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

¹ European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany
e-mail: gpopping@eso.org
² Steward Observatory, University of Arizona, Tucson, AZ 85721, USA
³ Department of Physics, University of California, Davis, One Shields Ave, Davis, CA 95616, USA
⁴ Department of Astronomy, University of Massachusetts, Amherst, MA 01003, USA
⁵ Department of Physics and Astronomy, University of California, Riverside, 900 University Avenue, Riverside, CA 92521, USA
⁶ Department of Physics & Astronomy, University of California, Los Angeles, 430 Portola Plaza, Los Angeles, CA 90095, USA
⁷ Center for Astrophysics and Space Sciences, University of California, San Diego, 9500 Gilman Dr., La Jolla, CA 92093-0424, USA
⁸ Leiden Observatory, Leiden University, PO Box 9513 2300 AA Leiden, The Netherlands

Received: 19 April 2022
Accepted: 18 November 2022

Abstract

Aims. 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.

Methods. 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 M_⊙ and cover a range in star-formation rate from 35 to 145 M_⊙ yr⁻¹. We calculated the gas-phase oxygen abundance of these galaxies from rest-optical nebular emission lines (8.4 < 12 + log(O/H) < 8.8, corresponding to 0.5−1.25 Z_⊙). We estimated the dust and H₂ masses of the galaxies (using a metallicity-dependent CO-to-H₂ conversion factor) from the 1.2 mm and CO J = 3 − 2 observations, respectively, from which we estimated a DTG.

Results. 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-H₂ 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. These results furthermore imply that the metallicity of galaxies should be taken into account when estimating cold-gas masses from dust-continuum emission, which is especially relevant when studying metal-poor low-mass or high-redshift galaxies.