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 ($\sim 100h^{-1}$ Mpc). Specifically, we employ two absorption line indices, H$\beta$ and $⟨\mathrm{Fe}⟩$ 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 ($M^{\ast }$) 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 ($10^{10}<M^{\ast }/M_{\odot }<10^{10.5}$) 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 $\sim 1$ Gyr. The massive galaxies ($M^{\ast }/M_{\odot }>10^{10.5}$), 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 $\sim 0.5$ Gyr. At fixed age however, Z of galaxies is independent of their $M^{\ast }$ in all environments, except the most massive ($M^{\ast }/M_{\odot }\gtrsim 10^{10.7}$), oldest galaxies ($\gtrsim 9$ Gyr) which show a sharp decline in their Z with $M^{\ast }$. 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.

Accepted for publication in New Astronomy. 18 pages, 11 figures

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• Study of galaxies on large-scale filaments in simulations
• The properties and environment of very young galaxies in the local Universe