Simulations of Galaxy Formation in a Λ Cold Dark Matter Universe. II. The Fine Structure of Simulated Galactic Disks

By M. Abadi, J. Navarro, Matthias Steinmetz, V. Eke. 2002

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We present a detailed analysis of the disk component of a simulated galaxy formed in the ΛCDM cosmogony. At redshift z = 0, two distinct dynamical components are easily identified solely on the basis of the orbital parameters of stars in the galaxy: a slowly rotating, centrally concentrated spheroid and a disklike component largely supported by rotation. The disk may be further decomposed into a thin, dynamically cold component with stars on nearly circular orbits and a hotter, thicker component with orbital parameters transitional between the thin disk and the spheroid. Supporting evidence for the presence of distinct thick- and thin-disk components is provided, as in the Milky Way, by the double-exponential vertical structure of the disk and in abrupt changes in the vertical velocity distribution as a function of stellar age. The dynamical origin of these components offers intriguing clues to the assembly of spheroids and disks in the Milky Way and other spiral galaxies. The spheroid is old and has essentially no stars younger than the time elapsed since the last major accretion event, ~8 Gyr ago for the system we consider here. The majority of thin-disk stars, on the other hand, form after the merging activity is over, although a significant fraction (~15%) of thin-disk stars are old enough to predate the last major merger event. This unexpected population of old-disk stars consists mainly of the tidal debris of satellites whose orbital plane was coincident with the disk and whose orbits were circularized by dynamical friction prior to full disruption. More than half of the stars in the thick disk share this origin, part of a trend that becomes more pronounced with age: 9 out of 10 stars presently in the old (age of ≳10 Gyr) disk component were actually brought into the disk by satellites. By contrast, only one in two stars belonging to the old spheroid are tidal debris; the rest may be traced to a major merger event that dispersed the luminous progenitor at z ~ 1.5 and seeded the formation of the spheroid. Our results highlight the role of satellite accretion events in shaping the disk, as well as the spheroidal, component and reveal some of the clues to the assembly process of a galaxy preserved in the detailed dynamics of old stellar populations.

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

View Paper: https://www.semanticscholar.org/paper/06fa1386194c7000a48e607f9bdc1adf59b73d85

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Citations in the corpus

Idealized models for galactic disc formation and evolution in ‘realistic’ ΛCDM haloes (2012, methodology): “Numerical hydrodynamical simulations of this formation scenario have been carried out in great number (e.g. Navarro & White E-mail: maumer@mpa-garching.mpg.de 1994; Navarro & Steinmetz 1997; Abadi et al. 2003; Governato et al. 2007; Scannapieco et al. 2009).”
The age–metallicity structure of the Milky Way disc using APOGEE (2017, background): “Examples of such models include the heating of the old disk by high redshift mergers (e.g. Brook et al. 2004; Villalobos & Helmi 2008; Kazantzidis et al. 2009; Minchev et al. 2013) and the formation of a dual disk by gradual accretion of stars into disk orbits (e.g. Abadi et al. 2003).”
Inclination- and dust-corrected galaxy parameters: bulge-to-disc ratios and size–luminosity relations (2008, background): “Early feedback could blow much of the baryons out of high-z galaxy discs for their late-time, and necessarily post majormerger, re-accretion into some preferred plane and thereby produce the disc-dominated galaxies observed in the local Universe (see Abadi et al. 2003a).”
Towards a more realistic population of bright spiral galaxies in cosmological simulations (2013, methodology): “…modeling the many baryonic astrophysical processes which play a role in the formation of galaxies has led to a long list of models over the last two decades (e.g. Navarro & White 1994; Navarro & Steinmetz 1997; Abadi et al. 2003; Governato et al. 2007; Scannapieco et al. 2009; Agertz et al. 2011).”
STRUCTURE AND KINEMATICS OF THE STELLAR HALOS AND THICK DISKS OF THE MILKY WAY BASED ON CALIBRATION STARS FROM SLOAN DIGITAL SKY SURVEY DR7 (2009, background): “…authors argue that the thick disk is likely to have formed in response to ancient accretion events (e.g., Quinn & Goodman (1986), Freeman (1987); Abadi et al. 2003, and references therein), recent suggestions have been made that some properties of the thick disk could be understood as the…”
Formation of Early-Type Galaxies from Cosmological Initial Conditions (2005, background): “…simulations from realistic cosmological initial conditions have been done so far, and most of these have concentrated on the formation of disk galaxies rather than early-type spheroidal systems (Sommer-Larsen et al. 2003; Abadi et al. 2003; Governato et al. 2004; Robertson et al. 2004).”
Galaxies–intergalactic medium interaction calculation – I. Galaxy formation as a function of large-scale environment (2009, background): “…associated transfer of angular momentum from baryons to dark matter (e.g. Navarro & Benz 1991; Weil, Eke & Efstathiou 1998; Thacker & Couchman 2001; Abadi et al. 2003a,b; Sommer-Larsen, Götz & Portinari 2003; Governato et al. 2004; Robertson et al. 2004; Okamoto et al. 2005; Governato et al.…”
The Milky Way Tomography with SDSS. II. Stellar Metallicity (2008, background): “…stars that make up the stellar populations in the Milky Way can be studied in great detail, their characterization will provide clues about the galaxy merging process that cannot be extracted from observations of distant galaxies (e.g., Abadi et al. 2003; Brook et al. 2004; and references therein).”
FORMATION AND EVOLUTION OF THE DISK SYSTEM OF THE MILKY WAY: [α/Fe] RATIOS AND KINEMATICS OF THE SEGUE G-DWARF SAMPLE (2011, methodology): “The accretion models (e.g., Abadi et al. 2003) distribute the eccentricities rather broadly over a wide range.”
Galaxy formation theory (2010, background): “The stars from these smaller galaxies are often found in numerical simulations to form a thickened disk structure, in the same plane as the pre-existing disk of the galaxy (Abadi et al. 2003; Villalobos and Helmi 2008).”
OXYGEN ABUNDANCES IN NEARBY FGK STARS AND THE GALACTIC CHEMICAL EVOLUTION OF THE LOCAL DISK AND HALO (2013, background): “Until recently, the different merger scenarios seemed to be the only ones capable of reproducing in detail most of the data observed in the solar neighborhood (e.g., Abadi et al. 2003; Brook et al. 2005).”
ESCAPE FRACTION OF IONIZING PHOTONS DURING REIONIZATION: EFFECTS DUE TO SUPERNOVA FEEDBACK AND RUNAWAY OB STARS (2014, background): “Early works have included it by depositing internal energy into the parent cell of the SN particle, but the energy is found to be radiated away quickly, making the feedback ineffective (e.g.Katz 1992; Abadi et al. 2003; Slyz et al. 2005; Hummels & Bryan 2012).”
Simulations of minor mergers - I. General properties of thick discs (2008, background): “In the “predominantly dissipationless” models the thick disk stars were either: (1) vertically “heated” from a pre-existent thin disk during a (signifi- cant) minor merger (Quinn et al. 1993; Mihos et al. 1995; Walker et al. 1996; Robin et al. 1996; Velázquez & White 1999; Aguerri et al. 2001; Chen”
The formation of disc galaxies in high-resolution moving-mesh cosmological simulations (2013, background): “Yet another kinematic measure of the disc fraction is based on the original approach of Abadi et al. (2003), who defined as bulge component twice the fraction of stars with < 0.”
THE EFFECT OF RADIAL MIGRATION ON GALACTIC DISKS (2014, background): “…does not rule out the possibility that thick disk-stars in the solar neighborhood might have formed elsewhere in the Galaxy: an external origin (Abadi et al. 2003) or a pre-existing thin disk heated by external perturbations (Quinn et al. 1993), early mergers (Brook et al. 2004), or the…”
The formation of disc galaxies in a ΛCDM universe (2010, background): “…of a late-type spiral galaxy, such as our own Milky Way, has been studied numerically in fully ΛCDM cosmological context by many authors (e.g. Abadi et al. 2003b; Sommer-Larsen et al. 2003; Governato et al. 2004; Robertson et al. 2004; Okamoto et al. 2005; Governato et al. 2007; Croft et…”
Metallicity gradients in disks - Do galaxies form inside-out? (2012, methodology): “…which provides a “sn pshot” of the present-day gradient, similar to that inferredfrom, for example, B-stars (i.e., stars with ages<100 Myrs).10 We employed a strict kinematic decomposition of spheroid and disk stars for each of the 25 simulations11, following the Abadi et al. (2003) formalism.”
Measuring the vertical age structure of the Galactic disc using asteroseismology and SAGA (2015, background): “…mechanism (in particular accretion and/or mergers) best fit the picture in which the thin and the thick disc are real separated entities (e.g. Chiappini, Matteucci & Gratton 1997; Abadi et al. 2003; Brook et al. 2004; Kazantzidis et al. 2008; Villalobos & Helmi 2008; Scannapieco et al. 2009).”