Galaxy morphology and star formation in the Illustris Simulation atz = 0

Abstract

We study how optical galaxy morphology depends on mass and star formation rate (SFR) in the Illustris Simulation. To do so, we measure automated galaxy structures in 10808 simulated galaxies at z = 0 with stellar masses 10 9.7 < M * /M < 10 12.3 . We add observational realism to idealized synthetic images and measure non-parametric statistics in rest-frame optical and near-IR images from four directions. We find that Illustris creates a morphologically diverse galaxy population, occupying the observed bulge strength locus and reproducing median morphology trends versus stellar mass, SFR, and compactness. Morphology correlates realistically with rotation, following classification schemes put forth by kinematic surveys. Type fractions as a function of environment agree roughly with data. These results imply that connections among mass, star formation, and galaxy structure arise naturally from models matching global star formation and halo occupation functions when simulated with accurate methods. This raises a question of how to construct experiments on galaxy surveys to better distinguish between models. We predict that at fixed halo mass near 10 12 M , discdominated galaxies have higher stellar mass than bulge-dominated ones, a possible consequence of the Illustris feedback model. While Illustris galaxies at M * ∼ 10 11 M have a reasonable size distribution, those at M * ∼ 10 10 M have half-light radii larger than observed by a factor of two. Furthermore, at M * ∼ 10 10.5 -10 11 M , a relevant fraction of Illustris galaxies have distinct "ring-like" features, such that the bright pixels have an unusually wide spatial extent.

The role of mergers and halo spin in shaping galaxy morphology

“…Kauffmann et al 2003). In Snyder et al (2015b), non-parametric optical morphologies were calculated for thousands of Illustris galaxies, and they were found to be in good agreement with their observational counterpart (Lotz et al 2008). Furthermore, Genel et al (2015) found that the specific stellar angular momenta of Illustris galaxies are consistent with observational trends (Romanowsky & Fall 2012;Fall & Romanowsky 2013).…”

“…In this work we explore the origin of discs and spheroids using the Illustris simulation (Vogelsberger et al 2014a,b;Genel et al 2014;Sijacki et al 2015), a hydrodynamic cosmological simulation that has been shown to reproduce several galaxy observables reasonably well, including stellar angular momenta and quantitative optical morphologies Snyder et al 2015b), over a wide range of stellar masses. This makes the Illustris simulation a powerful tool to study the physical mechanisms that shape galaxy morphology in a cosmological context.…”

The relationship between star formation activity and galaxy structural properties in CANDELS and a semi-analytic model

“…Such an analysis has been done for the Illustris numerical hydrodynamical simulations at z = 0, by Snyder et al (2015). The top left panel of their Figure 5 is strikingly similar to our redshift zero panel from Figure 3, although it should be kept in mind that their color coding is based on a different metric representing how bulge-dominated the galaxy is (Gini-M20).…”

“…On the simulation side, Snyder et al (2015) investigated the relationship between optical morphology, stellar mass and star formation rate for a sample of simulated galaxies from the Illustris simulation (Vogelsberger et al 2014). They found that their model, which includes feedback from accreting supermassive black holes, was able to produce the population of quiescent bulge-dominated galaxies at z ∼ 0 needed to reproduce the distribution of observed morphologies.…”

Massive close pairs measure rapid galaxy assembly in mergers at high redshift

“…Initial efforts are underway to systematically mock-observe large sets of galaxies from hydrodynamical simulations (e.g., Torrey et al 2015;Snyder et al 2015b;Trayford et al 2015Trayford et al , 2016Kaviraj et al 2016). Because Illustris resolves galaxy structures on spatial scales below ∼ 1 kpc at z 1, its mock survey fields contain sources appropriate for comparing with existing deep, high resolution, but narrow survey fields.…”