The three causes of low-mass assembly bias Mansfield, Philip; Kravtsov, Andrey V
Monthly notices of the Royal Astronomical Society,
04/2020, Letnik:
493, Številka:
4
Journal Article
Recenzirano
ABSTRACT
We present a detailed analysis of the physical processes that cause halo assembly bias – the dependence of halo clustering on proxies of halo formation time. We focus on the origin of ...assembly bias in the mass range corresponding to the hosts of typical galaxies and use halo concentration as our chief proxy of halo formation time. We also repeat our key analyses across a broad range of halo masses and for alternative formation time definitions. We show that splashback subhaloes are responsible for two-thirds of the assembly bias signal, but do not account for the entire effect. After splashback subhaloes have been removed, we find that the remaining assembly bias signal is due to a relatively small fraction ($\lesssim \!10{{\ \rm per\ cent}}$) of haloes in dense regions. We test a number of additional physical processes thought to contribute to assembly bias and demonstrate that the two key processes are the slowing of mass growth by large-scale tidal fields and by the high velocities of ambient matter in sheets and filaments. We also rule out several other proposed physical causes of halo assembly bias. Based on our results, we argue that there are three processes that modify the assembly bias of small-mass haloes arising from the properties of the primordial Gaussian field: large-scale tidal fields, gravitational heating due to the collapse of large-scale structures, and splashback subhaloes located outside the virial radius.
ABSTRACT
We use GRUMPY, a simple regulator-type model for dwarf galaxy formation and evolution, to forward model the dwarf galaxy satellite population of the Milky Way (MW) using the Caterpillar ...zoom-in simulation suite. We show that luminosity and distance distributions of the model satellites are consistent with the distributions measured in the DES, PS1, and SDSS surveys, even without including a model for the orphan galaxies. We also show that our model for dwarf galaxy sizes can simultaneously reproduce the observed distribution of stellar half-mass radii, r1/2, of the MW satellites and the overall r1/2–M⋆ relation exhibited by observed dwarf galaxies. The model predicts that some of the observed faint stellar systems with r1/2 < 10 pc are ultra-faint dwarf galaxies. Scaling of the stellar mass M⋆ and peak halo mass Mpeak for the model satellites is not described by a power law, but has a clear flattening of M⋆–Mpeak scaling at $M_{\rm peak}\lt 10^8\, \, M_{\odot }$ imprinted by reionization. As a result, the fraction of low mass haloes ($M_{\rm peak}\lt 10^8 \, M_{\odot }$) hosting galaxies with MV < 0 is predicted to be 50 per cent at $M_{\rm peak}\sim 3.6 \times 10^7\, \, M_{\odot }$. We find that such high fraction at that halo mass helps to reproduce the number of dwarf galaxies discovered recently in the HSC-SSP survey. Using the model we forecast that there should be the total of $440^{+201}_{-147}$ (68 per cent confidence interval) MW satellites with MV < 0 and r1/2 > 10 pc within 300 kpc and make specific predictions for the HSC-SSP, DELVE-WIDE, and LSST surveys.
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, R sub(200), for galaxies of ...different morphological types and a wide range of stellar masses. I show that over eight orders of magnitude in stellar mass galaxies of all morphological types follow an approximately linear relation between half-mass radius of their stellar distribution, r sub(1/2), and virial radius, r sub(1/2) asymptotically = 0.015 R sub(200), with scatter of asymptotically =0.2 dex. Such scaling is in remarkable agreement with the expectation of models that assume that galaxy sizes are controlled by halo angular momentum, r sub(1/2) proportional, variant lambdaR sub(200), 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. Moreover, I show that when the stellar and gas surface density profiles of galaxies of different morphological types are rescaled by the radius r sub(n) = 0.015 R sub(200), the rescaled profiles follow approximately universal exponential (for late types) and de Vaucouleurs (for early types) form with scatter of only asymptotically =30%-50% at R asymptotically = 1-3r sub(n). Remarkably, both late- and early-type galaxies have similar mean stellar surface density profiles at R > ~ 1r sub(n). The main difference between their stellar distributions is thus at R < r sub(n). The results of this study imply that galaxy sizes and radial distribution of baryons are shaped primarily by properties of their parent halos and that the sizes of both late-type disks and early-type spheroids are controlled by halo angular momentum.
ABSTRACT The boundaries of cold dark matter halos are commonly defined to enclose a density contrast Δ relative to a reference (mean or critical) density. We argue that a more physical halo boundary ...choice is the radius at which accreted matter reaches its first orbital apocenter after turnaround. This splashback radius, , 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 and the enclosed mass, , as a function of mass accretion rate and peak height. We find that is in the range for rapidly accreting halos and is for slowly accreting halos. Thus, halos and their environmental effects can extend well beyond the conventionally defined "virial" radius. We show that and evolve relatively strongly compared to other commonly used definitions. In particular, evolves significantly even for the smallest dwarf-sized halos at z = 0. We also contrast with the mass enclosed within four scale radii of the halo density profile, , which characterizes the inner halo. During the early stages of halo assembly, and evolve similarly, but in the late stages stops increasing while 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.
We present a numerical study of dark matter halo concentrations in LambdaCDM and self-similar cosmologies. We show that the relation between concentration, c, and peak height, v, 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-v relation. In particular, there is no well-defined floor in the concentration values. Instead, the minimum concentration depends on redshift: at fixed v, 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 v and n. This model matches our LambdaCDM results to <, ~5% accuracy up to z = 6, and matches scale-free Omega sub(m) = 1 models to <, ~15%. The model also reproduces the low concentration values of Earth-mass halos at z asymptotically = 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.
ABSTRACT We investigate the star formation-feedback cycle in cosmological galaxy formation simulations, focusing on the progenitors of Milky Way (MW)-sized galaxies. We find that in order to ...reproduce key properties of the MW progenitors, such as semi-empirically derived star formation histories (SFHs) and the shape of rotation curves, our implementation of star formation and stellar feedback requires (1) a combination of local early momentum feedback via radiation pressure and stellar winds, and subsequent efficient supernovae feedback, and (2) an efficacy of feedback that results in the self-regulation of the global star formation rate on kiloparsec scales. We show that such feedback-driven self-regulation is achieved globally for a local star formation efficiency per free fall time of . Although this value is larger that the value usually inferred from the Kennicutt-Schmidt (KS) relation, we show that it is consistent with direct observational estimates of in molecular clouds. Moreover, we show that simulations with local efficiency of reproduce the global observed KS relation. Such simulations also reproduce the cosmic SFH of the MW-sized galaxies and satisfy a number of other observational constraints. Conversely, we find that simulations that a priori assume an inefficient mode of star formation, instead of achieving it via stellar feedback regulation, fail to produce sufficiently vigorous outflows and do not reproduce observations. 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.
ABSTRACT We use cosmological zoom-in simulations of galaxy formation in a Milky-Way-sized halo started from identical initial conditions to investigate the evolution of galaxy sizes, baryon ...fractions, morphologies, and angular momenta in runs with different parameters of the star formation-feedback cycle. Our fiducial model with a high local star formation efficiency, which results in efficient feedback, produces a realistic late-type galaxy that matches the evolution of basic properties of late-type galaxies: stellar mass, disk size, morphology dominated by a kinematically cold disk, stellar and gas surface density profiles, and specific angular momentum. We argue that feedback's role in this success is twofold: (1) removal of low angular momentum gas, and (2) maintaining a low disk-to-halo mass fraction, which suppresses disk instabilities that lead to angular momentum redistribution and a central concentration of baryons. However, our model with a low local star formation efficiency, but large energy input per supernova, chosen to produce a galaxy with a similar star formation history as our fiducial model, leads to a highly irregular galaxy with no kinematically cold component, overly extended stellar distribution, and low angular momentum. This indicates that only when feedback is allowed to become vigorous via locally efficient star formation in dense cold gas do resulting galaxy sizes, gas/stellar surface density profiles, and stellar disk angular momenta agree with observed z = 0 galaxies.
THE PSEUDO-EVOLUTION OF HALO MASS Diemer, Benedikt; More, Surhud; Kravtsov, Andrey V
Astrophysical journal/The Astrophysical journal,
03/2013, Letnik:
766, Številka:
1
Journal Article
Recenzirano
Odprti dostop
A dark matter halo is commonly defined as a spherical overdensity of matter with respect to a reference density, such as the critical density or the mean matter density of the universe. Such ...definitions can lead to a spurious pseudo-evolution of halo mass simply due to redshift evolution of the reference density, even if its physical density profile remains constant over time. We estimate the amount of such pseudo-evolution of mass between z = 1 and 0 for halos identified in a large N-body simulation, and show that it accounts for almost the entire mass evolution of the majority of halos with M sub(200rho) <, ~ 10 super(12) h super(-1)M sub(middot in circle) and can be a significant fraction of the apparent mass growth even for cluster-sized halos. We estimate the magnitude of the pseudo-evolution assuming that halo density profiles remain static in physical coordinates, and show that this simple model predicts the pseudo-evolution of halos identified in numerical simulations to good accuracy, albeit with significant scatter. We discuss the impact of pseudo-evolution on the evolution of the halo mass function and show that the non-evolution of the low-mass end of the halo mass function is the result of a fortuitous cancellation between pseudo-evolution and the absorption of small halos into larger hosts. We also show that the evolution of the low-mass end of the concentration-mass relation observed in simulations is almost entirely due to the pseudo-evolution of mass. Finally, we discuss the implications of our results for the interpretation of the evolution of various scaling relations between the observable properties of galaxies and galaxy clusters and their halo masses.
The density field in the outskirts of dark matter halos is discontinuous as a result of a caustic formed by matter at its first apocenter after infall. In this paper, we present an algorithm to ...identify the "splashback shell" formed by these apocenters in individual simulated halos using only a single snapshot of the density field. We implement this algorithm in the code Shellfish (SHELL Finding In Spheroidal Halos) and demonstrate that the code identifies splashback shells correctly and measures their properties with an accuracy of for halos with more than 50,000 particles and mass accretion rates of . Using Shellfish, we present the first estimates for several basic properties of individual splashback shells, such as radius, , mass, and overdensity, and provide fits to the distribution of these quantities as functions of , , and We confirm previous findings that decreases with increasing , but we show that, independent of accretion rate, it also decreases with increasing . We also study the 3D structures of these shells and find that they generally have non-ellipsoidal oval shapes. We find that splashback radii estimated by Shellfish are 20%-30% larger than those estimated in previous studies from stacked density profiles at high accretion rates. We demonstrate that the latter are biased low owing to the contribution of high-mass subhalos to these profiles, and we show that using the median instead of mean density in each radial bin mitigates the effect of substructure on density profiles and removes the bias.
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