Age and metallicity of galaxies in different environments of the Coma supercluster

Abstract

We analyse luminosity-weighted ages and metallicity (Z) of galaxies in a continuous range of environments, i.e. clusters, filaments and voids prevalent in the Coma supercluster (∼100h−1 Mpc). Specifically, we employ two absorption line indices, Hβ and ⟨Fe⟩ as tracers of age and metallicity of galaxies. We find that the stellar-phase metallicity of galaxies declines with increasing age as a function of stellar mass (M*) as well as environment. On the filaments, metallicity of galaxies varies as a function of their distance from the spine of the filament, such that galaxies closer to the centre of the filaments have lower metallicity relative to their counterparts 1 Mpc away from it. The mean age of intermediate mass galaxies (1010 < M*/M⊙ < 1010.5) galaxies is statistically significantly different in different environments such that, the galaxies in clusters are older than the filament galaxies by 1-1.5 Gyr, while their counterparts in the voids are younger than filament galaxies by ~ 1 Gyr. The massive galaxies (M*/M⊙ > 1010.5), on the other hand show no such difference for the galaxies in clusters and filaments, but their counterparts in voids are found to be younger by ~ 0.5 Gyr. At fixed age however, Z of galaxies is independent of their M* in all environments, except the most massive (M*/M⊙ ≳ 1010.7), oldest galaxies ( ≳ 9 Gyr) which show a sharp decline in their Z with M*. Our results support a scenario where galaxies in the nearby Universe have grown by accreting smaller galaxies or primordial gas from the large-scale cosmic web.