The weak imprint of environment on the stellar populations of galaxies

Abstract

We investigate the environmental dependence of the stellar populations of galaxies in SDSS DR7. Echoing earlier works, we find that satellites are both more metal-rich (<0.1 dex) and older (<2 Gyr) than centrals of the same stellar mass. However, after separating star-forming, green valley and passive galaxies, we find that the true environmental dependence of both stellar metallicity (<0.03 dex) and age (<0.5 Gyr) is in fact much weaker. We show that the strong environmental effects found when galaxies are not differentiated result from a combination of selection effects brought about by the environmental dependence of the quenched fraction of galaxies, and thus we strongly advocate for the separation of star-forming, green valley and passive galaxies when the environmental dependence of galaxy properties are investigated. We also study further environmental trends separately for both central and satellite galaxies. We find that star-forming galaxies show no environmental effects, neither for centrals nor for satellites. In contrast, the stellar metallicities of passive and green valley satellites increase weakly (<0.05 dex and <0.08 dex, respectively) with increasing halo mass, increasing local overdensity and decreasing projected distance from their central; this effect is interpreted in terms of moderate environmental starvation (‘strangulation’) contributing to the quenching of satellite galaxies. Finally, we find a unique feature in the stellar mass–stellar metallicity relation for passive centrals, where galaxies in more massive haloes have larger stellar mass (∼0.1 dex) at constant stellar metallicity; this effect is interpreted in terms of dry merging of passive central galaxies and/or progenitor bias.

Using angular momentum maps to detect kinematically distinct galactic components

“…The age and metallicity of galactic components reflect their formation processes and time-scales (Gadotti 2009;Obreja et al 2013;Trussler et al 2020), hence distinct components should follow different relations.…”

Toward a Better Understanding of Cosmic Chronometers: Stellar Population Properties of Passive Galaxies at Intermediate Redshift

“…The difference be-tween their shape can be interpreted either as an evidence for 'strangulation' (i.e. the lack of new gas supply Peng et al 2015;Trussler et al 2021), or for shorter formation time-scales coupled with galactic winds (Spitoni et al 2017) as the main mechanism driving galaxy quenching. The relative α-element abundance with respect to iron is another key-parameter.…”

“…In addition to stellar population properties, the environment can in principle have a role in shaping galaxy evolution. However, its effects seems weak once the correlation with mass is removed (Thomas et al 2010;Barbera et al 2014;McDermid et al 2015;Trussler et al 2021). To explore in greater detail these effect, very large samples are needed (e.g.…”

Stellar mass as the "glocal" driver of galaxies' stellar population properties

“…Peng et al (2015) used the stellar metallicity of 26 000 SDSS galaxies from Gallazzi et al (2005) and discovered the presence of two distinct MZRs: a flatter relation with higher normalization for passive galaxies and a steeper relation for the star-forming galaxies, which converges to the passive relation at log(𝑍 * /𝑍 ) ∼ 0.15 for 𝑀 * ∼ 10 11 M . This result was confirmed by Trussler et al (2020Trussler et al ( , 2021, using a different stellar population analysis, and by Gallazzi et al (2021). Both groups highlighted that the difference between passive and star-forming galaxies is the fundamental driver of the scatter in the MZR, largely independent of the external conditions (e.g.…”