Testing the Stellar Feedback-driven Breathing Mode in Low-mass Galaxies with Gas Kinematics

Abstract

Hydrodynamic simulations have proposed that stellar feedback and bursty star-formation can produce dark matter cores in low-mass galaxies. A key prediction is that feedback-driven gas outflow and inflow cycles can lead to ``breathing modes'' (rapid fluctuations in the global gravitational potential) which drive correlated variations in galaxy size, kinematics, and star-formation rate. In this paper, we test the dynamical effects of feedback-driven breathing modes using a sample of 103 star-forming low-mass galaxies with stellar masses between $7.9<\log {\mathrm{M}}_{\ast }/{\mathrm{M}}_{\odot }<9.6$ and $0.02<z<0.19$. We measure ionized gas velocity dispersions from H$\hat{I}\pm$ emission lines and compare them to mock observations from the FIRE-2 simulations. We compare gas velocity dispersions ($\ddot{\mathrm{I}}{ƒ}_{\mathrm{gas}}$), stellar masses, and specific star-formation rates (sSFR). We find a positive correlation between gas velocity dispersion residuals at fixed stellar masses ($\hat{\mathrm{I}}”\ddot{\mathrm{I}}{ƒ}_{\mathrm{gas}}$) and sSFR in both data and simulations. However, the relation is tighter in FIRE-2 compared to the data. FIRE-2 produces more low-sSFR galaxies compared to our observational sample, however, the sSFR distributions agree after limiting both samples to a minimum sSFR. A deeper and more complete photometric sample further indicates that observed low-mass galaxies could span the full range of sSFR predicted in the FIRE-2 simulations. Our results support the existence of short-timescale dynamical effects driven by gas outflow and inflow cycles in low-mass galaxies and motivate additional tests of the breathing mode.

23 pages, 12 figures