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The stellar mass assembly of galaxies in the Illustris simulation: growth by mergers and the spatial distribution of accreted stars

Rodriguez-Gomez, Vicente and Pillepich, Annalisa and Sales, Laura V. and Genel, Shy and Vogelsberger, Mark and Zhu, Qirong and Wellons, Sarah and Nelson, Dylan and Torrey, Paul and Springel, Volker and Ma, Chung-Pei and Hernquist, Lars (2016) The stellar mass assembly of galaxies in the Illustris simulation: growth by mergers and the spatial distribution of accreted stars. Monthly Notices of the Royal Astronomical Society, 458 (3). pp. 2371-2390. ISSN 0035-8711.

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We use the Illustris simulation to study the relative contributions of in situ star formation and stellar accretion to the build-up of galaxies over an unprecedentedly wide range of masses (M_* = 10^9-10^(12) M_⊙), galaxy types, environments, and assembly histories. We find that the ‘two-phase’ picture of galaxy formation predicted by some models is a good approximation only for the most massive galaxies in our simulation – namely, the stellar mass growth of galaxies below a few times 10^(11) M_⊙ is dominated by in situ star formation at all redshifts. The fraction of the total stellar mass of galaxies at z = 0 contributed by accreted stars shows a strong dependence on galaxy stellar mass, ranging from about 10 per cent for Milky Way-sized galaxies to over 80 per cent for M_* ≈ 10^(12) M_⊙ objects, yet with a large galaxy-to-galaxy variation. At a fixed stellar mass, elliptical galaxies and those formed at the centres of younger haloes exhibit larger fractions of ex situ stars than disc-like galaxies and those formed in older haloes. On average, ∼50 per cent of the ex situ stellar mass comes from major mergers (stellar mass ratio μ > 1/4), ∼20 per cent from minor mergers (1/10 < μ < 1/4), ∼20 per cent from very minor mergers (μ < 1/10), and ∼10 per cent from stars that were stripped from surviving galaxies (e.g. flybys or ongoing mergers). These components are spatially segregated, with in situ stars dominating the innermost regions of galaxies, and ex situ stars being deposited at larger galactocentric distances in order of decreasing merger mass ratio.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Rodriguez-Gomez, Vicente0000-0002-9495-0079
Pillepich, Annalisa0000-0003-1065-9274
Genel, Shy0000-0002-3185-1540
Vogelsberger, Mark0000-0001-8593-7692
Torrey, Paul0000-0002-5653-0786
Springel, Volker0000-0001-5976-4599
Hernquist, Lars0000-0001-6950-1629
Additional Information:© 2016 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. Accepted 2016 February 23. Received 2016 February 23. In original form 2015 November 27. First published online February 26, 2016. We thank Jeremiah P. Ostriker, Gurtina Besla, and Benedikt Diemer for useful comments and discussions. SG acknowledges support provided by NASA through Hubble Fellowship grant HST-HF2-51341.001-A awarded by the STScI, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS5-26555. VS acknowledges support through the European Research Council through ERC-StG grant EXAGAL-308037. LH acknowledges support from NSF grant AST-1312095 and NASA grant NNX12AC67G. Simulations were run on the Harvard Odyssey and CfA/ITC clusters, the Ranger and Stampede supercomputers at the Texas Advanced Computing Center as part of XSEDE, the Kraken supercomputer at Oak Ridge National Laboratory as part of XSEDE, the CURIE supercomputer at CEA/France as part of PRACE project RA0844, and the SuperMUC computer at the Leibniz Computing Centre, Germany, as part of project pr85je.
Funding AgencyGrant Number
NASA Hubble FellowshipHST-HF2-51341.001-A
Space Telescope Science InstituteUNSPECIFIED
European Research Council (ERC)EXAGAL-308037
Subject Keywords:methods: numerical galaxies: formation galaxies: haloes galaxies: interactions cosmology: theory
Issue or Number:3
Record Number:CaltechAUTHORS:20160603-151011265
Persistent URL:
Official Citation:Vicente Rodriguez-Gomez, Annalisa Pillepich, Laura V. Sales, Shy Genel, Mark Vogelsberger, Qirong Zhu, Sarah Wellons, Dylan Nelson, Paul Torrey, Volker Springel, Chung-Pei Ma, and Lars Hernquist The stellar mass assembly of galaxies in the Illustris simulation: growth by mergers and the spatial distribution of accreted stars MNRAS (May 21, 2016) Vol. 458 2371-2390 doi:10.1093/mnras/stw456 first published online February 26, 2016
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:67657
Deposited By: Ruth Sustaita
Deposited On:04 Jun 2016 17:40
Last Modified:09 Mar 2020 13:19

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