The evolution of gas-phase metallicity and resolved abundances in star-forming galaxies at z ≈0.6-1.8

Abstract

We present an analysis of the chemical abundance properties of ≈650 star-forming galaxies at z ≈ 0.6–1.8. Using integral-field observations from the K-band multi-object spectrograph (KMOS), we quantify the [N II]/H α emission-line ratio, a proxy for the gas-phase oxygen abundance within the interstellar medium. We define the stellar mass–metallicity relation at z ≈ 0.6–1.0 and z ≈ 1.2–1.8 and analyse the correlation between the scatter in the relation and fundamental galaxy properties (e.g. H α star formation rate, H α specific star formation rate, rotation dominance, stellar continuum half-light radius, and Hubble-type morphology). We find that for a given stellar mass, more highly star-forming, larger, and irregular galaxies have lower gas-phase metallicities, which may be attributable to their lower surface mass densities and the higher gas fractions of irregular systems. We measure the radial dependence of gas-phase metallicity in the galaxies, establishing a median, beam smearing corrected, metallicity gradient of Z/R = 0.002 ± 0.004 dex kpc−1, indicating on average there is no significant dependence on radius. The metallicity gradient of a galaxy is independent of its rest-frame optical morphology, whilst correlating with its stellar mass and specific star formation rate, in agreement with an inside–out model of galaxy evolution, as well as its rotation dominance. We quantify the evolution of metallicity gradients, comparing the distribution of Z/R in our sample with numerical simulations and observations at z ≈ 0–3. Galaxies in our sample exhibit flatter metallicity gradients than local star-forming galaxies, in agreement with numerical models in which stellar feedback plays a crucial role redistributing metals.