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 time-scales. 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 per cent efficiency for converting the mechanical energy of stellar feedback to thermal, soft X-ray emission on the 25 Myr time-scale, somewhat higher than simulations predict. The outflows have likely been sustained for timescales comparable to the duration of the starbursts (i.e. 100s Myr), after taking into account the time for the development and cessation of the wind. The wind time-scales 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 time-scales. In the detected outflows, the expelled hot gas shows various morphologies that 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 life cycle and impact of starburst activity in low-mass systems.
Bibliographical noteFunding Information:
This study was funded by the Smithsonian Astrophysical Observatory Award AR2-13015X under NASA contract NAS 8-03060. This research has made use of NASA’s Astrophysics Data System, the ‘Aladin Sky Atlas’ developed at CDS, Strasbourg Observatory, France (Bonnarel et al. 2000; Boch & Fernique 2014), the ACIS EXTRACT software package (Broos et al. 2010), and the NASA/IPAC Extragalactic Database (NED), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. We acknowledge the usage of the HyperLeda data base (http://leda.univ-lyon1.fr). We would like to thank the referee for helpful comments and suggestions that have improved the paper and Nick Lee at the Chandra X-ray Center for providing valuable expertise on the data reduction process.
- Galaxies: Dwarf
- Galaxies: Evolution
- ISM: Jets and outflows
- X-rays: ISM