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

By V. Rodriguez-Gomez, A. Pillepich, L. Sales, Shy Genel, M. Vogelsberger, Qirong Zhu, S. Wellons, D. Nelson, P. Torrey, Volker Springel and 2 more. 2015

297 citations recorded by the source corpus.

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.

Subfields: Astronomy and Astrophysics, Global and Planetary Change

View Paper: https://www.semanticscholar.org/paper/799b1a16616e477e8f2ee3c2152f1f085fd9cd50

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Citations in the corpus

A-type stars in the Canada–France Imaging Survey – II. Tracing the height of the disc at large distances with Blue Stragglers (2018, background): “…of the Galaxy that formed in situ and the fraction that originally came from the Galactic disc (e.g. Eggen, Lynden-Bell & Sandage 1962; Searle & Zinn 1978; Carollo et al. 2007, 2010; Font et al. 2011; Rodriguez-Gomez et al. 2016; Deason et al. 2017; Belokurov et al. 2018; Pillepich et al. 2018).”
The Horizon-AGN Simulation: Morphological Diversity of Galaxies ,Promoted by AGN Feedback (2016, background): “Finally, the transition radius, which separates the in situ-dominated (central parts) from the ex situ-dominated (outskirts), is decreasing with increasing galaxy mass (see also Rodriguez-Gomez et al. 2016).”
A unified multiwavelength model of galaxy formation (2015, background): “…totals e lar mass of galaxies has now been analysed in detail in cosmological gas-dynamical simulations of galaxy formation (e.g. Oser et al. 2010; Rodriguez-Gomez et al. 2016), but such studies have not yet yielded robust measurements of the contribution of different channels (mergers vs. disk…”
Theoretical Challenges in Galaxy Formation (2016, methodology): “The general trend is similar to simulations (e.g. Gabor & Davé 2012, Lackner et al. 2012, Oser et al. 2010, Qu et al. 2017, Rodriguez-Gomez et al. 2016).”
First results from the IllustrisTNG simulations: a tale of two elements - chemical evolution of magnesium and europium (2017, background): “Here, “in-situ” stars are those formed within the main halo, while “ex-situ” stars are those accreted by mergers (Rodriguez-Gomez et al. 2016).”
First results from the IllustrisTNG simulations: the stellar mass content of groups and clusters of galaxies (2017, methodology): “More quantitatively, the fractional contribution of accreted stars to the total stellar mass of a galaxy is a steep function of stellar or halo mass (Oser et al. 2010; Lackner et al. 2012; Rodriguez-Gomez et al. 2016).”
The cosmic baryon cycle and galaxy mass assembly in the FIRE simulations (2016, background): “In a different set of large-volume simulations with the Illustris feedback model, Nelson et al. (2015) considered a “stripped" growth mode for the smooth accretion of gas previously identified in a gravitationally bound substructure.”
How to Measure Galaxy Star Formation Histories. II. Nonparametric Models (2018, background): “For high-mass galaxies, however, a large fraction of their stars have formed in other halos/galaxies and merged with a more massive galaxies (Rodriguez-Gomez et al. 2016).”
The dark nemesis of galaxy formation : why hot haloes trigger black hole growth and bring star formation to an end (2016, background): “…grow through star formation, doubling their stellar mass on a timescale comparable to the age of the Universe; above the transition mass, galaxy growth slows and is driven primarily by galaxy mergers (eg., De Lucia et al. 2006; Parry et al. 2009; Qu et al. 2016; Rodriguez-Gomez et al. 2016).”
Constraining the galaxy–halo connection over the last 13.3 Gyr: star formation histories, galaxy mergers and structural properties (2017, result): “This question has been studied in a number of previous works (Zheng, Coil & Zehavi 2007; Stewart et al. 2009; Hopkins et al. 2010a,b; Zavala et al. 2012; AvilaReese, Zavala & Lacerna 2014; Rodriguez-Gomez et al. 2015, 2016).”