THE TWO PHASES OF GALAXY FORMATION

By Ludwig Oser, Jeremiah P. Ostriker, T. Naab, Peter H. Johansson, A. Burkert. 2010

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Cosmological simulations of galaxy formation appear to show a “two-phase” character with a rapid early phase at z ≳ 2 during which “in situ” stars are formed within the galaxy from infalling cold gas followed by an extended phase since z ≲ 3 during which “ex situ” stars are primarily accreted. In the latter phase, massive systems grow considerably in mass and radius by accretion of smaller satellite stellar systems formed at quite early times (z>3) outside of the virial radius of the forming central galaxy. These tentative conclusions are obtained from high-resolution re-simulations of 39 individual galaxies in a full cosmological context with present-day virial halo masses ranging from 7 × 1011 M☉ h−1 ≲Mvir ≲ 2.7 × 1013 M☉ h−1 (h = 0.72) and central galaxy masses between 4.5 × 1010 M☉ h−1 ≲ M* ≲ 3.6 × 1011 M☉ h−1. The simulations include the effects of a uniform UV background, radiative cooling, star formation, and energetic feedback from Type II supernova. The importance of stellar accretion increases with galaxy mass and toward lower redshift. In our simulations, lower mass galaxies (M* ≲ 9 × 1010 M☉ h−1) accrete about 60% of their present-day stellar mass. High-mass galaxy (M* ≳ 1.7 × 1011 M☉ h−1) assembly is dominated by accretion and merging with about 80% of the stars added by the present day. In general the simulated galaxies approximately double their mass since z = 1. For massive systems this mass growth is not accompanied by significant star formation. The majority of the in situ created stars are formed at z>2, primarily out of cold gas flows. We recover the observational result of “archaeological downsizing,” where the most massive galaxies harbor the oldest stars. We find that this is not in contradiction with hierarchical structure formation. Most stars in the massive galaxies are formed early on in smaller structures; the galaxies themselves are assembled late.

Subfields: Astronomy and Astrophysics, Atomic and Molecular Physics, and Optics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/11df12dcd8d239a84f2f89188c40ebc5b878cc76

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Citations in the corpus

CAN MINOR MERGING ACCOUNT FOR THE SIZE GROWTH OF QUIESCENT GALAXIES? NEW RESULTS FROM THE CANDELS SURVEY (2011, background): “Oser et al. (2010) described a “two phase” picture that, while obviously a simplification at some level, still provides a useful paradigm for galaxy growth.”
Dancing in the dark: galactic properties trace spin swings along the cosmic web (2014, background): “…galaxies acquire a non-negligible fraction of their mass by mergers (at least 1000 particles of star particles, up to 20 per cent at z = 1.83), while low-mass galaxies grow their stellar mass content almost exclusively by in situ star formation (e.g. De Lucia & Blaizot 2007; Oser et al. 2010).”
Compaction and quenching of high-z galaxies in cosmological simulations: blue and red nuggets (2014, background): “This reflects the slow evolution of accretion rate in a growing galaxy (Dekel et al. 2013), the slow growth of stellar fraction in the total accreted baryons (Oser et al. 2010), and the evolution of SFR in the disc and bulge.”
Early type galaxies have been the predominant morphological class for massive galaxies since only z~1 (2011, methodology): “…massive galaxies are predicted to suffer a period of intense bombardment by minor satellites (Khochfar & Silk 2006; Hopkins et al. 2009; Feldmann et al. 2010; Oser et al. 2010) that may eventually transform the original disk-like population into the predominant present-day spheroid-like population.”
The ATLAS3D project - XXIX. The new look of early-type galaxies and surrounding fields disclosed by extremely deep optical images (2014, background): “…of the hierarchical model, they figure out that todays massive galaxies grew from series of galactic collisions that left around them various types of vestiges, including shells and tails (e.g Bullock & Johnston 2005; Naab et al. 2007; Oser et al. 2010; Helmi et al. 2011; Cooper et al. 2014).”
THE COSMOLOGICAL SIZE AND VELOCITY DISPERSION EVOLUTION OF MASSIVE EARLY-TYPE GALAXIES (2011, methodology): “…- build-up of extended stellar envelopes can originate from minor mergers and was predicted from cosmological simulations (Naab et al. 2007, 2009; Oser et al. 2010) and recently, for the first time such minor mergers at high redshift might have been directly observed (van Dokkum & Brammer 2010;…”
First results from the IllustrisTNG simulations: the stellar mass content of groups and clusters of galaxies (2017, background): “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).”
Galactic accretion and the outer structure of galaxies in the CDM model (2013, background): “Like many recent numerical studies of the size evolution of massive quiescent galaxies (Meza et al. 2003; Naab et al. 2009; Oser et al. 2010) and Milky Way-like galaxies (Abadi, Navarro & Steinmetz 2006; Cooper et al. 2010; Font et al. 2011; Sales et al. 2012) we emphasize the difference between in…”
Galaxies on FIRE (Feedback In Realistic Environments): stellar feedback explains cosmologically inefficient star formation (2013, methodology): “…and numerical methods (Pelupessy et al. 2004; Stinson et al. 2007, 2013; Mashchenko et al. 2008; Valcke et al. 2008; Governato et al. 2010, 2012; Oser et al. 2010; Feldmann et al. 2009; Brooks et al. 2011; Guedes et al. 2011; Sawala et al. 2011; Scannapieco et al. 2011; De Rossi et al. 2013;…”
CONNECTING ANGULAR MOMENTUM AND GALACTIC DYNAMICS: THE COMPLEX INTERPLAY BETWEEN SPIN, MASS, AND MORPHOLOGY (2015, background): “Thus, an alternative formation scenario through a series of multiple minor merger events was proposed by Meza et al. (2003) and established by, e.g., Naab et al. (2009), González-García et al. (2009), Oser et al. (2010), and Johansson et al. (2012).”
ANGULAR MOMENTUM AND GALAXY FORMATION REVISITED (2012, result): “Synthesizing the scenarios above, it seems plausible that ellipticals might be explained through a combination of collapse bias and multiple mergers–which bears a notable resemblance to recent discussions of two-phase galaxy formation (Oser et al. 2010).”
The cosmic baryon cycle and galaxy mass assembly in the FIRE simulations (2016, methodology): “Galaxy mass assembly is commonly analyzed in simulations in terms of the contributions from in situ star formation and ex situ stellar growth (Oser et al. 2010; Lackner et al. 2012; Tissera et al. 2012; Naab et al. 2014; Hirschmann et al. 2015; Pillepich et al. 2015; Qu et al. 2016; Rodriguez-Gomez…”
Cosmological simulations of the formation of the stellar haloes around disc galaxies (2011, background): “Our in situ stellar population is also younger than that of Zolotov et al. (2009) (who found zform ≈ 3), having formed primarily at z ∼ 1 − 1.5, which is similar to that also reported recently by Oser et al. (2010) for galaxies with masses similar to those in our sample.”
The ATLAS3D project – I. A volume-limited sample of 260 nearby early-type galaxies: science goals and selection criteria (2010, methodology): “We will use a new sample of simulations (Oser et al. 2010) covering the full mass range of the ATLAS3D galaxies.”
Galactic star formation and accretion histories from matching galaxies to dark matter haloes (2012, background): “For the most massive galaxies this can be up to 80 per cent (Oser et al. 2010; Feldmann et al. 2010).”
THE SINS SURVEY OF z ∼ 2 GALAXY KINEMATICS: PROPERTIES OF THE GIANT STAR-FORMING CLUMPS (2010, background): “…finds that the buildup of z > 1 SFGs in the mass range of 1010 to 1011 M is dominated by smooth accretion of gas and/or minor mergers (Kereš et al. 2005, 2009; Dekel & Birnboim 2006; Bower et al. 2006; Kitzbichler & White 2007; Ocvirk et al. 2008; Davé 2008; Dekel et al. 2009b; Oser et al. 2010).”
STELLAR KINEMATICS OF z ∼ 2 GALAXIES AND THE INSIDE-OUT GROWTH OF QUIESCENT GALAXIES, (2012, background): “In this scenario, the observed compact high-redshift galaxies may simply be the cores of local massive early-type galaxies, which grow inside-out by accreting (smaller) galaxies, and thus assemble a significant part of their mass at later times (van der Wel et a. 2009; Oser et al. 2010).”
SHORT-LIVED STAR-FORMING GIANT CLUMPS IN COSMOLOGICAL SIMULATIONS OF z ≈ 2 DISKS (2010, methodology): “From this sample, we randomly selected nine halos and generated ’zoom-in’ initial conditions for re-simulations including baryons, as in Oser et al. 2010, 2011.”
Simulations of binary galaxy mergers and the link with fast rotators, slow rotators, and kinematically distinct cores (2011, background): “…should be much more frequent than major mergers and are therefore expected (see e.g. Khochfar & Silk 2006; Naab et al. 2007; Bournaud, Jog & Combes 2007; Genel et al. 2008, 2010; Naab, Johansson & Ostriker 2009; Hopkins et al. 2010; Oser et al. 2010; Qu et al. 2010; Abadi et al. 2010, CDM models).”