Shaken, but not expelled : Gentle baryonic feedback from nearby starburst dwarf galaxies

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 of β∼1- 50. We test this prediction using a sample of 19 nearby systems with stellar masses of 107 < M∗/M· < 1010, mostly lying above the main sequence of star-forming galaxies. We used MUSE at VLT optical integral field spectroscopy to study the warm ionised gas kinematics of these galaxies via a detailed modelling of their Hα 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-1 within galaxy discs, but with intrinsic velocity dispersion of 40- 60 km s-1 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∗, the star formation rate (SFR), SFR surface density, and specific SFR (sSFR). For M∗ of 108 M· we find β 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.