A mass threshold for galactic gas discs by spin flips

TL;DR

This paper predicts a critical halo mass threshold around 2×10^{11} solar masses, above which galactic gas discs tend to survive, influenced by merger rates, feedback processes, and cosmic-web feeding patterns.

Contribution

It introduces an analytical and simulation-based model identifying a mass threshold for gas disc survival, highlighting the roles of mergers, feedback, and cosmic web streams.

Findings

Gas discs survive mainly in haloes above 2×10^{11} M_sun.

Below the threshold, discs are disrupted by rapid spin flips due to mergers.

Supernova feedback significantly influences disc disruption below the critical mass.

Abstract

We predict, analytically and by simulations, that gas discs tend to survive only in haloes above a threshold mass $\sim 2 \times 10^{11} M_\odot$ (stellar mass $\sim 10^9 M_\odot$), with only a weak redshift dependence. At lower masses, the disc spins typically flip in less than an orbital time due to mergers associated with a change in the pattern of the feeding cosmic-web streams. This threshold arises from the halo merger rate when accounting for the mass dependence of the ratio of galactic baryons and halo mass. Above the threshold, wet compactions lead to massive central nuggets that allow the longevity of extended clumpy gas rings. Supernova feedback has a major role in disrupting discs below the critical mass, by driving the stellar-to-halo mass ratio that affects the merger rate, by stirring up turbulence and suppressing high-angular-momentum gas supply, and by confining major compactions to the critical mass. Our predictions seem consistent with current observed fractions of gas discs, to be explored by future observations that will resolve galaxies below $10^9 M_\odot$ at high redshifts, e.g. by JWST.