Galaxy evolution across environments as probed by the ages, stellar metallicities and [alpha/Fe] of central and satellite galaxies

Abstract

We explore how the star formation and metal enrichment histories of present-day galaxies have been affected by environment combining stellar population parameter estimates and group environment characterization for SDSS DR7. We compare stellar ages, stellar metallicities and, crucially, element abundance ratios [𝛼/Fe] of satellite and central galaxies, as a function of their stellar and host group halo mass, controlling for the current star formation rate and for the infall epoch. We confirm that below 𝑀 * ∼ 10 10.5 𝑀 satellites are older and slightly metalricher than equally-massive central galaxies. On the contrary, we do not detect any difference in their [𝛼/Fe]: [𝛼/Fe] depends primarily on stellar mass and not on group hierarchy nor host halo mass. We also find that the differences in the median age and metallicity of satellites and centrals at stellar mass below 10 10.5 M are largely due to the higher fraction of passive galaxies among satellites and as a function of halo mass. We argue that the observed trends at low masses reveal the action of satellite-specific environmental effects in a 'delayed-then-rapid' fashion. When accounting for the varying quiescent fraction, small residual excess in age, metallicity and [𝛼/Fe] emerge for satellites dominated by old stellar populations and residing in halos more massive than 10 14 𝑀 , compared to equally-massive central galaxies. This excess in age, metallicity and [𝛼/Fe] pertain to ancient infallers, i.e. satellites that have accreted onto the current halo more than 5 Gyr ago. This result points to the action of environment in the early phases of star formation in galaxies located close to cosmic density peaks.

The Imprint of Cosmic Web Quenching on Central Galaxies

“…We use the catalogue of stellar ages, metallicities and element abundance ratios [𝛼/Fe] from Gallazzi et al (2021) which were computed following the same procedure as described in Gallazzi et al (2005Gallazzi et al ( , 2006. The stellar population parameters are constrained by the spectral indices D4000 n , H𝛽, H𝛿 𝐴 + H𝛾 𝐴 , [MgFe]' and [Mg 2 Fe] which were measured in the 3 arcsec fibres of the SDSS spectrograph.…”

“…The [𝛼/Fe] estimate is based on the excess in the observed index ratio Mgb/<Fe> with respect to that of the BC03-based models. The calibration of the excess in Mgb/ Fe with [𝛼/Fe] is shown to be largely independent of age and metallicity in particular for age > 1 Gyr and 𝑍 ★ > 0.5 Z and of the models used for the calibration (see Gallazzi et al 2021, for more details). The methodology by which the [𝛼/Fe] abundances were computed is described in Gallazzi et al (2006).…”

“…We extract central galaxies from Wang et al (2014) whose sSFR glo is estimated by Brinchmann et al (2004). Gallazzi et al (2021) compared the stellar masses from Bell et al (2003) with other estimates and found an average scatter of 𝜎 = 0.1 dex. Thus, we consider genuine centrals those galaxies whose 𝑀 ★ is 3𝜎 higher than their associated satellites' mass.…”

“…Although internal processes, as characterised by galaxy stellar mass 𝑀 ★ , appear to be the main drivers of galaxy evolution (Gavazzi et al 1996;Mouhcine et al 2007;Pasquali et al 2010;Peng et al 2010;Hughes et al 2013;Gallazzi et al 2021), it is well-established that the environment in which galaxies reside also plays an important role in their evolution. Already four decades ago, Dressler (1980) showed that galaxy morphology is a continuous function of the projected local galaxy density.…”

A search for active galactic nuclei in low-mass compact galaxies

“…This is tightly followed at the high-mass end in particular (e.g. Gallazzi et al 2005;Gallazzi et al 2020), but it branches out into two different regimes at a characteristic stellar mass scale of ∼ 3 × 10 10 M (e.g. Baldry et al 2012;Cappellari 2016).…”