The EDGE-CALIFA survey: the influence of galactic rotation on the molecular depletion time across the Hubble sequence

TL;DR

This study analyzes how galactic rotation influences molecular gas depletion times across different galaxy types, revealing that morphology affects star formation efficiency and that early-type galaxies may be quenched by disc stabilization rather than lack of gas.

Contribution

It provides a detailed kpc-scale analysis of the relationship between molecular depletion time and orbital time across diverse galaxy morphologies, highlighting the role of morphology in star formation efficiency.

Findings

On average, 5% of molecular gas converts into stars per orbital time.

Different galaxy morphologies follow distinct $ au_ ext{dep}^ ext{mol}- au_ ext{orb}$ relations.

Early-type galaxies show signs of morphological quenching affecting star formation.

Abstract

We present a kpc-scale analysis of the relationship between the molecular depletion time ($\tau_\mathrm{dep}^\mathrm{mol}$) and the orbital time ($\tau_\mathrm{orb}$) across the field of 39 face-on local galaxies, selected from the EDGE-CALIFA sample. We find that, on average, 5% of the available molecular gas is converted into stars per orbital time, or $\tau_\mathrm{dep}^\mathrm{mol}\sim20\tau_\mathrm{orb}$. The resolved relation shows a scatter of $\sim0.5$ dex. The scatter is ascribable to galaxies of different morphologies that follow different $\tau_\mathrm{dep}^\mathrm{mol}-\tau_\mathrm{orb}$ relations which decrease in steepness from early- to late-types. The morphologies appear to be linked with the star formation rate surface density, the molecular depletion time, and the orbital time, but they do not correlate with the molecular gas content of the galaxies in our sample. We speculate that in our molecular gas rich, early-type galaxies, the morphological quenching (in particular the disc stabilization via shear), rather than the absence of molecular gas, is the main factor responsible for their current inefficient star formation.