Strong suppression of star formation and spiral arm formation in disk galaxies with counter-rotating gas disks

TL;DR

This study uses numerical simulations to show that counter-rotating gas disks in galaxies significantly suppress star formation and spiral arm formation, leading to low star formation rates even with abundant gas.

Contribution

It introduces a new mechanism for star formation suppression in disk galaxies caused by counter-rotating gas, which is less dependent on galaxy parameters.

Findings

Counter-rotating gas disks suppress spiral arm formation.

Star formation is severely quenched in galaxies with counter-rotation.

Counter-rotating gas leads to long gas depletion timescales.

Abstract

Galaxy-wide star formation can be quenched by a number of physical processes such as environmental effects (e.g., ram pressure stripping) and supernova feedback. Using numerical simulations, we here demonstrate that star formation can be severely suppressed in disk galaxies with their gas disks counter-rotating with respect to their stellar disks. This new mechanism of star formation suppression (or quenching) does not depend so strongly on model parameters of disk galaxies, such as bulge-to-disk- ratios and gas mass fractions. Such severe suppression of star formation is due largely to the suppression of the gas density enhancing mechanism i.e spiral arm formation in disk galaxies with counter-rotating gas. Our simulations also show that molecular hydrogen and dust can be rather slowly consumed by star formation in disk galaxies with counter-rotating gas disks (i.e., long gas depletion timescale). Based on these results, we suggest that spiral and S0 galaxies with counter-rotation can have rather low star formation rate for their gas densities. Also we suggest that a minor fraction of S0 galaxies have no prominent spiral arms, because they have a higher fraction of counter-rotating gas. We predict that poststarburst E+A disk galaxies with cold gas could have counter-rotating gas.