Title: Galactic Outflows, Star Formation Histories, and Timescales in Starburst Dwarf Galaxies from STARBIRDS,
Abstract: Winds are predicted to be ubiquitous in low-mass, actively star-forming
galaxies. Observationally, winds have been detected in relatively few local
dwarf galaxies, with even fewer constraints placed on their timescales. Here,
we compare galactic outflows traced by diffuse, soft X-ray emission from
Chandra Space Telescope archival observations to the star formation histories
derived from Hubble Space Telescope imaging of the resolved stellar populations
in six starburst dwarfs. We constrain the longevity of a wind to have an upper
limit of 25 Myr based on galaxies whose starburst activity has already
declined, although a larger sample is needed to confirm this result. We find an
average 16% efficiency for converting the mechanical energy of stellar feedback
to thermal, soft X-ray emission on the 25 Myr timescale, somewhat higher than
simulations predict. The outflows have likely been sustained for timescales
comparable to the duration of the starbursts (i.e., 100's Myr), after taking
into account the time for the development and cessation of the wind. The wind
timescales imply that material is driven to larger distances in the
circumgalactic medium than estimated by assuming short, 5-10 Myr starburst
durations, and that less material is recycled back to the host galaxy on short
timescales. In the detected outflows, the expelled hot gas shows various
morphologies which are not consistent with a simple biconical outflow
structure. The sample and analysis are part of a larger program, the STARBurst
IRregular Dwarf Survey (STARBIRDS), aimed at understanding the lifecycle and
impact of starburst activity in low-mass systems.