic tensions, we are faced with the question of whether the simple model of cold dark matter needs to be extended and whether doing so can alleviate the tensions and improve our understanding of the properties of dark matter. In this study, we investigate one of the generalized models of dark matter so that the behavior of this dark matter changes according to the scale of $k$. In large scales (small $k$'s), the dark matter is cold, while it becomes warm for small scales (large $k$'s). This behavior is modeled phenomenologically for two different scenarios. We show that the $S_8$ tension can be alleviated, but the $H_0$ tension becomes milder while not too much.
... Recently there have been significant developments in theoretical and observational studies of low-mass galaxies, which are promising targets to test the nature of dark matter [10,27,70,[100][101][102][103][104]. Here we follow Ref. [27] and use the reported minimum halo mass to perform an order-of-magnitude estimate of the bound on R T eq . ...
Cosmology and astrophysics provide various ways to study the properties of dark matter even if they have negligible non-gravitational interactions with the Standard Model particles and remain hidden. We study a type of hidden dark matter model in which the dark matter is completely decoupled from the Standard Model sector except gravitationally, and consists of a single species with a conserved comoving particle number. This category of hidden dark matter includes models that act as warm dark matter but is more general. In particular, in addition to having an independent temperature from the Standard Model sector, it includes cases in which dark matter is in its own thermal equilibrium or is free-streaming, obeys fermionic or bosonic statistics, and processes a chemical potential that controls the particle occupation number. While the usual parameterization using the free-streaming scale or the particle mass no longer applies, we show that all cases can be well approximated by a set of functions parameterized by only one parameter as long as the chemical potential is nonpositive: the characteristic scale factor at the time of the relativistic-to-nonrelativistic transition. We study the constraints from Big Bang Nucleosynthesis, the cosmic microwave background, the Lyman-$\alpha$ forest, and the smallest halo mass. We show that the most significant phenomenological impact is the suppression of the small-scale matter power spectrum -- a typical feature when the dark matter has a velocity dispersion or pressure at early times. So far, small dark matter halos provide the strongest constraint, limiting the transition scale factor to be no larger than $\sim1.4\times10^{-4}$ times the scale factor at matter-radiation equality.
... In particular, if DM particles were more relativistic in the early Universe ("warm"; WDM) or have a non-negligible cross-section for self-interactions (SIDM), the central slope will flatten (e.g. Macciò et al. 2013;Ludlow et al. 2017;Robertson et al. 2019) compared to clusters in the standard ΛCDM model, which DM-only simulations predict to have near-universal NFW (Navarro et al. 1997) profiles. This is especially true in the innermost ( < 50 kpc) regions of galaxy clusters, where DM concentrations are highest. ...
We present the first strong-gravitational-lensing analysis of the galaxy cluster RXJ0437.1+0043 (RXJ0437; z = 0.285). Newly obtained, deep MUSE observations, Keck/MOSFIRE near-infrared spectroscopy, and Hubble Space Telescope SNAPshot imaging reveal 13 multiply imaged background galaxies, three of them (at z=1.98, 2.97, and 6.02, respectively) in hyperbolic umbilic (H-U) lensing configurations. The H-U images are located only 20 -- 50 kpc from the cluster centre, i.e., at distances well inside the Einstein radius where images from other lens configurations are demagnified and often unobservable. Extremely rare (only one H-U lens was known previously) these systems are able to constrain the inner slope of the mass distribution -- and unlike radial arcs, the presence of H-U configurations is not biased towards shallow cores. The galaxies lensed by RXJ0437 are magnified by factors ranging from 30 to 300 and (in the case of H-U systems) stretched nearly isotropically. Taking advantage of this extreme magnification, we demonstrate how the source galaxies in H-U systems can be used to probe for small-scale ($\sim 10^{9} M_{\odot}$) substructures, providing additional insight into the nature of dark matter.
... A prominent feature of a FDM halo is its peculiar density profile: a dense central soliton core with a sharp transition to the less dense outer region with granular structure (see, e.g., Schive et al. 2014a,b). This shape significantly differs from other cored density profiles, e.g., CDM halos modified by the baryonic feedback (see, e.g., Read et al. 2016a,b), profiles of fermionic DM (see, e.g., Shao et al. 2013;Macciò et al. 2013;Savchenko & Rudakovskyi 2019) or density profiles of self-interacting DM (see, e.g., Tulin & Yu 2018). Moreover, the FDM model implies a scaling relation which links the central density, the characteristic radius of the central soliton, and the FDM particle mass (see, e.g., Schive et al. 2014a). ...
Stellar and gas kinematics of galaxies are a sensitive probe of the dark matter distribution in the halo. The popular fuzzy dark matter models predict the peculiar shape of density distribution in galaxies: specific dense core with sharp transition to the halo. Moreover, fuzzy dark matter predicts scaling relations between the dark matter particle mass and density parameters. In this work, we use a Bayesian framework and several dark matter halo models to analyse the stellar kinematics of galaxies using the Spitzer Photometry and Accurate Rotation Curves database. We then employ a Bayesian model comparison to select the best halo density model. We find that more than half of the galaxies prefer the fuzzy dark model against standard dark matter profiles (NFW, Burkert, and cored NFW). While this seems like a success for fuzzy dark matter, we also find that there is no single value for the particle mass that provides a good fit for all galaxies.
... In Warm Dark Matter (WDM) cosmologies, where the power spectrum is damped on small scales due to the thermal motion of the dominant DM component, the mean relationship between the mass and concentration of dark matter halos is found to be different from that seen in a Cold Dark Matter model Macciò et al. 2013;Ludlow et al. 2016). Heuristically, this happens because the damping delays the onset of nonlinear evolution on small scales, and low mass halos form later than in a CDM scenario. ...
Cosmologies with Light Massive Relics (LiMRs) as a subdominant component of the dark sector are well-motivated from a particle physics perspective, and can also have implications for the $\sigma_8$ tension between early and late time probes of matter clustering. The effects of LiMRs on the Cosmic Microwave Background (CMB) and structure formation on large (linear) scales have been investigated extensively. In this paper, we initiate a systematic study of the effects of LiMRs on smaller, nonlinear scales using cosmological $N$-body simulations; focusing on quantities relevant for photometric galaxy surveys. For most of our study, we use a particular model of nonthermal LiMRs but the methods developed easily generalize to a large class of models of LiMRs -- we explicitly demonstrate this by considering the Dodelson-Widrow form of the velocity distribution. We find that, in general, the effects of LiMR on small scales are distinct from those of a $\Lambda$CDM universe, even when the value of $\sigma_8$ is matched between the models. We show that weak lensing measurements around massive clusters, between $\sim 0.1 h^{-1}$Mpc and $\sim 10 h^{-1}$Mpc, should have sufficient signal-to-noise in future surveys to distinguish between $\Lambda$CDM and LiMR models that are tuned to fit both CMB data and large (linear) scale structure data at late times. Furthermore, we find that different LiMR cosmologies which are indistinguishable by conventional linear probes can be distinguished by these probes if their velocity distributions are sufficiently different. LiMR models can, therefore, be best tested and constrained by jointly analyzing data from CMB and late-time structure formation on both large \textit{and} small scales.
... For instance, the combination of a low M wdm with a low f wdm is in agreement with observations and can in principle be detected by large-scale structure surveys. Previous works on CWDM have focused on the physics at the halo/galactic scale, highlighting how models sharing similar freestreaming lengths but with different combinations of f wdm and M wdm can produce halos with different properties below masses of 10 11 M /h due to the different behaviour of the power spectra at small scales [35,36]. Another work [37] used Lyman-α data in combination with WMAP5 [38] to constrain CWDM models, finding that f wdm < 0.2 is allowed independently of the WDM mass. ...
We investigate and quantify the impact of mixed (cold and warm) dark matter models on large-scale structure observables. In this scenario, dark matter comes in two phases, a cold one (CDM) and a warm one (WDM): the presence of the latter causes a suppression in the matter power spectrum which is allowed by current constraints and may be detected in present-day and upcoming surveys. We run a large set of N-body simulations in order to build an efficient and accurate emulator to predict the aforementioned suppression with percent precision over a wide range of values for the WDM mass, M wdm , and its fraction with respect to the totality of dark matter, f wdm . The suppression in the matter power spectrum is found to be independent of changes in the cosmological parameters at the 2% level for k≲ 10 h/Mpc and z≤ 3.5. In the same ranges, by applying a baryonification procedure on both ΛCDM and CWDM simulations to account for the effect of feedback, we find a similar level of agreement between the two scenarios. We examine the impact that such suppression has on weak lensing and angular galaxy clustering power spectra. Finally, we discuss the impact of mixed dark matter on the shape of the halo mass function and which analytical prescription yields the best agreement with simulations. We provide the reader with an application to galaxy cluster number counts.
... For instance, the combination of a low M wdm with a low f wdm is in agreement with observations and can in principle be detected by large-scale structure surveys. Previous works on CWDM have focused on the physics at the halo/galactic scale, highlighting how models sharing similar freestreaming lengths but with different combinations of f wdm and M wdm can produce halos with different properties below masses of 10 11 M /h due to the different behaviour of the power spectra at small scales [35,36]. Another work [37] used Lyman-α data in combination with WMAP5 [38] to constrain CWDM models, finding that f wdm < 0.2 is allowed independently of the WDM mass. ...
We investigate and quantify the impact of mixed (cold and warm) dark matter models on large-scale structure observables. In this scenario, dark matter comes in two phases, a cold one (CDM) and a warm one (WDM): the presence of the latter causes a suppression in the matter power spectrum which is allowed by current constraints and may be detected in present-day and upcoming surveys. We run a large set of $N$-body simulations in order to build an efficient and accurate emulator to predict the aforementioned suppression with percent precision over a wide range of values for the WDM mass, $M_\mathrm{wdm}$, and its fraction with respect to the totality of dark matter, $f_\mathrm{wdm}$. The suppression in the matter power spectrum is found to be independent of changes in the cosmological parameters at the 2% level for $k\lesssim 10 \ h/$Mpc and $z\leq 3.5$. In the same ranges, by applying a baryonification procedure on both $\Lambda$CDM and CWDM simulations to account for the effect of feedback, we find a similar level of agreement between the two scenarios. We examine the impact that such suppression has on weak lensing and angular galaxy clustering power spectra. Finally, we discuss the impact of mixed dark matter on the shape of the halo mass function and which analytical prescription yields the best agreement with simulations. We provide the reader with an application to galaxy cluster number counts.
... A keV ALP can also be produced thermally by the freeze-in mechanism, in which case it constitutes a warm DM component [79,80]. The allowed abundance of warm DM is constrained by the observed Lyman-alpha flux power spectrum, which favours η 0.1 for m a ∼ 1 keV [81][82][83]. For further discussion of the production mechanisms relevant to this scenario, and the warm DM limits, see ref. [19]. ...
A bstract
The excess of electron recoil events seen by the XENON1T experiment has been interpreted as a potential signal of axion-like particles (ALPs), either produced in the Sun, or constituting part of the dark matter halo of the Milky Way. It has also been explained as a consequence of trace amounts of tritium in the experiment. We consider the evidence for the solar and dark-matter ALP hypotheses from the combination of XENON1T data and multiple astrophysical probes, including horizontal branch stars, red giants, and white dwarfs. We briefly address the influence of ALP decays and supernova cooling. While the different datasets are in clear tension for the case of solar ALPs, all measurements can be simultaneously accommodated for the case of a sub-dominant fraction of dark-matter ALPs. Nevertheless, this solution requires the tuning of several a priori unknown parameters, such that for our choices of priors a Bayesian analysis shows no strong preference for the ALP interpretation of the XENON1T excess over the background hypothesis.
... Many previous works studied the dark matter fraction in subhaloes (Gao et al. 2004a;Springel et al. 2008a;Xu et al. 2015;Despali & Vegetti 2017). In WDM models, the halo concentrations are lower (Macciò et al. 2013;Ludlow et al. 2016, -and as in the previous section) and the number of dark subhaloes is suppressed, which can lead to a lower fraction of the total halo mass being located in dark matter subhaloes. ...
We use high-resolution hydrodynamical simulations run with the EAGLE model of galaxy formation to study the differences between the properties of – and subsequently the lensing signal from – subhaloes of massive elliptical galaxies at redshift 0.2, in Cold and Sterile Neutrino (SN) Dark Matter models. We focus on the two 7 keV SN models that bracket the range of matter power spectra compatible with resonantly produced SN as the source of the observed 3.5 keV line. We derive an accurate parametrization for the subhalo mass function in these two SN models relative to cold dark matter (CDM), as well as the subhalo spatial distribution, density profile, and projected number density and the dark matter fraction in subhaloes. We create mock lensing maps from the simulated haloes to study the differences in the lensing signal in the framework of subhalo detection. We find that subhalo convergence is well described by a lognormal distribution and that signal of subhaloes in the power spectrum is lower in SN models with respect to CDM, at a level of 10–80 per cent, depending on the scale. However, the scatter between different projections is large and might make the use of power spectrum studies on the typical scales of current lensing images very difficult. Moreover, in the framework of individual detections through gravitational imaging a sample of ≃30 lenses with an average sensitivity of $M_{\rm {sub}} = 5 \times 10^{7}\, {\rm M}_{\odot}$ would be required to discriminate between CDM and the considered sterile neutrino models.
... Accurate rotation curve decomposition is crucial in determining the potential of a galaxy and the parameters of its dark matter (DM) halo. The densities and scale radii of dark haloes are known to follow welldefined scaling laws and can therefore be used to measure the redshift of assembly of haloes of different masses (Macciò et al. 2013;Kormendy & Freeman 2016;Somerville et al. 2018). ...
The mass-to-light ratio (M/L) is a key parameter in decomposing galactic rotation curves into contributions from the baryonic components and the dark halo of a galaxy. One direct observational method to determine the disc M/L is by calculating the surface mass density of the disc from the stellar vertical velocity dispersion and the scale height of the disc. Usually, the scale height is obtained from near-IR studies of edge-on galaxies and pertains to the older, kinematically hotter stars in the disc, while the vertical velocity dispersion of stars is measured in the optical band and refers to stars of all ages (up to ∼ 10 Gyr) and velocity dispersions. This mismatch between the scale height and the velocity dispersion can lead to underestimates of the disc surface density and a misleading conclusion of the sub-maximality of galaxy discs. In this paper we present the study of the stellar velocity dispersion of the disc galaxy NGC 6946 using integrated star light and individual planetary nebulae as dynamical tracers. We demonstrate the presence of two kinematically distinct populations of tracers which contribute to the total stellar velocity dispersion. Thus, we are able to use the dispersion and the scale height of the same dynamical population to derive the surface mass density of the disc over a radial extent. We find the disc of NGC 6946 to be closer to maximal with the baryonic component contributing most of the radial gravitational field in the inner parts of the galaxy ($\rm V_{max}(bar)=0.76(\pm 0.14)V_{max}$).
... Abazajian, E-mail: rudakovskyi@bitp.kiev.ua Fuller & Tucker 2001b;Dolgov & Hansen 2002) or of a mixture of cold and warm dark matter (Boyarsky et al. 2009a;Macciò et al. 2013). It can be traced by a number of observations related to structure formation at different redshifts, such as Lyman-alpha forest power spectrum (Narayanan et al. 2000;Hansen et al. 2002;Viel et al. 2005Viel et al. , 2006Viel et al. , 2008Viel et al. , 2013Abazajian 2006;Seljak et al. 2006;Boyarsky et al. 2009a,b;Garzilli, Boyarsky & Ruchayskiy 2015;Baur et al. 2017;Iršič et al. 2017;Yeche et al. 2017), reionization of the Universe (Barkana, Haiman & Ostriker 2001;Somerville, Bullock & Livio 2003;Yoshida et al. 2003;Jedamzik, Lemoine & Moultaka 2006;Yue & Chen 2012;Schultz et al. 2014;Rudakovskyi & Iakubovskyi 2016;Bose et al. 2016;Cen 2017;Dayal et al. 2017b;Lopez-Honorez et al. 2017), subhalo counts in the Local Group (Macciò & Fontanot 2010;Polisensky & Ricotti 2011;Horiuchi et al. 2014;Kennedy et al. 2014;Lovell et al. 2014Lovell et al. , 2016Lovell et al. , 2017aCherry & Horiuchi 2017), luminosity functions at low (Menci et al. 2016(Menci et al. , 2017a and high (Song & Lee 2009;Schultz et al. 2014;Corasaniti et al. 2017;Menci et al. 2017b) redshifts, substructure counts in gravitational lensing systems (Zentner & Bullock 2003;Miranda & Macciò 2007;Inoue et al. 2015;Birrer, Amara & Refregier 2017), galaxy velocity function (Klypin et al. 2015;Schneider et al. 2017), stellar mass-halo mass relation of isolated field dwarf galaxies (Read et al. 2017), stellar mass functions at redshifts z 3.5 together with the Tully-Fisher relation (Kang, Macciò & Dutton 2013), star-formation history of the Local Group dSphs (Chau, Mayer & Governato 2017), and number density of direct collapse black hole hosts (Dayal et al. 2017a). ...
One of possible explanations of a faint narrow emission line at 3.5 keV reported in our Galaxy, Andromeda galaxy and a number of galaxy clusters is the dark matter made of 7 keV sterile neutrinos. Another signature of such sterile neutrino dark matter could be fewer ionizing sources in the early Universe [compared to the standard ‘cold dark matter’ (CDM) scenario], which should affect the reionization of the Universe. By using a semi-analytical model of reionization, we compare the model predictions for CDM and two different models of 7 keV sterile neutrino dark matter (consistent with the 3.5 keV line interpretation as decaying dark matter line) with available observations of epoch of reionization (including the final measurements of electron scattering optical depth made by Planck observatory). We found that both CDM and 7 keV sterile neutrino dark matter well describe the data. The overall fit quality for sterile neutrino dark matter is slightly (with Δχ² ≃ 2 − 3) better than for CDM, although it is not possible to make a robust distinction between these models on the basis of the given observations.
... The model accurately reproduces the concentrations of DM haloes in both CDM and WDM cosmologies. This may appear surprising at first as DM haloes in WDM simulations have been found to display different concentrations and formation times than in CDM (Macciò et al. 2013;Bose et al. 2016). However, these changes act to preserve the ρ −2 -ρ crit (z −2 ) relation seen in CDM. ...
We use two high-resolution N-body simulations, one assuming general relativity (GR) and the other the Hu–Sawicki form of f(R) gravity with $\vert \bar{f}_{\mathrm{ R}} \vert = 10^{-6}$, to investigate the concentration–formation time relation of dark matter haloes. We assign haloes to logarithmically spaced mass bins, and fit median density profiles and extract median formation times in each bin. At fixed mass, haloes in modified gravity are more concentrated than those in GR, especially at low masses and low redshift, and do not follow the concentration–formation time relation seen in GR. We assess the sensitivity of the relation to how concentration and formation time are defined, as well as to the segregation of the halo population by the amount of gravitational screening. We find a clear difference between halo concentrations and assembly histories displayed in modified gravity and those in GR. Existing models for the mass–concentration–redshift relation that have gained success in cold and warm dark matter models require revision in f(R) gravity.
... For the WDM model, it is found that the halo profile can still be described by the NFW profile (e.g. Eke, Navarro & Steinmetz 2001;Schneider et al. 2012;Macciò et al. 2013;Lovell et al. 2014;Schneider 2015;Ludlow et al. 2016), but the concentration, c WDM , is generally reduced, and the c WDM -M relation is also non-monotonic, reaching a peak at a mass scale indicated by the truncation scale and decreasing at higher and lower masses. Here we use the fitting formula from Schneider et al. (2012) to describe the connection between the concentration c CDM in CDM and c WDM in WDM models ...
Theoretical studying of the very inner structure of faint satellite galaxy requires very high-resolution hydro-dynamical simulations with realistic model for star formation, which are beginning to emerge recently. In this work, we present an analytical description to model the inner kinematic of satellites in the Milky Way (MW). We use a Monte Carlo method to produce merger trees for MW mass halo and analytical models to produce stellar mass in the satellite galaxies. We consider two important processes which can significantly modify the inner mass distribution in satellite galaxy. The first is baryonic feedback which can induce a flat inner profile depending on the star formation efficiency in the galaxy. The second is the tidal stripping to reduce and re-distribute the mass inside satellite. We apply this model to MW satellite galaxies in both CDM and thermal relic WDM models. It is found that tidal heating must be effective to produce a relatively flat distribution of the satellite circular velocities, to agree with the data. The constraint on WDM mass depends on the host halo mass. For a MW halo with dark matter mass lower than $2\times 10^{12}\, \text{ M}_\odot$, a 2 keV WDM model can be safely excluded as the predicted satellite circular velocities are systematically lower than the data. For WDM with mass of 3.5 keV, it requires the MW halo mass to be larger than $1.5\times 10^{12}\, {\text{ M}}_{\odot }$.
... If the velocity distribution of the dark matter particles causes them to diffuse out of small peaks in the density field, this will prevent the direct collapse of overdensities below a characteristic scale referred to as the free-streaming length (Benson et al. 2013;Schneider, Smith & Reed 2013). The delay in structure formation in these scenarios also suppresses the central densities of the smallest collapsed haloes, changing the massconcentration relation for low-mass objects (Avila-Reese et al. 2001;Schneider et al. 2012;Macciò et al. 2013;Bose et al. 2016;Ludlow et al. 2016). By definition, free-streaming effects are negligible in CDM, while models with cosmologically relevant free-streaming lengths are collectively referred to as warm dark matter (WDM). ...
The free-streaming length of dark matter depends on fundamental dark matter physics, and determines the abundance and concentration of dark matter haloes on sub-galactic scales. Using the image positions and flux ratios from eight quadruply imaged quasars, we constrain the free-streaming length of dark matter and the amplitude of the subhalo mass function (SHMF). We model both main deflector subhaloes and haloes along the line of sight, and account for warm dark matter free-streaming effects on the mass function and mass–concentration relation. By calibrating the scaling of the SHMF with host halo mass and redshift using a suite of simulated haloes, we infer a global normalization for the SHMF. We account for finite-size background sources, and marginalize over the mass profile of the main deflector. Parametrizing dark matter free-streaming through the half-mode mass mhm, we constrain the thermal relic particle mass mDM corresponding to mhm. At $95 \, {\rm per\, cent}$ CI: mhm < 107.8 M⊙ ($m_{\rm {DM}} \gt 5.2 \ \rm {keV}$). We disfavour $m_{\rm {DM}} = 4.0 \,\rm {keV}$ and $m_{\rm {DM}} = 3.0 \,\rm {keV}$ with likelihood ratios of 7:1 and 30:1, respectively, relative to the peak of the posterior distribution. Assuming cold dark matter, we constrain the projected mass in substructure between 106 and 109 M⊙ near lensed images. At $68 \, {\rm per\, cent}$ CI, we infer $2.0{-}6.1 \times 10^{7}\, {{\rm M}_{\odot }}\,\rm {kpc^{-2}}$, corresponding to mean projected mass fraction $\bar{f}_{\rm {sub}} = 0.035_{-0.017}^{+0.021}$. At $95 \, {\rm per\, cent}$ CI, we obtain a lower bound on the projected mass of $0.6 \times 10^{7} \,{{\rm M}_{\odot }}\,\rm {kpc^{-2}}$, corresponding to $\bar{f}_{\rm {sub}} \gt 0.005$. These results agree with the predictions of cold dark matter.
... Haloes that form earlier typically have higher concentrations (Navarro et al. 1996(Navarro et al. , 1997. Since the reduction in small-scale power in a WDM model leads to later formation time for low mass haloes these are less concentrated than their CDM counterparts (Lovell et al. 2012;Schneider et al. 2012;Macciò et al. 2013;Bose et al. 2016;Ludlow et al. 2016). ...
A fundamental prediction of the cold dark matter (CDM) model of structure formation is the existence of a vast population of dark matter haloes extending to subsolar masses. By contrast, other possibilities for the nature of the dark matter, such as a warm thermal relic or a sterile neutrino (WDM) predict a cutoff in the mass function at a mass of $\sim 10^8~{\rm M}_\odot$. We use mock observations to demonstrate the viability of a forward modelling approach to extract information on the cosmological number density of low-mass dark matter haloes along the line-of-sight to galaxy-galaxy strong lenses. This can be used to constrain the mass of a thermal relic dark matter particle, $m_\mathrm{DM}$. With 50 strong lenses at Hubble Space Telescope resolution and signal-to-noise (similar to the existing SLACS survey), the expected 2$\sigma$ constraint for CDM is $m_\mathrm{DM} > 3.7 \, \mathrm{keV}$. If, however, the dark matter is a warm particle of $m_\mathrm{DM}=2.2 \, \mathrm{keV}$, one could rule out $m_\mathrm{DM} > 3.2 \, \mathrm{keV}$. Our [Approximate Bayesian Computation] method can be extended to the large samples of strong lenses that will be observed by future space telescopes, potentially to rule out the standard CDM model of cosmogony. To aid future survey design, we quantify how these constraints will depend on data quality (spatial resolution and integration time) as well as on the lensing geometry (source and lens redshifts).
... In addition to a suppressed mass function below the freestreaming scale, free streaming alters the concentration-mass relation of WDM haloes (Schneider et al. 2012;Macciò et al. 2013;Bose et al. 2016;Ludlow et al. 2016). We model this suppression using the parametrization given by ) ...
Strong lensing provides a powerful means of investigating the nature of dark matter as it probes dark matter structure on sub-galactic scales. We present an extension of a forward modelling framework that uses flux ratios from quadruply imaged quasars (quads) to measure the shape and amplitude of the halo mass function, including line-of-sight (LOS) haloes and main deflector subhaloes. We apply this machinery to 50 mock lenses – roughly the number of known quads – with warm dark matter (WDM) mass functions exhibiting free-streaming cut-offs parametrized by the half-mode mass mhm. Assuming cold dark matter (CDM), we forecast bounds on mhm and the corresponding thermal relic particle masses over a range of tidal destruction severity, assuming a particular WDM mass function and mass–concentration relation. With significant tidal destruction, at 2σ we constrain $m_{\rm {hm}}\lt 10^{7.9} \left(10^{8.4}\right) \, \mathrm{M}_{\odot }$, or a 4.4 (3.1) keV thermal relic, with image flux uncertainties from measurements and lens modelling of $2{{\ \rm per\ cent}} \left(6{{\ \rm per\ cent}}\right)$. With less severe tidal destruction we constrain $m_{\rm {hm}}\lt 10^{7} \left(10^{7.4}\right) \, \mathrm{M}_{\odot }$, or an 8.2 (6.2) keV thermal relic. If dark matter is warm, with $m_{\rm {hm}} = 10^{7.7} \, \mathrm{M}_{\odot }$ (5.1 keV), we would favour WDM with $m_{\rm {hm}} \gt 10^{7.7} \, \mathrm{M}_{\odot }$ over CDM with relative likelihoods of 22:1 and 8:1 with flux uncertainties of $2{{\ \rm per\ cent}}$ and $6{{\ \rm per\ cent}}$, respectively. These bounds improve over those obtained by modelling only main deflector subhaloes because LOS objects produce additional flux perturbations, especially for high-redshift systems. These results indicate that ∼50 quads can conclusively differentiate between WDM and CDM.
... Accurate rotation curve decomposition is crucial in determining the potential of a galaxy and the parameters of its dark matter (DM) halo. The densities and scale radii of dark haloes are known to follow well-defined scaling laws and can therefore be used to measure the redshift of assembly of haloes of different masses (Macciò et al. 2013;Kormendy & Freeman 2016;Somerville et al. 2018). ...
The mass-to-light ratio (M/L) is a key parameter in decomposing galactic rotation curves into contributions from the baryonic components and the dark halo of a galaxy. One direct observational method to determine the disc M/L is by calculating the surface mass density of the disc from the stellar vertical velocity dispersion and the scale height of the disc. Usually, the scale height is obtained from near-IR studies of edge-on galaxies and pertains to the older, kinematically hotter stars in the disc, while the vertical velocity dispersion of stars is measured in the optical band and refers to stars of all ages (up to ~10 Gyr) and velocity dispersions. This mismatch between the scale height and the velocity dispersion can lead to underestimates of the disc surface density and a misleading conclusion of the sub-maximality of galaxy discs. In this paper we present the study of the stellar velocity dispersion of the disc galaxy NGC 6946 using integrated star light and individual planetary nebulae as dynamical tracers. We demonstrate the presence of two kinematically distinct populations of tracers which contribute to the total stellar velocity dispersion. Thus, we are able to use the dispersion and the scale height of the same dynamical population to derive the surface mass density of the disc over a radial extent. We find the disc of NGC 6946 to be closer to maximal with the baryonic component contributing most of the radial gravitational field in the inner parts of the galaxy (Vmax(bar) = 0.76($\pm$0.14)Vmax).
... A keV ALP can also be produced thermally by the freeze-in mechanism, in which case it constitutes a warm DM component [73,74]. The allowed abundance of warm DM is constrained by the observed Lyman-alpha flux power spectrum, which favours η 0.1 for m a ∼ 1 keV [75][76][77]. For further discussion of the production mechanisms relevant to this scenario, and the warm DM limits, see ref. [19]. ...
The excess of electron recoil events seen by the XENON1T experiment has been interpreted as a potential signal of axion-like particles (ALPs), either produced in the Sun, or constituting part of the dark matter halo of the Milky Way. It has also been explained as a consequence of trace amounts of tritium in the experiment. We consider the evidence for the solar and dark-matter ALP hypotheses from the combination of XENON1T data and multiple astrophysical probes, including horizontal branch stars, red giants, and white dwarfs. We briefly address the influence of ALP decays and supernova cooling. While the different datasets are in clear tension for the case of solar ALPs, all measurements can be simultaneously accommodated for the case of a sub-dominant fraction of dark-matter ALPs. Nevertheless, this solution requires the tuning of several a priori unknown parameters, such that for our choices of priors a Bayesian analysis shows no strong preference for the ALP interpretation of the XENON1T excess over the background hypothesis.
... Many previous works studied the dark matter fraction in subhaloes (Gao et al. 2004a;Springel et al. 2008a;Xu et al. 2015;Despali & Vegetti 2017). In WDM models, the halo concentrations are lower (Macciò et al. 2013;Ludlow et al. 2016, -and as in the previous section) and the number of dark subhaloes is suppressed, which can lead to a lower fraction of the total halo mass being located in dark matter subhaloes. ...
We use high-resolution hydrodynamical simulations run with the EAGLE model of galaxy formation to study the differences between the properties of - and subsequently the lensing signal from subhaloes of massive elliptical galaxies at redshift 0.2, in Cold and Sterile Neutrino Dark matter models. We focus on the two 7 keV SN models that bracket the range of matter power spectra compatible with resonantly-produced SN as the source of the observed 3.5 keV line. We derive an accurate parametrization for the subhalo mass function in these two SN models relative to CDM, as well as the subhalo spatial distribution, density profile, and projected number density and the dark matter fraction in subhaloes. We create mock lensing maps from the simulated haloes to study the differences in the lensing signal in the framework of subhalo detection. We find that subhalo convergence is well described by a log-normal distribution and that signal of subhaloes in the power spectrum is lower in SN models with respect to CDM, at a level of 10 to 80 per cent, depending on the scale. However, the scatter between different projections is large and might make the use of power-spectrum studies on the typical scales of current lensing images very difficult. Moreover, in the framework of individual detections through gravitational imaging a sample of ~30 lenses with an average sensitivity of M_sub=5 10^7 M_sun would be required to discriminate between CDM and the considered sterile neutrino models.
... The model accurately reproduces the concentrations of dark matter haloes in both CDM and WDM cosmologies. This may appear surprising at first as dark matter haloes in WDM simulations have been found to display different concentrations and formation times than in CDM (Macciò et al. 2013;Bose et al. 2016). However, these changes act to preserve the ρ−2 − ρcrit(z−2) relation seen in CDM. ...
We use two high resolution N-body simulations, one assuming general relativity and the other the Hu-Sawicki form of $f\left(R\right)$ gravity with $\vert \bar{f}_{R} \vert = 10^{-6}$, to investigate the concentration--formation time relation of dark matter haloes. We stack haloes in logarithmically spaced mass bins to fit median density profiles and extract median formation times. At fixed mass, haloes in modified gravity are more concentrated than those in GR, especially at low masses and at low redshift, and do not follow the concentration--formation time relation seen in GR. We assess the sensitivity of the relation to how concentration and formation time are defined, as well as to the segregation of the halo population by the amount of gravitational screening. We find a clear difference between halo concentrations and assembly histories displayed in modified gravity and those in GR. Existing models for the mass--concentration--redshift relation that have gained success in cold and warm dark matter models require revision in $f\left(R\right)$ gravity.
... In addition to a suppressed mass function below the free streaming scale, free streaming alters the concentrationmass relation of WDM halos (Schneider et al. 2012;Macciò et al. 2013;Bose et al. 2016;Ludlow et al. 2016). We model this suppresion using the parameterization given by ) ...
Strong lensing provides a powerful means of investigating the nature of dark matter as it probes the mass function and density profiles of halos on sub-galactic scales. We present an extension of a forward modeling framework that uses flux ratios from quadruply imaged quasars (quads) to measure the shape and amplitude of the halo mass function, including line of sight (LOS) halos and main deflector subhalos. We apply this machinery to 50 mock lenses --- roughly the number of known quads --- with mass functions exhibiting a free-streaming cutoff parameterized by the half-mode mass $m_{\rm{hm}}$. Assuming cold dark matter (CDM), we forecast bounds on $m_{\rm{hm}}$ and the corresponding thermal relic particle masses for scenarios with a range of tidal destruction severity. With significant tidal destruction, at $2 \sigma$ we constrain $m_{\rm{hm}}<10^{7.9} \left(10^{8.4}\right) M_{\odot}$, or a 4.4 (3.1) keV thermal relic, with image flux uncertainties from measurements and lens modeling of $2\% \left(6\%\right)$. With less severe tidal destruction we constrain $m_{\rm{hm}}<10^{7} \left(10^{7.4}\right) M_{\odot}$, or an 8.2 (6.2) keV thermal relic. If dark matter is warm, with $m_{\rm{hm}} = 10^{7.7} M_{\odot}$ (5.1 keV), we would favor WDM with $m_{\rm{hm}} > 10^{7.7} M_{\odot}$ over CDM with relative likelihoods of 22:1 and 8:1 with flux uncertainties of $2\%$ and $6\%$, respectively. These bounds improve over those obtained by modeling only main deflector subhalos because LOS objects produce additional flux perturbations, especially for high redshift systems. These results indicate that $\sim 50$ quads can conclusively differentiate between warm and cold dark matter.
... Such smearing, indeed, can be a result of warm dark matter with a few keV mass (see e.g. Dolgov & Hansen 2002;Abazajian et al. 2001b) or of a mixture of cold and warm dark matter (Boyarsky et al. 2009a;Macciò et al. 2013). It can be traced by a number of observations related to structure formation at different redshifts, such as Lyman-alpha forest power spectrum (Narayanan et al. 2000;Hansen et al. 2002;Viel et al. 2005Viel et al. , 2006Viel et al. , 2008Viel et al. , 2013Abazajian 2006;Seljak et al. 2006;Boyarsky et al. 2009a,b;Garzilli et al. 2015;Iršič et al. 2017;Yeche et al. 2017;Baur et al. 2017), reionization of the Universe Yoshida et al. 2003;Somerville et al. 2003;Jedamzik et al. 2006;Yue & Chen 2012;Schultz et al. 2014;Dayal et al. 2017b;Rudakovskyi & Iakubovskyi 2016;Bose et al. 2016;Cen 2017;Lopez-Honorez et al. 2017), subhalo counts in the Local Group (Macciò & Fontanot 2010;Polisensky & Ricotti 2011;Lovell et al. 2014;Kennedy et al. 2014;Horiuchi et al. 2014;Lovell et al. 2016Lovell et al. , 2017aCherry & Horiuchi 2017), luminosity functions at low (Menci et al. 2016(Menci et al. , 2017a and high (Song & Lee 2009;Schultz et al. 2014;Corasaniti et al. 2017;Menci et al. 2017b) redshifts, substructure counts in gravitational lensing systems (Zentner & Bullock 2003;Miranda & Macciò 2007;Inoue et al. 2015;Birrer et al. 2017), galaxy velocity function (Klypin et al. 2015;Schneider et al. 2017), stellar mass -halo mass relation of isolated field dwarf galaxies (Read et al. 2017), stellar mass functions at redshifts z 3.5 together with the Tully-Fisher relation (Kang et al. 2013), star-formation history of the Local Group dSphs (Chau et al. 2017), and number density of direct collapse black hole hosts (Dayal et al. 2017a). ...
One of possible explanations of a faint narrow emission line at 3.5 keV reported in our Galaxy, Andromeda galaxy and a number of galaxy clusters is the dark matter made of 7 keV sterile neutrinos. Another signature of such sterile neutrino dark matter could be fewer ionizing sources in the early Universe (compared to the standard "cold dark matter" (CDM) scenario), which should affect the reionization of the Universe. By using a semi-analytical model of reionization, we compare the model predictions for CDM and two different models of 7 keV sterile neutrino dark matter (consistent with the 3.5 keV line interpretation as decaying dark matter line) with available observations of epoch of reionization (including the final measurements of electron scattering optical depth made by Planck observatory). We found that both CDM and 7 keV sterile neutrino dark matter well describe the data. The overall fit quality for sterile neutrino dark matter is slightly (with $\Delta \chi^2 \simeq 2-3$) better than for CDM, although it is not possible to make a robust distinction between these models on the basis of the given observations.
... Similar types of multiple Dark Matter models have already been considered in the literature in the context of Warm Dark Matter cosmologies (see e.g. [10,34]) and also for the case of interacting DE scenarios (see e.g. [8,35,36,37,38]). ...
... We combine this mass definition with a form for the mass-concentration relation for warm dark matter halos presented by Bose et al. (2016) (see also Macciò et al. 2013;Ludlow et al. 2016) c (ms) = 6 ms 10 12 M −0.098 ...
The free streaming length of the dark matter particle, and its possible interactions, imprint a measurable signature on the density profiles and abundance of structure on sub-galactic scales. We present a statistical technique for probing dark matter via substructure through a joint analysis of samples of strong lens systems with four multiple images (quads). Our method is amenable to any parameterization of the subhalo mass function and density profile for individual substructures. As an example, we apply it to a mass function of a warm dark matter particle characterized by a normalization $A_0$, and a free streaming length parameterized by the half-mode mass $m_{\rm{hm}}$. We demonstrate that limits on $m_{\rm{hm}}$ deteriorate rapidly with increasing uncertainty in image fluxes, highlighting the importance of precisely measuring them, and controlling for external sources of error. We omit subhalos outside of the lens plane, which are believed to boost the signal, so our results can be interpreted as conservative constraints. We forecast bounds on dark matter warmth for samples of 180 quads, attainable with upcoming surveys such as Euclid, LSST, and WFIRST. Assuming a cold dark matter scenario, we forecast $2\sigma$ bounds of $m_{\rm{hm}}<10^{6.4} M_{\odot}$, $10^{7.5} M_{\odot}$, $10^{8} M_{\odot}$, and $10^{8.4} M_{\odot}$ for flux errors of 0$\%$, $2\%$, $4\%$, and $8\%$, corresponding to thermal relic masses of 13.9 keV, 6.4 keV, 4.6 keV, and 3.3 keV, respectively.
... We also note that in our simulations we do not include thermal velocities because their physical effects are negligible for our choice of WDM candidate masses and N-body parameters (see e.g. [49][50][51][52]), and including them introduces extra numerical noise in the simulations, reducing the range of scales we can trust [43]. ...
We investigate the nonlinear evolution of structure in variants of the standard cosmological model which display damped density fluctuations relative to cold dark matter (e.g. in which cold dark matter is replaced by warm or interacting DM). Using N-body simulations, we address the question of how much information is retained from the initial linear power spectrum following the nonlinear growth of structure. We run a suite of N-body simulations with different initial linear matter power spectra to show that, once the system undergoes nonlinear evolution, the shape of the linear power spectrum at high wavenumbers does not affect the non-linear power spectrum, while it still matters for the halo mass function. Indeed, we find that linear power spectra which differ from one another only at wavenumbers larger than their half-mode wavenumber give rise to (almost) identical nonlinear power spectra at late times, regardless of the fact that they originate from different models with damped fluctuations. On the other hand, the halo mass function is more sensitive to the form of the linear power spectrum. Exploiting this result, we propose a two parameter model of the transfer function in generic damped scenarios, and show that this parametrisation works as well as the standard three parameter models for the scales on which the linear spectrum is relevant.
... An important subset of these models, where today's DM consists of an admixture of cold and warm DM particles, have been dubbed mixed DM (MDM) models; see refs. [24][25][26]. They are a plausible solution to alleviate the small-scale crisis of the ΛCDM cosmology, while leaving the predictions from the CDM model at large scales unchanged. ...
Various particle physics models suggest that, besides the (nearly) cold dark matter that accounts for current observations, additional but sub-dominant dark relics might exist. These could be warm, hot, or even contribute as dark radiation. We present here a comprehensive study of two-component dark matter scenarios, where the first component is assumed to be cold, and the second is a non-cold thermal relic. Considering the cases where the non-cold dark matter species could be either a fermion or a boson, we derive consistent upper limits on the non-cold dark relic energy density for a very large range of velocity dispersions, covering the entire range from dark radiation to cold dark matter. To this end, we employ the latest Planck Cosmic Microwave Background data, the recent BOSS DR11 and other Baryon Acoustic Oscillation measurements, and also constraints on the number of Milky Way satellites, the latter of which provides a measure of the suppression of the matter power spectrum at the smallest scales due to the free-streaming of the non-cold dark matter component. We present the results on the fraction $f_{\rm ncdm}$ of non-cold dark matter with respect to the total dark matter for different ranges of the non-cold dark matter masses. We find that the 2$\sigma$ limits for non-cold dark matter particles with masses in the range 1--10 keV are $f_{\rm ncdm}\leq 0.29$ (0.23) for fermions (bosons), and for masses in the 10--100 keV range they are $f_{\rm ncdm}\leq 0.43$ (0.45), respectively.
... Apart from considerations on alternative approaches to DM, like self-interacting DM (Spergel & Steinhardt 2000;Rocha et al. 2013), change of the spectrum at small scales (Bode et al. 2001;Zentner & Bullock 2003;Macciò et al. 2013), or modified gravity (e.g., van den Bosch & Dalcanton 2000;Zlosnik et al. 2007;Rodrigues et al. 2010;Famaey & McGaugh 2012;Rodrigues et al. 2014;de Almeida et al. 2016;Sánchez-Salcedo et al. 2016), different proposals on how to solve this disagreement between simulations and observational data consider that baryonic effects may play a relevant role. Within the latter picture, baryons interaction with DM through gravity could "heat" the DM component giving rise to flatter inner profiles (Del Popolo 2009;Governato et al. 2010;Del Popolo 2012a;Pontzen & Governato 2012;Governato et al. 2012;. ...
We develop and apply new techniques in order to disclose galaxy rotation curves (RC) systematics. Considering that an ideal dark matter (DM) profile should yield RCs that have no bias towards any particular radius, we find that the Burkert DM profile satisfies the test, while the Navarro-Frenk-While (NFW) profile has a tendency of better fitting the region between one and two disc scale lengths than the inner disc scale length region. Our sample indicates that this behaviour happens to more than 75% of the galaxies fitted with a NFW halo. Also, this tendency does not weaken by considering "large" galaxies, for instance those with $M_*\gtrsim 10^{10} M_\odot$ (where $M_*$ is the stellar mass). No specific correlation between the NFW parameters is assumed, hence we derive the best possible NFW fits. Besides the tests on the homogeneity of the fits, we also use a sample of 62 galaxies of diverse types to perform tests on the quality of the overall fit of each galaxy, and to search for correlations with stellar mass, gas mass and the disc scale length. In particular, we find that only 13 galaxies are better fitted by the NFW halo, and that even considering only the galaxies with $M_* \gtrsim 10^{10} M_\odot$ the Burkert profile fits either as good as, or better than, the NFW profile. This result is relevant since different baryonic effects important for the smaller galaxies, like supernova feedback and dynamical friction from baryonic clumps, indicate that at such large stellar masses the NFW profile should be preferred over the Burkert profile.
... Moreover the two avenues of DM evolution in the bounce cosmology, Route I and Route II, can be distinguished in the level of thermal perturbation. Such results are, hopefully, to be applied to the issues of formation of large scale structure as well as the primordial black hole in near future study [72][73][74][75][76][77][78][79][80]. Moreover, in BBG, such predictions from thermal fluctuation can be used to cross-check with the prediction from direct detection of DM. ...
We review the recent status of big bounce genesis as a new possibility of using dark matter particle's mass and interaction cross section to test the existence of a bounce universe at the early stage of evolution in our currently observed universe. To study the dark matter production and evolution inside the bounce universe, called big bounce genesis for short, we propose a model independent approach. We shall present the motivation for proposing big bounce as well the model independent predictions which can be tested by dark matter direct searches. A positive finding shall have profound impact on our understanding of the early universe physics.
... in projection (e.g. Jing & Suto 2002;Macciò et al. 2013). Direct measurements of halo ellipticities therefore constitute a powerful test of the current cosmological paradigm, and serve as a test bed for modified gravity models, as some of these predict different halo ellipticity distributions (e.g. ...
We constrain the average halo ellipticity of ~2 600 galaxy groups from the Galaxy And Mass Assembly (GAMA) survey, using the weak gravitational lensing signal measured from the overlapping Kilo Degree Survey (KiDS). To do so, we quantify the azimuthal dependence of the stacked lensing signal around seven different proxies for the orientation of the dark matter distribution, as it is a priori unknown which one traces the orientation best. On small scales, the major axis of the brightest group/cluster member (BCG) provides the best proxy, leading to a clear detection of an anisotropic signal. In order to relate that to a halo ellipticity, we have to adopt a model density profile. We derive new expressions for the quadrupole moments of the shear field given an elliptical model surface mass density profile. Modeling the signal with an elliptical Navarro-Frenk-White (NFW) profile on scales < 250 kpc, which roughly corresponds to half the virial radius, and assuming that the BCG is perfectly aligned with the dark matter, we find an average halo ellipticity of e_h=0.38 +/- 0.12. This agrees well with results from cold-dark-matter-only simulations, which typically report values of e_h ~ 0.3. On larger scales, the lensing signal around the BCGs does not trace the dark matter distribution well, and the distribution of group satellites provides a better proxy for the halo's orientation instead, leading to a 3--4 sigma detection of a non-zero halo ellipticity at scales between 250 kpc and 750 kpc. Our results suggest that the distribution of stars enclosed within a certain radius forms a good proxy for the orientation of the dark matter within that radius, which has also been observed in hydrodynamical simulations.
... in section 3.2, in principle, one could refine the analysis presented, as we intend to do, and/or study further halo properties of settings like the one presented, as done e.g. for mixed Dark Matter settings [126,127]. The distribution functions obtained from scalar decay are conceptually not very different, however, as we have seen, they are highly non-thermal in both shape and number of momentum scales, so that even a description by a superposition of two thermally-shaped distributions may in fact not be sufficient. ...
We investigate the early Universe production of sterile neutrino Dark Matter by the decays of singlet scalars. All previous studies applied simplifying assumptions and/or studied the process only on the level of number densities, which makes it impossible to give statements about cosmic structure formation. We overcome these issues by dropping all simplifying assumptions (except for one we showed earlier to work perfectly) and by computing the full course of Dark Matter production on the level of non-thermal momentum distribution functions. We are thus in the position to study all aspects of the resulting settings and apply all relevant bounds in a reliable manner. We have a particular focus on how to incorporate bounds from structure formation on the level of the linear power spectrum, since the simplistic estimate using the free-streaming horizon clearly fails for highly non-thermal distributions. Our work comprises the most detailed and comprehensive study of sterile neutrino Dark Matter production by scalar decays presented so far.
We argue that the lensing power spectrum of astrometric shift (lensing shift power spectrum) is a powerful tool for probing the clustering property of dark matter on subgalactic scales. First we give the formalism to probe the nature of dark matter by using the lensing shift power spectrum. Then, leveraging recent measurements of the lensing shift power spectrum on an angular scale of approximately 1 arcsec toward the gravitationally lensed quasar MG J0414+0534 at the redshift of zS=2.639, we place constraints on the mass of warm dark matter (WDM) particles mWDM and their fraction in a mixed dark matter (MDM) model rWDM, in which WDM and cold dark matter coexist. Although the constraint derived from the above single lensing system is not as strong as the existing constraints, as we show in this paper, the lensing shift power spectrum has a great potential to obtain much tighter constraints on WDM and MDM models through future observations, highlighting the importance of well-controlled systematic error considerations for achieving enhanced precision.
The forest of Lyman-α absorption lines detected in the spectra of distant quasars encodes information on the nature and properties of dark matter and the thermodynamics of diffuse baryonic material. Its main observable—the 1D flux power spectrum (FPS)—should exhibit a suppression on small scales and an enhancement on large scales in warm dark matter (WDM) cosmologies compared to standard ΛCDM. Here, we present an unprecedented suite of 1080 high-resolution cosmological hydrodynamical simulations run with the graphics processing unit-accelerated code cholla to study the evolution of the Lyman-α forest under a wide range of physically motivated gas thermal histories along with different free-streaming lengths of WDM thermal relics in the early Universe. A statistical comparison of synthetic data with the forest FPS measured down to the smallest velocity scales ever probed at redshifts 4.0≲z≲5.2 [E. Boera et al., Revealing reionization with the thermal history of the intergalactic medium: New constraints from the Lyα flux power spectrum, Astrophys. J. 872, 101 (2019)] yields a lower-limit mWDM>3.1 keV (95% C.L.) for the WDM particle mass and constrains the amplitude and spectrum of the photoheating and photoionizing background produced by star-forming galaxies and active galactic nuclei at these redshifts. Interestingly, our Bayesian inference analysis appears to weakly favor WDM models with a peak likelihood value at the thermal relic mass of mWDM=4.5 keV. We find that the suppression of the FPS from free-streaming saturates at k≳0.1 s km−1 because of peculiar velocity smearing, and this saturated suppression combined with a slightly lower gas temperature provides a moderately better fit to the observed small-scale FPS for WDM cosmologies.
We consider the consequences of a matter power spectrum which rises on small scales until eventually being cut off by microphysical processes associated with the particle nature of dark matter. Evolving the perturbations of a weakly interacting massive particle from before decoupling until deep in the nonlinear regime, we show that nonlinear structure can form abundantly at very high redshifts. In such a scenario, dark matter annihilation is substantially increased after matter-radiation equality. Furthermore, since the power spectrum can be increased over a broad range of scales, the first star forming halos may form earlier than usual as well. The next challenge is determining how early Universe observations may constrain such enhanced dark matter perturbations.
Stellar and gas kinematics of galaxies are a sensitive probe of the dark matter distribution in the halo. The popular fuzzy dark matter models predict the peculiar shape of density distribution in galaxies: specific dense core with sharp transition to the halo. Moreover, fuzzy dark matter predicts scaling relations between the dark matter particle mass and density parameters. In this work, we use a Bayesian framework and several dark matter halo models to analyse the stellar kinematics of galaxies using the Spitzer Photometry & Accurate Rotation Curves database. We then employ a Bayesian model comparison to select the best halo density model. We find that more than half of the galaxies prefer the fuzzy dark model against standard dark matter profiles (NFW, Burkert, and cored NFW). While this seems like a success for fuzzy dark matter, we also find that there is no single value for the particle mass that provides a good fit for all galaxies.
We present the first strong-gravitational-lensing analysis of the galaxy cluster RX J0437.1+0043 (RXJ0437; z = 0.285). Newly obtained, deep MUSE observations, Keck/MOSFIRE near-infrared spectroscopy, and Hubble Space Telescope SNAPshot imaging reveal 13 multiply imaged background galaxies, three of them (at z = 1.98, 2.97, and 6.02, respectively) in hyperbolic umbilic (H–U) lensing configurations. The H–U images are located only 20–50 kpc from the cluster centre, i.e. at distances well inside the Einstein radius where images from other lens configurations are demagnified and often unobservable. Extremely rare (only one H–U lens was known previously) these systems are able to constrain the inner slope of the mass distribution – and unlike radial arcs, the presence of H–U configurations is not biased towards shallow cores. The galaxies lensed by RXJ0437 are magnified by factors ranging from 30 to 300 and (in the case of H–U systems) stretched nearly isotropically. Taking advantage of this extreme magnification, we demonstrate how the source galaxies in H–U systems can be used to probe for small-scale (∼109 M⊙) substructures, providing additional insight into the nature of dark matter.
Cosmologies with Light Massive Relics (LiMRs) as a subdominant component of the dark sector are well-motivated from a particle physics perspective, and can also have implications for the σ8 tension between early and late time probes of clustering. The effects of LiMRs on the Cosmic Microwave Background (CMB) and structure formation on large (linear) scales have been investigated extensively. In this paper, we initiate a systematic study of the effects of LiMRs on smaller, nonlinear scales using cosmological N-body simulations; focusing on quantities relevant for photometric galaxy surveys. For most of our study, we use a particular model of nonthermal LiMRs but the methods developed generalize to a large class of LiMR models — we explicitly demonstrate this by considering the Dodelson-Widrow velocity distribution. We find that, in general, the effects of LiMR on small scales are distinct from those of a ΛCDM universe, even when the value of σ8 is matched between the models. We show that weak lensing measurements around massive clusters, between ∼0.1h−1Mpc and ∼10h−1Mpc, should have sufficient signal-to-noise in future surveys to distinguish between ΛCDM and LiMR models that are tuned to fit both CMB data and linear scale clustering data at late times. Furthermore, we find that different LiMR cosmologies indistinguishable by conventional linear probes can be distinguished by nonlinear probes if their velocity distributions are sufficiently different. LiMR models can, therefore, be best tested by jointly analyzing the CMB and late-time structure formation on both large and small scales.
The mass profiles of massive dark matter halos are highly sensitive to the nature of dark matter and potential modifications of the theory of gravity on large scales. The Λ cold dark matter (CDM) paradigm makes strong predictions on the shape of dark matter halos and on the dependence of the shape parameters on halo mass, such that any deviation from the predicted universal shape would have important implications for the fundamental properties of dark matter. Here we use a set of 12 galaxy clusters with available deep X-ray and Sunyaev–Zel’dovich data to constrain the shape of the gravitational field with an unprecedented level of precision over two decades in radius. We introduce a nonparametric framework to reconstruct the shape of the gravitational field under the assumption of hydrostatic equilibrium and compare the resulting mass profiles to the expectations of Navarro–Frenk–White (NFW) and Einasto parametric mass profiles. On average, we find that the NFW profile provides an excellent description of the recovered mass profiles, with deviations of less than 10% over a wide radial range. However, there appears to be more diversity in the shape of individual profiles than can be captured by the NFW model. The average NFW concentration and its scatter agree very well with the prediction of the ΛCDM framework. For a subset of systems, we disentangle the gravitational field into the contribution of baryonic components (gas, brightest cluster galaxy, and satellite galaxies) and that of dark matter. The stellar content dominates the gravitational field inside ∼0.02 R 500 but is responsible for only 1–2% of the total gravitational field inside R 200 . The total baryon fraction reaches the cosmic value at R 200 and slightly exceeds it beyond this point, possibly indicating a mild level of nonthermal pressure support (10 − 20%) in cluster outskirts. Finally, the relation between observed and baryonic acceleration exhibits a complex shape that strongly departs from the radial acceleration relation in spiral galaxies, which shows that the aforementioned relation does not hold at the galaxy-cluster scale.
A fundamental prediction of the cold dark matter (CDM) model of structure formation is the existence of a vast population of dark matter haloes extending to subsolar masses. By contrast, other dark matter models, such as a warm thermal relic (WDM), predict a cutoff in the mass function at a mass which, for popular models, lies approximately between 107 and 1010 M⊙. We use mock observations to demonstrate the viability of a forward modelling approach to extract information about low-mass dark haloes lying along the line-of-sight to galaxy-galaxy strong lenses. This can be used to constrain the mass of a thermal relic dark matter particle, mDM. With 50 strong lenses at Hubble Space Telescope resolution and a maximum pixel signal-to-noise ratio of ∼50, the expected median 2σ constraint for a CDM-like model (with a halo mass cutoff at 107 M⊙) is mDM > 4.10 keV (50% chance of constraining mDM to be better than 4.10 keV). If, however, the dark matter is a warm particle of mDM = 2.2 keV, our ‘Approximate Bayesian Computation’ method would result in a median estimate of mDM between 1.43 and 3.21 keV. Our method can be extended to the large samples of strong lenses that will be observed by future telescopes, and could potentially rule out the standard CDM model of cosmogony. To aid future survey design, we quantify how these constraints will depend on data quality (spatial resolution and integration time) as well as on the lensing geometry (source and lens redshifts).
Being free of the initial singularity, bouncing cosmology serves as a promising alternative to inflation. However, how entropy production occurs during the postbounce phase is still unclear. In this work, we use a newly identified dark matter (DM) candidate called thermal equilibrium freeze-in DM (EQFIDM), which can directly freeze into thermal equilibrium shortly after a bounce, to trace the entropy-producing decay process of the residual bouncing field (RBF). Specifically, we present a model-independent formalism to obtain all nine possible types of entropy-producing RBF decay within a generic bouncing universe. We show that due to the different types of entropy production, the particle mass of this new DM candidate can range from the sub-keV scale to the super-TeV scale. From current Lyman-α forest observations, we find that although four of the possible types of entropy-producing processes have been excluded, five types remain, suggesting both warm and cold EQFIDM candidates with efficient entropy production mechanisms that are accommodated by the current observations. Then, we illustrate how the nature of the RBF can be constrained by current observations and investigate the potential of EQFIDM to alleviate the small-scale crisis.
Dwarf spheroidal galaxies (dSphs) are the most compact dark-matter-dominated objects observed so far. The Pauli exclusion principle limits the number of fermionic dark matter particles that can compose a dSph halo. This results in a well-known lower bound on their particle mass. So far, such bounds were obtained from the analysis of individual dSphs. In this paper, we model dark matter halo density profiles via the semi-analytical approach and analyse the data from eight ‘classical’ dSphs assuming the same mass of dark matter fermion in each object. First, we find out that modelling of Carina dSph results in a much worse fitting quality compared to the other seven objects. From the combined analysis of the kinematic data of the remaining seven ‘classical’ dSphs, we obtain a new 2σ lower bound of m ≳ 190 eV on the dark matter fermion mass. In addition, by combining a sub-sample of four dSphs – Draco, Fornax, Leo I, and Sculptor – we conclude that 220 eV fermionic dark matter appears to be preferred over the standard cold dark matter at about the 2σ level. However, this result becomes insignificant if all seven objects are included in the analysis. Future improvement of the obtained bound requires more detailed data, both from ‘classical’ and ultra-faint dSphs.
Dwarf spheroidal galaxies (dSphs) are the most compact dark matter-dominated objects observed so far. The Pauli exclusion principle limits the number of fermionic dark matter particles that can compose a dSph halo. This results in a well-known lower bound on their particle mass. So far, such bounds were obtained from the analysis of individual dSphs. In this paper, we model dark matter halo density profiles via the semi-analytical approach and analyse the data from eight `classical' dSphs assuming the same mass of dark matter fermion in each object. First, we find out that modelling of Carina dSph results in a much worse fitting quality compared to the other seven objects. From the combined analysis of the kinematic data of the remaining seven `classical' dSphs, we obtain a new $2\sigma$ lower bound of $m\gtrsim 190$ eV on the dark matter fermion mass. In addition, by combining a sub-sample of four dSphs -- Draco, Fornax, Leo I and Sculptor -- we conclude that 220 eV fermionic dark matter appears to be preferred over the standard CDM at about 2$\sigma$ level. However, this result becomes insignificant if all seven objects are included in the analysis. Future improvement of the obtained bound requires more detailed data, both from `classical' and ultra-faint dSphs.
We formulate a new model of density distribution for halos made of warm dark matter (WDM) particles. The model is described by a single microphysical parameter – the mass (or, equivalently, the maximal value of the initial phase-space density distribution) of dark matter particles. Given the WDM particle mass and the parameters of a dark matter density profile at the halo periphery, this model predicts the inner density profile. In the case of initial Fermi–Dirac distribution, we successfully reproduce cored dark matter profiles from N-body simulations. We calculate also the core radii of warm dark matter halos of dwarf spheroidal galaxies for particle masses mFD = 100, 200, 300, and 400 eV.
Non-linear structure formation in thermally produced WDM cosmologies has been extensively studied using simulations in the past few years (e.g. Colín et al. 2000, Bode et al. 2001, Viel et al. 2005, Knebe et al. 2008, Schneider et al. 2012, Lovell et al. 2012, Macció et al. 2013, Lovell et al. 2014, Reed et al. 2015, Colín et al. 2015, Yang et al. 2015, Bose et al. 2016, Horiuchi et al. 2016). In this chapter we use the Copernicus Complexio (coco-warm) high resolution N-body simulation to investigate the properties of subhaloes in a WDM model.
The identity of dark matter, the dominant matter component of the Universe, has long been a subject of great interest in cosmology. In the last three decades, the model of non-relativistic dark matter consisting of heavy weakly-interacting particles with negligible thermal velocities at early times, the Cold Dark Matter (CDM) model, has become the cornerstone of the standard cosmological paradigm.
We characterize the contribution from accreted material to the galactic discs of the Auriga Project, a set of high resolution magnetohydrodynamic cosmological simulations of late-type galaxies performed with the moving-mesh code AREPO. Our goal is to explore whether a significant accreted (or ex-situ) stellar component in the Milky Way disc could be hidden within the near-circular orbit population, which is strongly dominated by stars born in-situ. One third of our models shows a significant ex-situ disc but this fraction would be larger if constraints on orbital circularity were relaxed. Most of the ex-situ material ($\gtrsim 50\%$) comes from single massive satellites ($> 6 \times 10^{10}~M_{\odot}$). These satellites are accreted with a wide range of infall times and inclination angles (up to $85^{\circ}$). Ex-situ discs are thicker, older and more metal-poor than their in-situ counterparts. They show a flat median age profile, which differs from the negative gradient observed in the in-situ component. As a result, the likelihood of identifying an ex-situ disc in samples of old stars on near-circular orbits increases towards the outskirts of the disc. We show three examples that, in addition to ex-situ discs, have a strongly rotating dark matter component. Interestingly, two of these ex-situ stellar discs show an orbital circularity distribution that is consistent with that of the in-situ disc. Thus, they would not be detected in typical kinematic studies.
We explore an extended cosmological scenario where the dark matter is an admixture of cold and additional non-cold species. The mass and temperature of the non-cold dark matter particles are extracted from a number of cosmological measurements. Among others, we consider tomographic weak lensing data and Milky Way dwarf satellite galaxy counts. We also study the potential of these scenarios in alleviating the existing tensions between local measurements and Cosmic Microwave Background (CMB) estimates of the $S_8$ parameter, with $S_8=\sigma_8\sqrt{\Omega_m}$, and of the Hubble constant $H_0$. In principle, a sub-dominant, non-cold dark matter particle with a mass $m_X\sim$~keV, could achieve the goals above. However, the preferred ranges for its temperature and its mass are different when extracted from weak lensing observations and from Milky Way dwarf satellite galaxy counts, since these two measurements require suppressions of the matter power spectrum at different scales. Therefore, solving simultaneously the CMB-weak lensing tensions and the small scale crisis in the standard cold dark matter picture via only one non-cold dark matter component seems to be challenging.
The observed number of dwarf galaxies as a function of rotation velocity is significantly smaller than predicted by the $\Lambda$CDM model. This discrepancy cannot be simply solved by assuming strong baryonic processes, since they would violate the observed relation between maximum circular velocity ($v_{\rm max}$) and baryon mass of galaxies. A speculative but tantalising possibility is that the mismatch between observation and theory points towards the existence of non-cold or non-collisionless dark matter (DM). In this paper, we investigate the effects of warm, mixed (i.e warm plus cold), and self-interacting DM scenarios on the abundance of dwarf galaxies and the relation between observed HI line-width and maximum circular velocity. Both effects have the potential to alleviate the apparent mismatch between the observed and theoretical abundance of galaxies as a function of $v_{\rm max}$. For the case of warm and mixed DM, we show that the discrepancy disappears, even for luke-warm models that evade stringent bounds from the Lyman-$\alpha$ forest. Self-interacting DM scenarios can also provide a solution as long as they lead to extended ($\gtrsim 1.5$ kpc) dark matter cores in the density profiles of dwarf galaxies. Only models with velocity-dependent cross sections can yield such cores without violating other observational constraints at larger scales.
As a result of their internal dynamical coherence, thin stellar streams formed by disrupting globular clusters (GCs) can act as detectors of dark matter (DM) substructure in the Galactic halo. Perturbations induced by close flybys amplify into detectable density gaps, providing a probe both of the abundance and of the masses of DM subhaloes. Here, we use N-body simulations to show that the Galactic population of giant molecular clouds (GMCs) can also produce gaps (and clumps) in GC streams, and so may confuse the detection of DM subhaloes. We explore the cases of streams analogous to the observed Palomar 5 and GD1 systems, quantifying the expected incidence of structure caused by GMC perturbations. Deep observations should detect such disturbances regardless of the substructure content of the Milky Way's halo. Detailed modelling will be needed to demonstrate that any detected gaps or clumps were produced by DM subhaloes rather than by molecular clouds.
We implement the efficient line-of-sight method to calculate the anisotropy and polarization of the cosmic microwave background for scalar and tensor modes in almost Friedmann-Robertson-Walker models with positive spatial curvature. We present new results for the polarization power spectra in such models.
Lambda Cold Dark Matter (ΛCDM) is now the standard theory of structure formation in the universe. We present the first results from the new Bolshoi dissipationless cosmological ΛCDM simulation that uses cosmological parameters favored by current observations. The Bolshoi simulation was run in a volume 250 h –1 Mpc on a side using ~8 billion particles with mass and force resolution adequate to follow subhalos down to the completeness limit of V circ = 50 km s–1 maximum circular velocity. Using merger trees derived from analysis of 180 stored time steps we find the circular velocities of satellites before they fall into their host halos. Using excellent statistics of halos and subhalos (~10 million at every moment and ~50 million over the whole history) we present accurate approximations for statistics such as the halo mass function, the concentrations for distinct halos and subhalos, the abundance of halos as a function of their circular velocity, and the abundance and the spatial distribution of subhalos. We find that at high redshifts the concentration falls to a minimum value of about 4.0 and then rises for higher values of halo mass—a new result. We present approximations for the velocity and mass functions of distinct halos as a function of redshift. We find that while the Sheth-Tormen (ST) approximation for the mass function of halos found by spherical overdensity is quite accurate at low redshifts, the ST formula overpredicts the abundance of halos by nearly an order of magnitude by z = 10. We find that the number of subhalos scales with the circular velocity of the host halo as V 1/2 host, and that subhalos have nearly the same radial distribution as dark matter particles at radii 0.3-2 times the host halo virial radius. The subhalo velocity function N(> V sub) scales as V –3 circ. Combining the results of Bolshoi and Via Lactea-II simulations, we find that inside the virial radius of halos with the number of satellites is N(> V sub) = (V sub/58 km s–1)–3 for satellite circular velocities in the range 4 km s–1 < V sub < 150 km s–1.
We use high-resolution N-body simulations to study the equilibrium density profiles of dark matter halos in hierarchically clustering universes. We find that all such profiles have the same shape, independent of the halo mass, the initial density fluctuation spectrum, and the values of the cosmological parameters. Spherically averaged equilibrium profiles are well fitted over two decades in radius by a simple formula originally proposed to describe the structure of galaxy clusters in a cold dark matter universe. In any particular cosmology, the two scale parameters of the fit, the halo mass and its characteristic density, are strongly correlated. Low-mass halos are significantly denser than more massive systems, a correlation that reflects the higher collapse redshift of small halos. The characteristic density of an equilibrium halo is proportional to the density of the universe at the time it was assembled. A suitable definition of this assembly time allows the same proportionality constant to be used for all the cosmologies that we have tested. We compare our results with previous work on halo density profiles and show that there is good agreement. We also provide a step-by-step analytic procedure, based on the Press-Schechter formalism, that allows accurate equilibrium profiles to be calculated as a function of mass in any hierarchical model.
A clear prediction of the Cold Dark Matter model is the existence of cuspy
dark matter halo density profiles on all mass scales. This is not in agreement
with the observed rotation curves of spiral galaxies, challenging on small
scales the otherwise successful CDM paradigm. In this work we employ high
resolution cosmological hydro-dynamical simulations to study the effects of
dissipative processes on the inner distribution of dark matter in Milky-Way
like objects (M~1e12 Msun). Our simulations include supernova feedback, and the
effects of the radiation pressure of massive stars before they explode as
supernovae. The increased stellar feedback results in the expansion of the dark
matter halo instead of contraction with respect to N-body simulations. Baryons
are able to erase the dark matter cuspy distribution creating a flat, cored,
dark matter density profile in the central several kpc of a massive Milky-Way
like halo. The profile is well fit by a Burkert profile, with fitting
parameters consistent with the observations. In addition, we obtain flat
rotation curves as well as extended, exponential stellar disk profiles. While
the stellar disk we obtain is still partially too thick to resemble the MW thin
disk, this pilot study shows that there is enough energy available in the
baryonic component to alter the dark matter distribution even in massive disc
galaxies, providing a possible solution to the long standing problem of cusps
vs. cores.
According to the hierarchical clustering scenario, galaxies are assembled by merging and accretion of numerous satellites of different sizes and masses. This ongoing process is not 100% efficient in destroying all of the accreted satellites, as evidenced by the satellites of our Galaxy and of M31. Using published data, we have compiled the circular velocity (Vcirc) distribution function (VDF) of galaxy satellites in the Local Group. We find that within the volumes of radius of 570 kpc (400 h-1 kpc assuming the Hubble constant h = 0.7) centered on the Milky Way and Andromeda, the average VDF is roughly approximated as n(> Vcirc) ≈ 55 ± 11(Vcirc/10 km s-1)-1.4±0.4 h3 Mpc-3 for Vcirc in the range ≈10-70 km s-1. The observed VDF is compared with results of high-resolution cosmological simulations. We find that the VDF in models is very different from the observed one: n(> Vcirc) ≈ 1200(Vcirc/10 km s-1)-2.75 h3 Mpc-3. Cosmological models thus predict that a halo the size of our Galaxy should have about 50 dark matter satellites with circular velocity greater than 20 km s-1 and mass greater than 3 × 108 M☉ within a 570 kpc radius. This number is significantly higher than the approximately dozen satellites actually observed around our Galaxy. The difference is even larger if we consider the abundance of satellites in simulated galaxy groups similar to the Local Group. The models predict ~300 satellites inside a 1.5 Mpc radius, while only ~40 satellites are observed in the Local Group. The observed and predicted VDFs cross at ≈50 km s-1, indicating that the predicted abundance of satellites with Vcirc 50 km s-1 is in reasonably good agreement with observations. We conclude, therefore, that unless a large fraction of the Local Group satellites has been missed in observations, there is a dramatic discrepancy between observations and hierarchical models, regardless of the model parameters. We discuss several possible explanations for this discrepancy including identification of some satellites with the high-velocity clouds observed in the Local Group and the existence of dark satellites that failed to accrete gas and form stars either because of the expulsion of gas in the supernovae-driven winds or because of gas heating by the intergalactic ionizing background.
We use measurements of the stellar velocity dispersion profile of the Fornax dwarf spheroidal galaxy to derive constraints on its dark matter distribution. Although the data are unable to distinguish between models with small cores and those with cusps, we show that a large 1 kpc dark matter core in Fornax is highly implausible. Irrespective of the origin of the core, reasonable dynamical limits on the mass of the Fornax halo constrain its core radius to be no larger than ~700 pc. We derive an upper limit of rcore 300 pc by demanding that the central phase-space density of Fornax not exceed that directly inferred from the rotation curves of low-mass spiral galaxies. Furthermore, if the halo is composed of warm dark matter, then phase-space constraints force the core to be quite small in order to avoid conservative limits from the Lyα forest power spectrum, rcore 85 pc. We discuss our results in the context of the idea that the extended globular cluster distribution in Fornax can be explained by the presence of a large ~1.5 kpc core. A self-consistent core of this size would be drastically inconsistent with the expectations of standard warm or cold dark matter models and would also require an unreasonably massive dark matter halo, with Vmax 200 km s-1.
The Wilkinson Microwave Anisotropy Probe (WMAP) 5-year data provide stringent limits on deviations from the minimal, six-parameter Λ cold dark matter model. We report these limits and use them to constrain the physics of cosmic inflation via Gaussianity, adiabaticity, the power spectrum of primordial fluctuations, gravitational waves, and spatial curvature. We also constrain models of dark energy via its equation of state, parity-violating interaction, and neutrino properties, such as mass and the number of species. We detect no convincing deviations from the minimal model. The six parameters and the corresponding 68% uncertainties, derived from the WMAP data combined with the distance measurements from the Type Ia supernovae (SN) and the Baryon Acoustic Oscillations (BAO) in the distribution of galaxies, are: Ω b h 2 = 0.02267+0.00058 –0.00059, Ω c h 2 = 0.1131 ± 0.0034, ΩΛ = 0.726 ± 0.015, ns = 0.960 ± 0.013, τ = 0.084 ± 0.016, and at k = 0.002 Mpc-1. From these, we derive σ8 = 0.812 ± 0.026, H 0 = 70.5 ± 1.3 km s-1 Mpc–1, Ω b = 0.0456 ± 0.0015, Ω c = 0.228 ± 0.013, Ω m h 2 = 0.1358+0.0037 –0.0036, z reion = 10.9 ± 1.4, and t 0 = 13.72 ± 0.12 Gyr. With the WMAP data combined with BAO and SN, we find the limit on the tensor-to-scalar ratio of r < 0.22(95%CL), and that ns > 1 is disfavored even when gravitational waves are included, which constrains the models of inflation that can produce significant gravitational waves, such as chaotic or power-law inflation models, or a blue spectrum, such as hybrid inflation models. We obtain tight, simultaneous limits on the (constant) equation of state of dark energy and the spatial curvature of the universe: –0.14 < 1 + w < 0.12(95%CL) and –0.0179 < Ω k < 0.0081(95%CL). We provide a set of "WMAP distance priors," to test a variety of dark energy models with spatial curvature. We test a time-dependent w with a present value constrained as –0.33 < 1 + w 0 < 0.21 (95% CL). Temperature and dark matter fluctuations are found to obey the adiabatic relation to within 8.9% and 2.1% for the axion-type and curvaton-type dark matter, respectively. The power spectra of TB and EB correlations constrain a parity-violating interaction, which rotates the polarization angle and converts E to B. The polarization angle could not be rotated more than –59 < Δα < 24 (95% CL) between the decoupling and the present epoch. We find the limit on the total mass of massive neutrinos of ∑m ν < 0.67 eV(95%CL), which is free from the uncertainty in the normalization of the large-scale structure data. The number of relativistic degrees of freedom (dof), expressed in units of the effective number of neutrino species, is constrained as N eff = 4.4 ± 1.5 (68%), consistent with the standard value of 3.04. Finally, quantitative limits on physically-motivated primordial non-Gaussianity parameters are –9 < f local NL < 111 (95% CL) and –151 < f equil NL < 253 (95% CL) for the local and equilateral models, respectively.
(abridged) We study the relation between the density profiles of dark matter halos and their mass assembly histories, using a statistical sample of halos in a high-resolution N-body simulation of the LCDM cosmology. For each halo at z=0, we identify its merger-history tree, and determine concentration parameters c_vir for all progenitors, thus providing a structural merger tree for each halo. We fit the mass accretion histories by a universal function with one parameter, the formation epoch a_c, defined when the log mass accretion rate dlogM/dloga falls below a critical value S. We find that late forming galaxies tend to be less concentrated, such that c_vir ``observed'' at any epoch a_o is strongly correlated with a_c via c_vir=c_1*a_o/a_c. Scatter about this relation is mostly due to measurement errors in c_v and a_c, implying that the actual spread in c_vir for halos of a given mass can be mostly attributed to scatter in a_c. We demonstrate that this relation can also be used to predict the mass and redshift dependence of c_v, and the scatter about the median c_vir(M,z), using accretion histories derived from the Extended Press-Schechter (EPS) formalism, after adjusting for a constant offset between the formation times as predicted by EPS and as measured in the simulations;this new ingredient can thus be easily incorporated into semi-analytic models of galaxy formation. The correlation found between halo concentration and mass accretion rate suggests a physical interpretation: for high mass infall rates the central density is related to the background density; when the mass infall rate slows, the central density stays approximately constant and the halo concentration just grows as R_vir. The tight correlation demonstrated here provides an essential new ingredient for galaxy formation modeling.
Using constrained simulations of the local universe for generic cold dark matter (CDM) and for 1 keV warm dark matter (WDM), we investigate the difference in the abundance of dark matter halos in the local environment. We find that the mass function (MF) within 20 h –1 Mpc of the Local Group is ~2 times larger than the universal MF in the 109-1013 h –1 M ☉ mass range. Imposing the field of view of the ongoing H I blind survey Arecibo Legacy Fast ALFA (ALFALFA) in our simulations, we predict that the velocity function (VF) in the Virgo-direction region (VdR) exceeds the universal VF by a factor of 3. Furthermore, employing a scheme to translate the halo VF into a galaxy VF, we compare the simulation results with a sample of galaxies from the early catalog release of ALFALFA. We find that our simulations are able to reproduce the VF in the 80-300 km s-1 velocity range, having a value ~10 times larger than the universal VF in the VdR. In the low-velocity regime, 35-80 km s-1, the WDM simulation reproduces the observed flattening of the VF. In contrast, the simulation with CDM predicts a steep rise in the VF toward lower velocities; for V max = 35 km s-1, it forecasts ~10 times more sources than the ones observed. If confirmed by the complete ALFALFA survey, our results indicate a potential problem for the CDM paradigm or for the conventional assumptions about energetic feedback in dwarf galaxies.
We investigate the structure of dark matter halos by means of the kinematics of a very large sample of spiral galaxies of all luminosities. The observed rotation curves show a universal profile which is the sum of an exponential thin disk term and a spherical halo term with a flat density core. We find that the Burkert profile proposed to describe the dark matter halo density distribution of dwarf galaxies also provides an excellent mass model for the dark halos around disk systems up to 100 times more massive. Moreover, we find that spiral dark matter core densities ρ0 and core radii r0 lie in the same scaling relation ρ0 = 4.5 × 10-2(r0/kpc)-2/3 M☉ pc-3 of dwarf galaxies with core radii up to 10 times smaller. At the highest masses ρ0 decreases with r0 faster than the - power law, implying a lack of objects with disk masses greater than 1011 M☉ and central densities greater than 1.5 × 10-2(r0/kpc)-3 M☉ pc-3 that can be explained by the existence of a maximum mass of about 2 × 1012 M☉ for a halo hosting a spiral galaxy.
We use numerical simulations to examine the substructure within galactic and cluster mass halos that form within a hierarchical universe. Clusters are easily reproduced with a steep mass spectrum of thousands of substructure clumps that closely matches the observations. However, the survival of dark matter substructure also occurs on galactic scales, leading to the remarkable result that galaxy halos appear as scaled versions of galaxy clusters. The model predicts that the virialized extent of the Milky Way's halo should contain about 500 satellites with circular velocities larger than the Draco and Ursa Minor systems, i.e., bound masses 108 M☉ and tidally limited sizes 1 kpc. The substructure clumps are on orbits that take a large fraction of them through the stellar disk, leading to significant resonant and impulsive heating. Their abundance and singular density profiles have important implications for the existence of old thin disks, cold stellar streams, gravitational lensing, and indirect/direct detection experiments.
We present a comprehensive analysis of the halo model of cosmological large
to small-scale structure statistics in the case of warm dark matter (WDM)
structure formation scenarios. We include the effects of WDM on the linear
matter power spectrum, halo density profile, halo concentration relation, halo
mass function, subhalo density profile, subhalo mass function and biasing of
the smooth dark matter component. As expected, we find large differences at the
smallest physical scales in the nonlinear matter power spectrum predicted in
the halo model between WDM and cold dark matter even for reasonably high-scale
WDM particle masses. We find that significant effects are contributed from the
alteration of the halo density profile and concentration, as well as the halo
mass function. We further find that the effects of WDM on the subhalo
population are important but sub-dominant. Clustering effects of the biasing of
the smooth component in WDM is not largely significant.
A number of dwarf spheroidal (dSph) galaxies are known to contain a more extended, metal-poor population with a flattish velocity dispersion profile, and a more concentrated, metal-rich population with a velocity dispersion declining with radius. The two populations can be modelled with Michie–King distribution functions (DFs) in the isothermal and in the sharply truncated limits, respectively. We argue that the truncation of the metal-rich population can be traced back to the spatial distribution of the star-forming gas. Suppose δ is the exponent of the first non-constant term in the Taylor expansion of the total potential at the centre (δ= 1 for Navarro–Frenk–White or NFW haloes, δ= 2 for cored haloes). Then, we show that the ratio of the half-light radii of the populations Rδ/2h, 2/Rh, 1δ/2 must be smaller than the ratio of the line-of-sight velocity dispersions σlos, 2(Rh, 2)/σlos, 1(Rh, 1).
Specializing to the case of the Sculptor dSph, we develop a technique to fit simultaneously both populations with Michie–King DFs. This enables us to determine the mass profile of the Sculptor dSph with unprecedented accuracy in the radial range 0.2 < r < 1.2 kpc. We show that cored halo models are preferred over cusped halo models, with a likelihood ratio test rejecting NFW models at any significance level higher than 0.05 per cent. Even more worryingly, the best-fitting NFW models require concentrations with c ≲ 20, which is not in the cosmologically preferred range for dwarf galaxies. We conclude that the kinematics of multiple populations in dSphs provides a substantial new challenge for theories of galaxy formation, with the weight of available evidence strongly against dark matter cusps at the centre.
We present observations and a dynamical analysis of the comet-like main-belt object, (596) Scheila. V-band photometry obtained on UT 2010 December 12 indicates that Scheila's dust cloud has a scattering cross-section ~1.4 times larger than that of the nucleus, corresponding to a dust mass of Md ~ 3 × 107 kg. V–R color measurements indicate that both the nucleus and dust are redder than the Sun, with no significant color differences between the dust cloud's northern and southern plumes. We also undertake an ultimately unsuccessful search for CN emission, where we find CN and H2O production rates of Q
CN < 9 × 1023 s–1 and s–1. Numerical simulations indicate that Scheila is dynamically stable for >100 Myr, suggesting that it is likely native to its current location. We also find that it does not belong to a dynamical asteroid family of any significance. We consider sublimation-driven scenarios that could produce the appearance of multiple plumes of dust emission, but reject them as being physically implausible. Instead, we concur with previous studies that the unusual morphology of Scheila's dust cloud is most simply explained by a single oblique impact, meaning that this object is likely not a main-belt comet but is instead the second disrupted asteroid after P/2010 A2 (LINEAR) to be discovered.
We explore the impact of a LWDM cosmological scenario on the clustering
properties of large-scale structure in the Universe. We do this by extending
the halo model. The new development is that we consider two components to the
mass density: one arising from mass in collapsed haloes, and the second from a
smooth component of uncollapsed mass. Assuming that the nonlinear clustering of
dark matter haloes can be understood, then from conservation arguments one can
precisely calculate the clustering properties of the smooth component and its
cross-correlation with haloes. We then explore how the three main ingredients
of the halo calculations, the mass function, bias and density profiles are
affected by WDM. We show that, relative to CDM: the mass function is suppressed
by ~50%, for masses ~100 times the free-streaming mass-scale; the bias of low
mass haloes can be boosted by up to 20%; core densities of haloes can be
suppressed. We also examine the impact of relic thermal velocities on the
density profiles, and find that these effects are constrained to scales r<1
kpc/h, and hence of little importance for dark matter tests, owing to
uncertainties in the baryonic physics. We use our modified halo model to
calculate the non-linear matter power spectrum, and find significant
small-scale power in the model. However, relative to the CDM case, the power is
suppressed. We then calculate the expected signal and noise that our set of
LWDM models would give for a future weak lensing mission. We show that the
models should in principle be separable at high significance. Finally, using
the Fisher matrix formalism we forecast the limit on the WDM particle mass for
a future full-sky weak lensing mission like Euclid or LSST. With Planck priors
and using multipoles l<5000, we find that a lower limit of 2.6 keV should be
easily achievable.
We have conducted N-body simulations of the growth of Milky Way-sized halos
in cold and warm dark matter cosmologies. The number of dark matter satellites
in our simulated Milky Ways decreases with decreasing mass of the dark matter
particle. Assuming that the number of dark matter satellites exceeds or equals
the number of observed satellites of the Milky Way we derive lower limits on
the dark matter particle mass. We find with 95% confidence m_s > 13.3 keV for a
sterile neutrino produced by the Dodelson and Widrow mechanism, m_s > 8.9 keV
for the Shi and Fuller mechanism, m_s > 3.0 keV for the Higgs decay mechanism,
and m_{WDM} > 2.3 keV for a thermal dark matter particle. The recent discovery
of many new dark matter dominated satellites of the Milky Way in the Sloan
Digital Sky Survey allows us to set lower limits comparable to constraints from
the complementary methods of Lyman-alpha forest modeling and X-ray observations
of the unresolved cosmic X-ray background and of dark matter halos from dwarf
galaxy to cluster scales. Future surveys like LSST, DES, PanSTARRS, and
SkyMapper have the potential to discover many more satellites and further
improve constraints on the dark matter particle mass.
Warm dark matter (WDM) and self-interacting dark matter (SIDM) are often motivated by the inferred cores in the dark matter halos of low surface brightness (LSB) galaxies. We test thermal WDM, non-thermal WDM, and SIDM using high-resolution rotation curves of nine LSB galaxies. We fit these dark matter models to the data and determine the halo core radii and central densities. While the minimum core size in WDM models is predicted to decrease with halo mass, we find that the inferred core radii increase with halo mass and also cannot be explained with a single value of the primordial phase space density. Moreover, if the core size is set by WDM particle properties, then even the smallest cores we infer would require primordial phase space density values that are orders of magnitude smaller than lower limits obtained from the Lyman alpha forest power spectra. We also find that the dark matter halo core densities vary by a factor of about 30 from system to system while showing no systematic trend with the maximum rotation velocity of the galaxy. This strongly argues against the core size being directly set by large self-interactions (scattering or annihilation) of dark matter. We therefore conclude that the inferred cores do not provide motivation to prefer WDM or SIDM over other dark matter models. Comment: Accepted to ApJL; additions to Figs 3 and 4; minor changes to text
We present a new method to remove the impact of random and small-scale noncircular motions from H I velocity fields in (dwarf) galaxies in order to better constrain the dark matter properties for these objects. This method extracts the circularly rotating velocity components from the H I data cube and condenses them into a so-called bulk velocity field. We derive high-resolution (~0.2 kpc) rotation curves of IC 2574 and NGC 2366 based on bulk velocity fields derived from The H I Nearby Galaxy Survey obtained at the Very Large Array. We compare the bulk velocity field rotation curves with those derived from the traditional intensity-weighted mean velocity fields and find significant differences. The bulk velocity field rotation curves are significantly less affected by noncircular motions and constrain the dark matter distribution in our galaxies, allowing us to address the discrepancy between the inferred and predicted dark matter distribution in galaxies (the "cusp/core" problem). Spitzer Infrared Nearby Galaxies Survey 3.6 mum data, which are largely unaffected by dust in these systems, as well as ancillary optical information, are used to separate the contribution of the baryons from the total matter content. Using stellar population synthesis models, assuming various sets of metallicity and star-formation histories, we compute stellar mass-to-light ratios for the 3.6 mum and 4.5 mum bands. Using our predicted value for the 3.6 mum stellar mass-to-light ratio, we find that the observed dark matter distributions of IC 2574 and NGC 2366 are inconsistent with the cusp-like dark matter halo predicted by Lambda Cold Dark Matter models, even after corrections for noncircular motions. This result also holds for other assumptions about the stellar mass-to-light ratio. The distribution of dark matter within our sample galaxies is best described by models with a kpc-sized constant-density core.
We introduce a method for measuring the slopes of mass profiles within dwarf spheroidal (dSph) galaxies directly from stellar spectroscopic data and without adopting a dark matter halo model. Our method combines two recent results: (1) spherically symmetric, equilibrium Jeans models imply that the product of half-light radius and (squared) stellar velocity dispersion provides an estimate of the mass enclosed within the half-light radius of a dSph stellar component, and (2) some dSphs have chemodynamically distinct stellar subcomponents that independently trace the same gravitational potential. We devise a statistical method that uses measurements of stellar positions, velocities, and spectral indices to distinguish two dSph stellar subcomponents and to estimate their individual half-light radii and velocity dispersions. For a dSph with two detected stellar subcomponents, we obtain estimates of masses enclosed at two discrete points in the same mass profile, immediately defining a slope. Applied to published spectroscopic data, our method distinguishes stellar subcomponents in the Fornax and Sculptor dSphs, for which we measure slopes Γ ≡ Δlog M/Δlog r = 2.61-0.37+0.43 and Γ = 2.95-0.39+0.51, respectively. These values are consistent with "cores" of constant density within the central few hundred parsecs of each galaxy and rule out "cuspy" Navarro-Frenk-White (NFW) profiles (dlog M/dlog r ≤ 2 at all radii) with a significance ≳ 96% and ≳ 99%, respectively. Tests with synthetic data indicate that our method tends systematically to overestimate the mass of the inner stellar subcomponent to a greater degree than that of the outer stellar subcomponent, and therefore to underestimate the slope Γ (implying that the stated NFW exclusion levels are conservative). © 2011. The American Astronomical Society. All rights reserved.
The results obtained from a study of the mass distribution of 36 spiral galaxies are presented. The galaxies were observed using Fabry-Perot interferometry as part of the GHASP survey. The main aim of obtaining high-resolution Halpha 2D velocity fields is to define more accurately the rising part of the rotation curves which should allow to better constrain the parameters of the mass distribution. The Halpha velocities were combined with low resolution HI data from the literature, when available. Combining the kinematical data with photometric data, mass models were derived from these rotation curves using two different functional forms for the halo: an isothermal sphere (ISO) and a Navarro-Frenk-White (NFW) profile. For the galaxies already modelled by other authors, the results tend to agree. Our results point at the existence of a constant density core in the centre of the dark matter haloes rather than a cuspy core, whatever the type of the galaxy from Sab to Im. This extends to all types the result already obtained by other authors studying dwarf and low surface brightness galaxies but would necessitate a larger sample of galaxies to conclude more strongly. Whatever model is used (ISO or NFW), small core radius haloes have higher central densities, again for all morphological types. We confirm different halo scaling laws, such as the correlations between the core radius and the central density of the halo with the absolute magnitude of a galaxy: low-luminosity galaxies have small core radius and high central density. We find that the product of the central density with the core radius of the dark matter halo is nearly constant, whatever the model and whatever the absolute magnitude of the galaxy. This suggests that the halo surface density is independent from the galaxy type.
We show that the extension of the standard model by three right-handed neutrinos with masses smaller than the electroweak scale (the nuMSM) can explain simultaneously dark matter and baryon asymmetry of the universe and be consistent with the experiments on neutrino oscillations. Several constraints on the parameters of the nuMSM are derived.
We present a new method for calculating linear cosmic microwave background (CM B) anisotropy spectra based on integration over sources along the photon past light cone. In this approach the temperature anisotropy is written as a time integral over the product of a geometrical term and a source term. The geometrical term is given by radial eigenfunctions, which do not depend on the particular cosmological model. The source term can be expressed in terms of photon, baryon, and metric perturbations, all of which can be calculated using a small number of differential equations. This split clearly separates the dynamical from the geometrical effects on the CMB anisotropies. More importantly, it allows us to significantly reduce the computational time compared to standard methods. This is achieved because the source term, which depends on the model and is generally the most time-consuming part of calculation, is a slowly varying function of wavelength and needs to be evaluated only in a small number of points. The geometrical term, which oscillates much more rapidly than the source term, does not depend on the particular model and can be precomputed in advance. Standard methods that do not separate the two terms require a much higher number of evaluations. The new method leads to about 2 orders of magnitude reduction in CPU time when compared to standard methods and typically requires a few minutes on a workstation for a single model. The method should be especially useful for accurate determinations of cosmological parameters from CMB anisotropy and polarization measurements that will become with the next generation of experiments. A program implementing this method can be obtained from the authors.
We use a series of cosmological N-body simulations for a flat LCDM cosmology to investigate the properties of dark matter haloes in the mass range 3.0e9-3.0e13 Msun. These properties include the concentration parameter (c), the spin parameter (lambda) and the mean axis ratio (q). For the concentration-mass relation we find c~M^(-0.11) in agreement with the model proposed by Bullock et al. even if we find a lower normalization (15%). The results for lambda and q are in good agreement with previous studies, while c and lambda are anti-correlated. In an attempt to remove unrelaxed haloes, we use the offset parameter (xoff), defined as the distance between the most bound particle and the center of mass. Removing haloes with large xoff increases the c by ~10%, lowers the lambda by ~15%, and removes the most prolate haloes. In addition, it largely removes the anti-correlation between c and lambda though not entirely. We also investigate the effects of the large-scale environment. We find that more concentrated haloes live in denser environments. Note, however, that the trend is weak compared to the scatter. For the spin parameters we find no environment dependence, while there is a weak indication that the most spherical haloes reside in denser region. Finally, using a simple model for disk galaxy formation we show that haloes that host low surface brightness galaxies are expected to be hosted by a biased sub-set of haloes. Not only do these haloes have spin parameters that are larger than average, they also have c that are 15% percent lower than the average at a given halo mass. We discuss the implications of all these findings for the claimed disagreement between halo concentrations inferred from LSB rotation curves, and those expected for a LCDM cosmology. (abridged)
Cold dark matter theory predicts that the Local Group should contain many more dwarf-sized objects than the observed number of dwarf galaxies—the so-called substructure problem. We investigate whether the suppression of star formation in these small objects due to the presence of a photoionizing background can resolve the problem. We make use of results from recent hydrodynamic simulations to build a recipe for the suppression of gas infall into semianalytic galaxy formation models and use these to predict the luminosity function of dwarf galaxies in the Local Group. In the models without photoionization "squelching," we predict a large excess of faint dwarf galaxies compared with the observed number in the Local Group—thus, the usual recipe for supernova feedback used in semianalytic models does not solve the substructure problem on its own. When we include photoionization squelching, we find good agreement with the observations. We have neglected tidal destruction, which probably further reduces the number of dwarf galaxies. We conclude that photoionizing squelching easily solves the substructure problem. In fact, it is likely that once this effect is taken into account, models with reduced small-scale power (e.g., warm dark matter) would underproduce dwarf galaxies.
This paper describes the generation of Gaussian random fields with multiple levels of resolution. We present the theory of adaptive mesh refinement of Gaussian random fields followed by the implementation and testing of a computer code package performing this refinement called "GRAFIC2." This package is available to the computational cosmology community at http://arcturus.mit.edu/grafic/ or by e-mail from the author.
ABSTRACTA generic property of the cuspy simulated virialized haloes in cold dark matter (CDM) cosmogenies is that their concentration is inversely correlated with their mass. This behaviour has also been confirmed in observations, although differences in the exact form and dispersion of this so-called mass–concentration relationship have been reported. Some observational studies of massive haloes suggest that they are statistically overconcentrated with respect to the expectations of ΛCDM. Here we investigate the impact that various published mass–concentration relationships, both from simulations and derived from observations, would have on other cosmological observables, in particular considering upcoming surveys. We find that an integral measure of lensing shear, such as counts of peaks from haloes, is very sensitive to the relationship between mass and concentration at fixed σ8, and the disparity between some reported fits is much larger than the impact of uncertainty in σ8 itself. We also briefly assess the impact of baryonic physics on cluster scale observables, using state-of-the-art simulations, concluding that it is unlikely to give rise to the high concentrations reported for some clusters.
We use a self-consistent model of galaxy formation and the evolution of the intergalactic medium to study the effects of the reionization of the Universe at high redshift on the properties of satellite galaxies like those seen around the Milky Way. Photoionization suppresses the formation of small galaxies, so that surviving satellites are preferentially those that formed before the Universe reionized. As a result, the number of satellites expected today is about an order of magnitude smaller than the number inferred by identifying satellites with subhaloes of the same circular velocity in high-resolution simulations of the dark matter. The resulting satellite population has an abundance similar to that observed in the Local Group, although the distribution of circular velocities differs somewhat from the available data. We explore many other properties of satellite galaxies, including their gas content, metallicity and star formation rate, and find generally good agreement with available data. Our model predicts the existence of many as yet undetected satellites in the Local Group. We quantify their observability in terms of their apparent magnitude and surface brightness, and also in terms of their constituent stars. A near-complete census of the Milky Way's satellites would require imaging to V≈20 and to a surface brightness fainter than 26 V-band magnitudes per square arcsecond. Satellites with integrated luminosity V=15 should contain of order 100 stars brighter than B=26, with central stellar densities of a few tens per square arcminute. Discovery of a large population of faint satellites would provide a strong test of current models of galaxy formation.
Using high-resolution simulations within the cold dark matter (CDM) and warm dark matter (WDM) models, we study the evolution
of small-scale structure in the local volume, a sphere of 8-Mpc radius around the Local Group. We compare the observed spectrum
of minivoids in the local volume with the spectrum of minivoids determined from the simulations. We show that the ΛWDM model
can easily explain both the observed spectrum of minivoids and the presence of low-mass galaxies observed in the local volume,
provided that all haloes with circular velocities greater than 20 km s−1 host galaxies. On the contrary, within the ΛCDM model the distribution of the simulated minivoids reflects the observed one
if haloes with maximal circular velocities larger than 35 km s−1 host galaxies. This assumption is in contradiction with observations of galaxies with circular velocities as low as 20 km
s−1 in our local Universe. A potential problem of the ΛWDM model could be the late formation of the haloes in which the gas can
be efficiently photoevaporated. Thus, star formation is suppressed and low-mass haloes might not host any galaxy at all.
Using six high-resolution dissipationless simulations with a varying box size in a flat Lambda cold dark matter (ΛCDM) universe,
we study the mass and redshift dependence of dark matter halo shapes for Mvir= 9.0 × 1011− 2.0 × 1014 h−1 M⊙, over the redshift range z= 0–3, and for two values of σ8= 0.75 and 0.9. Remarkably, we find that the redshift, mass and σ8 dependence of the mean smallest-to-largest axis ratio of haloes is well described by the simple power-law relation 〈s〉= (0.54 ± 0.02)(Mvir/M*)−0.050±0.003, where s is measured at 0.3Rvir, and the z and σ8 dependences are governed by the characteristic non-linear mass, M*=M*(z, σ8). We find that the scatter about the mean s is well described by a Gaussian with σ∼ 0.1, for all masses and redshifts. We compare our results to a variety of previous
works on halo shapes and find that reported differences between studies are primarily explained by differences in their methodologies.
We address the evolutionary aspects of individual halo shapes by following the shapes of the haloes through ∼100 snapshots
in time. We determine the formation scalefactor ac as defined by Wechsler et al. and find that it can be related to the halo shape at z= 0 and its evolution over time.
We present a detailed study of the redshift evolution of dark matter halo structural parameters in a Λ cold dark matter cosmology. We study the mass and redshift dependence of the concentration, shape and spin parameter in N-body simulations spanning masses from 1010 to 1015 h−1 M⊙ and redshifts from 0 to 2. We present a series of fitting formulae that accurately describe the time evolution of the concentration–mass (cvir–Mvir) relation since z= 2. Using arguments based on the spherical collapse model, we study the behaviour of the scalelength of the density profile during the assembly history of haloes, obtaining physical insights into the origin of the observed time evolution of the cvir–Mvir relation. We also investigate the evolution with redshift of dark matter halo shape and its dependence on mass. Within the studied redshift range, the relation between the halo shape and mass can be well fitted by a redshift-dependent power law. Finally we show that although for z= 0 the spin parameter is practically mass independent, at increasing redshift it shows an increasing correlation with mass.
We show that massive sterile neutrinos mixed with the ordinary ones may be produced in the early universe in the right amount to be natural warm dark matter particles. Their mass should be below 40 keV and the corresponding mixing angles sin22θ>10−11 for mixing with νμ or ντ, while mixing with νe is slightly stronger bounded with mass less than 30 keV.
The free streaming of warm dark matter particles dampens the fluctuation
spectrum, flattens the mass function of haloes and imprints a fine grained
phase density limit for dark matter structures. The phase space density limit
is expected to imprint a constant density core at the halo center on the
contrary to what happens for cold dark matter. We explore these effects using
high resolution simulations of structure formation in different warm dark
matter scenarios. We find that the size of the core we obtain in simulated
haloes is in good agreement with theoretical expectations based on Liouville's
theorem. However, our simulations show that in order to create a significant
core, (r_c~1 kpc), in a dwarf galaxy (M~1e10 Msun), a thermal candidate with a
mass as low as 0.1 keV is required. This would fully prevent the formation of
the dwarf galaxy in the first place. For candidates satisfying large scale
structure constrains (m_wdm larger than 1-2 keV) the expected size of the core
is of the order of 10 (20) pc for a dark matter halo with a mass of 1e10 (1e8)
Msun. We conclude that "standard" warm dark matter is not viable solution for
explaining the presence of cored density profiles in low mass galaxies.
The dark energy dominated warm dark matter (WDM) model is a promising alternative cosmological scenario. We explore large-scale
structure formation in this paradigm. We do this in two different ways: with the halo model approach and with the help of
an ensemble of high-resolution N-body simulations. Combining these quasi-independent approaches leads to a physical understanding of the important processes
which shape the formation of structures. We take a detailed look at the halo mass function, the concentrations and the linear
halo bias of WDM. In all cases we find interesting deviations with respect to cold dark matter (CDM). In particular, the concentration–mass
relation displays a turnover for group scale dark matter haloes, for the case of WDM particles with masses of the order of
mWDM∼ 0.25 keV. This may be interpreted as a hint for top–down structure formation on small scales. We implement our results into
the halo model and find much better agreement with simulations. On small scales, the WDM halo model now performs as well as
its CDM counterpart.
We investigate the non-linear evolution of the matter power spectrum by using a large set of high-resolution N-body/hydrodynamic simulations. The linear matter power in the initial conditions is consistently modified to mimic the presence
of warm dark matter (WDM) particles which induce a small-scale cut-off in the power as compared to standard cold dark matter
scenarios. The impact of such thermal relics is examined at small scales k > 1 h Mpc−1, at redshifts of z < 5, which are particularly important for the next generation of Lyman α forest, weak lensing and galaxy clustering surveys.
We measure the mass and redshift dependence of the WDM non-linear matter power and provide a fitting formula which is accurate
at the ∼2 per cent level below z= 3 and for particle masses of mWDM≥ 0.5 keV. The role of baryonic physics on the WDM-induced suppression is also quantified. In particular, we examine the effects
of cooling, star formation and feedback from strong galactic winds. Finally, we find that a modified version of the halo model
describes the shape of the WDM suppressed power spectra better than halofit. In the case of weak lensing however, the latter works better than the former, since it is more accurate on the relevant,
mid-range scales, albeit very inaccurate on the smallest scales (k > 10 h Mpc−1) of the matter power spectrum.
The ongoing Arecibo Legacy Fast ALFA (ALFALFA) survey is a wide-area,
extragalactic HI-line survey conducted at the Arecibo Observatory. Sources have
so far been extracted over ~3,000 sq.deg of sky (40% of its final area),
resulting in the largest HI-selected sample to date. We measure the space
density of HI-bearing galaxies as a function of their observed velocity width
(uncorrected for inclination) down to w = 20 km/s, a factor of 2 lower than the
previous generation HI Parkes All-Sky Survey. We confirm previous results that
indicate a substantial discrepancy between the observational distribution and
the theoretical one expected in a cold dark matter (CDM) universe, at low
widths. In particular, a comparison with synthetic galaxy samples populating
state-of-the-art CDM simulations imply a factor of ~8 difference in the
abundance of galaxies with w = 50 km/s (increasing to a factor of ~100 when
extrapolated to the ALFALFA limit of w = 20 km/s). We furthermore identify
possible solutions, including a keV warm dark matter scenario and the fact that
HI disks in low mass galaxies are usually not extended enough to probe the full
amplitude of the galactic rotation curve. In this latter case, we can
statistically infer the relationship between the measured HI rotational
velocity of a galaxy and the mass of its host CDM halo. Observational
verification of the presented relationship at low velocities would provide an
important test of the validity of the established dark matter model.
We propose and successfully test against new cosmological simulations a novel analytical description of the physical processes
associated with the origin of cored dark matter density profiles. In the simulations, the potential in the central kiloparsec
changes on sub‐dynamical time‐scales over the redshift interval 4 > z > 2, as repeated, energetic feedback generates large underdense bubbles of expanding gas from centrally concentrated bursts
of star formation. The model demonstrates how fluctuations in the central potential irreversibly transfer energy into collisionless
particles, thus generating a dark matter core. A supply of gas undergoing collapse and rapid expansion is therefore the essential
ingredient. The framework, based on a novel impulsive approximation, breaks with the reliance on adiabatic approximations
which are inappropriate in the rapidly changing limit. It shows that both outflows and galactic fountains can give rise to
cusp flattening, even when only a few per cent of the baryons form stars. Dwarf galaxies maintain their core to the present
time. The model suggests that constant density dark matter cores will be generated in systems of a wide mass range if central
starbursts or active galactic nucleus phases are sufficiently frequent and energetic.
We present a new flexible, fast and accurate way to implement massive
neutrinos, warm dark matter and any other non-cold dark matter relics in
Boltzmann codes. For whatever analytical or numerical form of the phase-space
distribution function, the optimal sampling in momentum space compatible with a
given level of accuracy is automatically found by comparing quadrature methods.
The perturbation integration is made even faster by switching to an approximate
viscous fluid description inside the Hubble radius, which differs from previous
approximations discussed in the literature. When adding one massive neutrino to
the minimal cosmological model, CLASS becomes just 1.5 times slower, instead of
about 5 times in other codes (for fixed accuracy requirements). We illustrate
the flexibility of our approach by considering a few examples of standard or
non-standard neutrinos, as well as warm dark matter models.
We use matter power spectra from cosmological hydrodynamic simulations to
quantify the effect of baryon physics on the weak gravitational lensing shear
signal. The simulations consider a number of processes, such as radiative
cooling, star formation, supernovae and feedback from active galactic nuclei
(AGN). Van Daalen et al. (2011) used the same simulations to show that baryon
physics, in particular the strong feedback that is required to solve the
overcooling problem, modifies the matter power spectrum on scales relevant for
cosmological weak lensing studies. As a result, the use of power spectra from
dark matter simulations can lead to significant biases in the inferred
cosmological parameters. We show that the typical biases are much larger than
the precision with which future missions aim to constrain the dark energy
equation of state, w_0. For instance, the simulation with AGN feedback, which
reproduces X-ray and optical properties of groups of galaxies, gives rise to a
~40% bias in w_0. We demonstrate that the modification of the power spectrum is
dominated by groups and clusters of galaxies, the effect of which can be
modelled. We consider an approach based on the popular halo model and show that
simple modifications can capture the main features of baryonic feedback.
Despite its simplicity, we find that our model, when calibrated on the
simulations, is able to reduce the bias in w_0 to a level comparable to the
size of the statistical uncertainties for a Euclid-like mission. While
observations of the gas and stellar fractions as a function of halo mass can be
used to calibrate the model, hydrodynamic simulations will likely still be
needed to extend the observed scaling relations down to halo masses of 10 ^12
M_sun/h.
High-resolution N-body simulations of galactic cold dark matter haloes indicate that we should expect to find a few satellite galaxies around
the Milky Way whose haloes have a maximum circular velocity in excess of 40 km s−1. Yet, with the exception of the Magellanic Clouds and the Sagittarius dwarf, which likely reside in subhaloes with significantly
larger velocities than this, the bright satellites of the Milky Way all appear to reside in subhaloes with maximum circular
velocities below 40 km s−1. As recently highlighted by Boylan-Kolchin et al., this discrepancy implies that the majority of the most massive subhaloes
within a cold dark matter galactic halo are too concentrated to be consistent with the kinematic data for the bright Milky
Way satellites. Here we show that no such discrepancy exists if haloes are made of warm rather than cold dark matter because
these haloes are less concentrated on account of their typically later formation epochs. Warm dark matter is one of several
possible explanations for the observed kinematics of the satellites.
Upcoming weak lensing surveys, such as LSST, EUCLID, and WFIRST, aim to
measure the matter power spectrum with unprecedented accuracy. In order to
fully exploit these observations, models are needed that, given a set of
cosmological parameters, can predict the non-linear matter power spectrum at
the level of 1% or better for scales corresponding to comoving wave numbers
0.1<k<10 h/Mpc. We have employed the large suite of simulations from the OWLS
project to investigate the effects of various baryonic processes on the matter
power spectrum. In addition, we have examined the distribution of power over
different mass components, the back-reaction of the baryons on the CDM, and the
evolution of the dominant effects on the matter power spectrum. We find that
single baryonic processes are capable of changing the power spectrum by up to
several tens of per cent. Our simulation that includes AGN feedback, which we
consider to be our most realistic simulation as, unlike those used in previous
studies, it has been shown to solve the overcooling problem and to reproduce
optical and X-ray observations of groups of galaxies, predicts a decrease in
power relative to a dark matter only simulation ranging, at z=0, from 1% at
k~0.3 h/Mpc to 10% at k~1 h/Mpc and to 30% at k~10 h/Mpc. This contradicts the
naive view that baryons raise the power through cooling, which is the dominant
effect only for k>70 h/Mpc. Therefore, baryons, and particularly AGN feedback,
cannot be ignored in theoretical power spectra for k>0.3 h/Mpc. It will thus be
necessary to improve our understanding of feedback processes in galaxy
formation, or at least to constrain them through auxiliary observations, before
we can fulfil the goals of upcoming weak lensing surveys.
ABSTRACT We study the luminosity function (LF) and the radial distribution of satellite galaxies within Milky Way (MW) sized haloes as predicted in cold dark matter based models of galaxy formation, making use of numerical N-body techniques as well as three different semi-analytic models (SAMs) galaxy formation codes. We extract merger trees from very high-resolution dissipationless simulations of four Galaxy-sized DM haloes, and use these as common input for the SAMs. We present a detailed comparison of our predictions with the observational data recently obtained on the MW satellite LF. We find that SAMs with rather standard astrophysical ingredients are able to reproduce the observed LF over six orders of magnitude in luminosity, down to magnitudes as faint as MV = -2. We also perform a comparison with the actual observed number of satellites as a function of luminosity, by applying the selection criteria of the SDSS survey to our simulations instead of correcting the observations for incompleteness. Using this approach, we again find good agreement for both the luminosity and radial distributions of MW satellites. We investigate which physical processes in our models are responsible for shaping the predicted satellite LF, and find that tidal destruction, suppression of gas infall by a photoionizing background, and supernova feedback all make important contributions. We conclude that the number and luminosity of MW satellites can be naturally accounted for within the (Ãâº)cold dark matter paradigm, and this should no longer be considered a problem.
We show that dissipationless Λ cold dark matter simulations predict that the majority of the most massive subhaloes of the
Milky Way are too dense to host any of its bright satellites (LV > 105 L⊙). These dark subhaloes have peak circular velocities at infall of Vinfall= 30–70 km s-1 and infall masses of (0.2–4) × 1010 M⊙. Unless the Milky Way is a statistical anomaly, this implies that galaxy formation becomes effectively stochastic at these
masses. This is in marked contrast to the well-established monotonic relation between galaxy luminosity and halo circular
velocity (or halo mass) for more massive haloes. We show that at least two (and typically four) of these massive dark subhaloes
are expected to produce a larger dark matter annihilation flux than Draco. It may be possible to circumvent these conclusions
if baryonic feedback in dwarf satellites or different dark matter physics can reduce the central densities of massive subhaloes
by order unity on a scale of 0.3–1 kpc.
We investigate potential constraints from cosmic shear on the dark matter particle mass, assuming all dark matter is made up of light thermal relic particles. Given the theoretical uncertainties involved in making cosmological predictions in such warm dark matter scenarios we use analytical fits to linear warm dark matter power spectra and compare
(i) the halo model using a mass function evaluated from these linear power spectra and
(ii) an analytical fit to the non-linear evolution of the linear power spectra.
We optimistically ignore the competing effect of baryons for this work. We find approach (ii) to be conservative compared to approach (i). We evaluate cosmological constraints using these methods, marginalising over four other cosmological parameters. Using the more conservative method we find that a Euclid-like weak lensing survey together with constraints from the Planck cosmic microwave background mission primary anisotropies could achieve a lower limit on the particle mass of 2.5 keV.
We investigate whether the subhalos of Lambda-CDM galaxy halos have
potentials consistent with the observed properties of Milky Way satellites,
particularly those with high-quality photometric and kinematic data: Fornax,
Leo I, Sculptor, Sextans, and Carina. We compare spherical models with
isotropic velocity dispersion tensors to the observed, circularly averaged star
counts, line-of-sight velocity dispersion profiles and line-of-sight velocity
distributions. We identify subhalos within the six high-resolution dark matter
halos of the Aquarius Project for which the spherically averaged potentials
result in excellent fits to each of the five galaxies. In particular, our
simple one-integral models reproduce the observations in the inner regions,
proving that these data are fully consistent with Lambda-CDM expectations and
do not require cored dark matter distributions. For four of the five satellites
the fits require moderately cusped {\it stellar} density profiles. The star
count data for Leo I, however, do require a cored distribution of star counts.
Current data suggest that these five satellites may be hosted by Lambda-CDM
subhalos with maximum circular velocities in the range 10 to 30 km/s.
The identity of dark matter is a question of central importance in both
astrophysics and particle physics. In the past, the leading particle candidates
were cold and collisionless, and typically predicted missing energy signals at
particle colliders. However, recent progress has greatly expanded the list of
well-motivated candidates and the possible signatures of dark matter. This
review begins with a brief summary of the standard model of particle physics
and its outstanding problems. We then discuss several dark matter candidates
motivated by these problems, including WIMPs, superWIMPs, light gravitinos,
hidden dark matter, sterile neutrinos, and axions. For each of these, we
critically examine the particle physics motivations and present their expected
production mechanisms, basic properties, and implications for direct and
indirect detection, particle colliders, and astrophysical observations.
Upcoming experiments will discover or exclude many of these candidates, and
progress may open up an era of unprecedented synergy between studies of the
largest and smallest observable length scales.
We test the luminosity function of Milky Way satellites as a constraint for the nature of dark matter particles. We perform
dissipationless high-resolution N-body simulations of the evolution of Galaxy-sized halo in the standard cold dark matter model and in four warm dark matter
(WDM) scenarios, with a different choice for the WDM particle mass mw. We then combine the results of the numerical simulations with semi-analytic models for galaxy formation, to infer the properties
of the satellite population. Quite surprisingly, we find that even WDM models with relatively low mw values (2–5keV) are able to reproduce the observed abundance of ultra faint (Mv < −9) dwarf galaxies, as well as the observed relation between luminosity and mass within 300pc. Our results suggest a lower
limit of 1keV for thermal WDM, in broad agreement with previous results from other astrophysical observations such as Lyman
α forest and gravitational lensing.
We investigate the effects of changes in the cosmological parameters between the Wilkinson Microwave Anisotropy Probe (WMAP) 1st, 3rd and 5th year results on the structure of dark matter haloes. We use a set of simulations that cover five decades in halo mass ranging from the scales of dwarf galaxies (Vc ~ 30 km s-1) to clusters of galaxies (Vc ~ 1000 km s-1). We find that the concentration mass relation is a power law in all three cosmologies. However, the slope is shallower and the zero-point is lower moving from WMAP1 to WMAP5 to WMAP3. For haloes of mass logM200/[h-1Msolar] = 10, 12 and 14 the differences in the concentration parameter between WMAP1 and WMAP3 are a factor of 1.55, 1.41 and 1.29, respectively. As we show, this brings the central densities of dark matter haloes in good agreement with the central densities of dwarf and low surface brightness galaxies inferred from their rotation curves, for both the WMAP3 and WMAP5 cosmologies. We also show that none of the existing toy models for the concentration-mass relation can reproduce our simulation results over the entire range of masses probed. In particular, the model of Bullock et al. fails at the higher mass end (M >~ 1013h-1Msolar), while the NFW model of Navarro, Frenk and White fails dramatically at the low-mass end (M <~ 1012h-1Msolar). We present a new model, based on a simple modification of that of Bullock et al., which reproduces the concentration-mass relations in our simulations over the entire range of masses probed (1010 <~ M <~ 1015h-1Msolar). Haloes in the WMAP3 cosmology (at a fixed mass) are more flatted compared to the WMAP1 cosmology, with a medium to long axis ration reduced by ~10 per cent. Finally, we show that the distribution of halo spin parameters is the same for all three cosmologies.
Thesis (Ph. D.)--University of Washington, 2001 The goal of this work is to show how large cosmological N-body simulations are computed, how structures within such simulations can be identified with observed galaxies, and how the weak gravitational lensing effect of large scale structure introduces changes in the observed brightness of high redshift sources. We describe PKDGRAV, a fully parallel N-body code that can both spatially adapt to large ranges in particle densities, and temporally adapt to large ranges in dynamical timescales. Care has been taken to insure that the code runs efficiently on a variety of parallel architectures. This has led us to using a non-standard data structure for efficiently calculating the gravitational forces, a variant on the k-D tree, and a new method for treating periodic boundary conditions. A major problem with the interpretation of cosmological N-body simulations has always been identifying the positions and velocities of the "galaxies" in simulations. Observational constraints almost always concern the position and velocities of galaxies, not of the dark matter background. We present our grouping algorithm, SKID, which can identify galaxy halos independent of the environment in which the halo is found, a property that is very important given the large dynamic range in background densities present in cosmological simulations. PKDGRAV has been used to perform many very high resolution cosmological N-body simulations. We give an overview of some of the scientific program that has been enabled by this code. We present the magnification distributions due to weak lensing through all the intervening large scale structure from an observer to a source at z = 1. We show that the distribution is a highly skewed one with a shifted mode implying a slight demagnification bias and an extended tail toward high magnification. We investigate the implications of these results on the observations of high redshift type-Ia supernovae and show how these can be used to provide a new cosmological test.
We present a detailed nonspherical modeling of dark matter halos on the basis of a combined analysis of high-resolution halo simulations (12 halos with N similar to 10(6) particles within their virial radius) and large cosmological simulations (five realizations with N = 512(3) particles in a 100 h(-1) Mpc box size). The density profiles of those simulated halos are well approximated by a sequence of the concentric triaxial distribution with their axis directions being fairly aligned. We characterize the triaxial model quantitatively by generalizing the universal density pro le, that has previously been discussed only in the framework of the spherical model. We obtain a series of practically useful fitting formulae in applying the triaxial model: the mass and redshift dependence of the axis ratio, the mean of the concentration parameter, and the probability distribution functions of the axis ratio and the concentration parameter. These accurate fitting formulae form a complete description of the triaxial density profiles of halos in cold dark matter models. Our current description of the dark halos will be particularly useful in predicting a variety of nonsphericity effects, to a reasonably reliable degree, including the weak and strong lens statistics, the orbital evolution of galactic satellites and triaxiality of galactic halos, and the nonlinear clustering of dark matter. In addition, this provides a useful framework for the nonspherical modeling of the intracluster gas, which is crucial in discussing the gas and temperature profiles of X-ray clusters and the Hubble constant estimated via the Sunyaev-Zeldovich effect.
Previous fits of sterile neutrino dark matter (DM) models to cosmological data ruled out masses smaller than approximately 8 keV, assuming a production mechanism that is not the best motivated from a particle physics point of view. Here we focus on a realistic extension of the standard model with three sterile neutrinos, consistent with neutrino oscillation data and baryogenesis, with the lightest sterile neutrino being the DM particle. We show that for each mass >or= 2 keV there exists at least one model accounting for 100% of DM and consistent with Lyman-alpha and other cosmological, astrophysical, and particle physics data.