Tracing Galaxy Formation with Stellar Halos. I. Methods

By James S. Bullock, K. Johnston. 2005

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If the favored hierarchical cosmological model is correct, then the Milky Way system should have accreted ~100-200 luminous satellite galaxies in the past ~12 Gyr. We model this process using a hybrid semianalytic plus N-body approach that distinguishes explicitly between the evolution of light and dark matter in accreted satellites. This distinction is essential to our ability to produce a realistic stellar halo, with mass and density profile much like that of our own Galaxy, and a surviving satellite population that matches the observed number counts and structural parameter distributions of the satellite galaxies of the Milky Way. Our accreted stellar halos have density profiles that typically drop off with radius faster than the dark matter and follow power laws at r ≳ 30 kpc with ρ ∝ r-α, α ≃ 3-4. They are well fit by Hernquist profiles over the full radial range. We find that stellar halos are assembled from the inside out, with the majority of mass (~80%) coming from the ~15 most massive accretion events. The satellites that contribute to the stellar halo have median accretion times of ~9 Gyr in the past, while surviving satellite systems have median accretion times of ~5 Gyr in the past. This implies that stars associated with the inner halo should be quite different chemically from stars in surviving satellites and also from stars in the outer halo or those liberated in recent disruption events. We briefly discuss the expected spatial structure and phase-space structure for halos formed in this manner. Searches for this type of structure offer a direct test of whether cosmology is indeed hierarchical on small scales.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/8006090c81f2ade15b471deaa07ed6cc48b068a9

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Citations in the corpus

THE SAGITTARIUS DWARF GALAXY: A MODEL FOR EVOLUTION IN A TRIAXIAL MILKY WAY HALO (2010, background): “…al. 2001a; McConnachie et al. 2003; Kalirai et al. 2006; Mart́ınez-Delgado et al. 2008, 2009), possibly constituting the primary source of the Galactic stellar halo (e.g., Searle & Zinn 1978; Majewski 1993, 2004; Majewski et al. 1996; Bullock et al. 2001b; Bullock & Johnston 2005; 1 Hubble Fellow.”
Not so lumpy after all: modelling the depletion of dark matter subhaloes by Milky Way-like galaxies (2017, background): “…halo, particularly close to the MW. Specifically, the majority of the destroyed satellites that make up the stellar halo (Bullock et al. 2001; Bullock & Johnston 2005; Bell et al. 2008) were likely on plunging, highly radial orbits, such that their resultant stellar streams are likely to be…”
Thin, thick and dark discs in ΛCDM (2008, background): “…thick disc (Walker, Mihos & Hernquist 1996; Peñarrubia, McConnachie & Babul 2006); highinclination ones contribute to the Milky Way stellar halo (Bullock & Johnston 2005; Gauthier, Dubinski & Widrow 2006); and both heat and distort the Milky Way thin disc (Quinn & Goodman 1 A connection with…”
CHEMICAL EVOLUTION IN HIERARCHICAL MODELS OF COSMIC STRUCTURE. II. THE FORMATION OF THE MILKY WAY STELLAR HALO AND THE DISTRIBUTION OF THE OLDEST STARS (2009, methodology): “Instead, these models adopt a prescription based on that of Bullock & Johnston (2005) that takes into account heuristically the influence of a photoionizing background from the aggregate star formation in all galaxies.”
Using chemical tagging to redefine the interface of the Galactic disc and halo (2015, background): “Simulations of the Galactic halo (e.g. Bullock & Johnston 2005; Zolotov et al. 2009; Cooper et al. 2010) have indicated that the halo may have been constructed primarily through a combination of dissipative collapse and accretion events of massive systems.”
The Milky Way stellar halo out to 40 kpc: squashed, broken but smooth (2011, methodology): “This has been seen as vindication of modern theories of c© 2011 RAS galaxy formation, which predict that stellar haloes are built p almost exclusively from the debris of disrupting satellites (e.g. Bullock & Johnston 2005; De Lucia & Helmi 2008; Cooper et al. 2010).”
Multiple populations in globular clusters (2012, background): “(2007): the globular clusters must have been initially a large factor (10-100) more massive than today and almost all the first generation stars must have been preferentially lost.”
Chemical Abundance Distributions of Galactic Halos and Their Satellite Systems in a ΛCDM Universe (2005, methodology): “…these models individually suggest solutions to the apparent contradiction between observations and the hierarchical structure formation scenario: Bullock & Johnston (2005) show that halo stars were likely to have been accreted much earlier than the surviving satellite population; and Robertson…”
Galaxy formation theory (2010, background): “…to the build-up of the Milky Way’s stellar halo (Cooper et al. 2009), and there may be remnant tidal streams which could provide information about the hierarchical growth of the Milky Way’s halo (Bullock and Johnston 2005; Robertson et al. 2005; Font et al. 2006a,b; Johnston et al. 2008).”
Merger Histories of Galaxy Halos and Implications for Disk Survival (2007, background): “The expectation is that most of the larger objects that were accreted have been shredded by the central galaxy potential, and have deposited their stars in the extended stellar halo (Bullock & Johnston 2005).”
The Galaxy in Context: Structural, Kinematic, and Integrated Properties (2016, background): “…profile is similar to an Einasto function (e.g., Xue et al. 2015), and qualitatively similar to density profiles predicted by halo formation models (Bullock & Johnston 2005, Cooper Table 6 Recent measurements of stellar halo density parameters Reference Tracer r (kpc) –αin qin rs (kpc) –αout Xue…”
Tracing Galaxy Formation with Stellar Halos. II. Relating Substructure in Phase and Abundance Space to Accretion Histories (2008, methodology): “…accretion events together leads to a spectrum of lumps in phase-space, as has been demonstrated in composite studies of halo distributions (Helmi & de Zeeuw 2000; Bullock et al. 2001; Johnston, Sackett, & Bullock 2001; Helmi, White, & Springel 2003; Bullock & Johnston 2005; De Lucia & Helmi 2008).”
The stellar halo of the Galaxy (2008, methodology): “They interpret this using the simulations of Bullock & Johnston (2005), where this statistic can vary from 20% to 80% depending on the detailed halo formation history.”
STELLAR TIDAL STREAMS IN SPIRAL GALAXIES OF THE LOCAL VOLUME: A PILOT SURVEY WITH MODEST APERTURE TELESCOPES (2010, background): “The current models predict that a survey of between 50 and 100 parent galaxies reaching to a surface brightness of ∼ 30mag/arcsec2 should reveal many tens of tidal features, perhaps nearly one detectable stream per galaxy (Bullock & Johnston 2005; Johnston et al. 2008; Cooper et al. 2010).”
Shredded Galaxies as the Source of Diffuse Intrahalo Light on Varying Scales (2007, background): “…heating processes to produce the diffuse, stellar halos around galaxies like theMilkyWay (Searle & Zinn 1978; Johnston et al. 1996, 2001; Johnston 1998; Bullock et al. 2001b; Bullock & Johnston 2005; Robertson et al. 2005; Diemand et al. 2005; Read et al. 2006; Font et al. 2006; Abadi et al. 2006).”
THE GHOSTS SURVEY. I. HUBBLE SPACE TELESCOPE ADVANCED CAMERA FOR SURVEYS DATA (2011, background): “ΛCDM models of hierarchical formation also predict that the ongoing accretion and disruption of many of these satellite galaxies should be observable today in our own stellar halo (e.g., Bullock et al. 2001; Bullock & Johnston 2005; Font et al. 2006).”
The ATLAS3D project - XXIX. The new look of early-type galaxies and surrounding fields disclosed by extremely deep optical images (2014, methodology): “…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 LARGE-SCALE STRUCTURE OF THE HALO OF THE ANDROMEDA GALAXY. I. GLOBAL STELLAR DENSITY, MORPHOLOGY AND METALLICITY PROPERTIES (2013, methodology): “Figures 13 and 14 show no sign of such a fall-off, either in the masked, or unmasked samples, possibly implying that the disrupted satellites that formed the M31 halo were fluffier than in the simulations of Bullock & Johnston (2005).”
The influence of Sagittarius and the Large Magellanic Cloud on the stellar disc of the Milky Way Galaxy (2017, methodology): “The presence of a smooth stellar halo (Deason, Belokurov & Evans 2011) possibly indicates that the MW may have had a more brutal past, the signatures of which were dynamically mixed during episodes of violent relaxation (Bullock & Johnston 2005).”