The resolved chemical abundance properties within the interstellar medium of star-forming galaxies at $\mathbf{ \textit{z} \approx 1.5}$

Abstract

We exploit the unprecedented depth of integral field data from the KMOS Ultra-deep Rotational Velocity Survey (KURVS) to analyse the strong (H$\alpha$) and forbidden ([NII], [SII]) emission line ratios in 22 main-sequence galaxies at $z\approx1.5$. Using the [NII]/H$\alpha$ emission-line ratio we confirm the presence of the stellar mass $-$ gas-phase metallicity relation at this epoch, with galaxies exhibiting on average 0.13$\pm$0.04 dex lower gas-phase metallicity (12+log(O/H)$_{\rm M13}$=8.40$\pm$0.03) for a given stellar mass ($\log_{10}$($M_{\rm *}$[$M_{\odot}$]=10.1$\pm$0.1) than local main-sequence galaxies. We determine the galaxy-integrated [SII] doublet ratio, with a median value of [SII]$\lambda$6716/$\lambda$6731=1.26$\pm$0.14 equivalent to an electron density of log$_{10}$($n_{\rm e}$[cm$^{-3}$])=1.95$\pm$0.12. Utilising CANDELS $HST$ multi-band imaging we define the pixel surface-mass and star-formation rate density in each galaxy and spatially resolve the fundamental metallicity relation at $z\approx1.5$, finding an evolution of 0.05$\pm$0.01 dex compared to the local relation. We quantify the intrinsic gas-phase metallicity gradient within the galaxies using the [NII]/H$\alpha$ calibration, finding a median annuli-based gradient of $\Delta$Z/$\Delta$R=$-$0.015$\pm$0.005 dex kpc$^{-1}$. Finally we examine the azimuthal variations in gas-phase metallicity, which show a negative correlation with the galaxy integrated star-formation rate surface density ($r_{\rm s}$=$-$0.40, $p_{\rm s}$=0.07) but no connection to the galaxies kinematic or morphological properties nor radial variations in stellar mass surface density or star formation rate surface density. This suggests both the radial and azimuthal variations in interstellar medium properties are connected to the galaxy integrated density of recent star formation.