The relation between galaxy morphology and colour in the EAGLE simulation

Abstract

We investigate the relation between kinematic morphology, intrinsic colour and stellar mass of galaxies in the EAGLE cosmological hydrodynamical simulation. We calculate the intrinsic u − r colours and measure the fraction of kinetic energy invested in ordered corotation of 3562 galaxies at z = 0 with stellar masses larger than 10 10 M . We perform a visual inspection of gri-composite images and find that our kinematic morphology correlates strongly with visual morphology. EAGLE produces a galaxy population for which morphology is tightly correlated with the location in the colourmass diagram, with the red sequence mostly populated by elliptical galaxies and the blue cloud by disc galaxies. Satellite galaxies are more likely to be on the red sequence than centrals, and for satellites the red sequence is morphologically more diverse. These results show that the connection between mass, intrinsic colour and morphology arises from galaxy formation models that reproduce the observed galaxy mass function and sizes.

Non-parametric morphologies of mergers in the Illustris simulation

“…(x) We find that a threshold value of κ co = 0.4 (Correa et al 2017) roughly corresponds to our F = 0 threshold separating bulge-, from disc-dominated systems. However, we notice that the optical and kinematic criteria do not select the same galaxy populations.…”

“…Scannapieco et al 2008). In the case of eagle, variations of these metrics have been studied by Correa et al (2017Correa et al ( , 2019, Clauwens et al (2018), Trayford et al (2019) and Tissera et al (2019).…”

On the galaxy–halo connection in the EAGLE simulation

“…P07 require an apparent axis ratio b/a ≤ 0.6 and usable Hα rotation curve, which they find not to significantly bias the admitted galaxy population in colour or concentration. We therefore do not make a morphology cut on the EAGLE galaxies in our fiducial analysis, although we have checked that our results change at no more than the ∼ 1σ level -and our qualitative conclusions remain unchanged -when only including galaxies with a substantial fraction of their kinetic energy in ordered corotation (κ co ≥ 0.4; Correa et al 2017). We compare the EAGLE results with two semi-empirical models, denoted "SHAM" and "SHAM+MMW" as in Section 1.…”

Quantifying the impact of mergers on the angular momentum of simulated galaxies

“…6 we show the 3D Sérsic index (measured from the 3D stellar mass distributions) and the kinematic bulge-to-total, B/T, ratio 1 as a function of stellar mass for galaxies at z = 0 that have not suffered mergers, and had at least one dry or wet merger. This figure shows that no-merger galaxies have much lower Sérsic indices and B/T ratios than galaxies that 1 B/T ≡ 1 − κ co , where κ co is the ratio of kinetic energy invested in ordered rotation calculated using only star particles that follow the direction of rotation of the galaxy (see Correa et al 2017 for more details). We also analysed the Abadi et al (2003) and Sales et al (2010) .…”

“…Recently, using cosmological hydrodynamical simulations, Sparre & Springel (2017) found that galaxy remnants of major mergers evolve into star-forming disc galaxies unless sufficiently strong feedback is present to prevent the disc regrowth. This feedback is an essential mechanism in the new generation of cosmological hydrodynamical simulations, such as EAGLE (Schaye et al 2015), Illustris (Vogelsberger et al 2014) and HORIZON-AGN (Dubois et al 2014), and most likely plays a major role in reproducing the morphological diversity seen in galaxies (Dubois et al 2016;Correa et al 2017).…”