The Cosmic Evolution of Metallicity from the SDSS Fossil Record

TL;DR

This study investigates the evolution of stellar metallicity in SDSS galaxies across different masses and environments, revealing that massive galaxies' metallicity remains stable over time while less massive ones evolve significantly, and environmental density influences metallicity.

Contribution

It provides the first comprehensive analysis of stellar metallicity evolution across a wide mass range and environmental densities using SDSS data, clarifying discrepancies between nebular and absorption line metallicities.

Findings

Massive galaxies show minimal metallicity evolution over cosmic time.

Less massive galaxies' metallicity increases by over an order of magnitude from redshift 3 to present.

High-density environments correlate with higher galaxy metallicity.

Abstract

We present the time evolution of the stellar metallicity for SDSS galaxies, a sample that spans five orders of magnitude in stellar mass (10^7 - 10^{12} Msun). Assuming the BC03 stellar population models, we find that more massive galaxies are more metal-rich than less massive ones at all redshifts; the mass-metallicity relation is imprinted in galaxies from the epoch of formation. For galaxies with present stellar masses > 10^{10} Msun, the time evolution of stellar metallicity is very weak, with at most 0.2-0.3 dex over a Hubble time- for this reason the mass-metallicity relation evolves little with redshift. However, for galaxies with present stellar masses < 10^{10} Msun, the evolution is significant, with metallicity increasing by more than a decade from redshift 3 to the present. By being able to recover the metallicity history, we have managed to identify the origin of a recent discrepancy between the metallicity recovered from nebular lines and absorption lines. As expected, we show that the young population dominates the former while the old population the latter. We have investigated the dependence on the stellar models used and find that older stellar population synthesis codes do not produce a clear result. Finally, we have explored the relationship between cluster environment and metallicity, and find a strong correlation in the sense that galaxies in high density regions have high metallicity.