Blow-Away in the Extreme Low-Mass Starburst Galaxy Pox 186

Abstract

Pox 186 is an exceptionally small dwarf starburst galaxy hosting a stellar mass of ~10^5 solar masses. Undetected in HI (M < 10^6 solar masses) from deep 21 cm observations and with an [OIII]/[OII] (5007/3727) ratio of 18.3 +/- 0.11, Pox 186 is a promising candidate Lyman continuum emitter. It may be a possible analog of low-mass reionization-era galaxies. We present a spatially resolved kinematic study of Pox 186. We identify two distinct ionized gas components: a broad one with sigma > 400 km/s, and a narrow one with sigma < 30 km/s. We find strikingly different morphologies between the two components and direct evidence of outflows as seen in the high velocity gas. Possible physical mechanisms driving the creation of high velocity gas seen in [OIII] are discussed, from outflow geometry to turbulent mixing between a hot (10^6 K) star-cluster wind and cooler (10^4 K) gas clouds. We find a modest mass-outflow rate of 0.022 solar masses yr^-1 with a small mass loading factor of 0.5, consistent with other low mass galaxies. Finally we compare the mass-loading factor of Pox 186 with extrapolations from numerical simulations and discuss possible reasons for the apparent discrepancy between them.