SDSS-IV MaNGA: how do star formation histories affect gas-phase abundances?

Abstract

Gas-phase abundances in galaxies are the products of those galaxies’ evolutionary histories. The star formation history (SFH) of a region might therefore be expected to influence that region’s present day gaseous abundances. Here, we employ data from the MaNGA survey to explore how local gas metallicities relate to SFHs of galaxy regions. We combine MaNGA emission line measurements with SFH classifications from absorption line spectra to compare gas-phase abundances in star-forming regions with those in regions classified as starburst, post-starburst, and green valley. We find that starburst regions contain gas that is more pristine than in normal star-forming regions, in terms of O/H and N/O; we further find that post-starburst regions (which have experienced stochastic SFHs) behave very similarly to ordinary star-forming regions (which have experienced far smoother SFHs) in O/H–N/O space. We argue from this that gas is diluted significantly by pristine infall but is then re-enriched rapidly after a starburst event, making gas-phase abundances insensitive to the precise form of the SFH at late times. We also find that green valley regions possess slightly elevated N/O abundances at a given O/H; this is potentially due to a reduced star formation efficiency in such regions, but it could also point to late-time rejuvenation of green valley regions in our sample.