Merger Histories of Galaxy Halos and Implications for Disk Survival

By Kyle R. Stewart, James S. Bullock, Risa Wechsler, A. Maller, A. Zentner. 2007

215 citations recorded by the source corpus.

We study the merger histories of galaxy dark matter halos using a high-resolution ΛCDM N-body simulation. Our merger trees follow ~17,000 halos with masses M0 = 1011–1013 h−1 M☉ at z = 0 and track accretion events involving objects as small as m≃ 1010 h−1 M☉. We find that mass assembly is remarkably self-similar in m/M0 and dominated by mergers that are ~10% of the final halo mass. While very large mergers, m≳ 0.4M0, are quite rare, sizeable accretion events, m ∼ 0.1M0, are common. Over the last ~10 Gyr, an overwhelming majority (~95%) of Milky Way-sized halos with M0 = 1012 h−1 M☉ have accreted at least one object with greater total mass than the Milky Way disk (m > 5 × 1010 h−1 M☉), and approximately 70% have accreted an object with more than twice that mass (m > 1011 h−1 M☉). Our results raise serious concerns about the survival of thin-disk-dominated galaxies within the current paradigm for galaxy formation in a ΛCDM universe. In order to achieve a ~70% disk-dominated fraction in Milky Way-sized ΛCDM halos, mergers involving m≃ 2 × 1011 h−1 M☉ objects must not destroy disks. Considering that most thick disks and bulges contain old stellar populations, the situation is even more restrictive: these mergers must not heat disks or drive gas into their centers to create young bulges.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/4aa3ba5dfa0b21a4299fa06c5b2f9d944fe7857e

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In Astronomy and Astrophysics

1. P. Hopkins
2. L. Hernquist
3. Volker Springel
4. R. Somerville
5. R. Dav'e
6. Thomas J. Cox
7. D. Keres̆
8. A. Dekel

In Instrumentation

1. P. Hopkins
2. L. Hernquist
3. Thomas J. Cox
4. Volker Springel
5. R. Somerville
6. A. Dekel
7. D. Keres̆
8. R. Dav'e

Citations in the corpus

• The effects of gas on morphological transformation in mergers: implications for bulge and disc demographics (2009, methodology): “…user on 21 M ay 2020 This has led to the concern that there may be too many mergers to explain the survival and abundance of galactic discs in the context of our present understanding of galaxy formation (see e.g. Stewart et al. 2008b; Purcell, Kazantzidis & Bullock 2009, and references therein).”
• Star formation in galaxy mergers with realistic models of stellar feedback and the interstellar medium (2012, background): “…subtle: inducing resonant disc perturbations (D’Onghia et al. 2009, 2010) and disc heating (Walker, Mihos & Hernquist 1996; Hopkins et al. 2008e; Stewart et al. 2008; Purcell, Kazantzidis & Bullock 2009; Moster et al. 2010), for which the gas response may depend significantly on its phase…”
• The role of dwarf galaxy interactions in shaping the Magellanic System and implications for Magellanic Irregulars (2012, background): “LMC-mass objects are expected to be the primary building blocks of MW-type galaxies (Stewart et al. 2008), making this study of direct relevance to our understanding of the evolution of the MW.”
• THE MAJOR AND MINOR GALAXY MERGER RATES AT z < 1.5 (2011, methodology): “…1999) with a Sheth & Tormen (1999) dark matter halo mass function; the C06 and St09 merger trees are derived from N-body simulations (the Millennium Simulation from Springel et al. 2005 and an Adaptive Refinement Tree N-body simulation from A. Klypin described in Stewart et al. 2008, respectively).”
• A BARYONIC SOLUTION TO THE MISSING SATELLITES PROBLEM (2012, background): “It has been shown that the number of subhalos at a given mass scales with host mass, since the mass assembly of DM halos is self-similar (Stewart et al. 2008; Fakhouri et al. 2010).”
• There's no place like home? Statistics of Milky Way-mass dark matter haloes (2009, methodology): “The most relevant study for this paper is Stewart et al. (2008), who used an N -body simulation to extract halo-halo merger rates for MW-mass halos.”
• THE IMPACT OF COLD GAS ACCRETION ABOVE A MASS FLOOR ON GALAXY SCALING RELATIONS (2009, background): “Halos more massive than Mmin accrete baryons that are embedded in other merging halos, which could themselves be more massive or less massive thanMmin, as well as smooth gas unbound to any halo (Stewart et al. 2008; Genel et al. 2010).”
• THIRD-EPOCH MAGELLANIC CLOUD PROPER MOTIONS. I. HUBBLE SPACE TELESCOPE/WFC3 DATA AND ORBIT IMPLICATIONS (2013, background): “Indeed, in the prevailing ΛCDM model of hierarchical structure formation, massive satellites that are accreted at early times are very rarely found on highly eccentric orbits about MW-type hosts at z=0 (Boylan-Kolchin et al. 2011; Wetzel 2010; Stewart et al. 2008).”
• ANGULAR MOMENTUM AND GALAXY FORMATION REVISITED (2012, background): “Even if spiral galaxies have systematically avoided the most extreme merger events, they will have still experienced events in the ∼ 1:10 range (e.g., Kauffmann & White 1993; Stewart et al. 2008; Fakhouri et al. 2010), which as shown in our toy models could significantly reduce j⋆.”
• Cosmological simulations of the formation of the stellar haloes around disc galaxies (2011, background): “Similarly, models that track only the accreted component of the 1 By volume, but not by mass as we argue later in this paper. stellar halo (e.g., Font et al. 2008) have difficulties matching the intermediate age (∼ 8 Gyr), metal-rich populations ([Fe/H]> −1) detected in the halo of M31 (see Brown et”
• The merger rates and mass assembly histories of dark matter haloes in the two Millennium simulations (2010, background): “Some such studies have emphasized potential challenges for hierarchical structure formation; for instance, Stewart et al. (2008) have noted that the frequency of major mergers among MilkyWay sized haloes poses a problem for thin-disk survivability.”
• MORPHOLOGICAL QUENCHING OF STAR FORMATION: MAKING EARLY-TYPE GALAXIES RED (2009, unknown): “While cosmologically realistic since directly motivated by a Λ-CDM simulation, the fiducial case may be less likely than this version without the final major merger, since the majority of massive galaxies do not undergo a major merger at z < 1 (e.g., Genel et al. 2008; Stewart et al. 2008).”
• Galaxy merger morphologies and time-scales from simulations of equal-mass gas-rich disc mergers (2008, background): “If hierarchical models of galaxy assembly are correct, then the majority of massive galaxies could be considered an on-going merger or a merger remnant which will undergo another merger event within a few Gyr (Stewart et al. 2008).”
• The formation and assembly history of the Milky Way revealed by its globular cluster population (2018, background): “E-mail: kruijssen@uni-heidelberg.de formation and evolution (e.g. Wyse 2001; Stewart et al. 2008; Shen et al. 2010; Deason et al. 2013; Mackereth et al. 2018, Hughes et al. in prep.).”
• LSD: Lyman-break galaxies Stellar populations and Dynamics – I. Mass, metallicity and gas at z∼ 3.1 (2009, background): “…stellar mass (M∗) has already been created, it is the redshift range where the most massive early-type galaxies are expected to form (see, for example, Saracco et al. 2003), the number of mergers among the galaxies is much larger than at later times (Conselice et al. 2007; Stewart et al. 2008).”