Shaken, not blown: the gentle baryonic feedback of nearby starburst dwarf galaxies

Abstract

Baryonic feedback is expected to play a key role in regulating the star formation of low-mass galaxies by producing galaxy-scale winds associated with mass-loading factors ${\hat{I}}^2\sim 1-50$. We have tested this prediction using a sample of 19 nearby systems with stellar masses $10^7<M_{\star }/{\mathrm{M}}_{\odot }<10^{10}$, mostly lying above the main sequence of star-forming galaxies. We used MUSE@VLT optical integral field spectroscopy to study the warm ionised gas kinematics of these galaxies via a detailed modelling of their H$\hat{I}\pm$ emission line. The ionised gas is characterised by irregular velocity fields, indicating the presence of non-circular motions of a few tens of km/s within galaxy discs, but with intrinsic velocity dispersion of $40$-$60$ km/s that are only marginally larger than those measured in main-sequence galaxies. Galactic winds, defined as gas at velocities larger than the galaxy escape speed, encompass only a few percent of the observed fluxes. Mass outflow rates and loading factors are strongly dependent on $M_{\star }$, star formation rate (SFR), SFR surface density and specific SFR. For $M_{\star }$ of $10^8$ M${}_{\odot }$ we find ${\hat{I}}^2\simeq 0.02$, which is more than two orders of magnitude smaller than the values predicted by theoretical models of galaxy evolution. In our galaxy sample, baryonic feedback stimulates a gentle gas cycle rather than causing a large-scale blow out.

26 pages, 12 figures, accepted by A&A