The origin of discs and spheroids in simulated galaxies

By L. Sales, J. Navarro, Tom Theuns, Joop Schaye, Simon D. M. White, Carlos S. Frenk, Robert A. Crain, Claudio Dalla Vecchia. 2011

206 citations recorded by the source corpus.

The major morphological features of a galaxy are thought to be determined by the assembly history and net spin of its surrounding dark halo. In the simplest scenario, disc galaxies form predominantly in haloes with high angular momentum and quiet recent assembly history, whereas spheroids are the slowly rotating remnants of repeated merging events. We explore these assumptions using 100 systems with halo masses similar to that of the Milky Way, identified in a series of cosmological gasdynamical simulations: the Galaxies–Intergalactic Medium Interaction Calculation (GIMIC). At z=0, the simulated galaxies exhibit a wide variety of morphologies, from dispersion-dominated spheroids to pure disc galaxies. Surprisingly, these morphological features are very poorly correlated with their halo properties: discs form in haloes with high and low net spin, and mergers play a negligible role in the formation of spheroids, whose stars form primarily in situ. With hindsight, this weak correlation between halo and galaxy properties is unsurprising given that a minority of the available baryons (∼40 per cent) end up in galaxies.More important to morphology is the coherent alignment of the angular momentum of baryons that accrete over time to form a galaxy. Spheroids tend to form when the spin of newly accreted gas is misaligned with that of the extant galaxy, leading to the episodic formation of stars with different kinematics that cancel out the net rotation of the system. Discs, on the other hand, form out of gas that flows in with similar angular momentum to that of earlier accreted material. Gas accretion from a hot corona thus favours disc formation, whereas gas that flows ‘cold’, often along separate, misaligned filaments, favours the formation of spheroids. In this scenario, many spheroids consist of the superposition of stellar components with distinct kinematics, age and metallicity, an arrangement that might survive to the present day given the paucity of major mergers. Since angular momentum is acquired largely at turnaround, morphology depends on the early interplay between the tidal field and the shape of the material destined to form a galaxy.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/a60638f81a8434d879e264775f352e08412fe499

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Citations in the corpus

Galaxy morphology and star formation in the Illustris Simulation at z = 0 (2015, background): “We follow previous studies (e.g., Scannapieco et al. 2010; Sales et al. 2012; Marinacci et al. 2013) to parameterize the orbits of star particles, and contrast these quantities with photometric morphologies.”
Towards a more realistic population of bright spiral galaxies in cosmological simulations (2013, methodology): “Despite significant recent progress (e.g. Sales et al. 2012; Guedes et al. 2011; Brook et al. 2012), these simulations continue to be plagued by a range of problems, with different codes often producing very different galaxies for the same initial conditions (Okamoto et al. 2005; Kereš et al.…”
Thin disc, thick disc and halo in a simulated galaxy (2012, background): “The first problem has been alleviated by improved feedback (Brook et al. 2004a; Okamoto et al. 2005; Governato et al. 2007; Guedes et al. 2011) but continues to plague even recent simulations (Sales et al. 2012; Scannapieco et al. 2012; Martig et al. 2012).”
CONNECTING ANGULAR MOMENTUM AND GALACTIC DYNAMICS: THE COMPLEX INTERPLAY BETWEEN SPIN, MASS, AND MORPHOLOGY (2015, background): “However, this was not seen in previous studies by Sales et al. (2012) and Scannapieco et al. (2009), who did not find a correlation between galaxy type and the spin parameter.”
REPRODUCING THE STELLAR MASS/HALO MASS RELATION IN SIMULATED ΛCDM GALAXIES: THEORY VERSUS OBSERVATIONAL ESTIMATES (2012, background): “As other works have highlighted the importance of having a representative sample before drawing general conclusions (Brooks et al. 2011; Sales et al. 2012; McCarthy et al. 2012), the halos in our sample span a representative range of halo spin values and accretion histories (Geha et al. 2006).”
Idealized models for galactic disc formation and evolution in ‘realistic’ ΛCDM haloes (2012, background): “Even if extended discs form, they are often destroyed by infalling satellites (Toth & Ostriker 1992) or the accretion of misaligned gas (Scannapieco et al. 2009; Sales et al. 2011).”
Galaxy Alignments: An Overview (2015, background): “Numerical simulations of individual (spiral) galaxies have shown the presence of cold gas accretion streams (Dekel et al. 2009; Kereš et al. 2009; Sales et al. 2012), which have a significant impact on the orientation of the disc and are able to tilt the orientation away from the initial one (Kimm e”
UNLEASHING POSITIVE FEEDBACK: LINKING THE RATES OF STAR FORMATION, SUPERMASSIVE BLACK HOLE ACCRETION, AND OUTFLOWS IN DISTANT GALAXIES (2013, background): “But for the formation of early-type galaxies, accretion is generically filamentary according to numerical simulations, e.g., Sales et al. (2012).”