Abstract

# Introduction

In order to understand how galaxies build up mass through cosmic time and become the objects we see around us in the present-day Universe, we need to accurately probe their cold gas content which reveals their capacity for making stars. As molecular hydrogen itself has no dipole moment, the majority of bulk molecular gas studies have depended on the $$^{12}$$CO lines to obtain molecular masses through the now (in)famous “X-factor” (mapping to H$$_{2}$$ column density) or $$\alpha_{\mathrm{CO}}$$ (mapping to H$$_{2}$$ mass).

# Data

## Reduction

The Herschel SPIRE FTS data were obtained over xxx-xxx and reduced as explained in Pellegrini et al., in prep. As a summary, we applied the calibration pipeline up to a certain point. However, corrections in between those of an extended and point source were required for all but thre