Ignacio Ferreras

University College London, Londinium, England, United Kingdom

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Publications (129)480.08 Total impact

  • Ignacio Ferreras · Francesco La Barbera · Alexandre Vazdekis
    [Show abstract] [Hide abstract] ABSTRACT: Ignacio Ferreras, Francesco La Barbera and Alexandre Vazdekis take a close look at one of the key ingredients in modelling star formation.
    No preview · Article · Apr 2016 · Astronomy & Geophysics
  • [Show abstract] [Hide abstract] ABSTRACT: Massive high-redshift quiescent compact galaxies (nicknamed red nuggets) have been traditionally connected to present-day elliptical galaxies, often overlooking the relationships that they may have with other galaxy types. We use large bulge–disc decomposition catalogues based on the Sloan Digital Sky Survey to check the hypothesis that red nuggets have survived as compact cores embedded inside the haloes or discs of present-day massive galaxies. In this study, we designate a compact core as the bulge component that satisfies a prescribed compactness criterion. Photometric and dynamic mass–size and mass–density relations are used to show that, in the inner regions of galaxies at z ∼ 0.1, there are abundant compact cores matching the peculiar properties of the red nuggets, an abundance comparable to that of red nuggets at z ∼ 1.5. Furthermore, the morphology distribution of the present-day galaxies hosting compact cores is used to demonstrate that, in addition to the standard channel connecting red nuggets with elliptical galaxies, a comparable fraction of red nuggets might have ended up embedded in discs. This result generalizes the inside-out formation scenario; present-day massive galaxies can begin as dense spheroidal cores (red nuggets), around which either a spheroidal halo or a disc is formed later.
    No preview · Article · Jan 2016 · Monthly Notices of the Royal Astronomical Society
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    [Show abstract] [Hide abstract] ABSTRACT: The stellar initial mass function is an important ingredient in galaxy formation, mainly linking the luminosity of a galaxy to its stellar mass, and driving chemical enrichment. In recent years there has been an ongoing discussion about systematic variations of the IMF in early-type galaxies and its connection with possible drivers such as velocity dispersion or metallicity. Strong gravitational lensing over galaxy scales in combination with photometric and spectroscopic data provides a powerful method to constrain the stellar mass-to-light ratio and hence the functional form of the IMF. We combine photometric and spectroscopic constraints from the latest set of population synthesis models of Charlot & Bruzual, including a varying IMF, with a non-parametric analysis of the lensing mass in a sample of 18 early-type lens galaxies from the SLACS survey, with velocity dispersions in the range 200-300 km/s. We find that very bottom-heavy IMFs are excluded. However, the upper limit to the IMF slope ($\mu \lesssim 2.2$ for a bimodal IMF, taking into account a 20-30% contribution to the lensing mass from dark matter, where $\mu=1.3$ corresponds to a Kroupa-like IMF) is compatible at the $1\sigma$ level with the constraints imposed by gravity-sensitive line strengths. A two-segment power law parameterisation of the IMF (keeping its index at the high mass end fixed at the Salpeter value) is more constrained ($\Gamma\lesssim1.5$, where $\Gamma$ is the power index at the low-mass end). Furthermore we find that for a standard Milky Way-like IMF to be applicable a significant amount of dark matter is required within an effective radius. Our results reveal a large scatter regarding possible values of the IMF slope, suggesting that the recent lenses of Smith et al. - who find a Milky Way-like IMF in a few massive lensing early-type galaxies - may be explained by such a scatter. (Abridged)
    Preview · Article · Dec 2015 · Monthly Notices of the Royal Astronomical Society
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    [Show abstract] [Hide abstract] ABSTRACT: We measure the projected density profile, shape and alignment of the stellar and dark matter mass distribution in 11 strong-lens galaxies. We find that the projected dark matter density profile – under the assumption of a Chabrier stellar initial mass function – shows significant variation from galaxy to galaxy. Those with an outermost image beyond ∼10 kpc are very well fit by a projected Navarro–Frenk–White (NFW) profile; those with images within 10 kpc appear to be more concentrated than NFW, as expected if their dark haloes contract due to baryonic cooling. We find that over several half-light radii, the dark matter haloes of these lenses are rounder than their stellar mass distributions. While the haloes are never more elliptical than edm = 0.2, their stars can extend to e* > 0.2. Galaxies with high dark matter ellipticity and weak external shear show strong alignment between light and dark; those with strong shear (γ ≳ 0.1) can be highly misaligned. This is reassuring since isolated misaligned galaxies are expected to be unstable. Our results provide a new constraint on galaxy formation models. For a given cosmology, these must explain the origin of both very round dark matter haloes and misaligned strong-lens systems.
    Preview · Article · Nov 2015 · Monthly Notices of the Royal Astronomical Society
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    [Show abstract] [Hide abstract] ABSTRACT: At present, the main challenge to the interpretation of variations in gravity-sensitive line strengths as driven by a non-universal initial mass function (IMF) lies in understanding the effect of the other population parameters. Most notably, [α/Fe]-enhanced populations or even departures in the individual element abundances with respect to the solar-scaled ratio may lead to similar observational results. We combine various TiO-based, IMF-sensitive indicators in the optical and NIR spectral windows, along with the FeH-based Wing–Ford band to break this degeneracy. We obtain a significant radial trend of the IMF slope in XSG1, a massive early-type galaxy (ETG), with velocity dispersion σ ∼ 300 km s−1, observed with the Very Large Telescope/X-shooter instrument. In addition, we constrain – for the first time – both the shape and normalization of the IMF, using only a stellar population analysis. We robustly rule out a single power law to describe the IMF, whereas a power law tapered off to a constant value at low masses (defined as a bimodal IMF) is consistent with all the observational spectroscopic data and with the stellar M/L constraints based on the Jeans anisotropic modelling method. The IMF in XSG1 is bottom-heavy in the central regions (corresponding to a bimodal IMF slope Γb ∼ 3, or a mass normalization mismatch parameter α ∼ 2), changing towards a standard Milky Way-like IMF (Γb ∼ 1.3; α ∼ 1) at around one half of the effective radius. This result, combined with previous observations of local IMF variations in massive ETGs, reflects the varying processes underlying the formation of the central core and the outer regions in this type of galaxies.
    Full-text · Article · Sep 2015 · Monthly Notices of the Royal Astronomical Society
  • No preview · Article · Jul 2015 · Astronomy and Astrophysics
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    Susan Hutton · Ignacio Ferreras · Vladimir Yershov
    [Show abstract] [Hide abstract] ABSTRACT: We use near ultraviolet and optical photometry to investigate the dust properties in the nearby starburst galaxy M82. By combining imaging from the Swift/UVOT instrument and optical data from the Sloan Digital Sky Survey, we derive the extinction curve parametrized by the standard RV factor, and the strength of the NUV 2175 Å feature – quantified by a parameter B – out to projected galactocentric distances of 4 kpc. Our analysis is robust against possible degeneracies from the properties of the underlying stellar populations. Both B and RV correlate with galactocentric distance, revealing a systematic trend of the dust properties. Our results confirm previous findings that dust in M82 is better fitted by a Milky Way standard extinction curve, in contrast to a Calzetti law. We find a strong correlation between RV and B, towards a stronger NUV bump in regions with higher RV, possibly reflecting a distribution with larger dust grain sizes. The data we use were taken before SN2014J, and therefore can be used to probe the properties of the interstellar medium before the event. Our RV values around the position of the supernova are significantly higher than recent measurements post-SN2014J (RV ≈ 1.4). This result is consistent with a significant change in the dust properties after the supernova event, either from disruption of large grains or from the contribution by an intrinsic circumstellar component. Intrinsic variations among supernovae not accounted for could also give rise to this mismatch.
    Full-text · Article · Jun 2015 · Monthly Notices of the Royal Astronomical Society
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    [Show abstract] [Hide abstract] ABSTRACT: Variations in the stellar initial mass function (IMF) have been invoked to explain the spectroscopic and dynamical properties of early-type galaxies. However, no observations have yet been able to disentangle the physical driver. We analyse here a sample of 24 early-type galaxies drawn from the CALIFA survey, deriving in a homogeneous way their stellar population and kinematic properties. We find that the local IMF is tightly related to the local metallicity, becoming more bottom-heavy towards metal-rich populations. Our result, combined with the galaxy mass-metallicity relation, naturally explains previous claims of a galaxy mass-IMF relation, derived from non-IFU spectra. If we assume that - within the star formation environment of early-type galaxies - metallicity is the main driver of IMF variations, a significant revision of the interpretation of galaxy evolution observables is necessary.
    Preview · Article · Jun 2015
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    [Show abstract] [Hide abstract] ABSTRACT: We present MUFFIT, a new generic code optimized to retrieve the main stellar population parameters of galaxies in photometric multi-filter surveys, and we check its reliability and feasibility with real galaxy data from the ALHAMBRA survey. Making use of an error-weighted $\chi^2$-test, we compare the multi-filter fluxes of galaxies with the synthetic photometry of mixtures of two single stellar populations at different redshifts and extinctions, to provide through a Monte Carlo method the most likely range of stellar population parameters (mainly ages and metallicities), extinctions, redshifts, and stellar masses. To improve the diagnostic reliability, MUFFIT identifies and removes from the analysis those bands that are significantly affected by emission lines. We highlight that the retrieved age-metallicity locus for a sample of $z \le 0.22$ early-type galaxies in ALHAMBRA at different stellar mass bins are in very good agreement with the ones from SDSS spectroscopic diagnostics. Moreover, a one-to-one comparison between the redshifts, ages, metallicities, and stellar masses derived spectroscopically for SDSS and by MUFFIT for ALHAMBRA reveals good qualitative agreements in all the parameters. In addition, and using as input the results from photometric-redshift codes, MUFFIT improves the photometric-redshift accuracy by $\sim 10$-$20\%$, and it also detects nebular emissions in galaxies, providing physical information about their strengths. Our results show the potential of multi-filter galaxy data to conduct reliable stellar population studies with the appropiate analysis techniques, as MUFFIT.
    Full-text · Article · May 2015
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    Francesco La Barbera · Ignacio Ferreras · Alexandre Vazdekis
    [Show abstract] [Hide abstract] ABSTRACT: The initial mass function (IMF) of early-type galaxies (ETGs) has been found to feature systematic variations by both dynamical and spectroscopic studies. In particular, spectral line strengths, based on gravity-sensitive features, suggest an excess of low-mass stars in massive ETGs, i.e. a bottom-heavy IMF. The physical drivers of IMF variations are currently unknown. The abundance ratio of α elements, such as [Mg/Fe], has been suggested as a possible driver of the IMF changes, although dynamical constraints do not support this claim. In this letter, we take advantage of the large Sloan Digital Sky Survey data base. Our sample comprises 24 781 high-quality spectra, covering a large range in velocity dispersion (100 < σ0 < 320 km s−1) and abundance ratio ( − 0.1 < [Mg/Fe] < +0.4). The large volume of data allows us to stack the spectra at fixed values of σ0 and [Mg/Fe]. Our analysis – based on gravity-sensitive line strengths – gives a strong correlation with central velocity dispersion and a negligible variation with [Mg/Fe] at fixed σ0. This result is robust against individual elemental abundance variations, and seems not to raise any apparent inconsistency with the alternative method based on galaxy dynamics.
    Preview · Article · Feb 2015 · Monthly Notices of the Royal Astronomical Society Letters
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    [Show abstract] [Hide abstract] ABSTRACT: Spectroscopic analyses of gravity-sensitive line strengths give growing evidence towards an excess of low-mass stars in massive early-type galaxies (ETGs). Such a scenario requires a bottom-heavy initial mass function (IMF). However, strong constraints can be imposed if we take into account galactic chemical enrichment. We extend the analysis of Weidner et al. and consider the functional form of bottom-heavy IMFs used in recent works, where the high-mass end slope is kept fixed to the Salpeter value, and a free parameter is introduced to describe the slope at stellar masses below some pivot mass scale (M < MP = 0.5 M⊙). We find that no such time-independent parametrization is capable to reproduce the full set of constraints in the stellar populations of massive ETGs – resting on the assumption that the analysis of gravity-sensitive line strengths leads to a mass fraction at birth in stars with mass M < 0.5 M⊙ above 60 per cent. Most notably, the large amount of metal-poor gas locked in low-mass stars during the early, strong phases of star formation results in average stellar metallicities [M/H] ≲ −0.6, well below the solar value. The conclusions are unchanged if either the low-mass end cutoff, or the pivot mass are left as free parameters, strengthening the case for a time-dependent IMF.
    Preview · Article · Jan 2015 · Monthly Notices of the Royal Astronomical Society Letters
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    [Show abstract] [Hide abstract] ABSTRACT: We explore the stellar initial mass function (IMF) of a sample of 49 massive quiescent galaxies (MQGs) at 0.9?< z <?1.5. We base our analysis on intermediate resolution spectro-photometric data in the GOODS-N field taken in the near-infrared and optical with the Hubble Space Telescope Wide Field Camera 3 G141 grism and the Survey for High-z Absorption Red and Dead Sources. To constrain the slope of the IMF, we have measured the TiO2 spectral feature, whose strength depends strongly on the content of low-mass stars, as well as on stellar age. Using ultraviolet to near-infrared individual and stacked spectral energy distributions, we have independently estimated the stellar ages of our galaxies. Knowing the age of the stellar population, we interpret the strong differences in the TiO2 feature as an IMF variation. In particular, for the heaviest z ~?1 MQGs (M >?1011M ?), we find an average age of 1.7???0.3?Gyr and a bottom-heavy IMF (?b = 3.2???0.2). Lighter MQGs (2?×?1010 < M <?1011M ?) at the same redshift are younger on average (1.0???0.2?Gyr) and present a shallower IMF slope (). Our results are in good agreement with the findings about the IMF slope in early-type galaxies of similar mass in the present-day universe. This suggests that the IMF, a key characteristic of the stellar populations in galaxies, is bottom-heavier for more massive galaxies and has remained unchanged in the last ~8?Gyr.
    Full-text · Article · Dec 2014 · The Astrophysical Journal Letters
  • I.G. De La Rosa · I. Ferreras · H. Domínguez · B. Coelho
    [Show abstract] [Hide abstract] ABSTRACT: An ongoing study is presented in which a photometric non-linear Scaling Relation of Early-Type Galaxies (ETGs) is proposed to carry out a consistency test on cosmic and galaxy evolution.
    No preview · Article · Oct 2014
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    [Show abstract] [Hide abstract] ABSTRACT: We study the total density distribution in the central regions (≲1 effective radius, Re) of early-type galaxies (ETGs), using data from SPIDER and ATLAS3D. Our analysis extends the range of galaxy stellar mass (M⋆) probed by gravitational lensing, down to ∼ 1010 M⊙. We model each galaxy with two components (dark matter halo + stars), exploring different assumptions for the dark matter halo profile (i.e. NFW, NFW-contracted, and Burkert profiles), and leaving stellar mass-to-light (M⋆/L) ratios as free fitting parameters to the data. For all plausible halo models, the best-fitting M⋆/L, normalized to that for a Chabrier initial mass function, increases systematically with galaxy size and mass. For an NFW profile, the slope of the total mass profile is non-universal, independently of several ingredients in the modelling (e.g. halo contraction, anisotropy, and rotation velocity in ETGs). For the most massive (M⋆ ∼ 1011.5 M⊙) or largest (Re∼ 15 kpc) ETGs, the profile is isothermal in the central regions (∼ Re/2), while for the low-mass (M⋆ ∼ 1010.2 M⊙) or smallest (Re∼ 0.5 kpc) systems, the profile is steeper than isothermal, with slopes similar to those for a constant-M/L profile. For a steeper concentration–mass relation than that expected from simulations, the correlation of density slope with galaxy mass tends to flatten, while correlations with Re and velocity dispersions are more robust. Our results clearly point to a ‘non-homology’ in the total mass distribution of ETGs, which simulations of galaxy formation suggest may be related to a varying role of dissipation with galaxy mass.
    Full-text · Article · Sep 2014 · Monthly Notices of the Royal Astronomical Society
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    [Show abstract] [Hide abstract] ABSTRACT: A detailed analysis of how environment affects the star formation history of early-type galaxies (ETGs) is undertaken via high signal-to-noise ratio stacked spectra obtained from a sample of 20 977 ETGs (morphologically selected) from the Sloan Digital Sky Survey-based SPIDER survey. Two major parameters are considered for the study: the central velocity dispersion (σ), which relates to local drivers of star formation, and the mass of the host halo, which relates to environment-related effects. In addition, we separate the sample between centrals (the most massive galaxy in a halo) and satellites. We derive trends of age, metallicity, and [α/Fe] enhancement, with σ. We confirm that the major driver of stellar population properties in ETGs is velocity dispersion, with a second-order effect associated with the central/satellite nature of the galaxy. No environmental dependence is detected for satellite ETGs, except at low σ – where satellites in groups or in the outskirts of clusters tend to be younger than those in the central regions of clusters. In contrast, the trends for centrals show a significant dependence on halo mass. Central ETGs in groups (i.e. with a halo mass >1012.5 M⊙) have younger ages, lower [α/Fe], and higher internal reddening, than ‘isolated’ systems (i.e. centrals residing in low-mass, <1012.5 M⊙, haloes). Our findings imply that central ETGs in groups formed their stellar component over longer time scales than ‘isolated’ centrals, mainly because of gas-rich interactions with their companion galaxies.
    Full-text · Article · Aug 2014 · Monthly Notices of the Royal Astronomical Society
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    [Show abstract] [Hide abstract] ABSTRACT: The hypothesis of a universal initial mass function (IMF) – motivated by observations in nearby stellar systems – has been recently challenged by the discovery of a systematic variation of the IMF with the central velocity dispersion, σ, of early-type galaxies (ETGs), towards an excess of low-mass stars in high-σ galaxies. This trend has been derived so far from integrated spectra, and remains unexplained at present. To test whether such trend depends on the local properties within a galaxy, we have obtained new, extremely deep, spectroscopic data, for three nearby ETGs, two galaxies with high σ (∼300 km s− 1), and one lower mass system, with σ ∼ 100 km s− 1. From the analysis of IMF-sensitive spectral features, we find that the IMF depends significantly on galactocentric distance in the massive ETGs, with the enhanced fraction of low-mass stars mostly confined to their central regions. In contrast, the low-σ galaxy does not show any significant radial gradient in the IMF, well described by a shallower distribution, relative to the innermost regions of massive galaxies, at all radii. Such a result indicates that the IMF should be regarded as a local (rather than global) property, and suggests a significant difference between the formation process of the core and the outer regions of massive ETGs.
    Preview · Article · Apr 2014 · Monthly Notices of the Royal Astronomical Society
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    [Show abstract] [Hide abstract] ABSTRACT: We analyse the stellar populations in the host galaxies of 53 X-ray selected optically dull active galactic nuclei (AGN) at 0.34<z<1.07 with ultra-deep (m=26.5) optical medium-band (R~50) photometry from the Survey for High-z Absorption Red and Dead Sources (SHARDS). The spectral resolution of SHARDS allows us to consistently measure the strength of the 4000 AA break, Dn(4000), a reliable age indicator for stellar populations. We confirm that most X-ray selected moderate-luminosity AGN (L_X<10^44 erg/s) are hosted by massive galaxies (typically M*>10^10.5 M_sun) and that the observed fraction of galaxies hosting an AGN increases with the stellar mass. A careful selection of random control samples of inactive galaxies allows us to remove the stellar mass and redshift dependencies of the AGN fraction to explore trends with several stellar age indicators. We find no significant differences in the distribution of the rest-frame U-V colour for AGN hosts and inactive galaxies, in agreement with previous results. However, we find significantly shallower 4000 AA breaks in AGN hosts, indicative of younger stellar populations. With the help of a model-independent determination of the extinction, we obtain extinction-corrected U-V colours and light-weighted average stellar ages. We find that AGN hosts have younger stellar populations and higher extinction compared to inactive galaxies with the same stellar mass and at the same redshift. We find a highly significant excess of AGN hosts with Dn(4000)~1.4 and light weighted average stellar ages of 300-500 Myr, as well as a deficit of AGN in intrinsic red galaxies. We interpret failure in recognising these trends in previous studies as a consequence of the balancing effect in observed colours of the age-extinction degeneracy.
    Preview · Article · Apr 2014 · Monthly Notices of the Royal Astronomical Society
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    [Show abstract] [Hide abstract] ABSTRACT: We combine near-ultraviolet (NUV), optical and IR imaging of the nearby starburst galaxy M82 to explore the properties of the dust both in the interstellar medium of the galaxy and the dust entrained in the superwind. The three NUV filters of Swift-Ultraviolet/Optical Telescope enable us to probe in detail the properties of the extinction curve in the region around the 2175 Å bump. The NUV colour–colour diagram strongly rules out a ‘bump-less’ Calzetti-type law, which can either reflect intrinsic changes in the dust properties or in the star formation history compared to starbursts well represented by such an attenuation law. We emphasize that it is mainly in the NUV region where a standard Milky Way-type law is preferred over the Calzetti law. The age and dust distribution of the stellar populations is consistent with the scenario of an encounter with M81 in the recent ≲400 Myr. The radial variation of NUV/optical/IR photometry in the galaxy region – including the polycyclic-aromatic-hydrocarbon-dominated emission at 8 μm – confirms the central location of the star formation. The radial gradients of the NUV and optical colours in the superwind region supports the hypothesis that the emission in the wind cone is driven by scattering from dust grains entrained in the ejecta. The observed wavelength dependence, ∝λ−1.5, reveals either a grain size distribution n(a) ∝ a−2.5, or a flatter distribution with a maximum size cutoff, suggesting that only small grains are entrained in the supernova-driven wind.
    Full-text · Article · Jan 2014 · Monthly Notices of the Royal Astronomical Society
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    [Show abstract] [Hide abstract] ABSTRACT: (Abridged) We probe the merging channel of massive galaxies over the z=0.3-1.3 redshift window by studying close pairs in a sample of 226 galaxies with stellar mass >1E11Msun, from the deep (m<26.5AB, 3 sigma) SHARDS survey. SHARDS provides medium band photometry equivalent to low-resolution optical spectra (R~50), allowing us to obtain extremely accurate photometric redshifts (|Dz|/(1+z)~0.8%, median) and to improve the constraints on the age distribution of the stellar populations. A strong correlation is found between the age difference of central and satellite galaxy and stellar mass ratio, from negligible age differences in major mergers to age differences ~4 Gyr for 1:100 minor mergers. This correlation is inherited from the general mass-age trend, suggesting that no significant bias is found between the satellites of massive centrals and galaxies with similar stellar mass in other environments. The dominant contributor to the growth of massive galaxies corresponds to mass ratios Omega=Msat/Mcen>0.3, followed by a decrease in the fractional mass growth rate linearly proportional to log Omega, at least down to Omega~0.01, suggesting a decreasing role of mergers involving low-mass satellites, especially if dynamical friction timescales are taken into account. A simple model results in an upper limit for the average mass growth rate of massive galaxies of DM/M/Dt~ 0.12+-0.06 per Gyr, over the z<1 range, with a ~60% fractional contribution from (major) mergers with Omega>0.3. The net mass growth from mergers in massive galaxies between z=1 and z=0 is M(z=0)/M(z=1)=1.9 (-0.5) (+0.7). These results suggest that the majority of the stellar mass contributed by satellites does not introduce significantly younger populations, in agreement with the small radial age gradients observed in present-day early-type galaxies.
    Full-text · Article · Dec 2013 · Monthly Notices of the Royal Astronomical Society
  • Dominik Leier · I. Ferreras · P. Saha
    [Show abstract] [Hide abstract] ABSTRACT: Both theoretical studies of structure formation and observations of X-ray emissions of hot halo gas find an inverse proportionality between the concentration of dark matter haloes and their virial mass. We present an alternative approach to explore the concentration of dark matter haloes over galaxy scales on a sample of 18 early-type lensing galaxies. Our c-Mvir relation is consistent with the X-ray analysis, extending towards lower virial masses, covering the range from 4e11 up to 5e12 Msol. A combination of the lensing analysis along with photometric data allows us to constrain the baryon fraction within a few effective radii, which is compared with prescriptions for adiabatic contraction (AC) of the dark matter haloes. We find that the standard methods for AC are strongly disfavoured, requiring additional mechanisms - such as mass loss during the contraction process - to play a role during the phases following the collapse of the haloes.
    No preview · Article · Jul 2013

Publication Stats

2k Citations
480.08 Total Impact Points

Institutions

  • 2005-2015
    • University College London
      • • Department of Space and Climate Physics
      • • Department of Physics and Astronomy
      Londinium, England, United Kingdom
  • 2013
    • Johns Hopkins University
      • Department of Physics and Astronomy
      Baltimore, Maryland, United States
  • 2012
    • Complutense University of Madrid
      • Department of Atomic, Molecular and Nuclear Physics
      Madrid, Madrid, Spain
  • 2009
    • Space Telescope Science Institute
      Baltimore, Maryland, United States
    • University of California, Riverside
      • Department of Physics and Astronomy
      Riverside, California, United States
  • 2006-2008
    • King's College London
      • Department of Physics
      Londinium, England, United Kingdom
  • 2001-2008
    • University of Oxford
      • Department of Physics
      Oxford, ENG, United Kingdom
  • 1998
    • Instituto de Física de Cantabria
      Santander, Cantabria, Spain