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The Physical Nature of the Cosmic Accretion of Baryons and Dark Matter into Halos and Their Galaxies

Wetzel, Andrew R. and Nagai, Daisuke (2015) The Physical Nature of the Cosmic Accretion of Baryons and Dark Matter into Halos and Their Galaxies. Astrophysical Journal, 808 (1). Art. No. 40. ISSN 0004-637X.

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The cosmic accretion of both dark matter and baryons into halos is typically measured using some evolving virial relation, but recent work suggests that most halo growth at late cosmic time (z ≾ 2) is not physical but is rather the by-product of an evolving virial radius ("pseudo-evolution"). Using Omega25, a suite of cosmological simulations that incorporate both dark matter and gas dynamics with differing treatments of gas cooling, star formation, and thermal feedback, we systematically explore the physics that governs cosmic accretion into halos and their galaxies. Physically meaningful cosmic accretion of both dark matter and baryons occurs at z ≳ 1 across our halo mass range: M_(200m) = 10^(11-14) M_⊙. However, dark matter, because it is dissipationless, is deposited (in a time-average sense) at ≳ R_(200m) (z) in a shell-like manner, such that dark matter mass and density experience little-to-no physical growth at any radius within a halo at z < 1. In contrast, gas, because it is able to cool radiatively, experiences significant accretion at all radii, at a rate that roughly tracks the accretion rate at R_(200m), at all redshifts. Infalling gas starts to decouple from dark matter at ≈2 R_(200m) and continues to accrete to smaller radii until the onset of strong angular-momentum support at ≈0.1 R_(200m). Thus, while the growth of dark matter is subject to pseudo-evolution, the growth of baryons is not. The fact that the accretion rate of gas on galactic scales tracks the accretion rate near R_(200m) provides insight into the tight relations between the masses/sizes of galaxies and those of their host halos across cosmic time.

Item Type:Article
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URLURL TypeDescription Paper
Wetzel, Andrew R.0000-0003-0603-8942
Nagai, Daisuke0000-0002-6766-5942
Additional Information:© 2015 American Astronomical Society. Received 2014 November 28; accepted 2015 June 7; published 2015 July 16. We thank Andrey Kravtsov, Surhud More, Phil Hopkins, Frank van den Bosch, Andrew Hearin, Erik Tollerud, Erwin Lau, and Benedikt Diemer for useful discussions and/or comments on an early draft. We also thank the reviewer for useful comments. A.R.W. acknowledges the hospitality and stimulating environment of the Aspen Center for Physics, supported in part by the NSF. A.R.W. also gratefully acknowledges support from the Moore Center for Theoretical Cosmology and Physics at Caltech. This work was supported in part by NSF grants AST-1412768 & 1009811, NASA ATP grant NNX11AE07G, NASA Chandra grants GO213004B and TM4-15007X, the Research Corporation, and by the facilities and staff of the Yale University Faculty of Arts and Sciences High Performance Computing Center.
Group:TAPIR, Moore Center for Theoretical Cosmology and Physics
Funding AgencyGrant Number
Caltech Moore Center for Theoretical Cosmology and PhysicsUNSPECIFIED
Research CorporationUNSPECIFIED
Subject Keywords: cosmology: theory; galaxies: evolution; galaxies: formation; galaxies: general; galaxies: halos; methods: numerical
Issue or Number:1
Record Number:CaltechAUTHORS:20150831-103016402
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Official Citation:The Physical Nature of the Cosmic Accretion of Baryons and Dark Matter into Halos and Their Galaxies Andrew R. Wetzel and Daisuke Nagai 2015 ApJ 808 40
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:59986
Deposited By: Ruth Sustaita
Deposited On:31 Aug 2015 19:44
Last Modified:20 Nov 2019 22:36

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