The Evolution of Gas-Phase Metallicity and Resolved Abundances in Star-forming Galaxies at $z \approx0.6-1.8$

TL;DR

This study analyzes the gas-phase metallicity and its radial distribution in approximately 650 star-forming galaxies at redshifts 0.6 to 1.8, revealing that metallicity gradients are generally flat and evolve with cosmic time, influenced by galaxy properties and feedback processes.

Contribution

It provides the first large sample analysis of metallicity gradients at these redshifts, linking galaxy properties to chemical abundance distributions and comparing observations with simulations.

Findings

Metallicity gradients are generally flat across the galaxy sample.

Galaxies with higher star formation rates and irregular morphology tend to have lower metallicities.

Metallicity gradients are flatter than those in local galaxies, consistent with feedback-driven metal redistribution.

Abstract

We present an analysis of the chemical abundance properties of $\approx$650 star-forming galaxies at $z \approx0.6-1.8$. Using integral-field observations from the $K$-band Multi-Object Spectrograph (KMOS), we quantify the [NII]/H$\alpha$ emission-line ratio, a proxy for the gas-phase Oxygen abundance within the interstellar medium. We define the stellar mass-metallicity relation at $z \approx0.6-1.0$ and $z \approx1.2-1.8$ and analyse the correlation between the scatter in the relation and fundamental galaxy properties (e.g. H$\alpha$ star-formation rate, H$\alpha$ 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 $ \Delta Z/ \Delta R=0.002 \pm0.004$ 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 $\Delta Z/ \Delta R$ in our sample with numerical simulations and observations at $z \approx0-3$. 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.