Andrey V. Kravtsov

University of Chicago, Chicago, Illinois, United States

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Publications (168)694.51 Total impact

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    Cameron J. Liang · Andrey V. Kravtsov · Oscar Agertz
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    ABSTRACT: We present a suite of high-resolution cosmological galaxy re-simulations of a Milky-Way size halo with variety of star-formation and feedback models to investigate the effects of the specific details of the star formation-feedback loop modeling on the observable properties of the circumgalactic medium (CGM). We show that properties of the CGM are quite sensitive to the details of star formation-feedback loop. The simulation which produces a very realistic late-type central galaxy fails to reproduce existing observations of CGM. At the same time, variations of parameters of star formation recipe or feedback modeling, such as cosmic rays feedback, brings predicted CGM in better agreement with observations. The simulations show that the column density profiles of ions arising in such gas are well described by an exponential function of the impact parameter. Ions with higher ionization energy have more extended profiles with the scale height of the exponential distribution scaling as a power law of the ionization energy: hs~Eion^0.72. At z~0, the scale height of warm gas traced by low-ionization species, such as MgII and CIV, have scale heights of 0.2-0.4Rvir, while higher ionization species, such as OVI and NeVIII, have scale heights of 1.6-2.4Rvir. The predicted trend is in good qualitative and reasonable quantitative agreement with observations for ions, such as CIV and OVI. Simulations do produce a sharp turnover in the column density profiles and covering fraction distribution for different ions seen in observations. This turnover however does not correspond to a "boundary" of an ion, but reflects the underlying steep exponential column density profile. We also find that the scale height evolves slower than the virial radius at z<2, but similarly to the halo scale radius, rs. Thus, column density profiles of galaxies at different redshifts can be rescaled using rs of their halos.
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    ABSTRACT: The fact that the clustering and concentration of dark matter halos depend not only on their mass, but also the formation epoch, is a prominent, albeit subtle, feature of the cold dark matter structure formation theory, and is known as assembly bias. At low mass scales ($\sim 10^{12}\,h^{-1}M_\odot$), early-forming halos are predicted to be more strongly clustered than the late-forming ones. In this study we aim to robustly detect the signature of assembly bias observationally, making use of formation time indicators of central galaxies in low mass halos as a proxy for the halo formation history. Weak gravitational lensing is employed to ensure our early- and late-forming halo samples have similar masses, and are free of contamination of satellites from more massive halos. For the two formation time indicators used (resolved star formation history and current specific star formation rate), we do not find convincing evidence of assembly bias. For a pair of early- and late-forming galaxy samples with mean mass $M_{200c} \approx 9\times 10^{11}\,h^{-1}M_\odot$, the relative bias is $1.00\pm 0.12$. We attribute the lack of detection to the possibilities that either the current measurements of these indicators are too noisy, or they do not correlate well with the halo formation history. Alternative proxies for the halo formation history that should perform better are suggested for future studies.
  • Surhud More · Benedikt Diemer · Andrey Kravtsov
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    ABSTRACT: The boundaries of cold dark matter halos are commonly defined to enclose a density contrast $\Delta$ relative to a reference (mean or critical) density. We argue that a more physical boundary of halos is the radius at which accreted matter reaches its first orbital apocenter after turnaround. This splashback radius, $R_{sp}$, manifests itself as a sharp density drop in the halo outskirts, at a location that depends upon the mass accretion rate. We present calibrations of $R_{sp}$ and the enclosed mass, $M_{sp}$, as a function of the accretion rate and alternatively peak height. We find that $R_{sp}$ varies between $\approx0.8-1R_{200m}$ for rapidly accreting halos and $\approx1.5R_{200m}$ for slowly accreting halos. The extent of a halo and its associated environmental effects can thus extend well beyond the conventionally defined "virial" radius. We show that $M_{sp}$ and $R_{sp}$ evolve relatively strongly compared to other commonly used definitions. In particular, $M_{sp}$ evolves significantly even for the smallest dwarf-sized halos at $z=0$. We also contrast $M_{sp}$ with the mass enclosed within four scale radii of the halo density profile, $M_{<4rs}$, which characterizes the inner halo. During the early stages of halo assembly, $M_{sp}$ and $M_{<4rs}$ evolve similarly, but in the late stages $M_{<4rs}$ stops increasing while $M_{sp}$ continues to grow significantly. This illustrates that halos at low $z$ can have "quiet" interiors while continuing to accrete mass in their outskirts. We discuss potential observational estimates of the splashback radius and show that it may already have been detected in galaxy clusters.
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    ABSTRACT: The stellar mass-halo mass relation is a key constraint in all semi-analytic, numerical, and semi-empirical models of galaxy formation and evolution. However, its exact shape and redshift dependence remain debated. Several recent works support a relation in the local Universe steeper than previously thought. Based on the comparisons with a variety of data on massive central galaxies, we show that this steepening holds up to z~1, for stellar masses Mstar>2e11 Msun. Specifically, we find significant evidence for a high-mass end slope of \beta>0.35-0.70, instead of the usual \beta~0.20-0.30 reported by a number of previous results. When including the independent constraints from the recent BOSS clustering measurements, the data, independent of any systematic errors in stellar masses, tend to favor a model with a very small scatter (< 0.15 dex) in stellar mass at fixed halo mass, in the redshift range z < 0.8 and for Mstar>3e11 Msun, suggesting a close connection between massive galaxies and host halos even at relatively recent epochs. We discuss the implications of our results with respect to the evolution of the most massive galaxies since z~1.
    11/2014; 797(2). DOI:10.1088/2041-8205/797/2/L27
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    Benedikt Diemer · Andrey V. Kravtsov
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    ABSTRACT: We present a numerical study of dark matter halo concentrations in $\Lambda$CDM and self-similar cosmologies. We show that the relation between concentration, $c$, and peak height, $\nu$, exhibits the smallest deviations from universality if halo masses are defined with respect to the critical density of the universe. These deviations can be explained by the residual dependence of concentration on the local slope of the matter power spectrum, $n$, which affects both the normalization and shape of the $c$-$\nu$ relation. In particular, there is no well-defined floor in the concentration values. Instead, the minimum concentration depends on redshift: at fixed $\nu$, halos at higher $z$ experience steeper slopes $n$, and thus have lower minimum concentrations. We show that the concentrations in our simulations can be accurately described by a universal seven--parameter function of only $\nu$ and $n$. This model matches our $\Lambda$CDM results to $\lesssim 5\%$ accuracy up to $z = 6$, and matches scale-free $\Omega_{\rm m} = 1$ models to $\lesssim 15\%$. The model also reproduces the low concentration values of Earth-mass halos at $z \approx 30$, and thus correctly extrapolates over $16$ orders of magnitude in halo mass. The predictions of our model differ significantly from all models previously proposed in the literature at high masses and redshifts. Our model is in excellent agreement with recent lensing measurements of cluster concentrations.
    The Astrophysical Journal 07/2014; 799(1). DOI:10.1088/0004-637X/799/1/108 · 6.28 Impact Factor
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    Oscar Agertz · Andrey V. Kravtsov
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    ABSTRACT: Using high resolution cosmological zoom-in simulations of galaxy formation, we investigate the star formation-feedback cycle at high redshifts ($z>1$), focusing on progenitors of Milky Way-sized galaxies. Our star formation model is based on the local density of molecular hydrogen (H$_2$) forming on dust grains, as this may be an important ingredient for regulating star formation in the high redshift, metal-poor regime of galaxy formation. Our stellar feedback model accounts for energy and momentum from supernovae, stellar winds and radiation pressure. We use a suite of simulations with different parameters and assumptions about star formation and prescription recipes. We find that in order to reproduce global properties of the Milky Way progenitors, such as star formation history and stellar mass-halo mass relation, simulations should include 1) a combination of local early ($t\lesssim 4$ Myr) momentum feedback via radiation pressure and stellar winds and subsequent efficient supernovae feedback, and 2) the global star formation efficiency on kiloparsec scales should be feedback regulated. In particular, we find that in models with efficient feedback, the local efficiency of star formation per free fall time can be substantially larger than the global star formation efficiency inferred from the Kennicutt-Schmidt relation. We find that simulations that adopt inefficient star formation inferred from such relation fail to produce vigorous outflows and eject sufficient amounts of enriched gas in order to regulate the galactic baryon content. This illustrates the importance of understanding the complex interplay between star formation and feedback and the detailed processes that contribute to the feedback-regulated formation of galaxies. (Abridged for arXiv)
    The Astrophysical Journal 04/2014; 804(1). DOI:10.1088/0004-637X/804/1/18 · 6.28 Impact Factor
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    ABSTRACT: We study relation between stellar mass and halo mass for high-mass halos using a sample of galaxy clusters with accurate measurements of stellar masses from optical and IR data and total masses from X-ray observations. We find that stellar mass of the brightest cluster galaxies (BCGs) scales as M*BCG\propto M500^a_BCG with the best fit slope of a_BCG~0.35+-0.1 and scatter of M*BCG at a fixed M500 of ~0.2 dex. We show that M*-M relations from abundance matching or halo modelling reported in recent studies underestimate stellar masses of BCGs by a factor of ~2-4, because these studies used stellar mass functions (SMF) based on photometry that severely underestimates the outer surface brightness profiles of massive galaxies. We show that M*-M relation derived using abundance matching with the recent SMF calibration by Bernardi et al. (2013) based on improved photometry is in a much better agreement with the relation we derive. The total stellar mass of galaxies correlates with total mass M500 with the slope of \approx 0.6+-0.1 and scatter of 0.1 dex. This indicates that efficiency with which baryons are converted into stars decreases with increasing cluster mass. We show that for a fixed choice of the initial mass function (IMF) total stellar fraction in clusters is only a factor of ~3-5 lower than the peak stellar fraction reached in M\approx 10^12 Msun halos, and only a factor of ~1.5-3 if the IMF becomes progressively more bottom heavy with increasing mass in early type galaxies, as indicated by recent observations. The larger normalization and slope of the M*-M relation derived in this study shows that the overall efficiency of star formation in massive halos is suppressed much less than was thought before and that feedback and associated suppression of star formation in massive halos should be weaker than assumed in most of the current semi-analytic models and simulations.
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    Benedikt Diemer · Andrey V. Kravtsov
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    ABSTRACT: We present a systematic study of the density profiles of halos forming in a LCDM cosmology, focusing on the outer regions of halos, 0.1 < r/Rvir < 9. We show that the median and mean density profiles of halo samples of a given peak height exhibit significant deviations from the universal analytic profiles discussed previously in the literature, such as the NFW and Einasto profiles, at radii r > 0.5 R200m. In particular, at these radii the logarithmic slope of the median density profiles of massive or rapidly accreting halos steepens more sharply than predicted. The steepening becomes more pronounced with increasing mass accretion rate. The steepest slope of the profiles occurs at r ~ R200m, and its absolute value increases with increasing peak height or mass accretion rate, reaching slopes of -4 and steeper. Importantly, we find that the outermost density profiles at r > R200m are remarkably self-similar when radii are rescaled by R200m. This self-similarity indicates that radii defined with respect to the mean density are preferred for describing the structure and evolution of the outer profiles. However, the inner density profiles are most self-similar when radii are rescaled by R200c, a radius enclosing a fixed overdensity with respect to the critical density of the universe. We propose a new fitting formula that describes the profiles at all radii out to r ~ 9 Rvir, including the transition region around r ~ R200m where the steepening occurs. The formula fits the median and mean density profiles of halo samples selected by their peak height or mass accretion rate with accuracy < 10% at all redshifts and masses we studied, 0 < z < 6 and Mvir > 1.7E10 Msun/h. We discuss observational signatures of the density profile features described above, and show that the steepening of the outer profile should be detectable in future weak lensing analyses of massive clusters. (abridged)
    The Astrophysical Journal 01/2014; 789(1). DOI:10.1088/0004-637X/789/1/1 · 6.28 Impact Factor
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    Roberto E. Gonzalez · Andrey V. Kravtsov · Nickolay Y. Gnedin
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    ABSTRACT: We use recent proper motion measurements of the tangential velocity of M31, along with its radial velocity and distance, to derive the likelihood of the sum of halo masses of the Milky Way and M31. This is done using a sample halo pairs in the Bolshoi cosmological simulation of $\Lambda$CDM cosmology selected to match properties and environment of the Local Group. The resulting likelihood gives estimate of the sum of masses of $M_{\rm MW,200}+M_{\rm M31,200}=$ $2.40_{-1.05}^{+1.95}\times10^{12}\,M_{\odot}$ ($90\%$ confidence interval). This estimate is consistent with individual mass estimates for the Milky Way and M31 and is consistent, albeit somewhat on the low side, with the mass estimated using the timing argument. We show that although the timing argument is unbiased on average for all pairs, for pairs constrained to have radial and tangential velocities similar to that of the Local Group the argument overestimates the sum of masses by a factor of $1.6$. Using similar technique we estimate the total dark matter mass enclosed within $1$ Mpc from the Local Group barycenter to be $M_{\rm LG}(r<1\, {\rm Mpc})=4.2_{-2.0}^{+3.4}\times10^{12}\,M_{\odot}$ ($90\%$ confidence interval).
    The Astrophysical Journal 12/2013; 793(2). DOI:10.1088/0004-637X/793/2/91 · 6.28 Impact Factor
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    C. M. Booth · Oscar Agertz · Andrey V. Kravtsov · Nickolay Y. Gnedin
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    ABSTRACT: We present results from high-resolution hydrodynamic simulations of isolated SMC- and Milky Way-sized galaxies that include a model for feedback from galactic cosmic rays (CRs). We find that CRs are naturally able to drive winds with mass loading factors of up to ~10 in dwarf systems. The scaling of the mass loading factor with circular velocity between the two simulated systems is consistent with \propto v_c^{1-2} required to reproduce the faint end of the galaxy luminosity function. In addition, simulations with CR feedback reproduce both the normalization and the slope of the observed trend of wind velocity with galaxy circular velocity. We find that winds in simulations with CR feedback exhibit qualitatively different properties compared to SN driven winds, where most of the acceleration happens violently in situ near star forming sites. In contrast, the CR-driven winds are accelerated gently by the large-scale pressure gradient established by CRs diffusing from the star-forming galaxy disk out into the halo. The CR-driven winds also exhibit much cooler temperatures and, in the SMC-sized system, warm (T~10^4 K) gas dominates the outflow. The prevalence of warm gas in such outflows may provide a clue as to the origin of ubiquitous warm gas in the gaseous halos of galaxies detected via absorption lines in quasar spectra.
    The Astrophysical Journal 08/2013; 777(1). DOI:10.1088/2041-8205/777/1/L16 · 6.28 Impact Factor
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    ABSTRACT: We introduce the AGORA project, a comprehensive numerical study of well-resolved galaxies within the LCDM cosmology. Cosmological hydrodynamic simulations with force resolutions of ~100 proper pc or better will be run with a variety of code platforms to follow the hierarchical growth, star formation history, morphological transformation, and the cycle of baryons in and out of 8 galaxies with halo masses M_vir ~= 1e10, 1e11, 1e12, and 1e13 Msun at z=0 and two different ("violent" and "quiescent") assembly histories. The numerical techniques and implementations used in this project include the smoothed particle hydrodynamics codes GADGET and GASOLINE, and the adaptive mesh refinement codes ART, ENZO, and RAMSES. The codes will share common initial conditions and common astrophysics packages including UV background, metal-dependent radiative cooling, metal and energy yields of supernovae, and stellar initial mass function. These are described in detail in the present paper. Subgrid star formation and feedback prescriptions will be tuned to provide a realistic interstellar and circumgalactic medium using a non-cosmological disk galaxy simulation. Cosmological runs will be systematically compared with each other using a common analysis toolkit, and validated against observations to verify that the solutions are robust - i.e., that the astrophysical assumptions are responsible for any success, rather than artifacts of particular implementations. The goals of the AGORA project are, broadly speaking, to raise the realism and predictive power of galaxy simulations and the understanding of the feedback processes that regulate galaxy "metabolism." The proof-of-concept dark matter-only test of the formation of a galactic halo with a z=0 mass of M_vir ~= 1.7e11 Msun by 9 different versions of the participating codes is also presented to validate the infrastructure of the project.
    The Astrophysical Journal Supplement Series 08/2013; 210(1). DOI:10.1088/0067-0049/210/1/14 · 14.14 Impact Factor
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    Benedikt Diemer · Andrey V. Kravtsov · Surhud More
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    ABSTRACT: We investigate whether the evolution of cluster scaling relations is affected by the spurious evolution of mass due to the evolving reference density with respect to which halo masses are defined (pseudo-evolution). We use the relation between mass, M, and velocity dispersion, sigma, as a test case, and find that the deviation from the M-sigma relation of cluster-sized halos due of pseudo-evolution is smaller than 10% for a wide range of mass definitions. The reason for this small impact is a tight relation between the velocity dispersion and mass profiles, sigma(<r) = const * (GM(<r) / r)^(1/2), which holds across a large radial range. We show that such a relation is generically expected for a wide range of density profiles, as long as halos are in approximate Jeans equilibrium. Thus, as the outer "virial" radius used to define the halo mass, R, increases due to pseudo-evolution, halos approximately preserve their M-sigma relation. This result explains why such relations are almost insensitive to the definition of the virial radius, and highlights the fact that tight scaling relations are the result of tight equilibrium relations between radial profiles of physical quantities, rather than a result of the virial theorem applied to the cluster as a whole within some unique boundary. We find exceptions at very small and very large radii, where the profiles deviate from the relations they exhibit at intermediate radii. We discuss the implications of these results for other cluster scaling relations, and argue that pseudo-evolution should have very small effects on most scaling relations, except for those which involve the stellar masses of galaxies. In particular, we show that the relation between stellar mass fraction and total mass is affected by pseudo-evolution, and is largely shaped by it for halo masses smaller than 1E14 Msun.
    The Astrophysical Journal 06/2013; 779(2). DOI:10.1088/0004-637X/779/2/159 · 6.28 Impact Factor
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    Kyu-Hyun Chae · Mariangela Bernardi · Andrey V. Kravtsov
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    ABSTRACT: We assemble a statistical set of global mass models for ~2,000 nearly spherical SDSS galaxies at a mean redshift of 0.12 based on their aperture velocity dispersions and newly derived luminosity profiles in conjunction with published velocity dispersion profiles and empirical properties and relations of galaxy and halo parameters. We consider two-component mass models, in which stellar mass distribution is assumed to follow the observationally-derived luminosity profile and dark matter (DM) distribution is modelled using the generalized Navarro-Frenk-White (gNFW) or Einasto profile, as well as single component models of total mass distribution. When the two-component mass models are fitted to the SDSS aperture velocity dispersions, the predicted velocity dispersion profile (VP) slopes within the effective radius R_eff match well the distribution in observed elliptical galaxies. In contrast, the single-component models cannot reproduce the VP slope distribution. From a number of input variations the models exhibit for the radial range 0.1 R_eff < r < R_eff a tight correlation gamma_e=(1.865+/-0.008)+(-4.93+/-0.15) where gamma_e is the mean slope absolute value of the total mass density and eta is the mean slope of the velocity dispersion profile, which leads to a super-isothermal gamma_e = 2.15+/-0.04 for empirical eta=-0.058+/-0.008. Furthermore, the successful two-component models appear to imply a typical slope curvature pattern in the total mass profile. Finally, it is intriguing to note that a combination analogous to the pseudo phase-space density of DM haloes from N-body simulations Q'(r)=rho(r)/sigma^3(r)$, where rho(r) is the total density profile and sigma(r) is the radial stellar velocity dispersion profile, may well have a universal profile within R_eff with a mean slope of ~-1.87, strikingly similar to the corresponding slope of self-gravitating DM haloes. (abridged)
    Monthly Notices of the Royal Astronomical Society 05/2013; 437(4). DOI:10.1093/mnras/stt2163 · 5.23 Impact Factor
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    Roberto E. Gonzalez · Andrey V. Kravtsov · Nickolay Y. Gnedin
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    ABSTRACT: Previous studies showed that an estimate of the likelihood distribution of the Milky Way halo mass can be derived using the properties of the satellites similar to the Large and Small Magellanic Clouds (LMC and SMC). However, it would be straightforward to interpret such an estimate only if the properties of the Magellanic Clouds (MCs) are fairly typical and are not biased by the environment. In this study we explore whether the environment of the Milky Way affects the properties of the SMC and LMC such as their velocities. To test for the effect of the environment, we compare velocity distributions for MC-sized subhalos around Milky Way hosts in a sample selected simply by mass and in the second sample of such halos selected with additional restrictions on the distance to the nearest cluster and the local galaxy density, designed to mimic the environment of the Local Group (LG). We find that satellites in halos in the LG-like environments do have somewhat larger velocities, as compared to the halos of similar mass in the sample without environmental constraints. We derive the host halo likelihood distribution for the samples in the LG-like envirionment and in the control sample and find that the environment does not significantly affect the derived likelihood. We use the updated properties of the SMC and LMC to derive the constraint on the MW halo mass $\log{({\rm M}_{200} /\msol)}=12.06^{+0.31}_{-0.19}$ (90% confidence interval). We also explore the incidence of close pairs with relative velocities and separations similar to those of the LMC and SMC and find that such pairs are quite rare among $\Lambda$CDM halos. Taking into account the close separation of the MCs in the Busha et al.\ 2011 method results in the shift of the MW halo mass estimate to smaller masses, with the peak shifting approximately by a factor of two.[Abridged]
    The Astrophysical Journal 01/2013; 770(2). DOI:10.1088/0004-637X/770/2/96 · 6.28 Impact Factor
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    Yongen Yu · Jingjin Wu · Zhiling Lan · D.H. Rudd · N.Y. Gnedin · Andrey Kravtsov
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    ABSTRACT: I/O performance is vital for most HPC applications especially those that generate a vast amount of data with the growth of scale. Many studies have shown that scientific applications tend to issue small and noncontiguous accesses in an interleaving fashion, causing different processes to access overlapping regions. In such scenario, collective I/O is a widely used optimization technique. However, the use of collective I/O deployed in existing MPI implementations is not trivial and sometimes even impossible. Collective I/O is an optimization based on a single collective I/O access. If the data reside in different places (e.g. in different arrays), the application has to maintain a buffer to first combine these data and then perform I/O operations on the buffer rather than the original data pieces. The process is very tedious for application developers. Besides, collective I/O requires the creating of a file view to describe the noncontiguous access patterns and additional coding is needed. Moreover, for the applications with complex data access using dynamic data sizes, it is hard or even impossible to use the file view mechanism to describe the access pattern through derived data types. In this study, we develop a user-level library called transparent collective I/O (TCIO) for application developers to easily incorporate collective I/O optimization into their applications. Preliminary experiments by means of a synthetic benchmark and a real cosmology application demonstrate that the library can significantly reduce the programming efforts required for application developers. Moreover, TCIO delivers better performance at large scales as compared to the existing collective functionality provided by MPI-IO.
    Parallel & Distributed Processing (IPDPS), 2013 IEEE 27th International Symposium on; 01/2013
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    ABSTRACT: Upcoming wide-area sky surveys offer the power to test the source of cosmic acceleration by placing extremely precise constraints on existing cosmological model parameters. These observational surveys will employ multiple tests based on statistical signatures of galaxies and larger-scale structures such as clusters of galaxies. Simulations of large-scale structure provide the means to maximize the power of sky survey tests by characterizing key sources of systematic uncertainties. We describe an XSEDE program to produce multiple synthetic sky surveys of galaxies and large-scale cosmic structure in support of science analysis for the Dark Energy Survey. We explain our Airavata-enabled methods and report extensions to our workflow processing over the last year. We highlight science analysis focused on counts of clusters of galaxies.
    Proceedings of the Conference on Extreme Science and Engineering Discovery Environment: Gateway to Discovery, San Diego, California; 01/2013
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    Andrey V. Kravtsov
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    ABSTRACT: Sizes of galaxies are an important diagnostic for galaxy formation models. In this study I use the abundance matching ansatz, which has proven to be successful in reproducing galaxy clustering and other statistics, to derive estimates of the virial radius, R200, for galaxies of different morphological types and wide range of stellar mass. I show that over eight of orders of magnitude in stellar mass galaxies of all morphological types follow an approximately linear relation between 3D half-mass radius of their stellar distribution, rhalf and virial radius, rhalf~0.015R200 with a scatter of ~0.2 dex. Such scaling is in remarkable agreement with expectation of models which assume that galaxy sizes are controlled by halo angular momentum, which implies rhalf\propto lambda R200, where lambda is the spin of galaxy parent halo. The scatter about the relation is comparable with the scatter expected from the distribution of $\lambda$ and normalization of the relation agrees with that predicted by the model of Mo, Mao & White (1998), if galaxy sizes were set on average at z~1-2. Moreover, I show that when stellar and gas surface density profiles of galaxies of different morphological types are rescaled using radius r_n= 0.015 R200, the rescaled surface density profiles follow approximately universal exponential (for late types) and de Vaucouleurs (for early types) profiles with scatter of only 30-50% at R~1-3r_n. Remarkably, both late and early type galaxies have similar mean stellar surface density profiles at R>r_n. The main difference between their stellar distributions is thus at R<r_n. The results of this study imply that galaxy sizes and radial distribution of baryons are shaped primarily by properties of their parent halo and that sizes of both late type disks and early type spheroids are controlled by halo angular momentum.
    The Astrophysical Journal Letters 12/2012; 764(2). DOI:10.1088/2041-8205/764/2/L31 · 5.60 Impact Factor
  • Ileana M. Vass · Stelios Kazantzidis · Monica Valluri · Andrey V. Kravtsov
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    ABSTRACT: We use dissipationless N-body simulations to investigate the evolution of the true coarse-grained phase-space density distribution f (x,v) in equal-mass mergers between dark matter (DM) halos. The halo models are constructed with various asymptotic power-law indices ρ ∝ r −γ ranging from steep cusps to core-like profiles and we employ the phase-space density estimator “Enbid ” developed by Sharma & Steinmetz to compute f (x,v). The adopted force resolution allows robust phase-space density profile estimates in the inner ∼ 1 % of the virial radii of the simulated systems. We confirm that merger events result in a decrease of the coarse-grained phase-space density in accordance with expectations from Mixing Theorems for collisionless systems. We demonstrate that binary mergers between identical DM halos produce remnants that retain excellent memories of the inner slopes and overall shapes of the phase-space density distribution of their progenitors. The robustness of the phase-space density profiles holds for a range of orbital energies, and a variety of encounter configurations including sequences of several consecutive merger events, designed to mimic hierarchical merging, and collisions occurring at different cosmological epochs. If the progenitor halos are constructed with appreciably different asymptotic power-law indices, we find that the inner slope and overall shape of the phasespace density distribution of the remnant are substantially closer to that of the initial system with the steepest central density cusp. These results explicitly demonstrate that mixing is incomplete in equal-mass mergers between DM halos, as it does not erase memory of the progenitor properties. Our results also confirm the recent analytical predictions of Dehnen (2005) regarding the preservation of merging self-gravitating central density cusps. Subject headings: cosmology: theory — dark matter — halos — halos: structure — halos: phase-space density profiles — halos: evolution — methods: numerical 1.
  • Erwin T. Lau · Daisuke Nagai · Andrey V. Kravtsov
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    ABSTRACT: We investigate effects of baryon dissipation on the dark matter virial scaling relation between total mass and velocity dispersion and the velocity bias of galaxies in groups and clusters using self-consistent cosmological simulations. We show that the baryon dissipation increases the velocity dispersion of dark matter within the virial radius by ≈ 5 − 10%. The effect is mainly driven by the change in density and gravitational potential in inner regions of cluster, and it is larger in lower mass systems where gas cooling and star formation are more efficient. We also show that the galaxy velocity bias depends on how galaxies are selected. Galaxies selected based on their stellar mass exhibit no velocity bias, while galaxies selected based on their total mass exhibit positive bias of ≈ 10%, consistent with previous results based on collisionless dark matter only simulations. We further find that observational estimates of galaxy velocity dispersion are unbiased with respect to the velocity dispersion of dark matter, provided that galaxies are selected using their stellar mass and velocity dispersions are computed using more than ten most massive galaxies. Velocity dispersion estimated with less than ten galaxies, on the other hand, lead to significant underestimate of the dynamical mass. Results presented in this paper should be useful in interpretation of high-redshift groups and clusters as well as cosmological constraints derived from upcoming optical cluster surveys.
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    ABSTRACT: We conduct a series of high-resolution, fully self-consistent dissipationless N-body simulations to investigate the cumulative effect of substructure mergers onto thin disk galaxies in the context of the ΛCDM paradigm of structure formation. Our simulation campaign is based on a hybrid approach combining cosmological simulations and controlled numerical experiments. Substructure mass functions, orbital distributions, internal structures, and accretion times are culled directly from cosmological simulations of galaxy-sized cold dark matter (CDM) halos. We demonstrate that accretions of massive subhalos onto the central regions of host halos, where the galactic disk resides, since z ∼ 1 should be common occurrences. In contrast, extremely few satellites in present-day CDM halos are likely to have a significant impact on the disk structure. This is due to the fact that massive subhalos with small orbital pericenters that are most capable of strongly perturbing the disk become either tidally disrupted or suffer substantial mass loss prior to z = 0. One host halo merger history is subsequently used to seed controlled N-body experiments of repeated satellite impacts on an initially-thin Milky Way-type disk galaxy. These simulations track the effects of six dark matter substructures, with initial masses in the range ∼ (0.7 − 2) × 10 10 M ⊙ ( ∼ 20 − 60 % of the disk mass), crossing the disk in the past ∼ 8 Gyr. We show that these accretion events produce several distinctive observational signatures in the stellar disk including: a

Publication Stats

13k Citations
694.51 Total Impact Points

Institutions

  • 2001–2014
    • University of Chicago
      • • Kavli Institute for Cosmological Physics
      • • Department of Astronomy and Astrophysics
      Chicago, Illinois, United States
  • 2011–2012
    • Fermi National Accelerator Laboratory (Fermilab)
      • Center for Particle Astrophysics
      Batavia, Illinois, United States
  • 1996–2009
    • New Mexico State University
      • Department of Astronomy
      Las Cruces, NM, United States
  • 1999–2008
    • The Ohio State University
      • • Department of Physics
      • • Department of Astronomy
      Columbus, Ohio, United States
  • 2007
    • University of Pittsburgh
      • Physics and Astronomy
      Pittsburgh, Pennsylvania, United States
  • 2006
    • Space Research Institute
      Moskva, Moscow, Russia