The dust-to-gas mass ratio of luminous galaxies as a function of their metallicity at cosmic noon

Abstract

We aim to quantify the relation between the dust-to-gas mass ratio (DTG) and gas-phase metallicity of $z=$2.1-2.5 luminous galaxies and contrast this high-redshift relation against analogous constraints at z$=$0. We present a sample of ten star-forming main-sequence galaxies in the redshift range $2.1<z<2.5$ with rest-optical emission-line information available from the MOSDEF survey and with ALMA 1.2 millimetre and CO J$=$3-2 follow-up observations. The galaxies have stellar masses ranging from $10^{10.3}$ to $10^{10.6}\,\rm{M}_\odot$ and cover a range in star-formation rate from 35 to 145 $\rm{M}_\odot\,\rm{yr}^{-1}$. We calculated the gas-phase oxygen abundance of these galaxies from rest-optical nebular emission lines (8.4 < $12 + \log{(\rm{O/H})} < 8.8$, corresponding to 0.5 - 1.25 Z$_\odot$). We estimated the dust and H$_2$ masses of the galaxies (using a metallicity-dependent CO-to-H$_2$ conversion factor) from the 1.2~mm and CO J$=$3-2 observations, respectively, from which we estimated a DTG. We find that the galaxies in this sample follow the trends already observed between CO line luminosity and dust-continuum luminosity from $z=0$ to $z=3$, extending such trends to fainter galaxies at $2.1<z<2.5$ than observed to date. We find no second-order metallicity dependence in the CO - dust-continuum luminosity relation for the galaxies presented in this work. The DTGs of main-sequence galaxies at $2.1<z<2.5$ are consistent with an increase in the DTG with gas-phase metallicity. The metallicity dependence of the DTG is driven by the metallicity dependence of the CO-to-H$_2$ conversion factor. Galaxies at z$=$2.1-2.5 are furthermore consistent with the DTG-metallicity relation found at z$=$0 (i.e. with no significant evolution), providing relevant constraints for galaxy formation models.