Cross-calibration of CO- vs dust-based gas masses and assessment of the dynamical mass budget in Herschel-SDSS Stripe82 galaxies

TL;DR

This study cross-calibrates CO- and dust-based molecular gas mass estimates in local galaxies, revealing a tight relation with a small systematic offset, and assesses the galaxy mass budget including stars, gas, and dark matter.

Contribution

It provides the first detailed comparison and calibration between CO- and dust-based gas masses at low redshift, incorporating metallicity effects and dynamical mass constraints.

Findings

CO and dust gas mass estimates are tightly correlated with 0.17 dex scatter.

A metallicity-dependent correction aligns the two methods within 0.05 dex.

Dynamical mass estimates agree with the combined stellar, gas, and dark matter mass budget.

Abstract

We present a cross-calibration of CO- and dust-based molecular gas masses at $z \leqslant 0.2$. Our results are based on a survey with the IRAM 30-m telescope collecting CO(1-0) measurements of 78 massive ($\log M_{\star} / M_{\odot} > 10$) galaxies with known gas-phase metallicities, and with IR photometric coverage from WISE (22 $\mu$m ) and Herschel SPIRE (250, 350, 500 $\mu$m). We find a tight relation ($\sim 0.17$ dex scatter) between the gas masses inferred from CO and dust continuum emission, with a minor systematic offset of 0.05 dex. The two methods can be brought into agreement by applying a metallicity-dependent adjustment factor ($\sim 0.13$ dex scatter). We illustrate that the observed offset is consistent with a scenario in which dust traces not only molecular gas, but also part of the ${\rm H \small I}$ reservoir, residing in the ${\rm H_2}$-dominated region of the galaxy. Observations of the CO(2-1) to CO(1-0) line ratio for two thirds of the sample indicate a narrow range in excitation properties, with a median ratio of luminosities $ \left\langle R_{21} \right\rangle \sim 0.64 $. Finally, we find dynamical mass constraints from spectral line profile fitting to agree well with the anticipated mass budget enclosed within an effective radius, once all mass components (stars, gas and dark matter) are accounted for.