DOES STELLAR FEEDBACK CREATE H I HOLES? A HUBBLE SPACE TELESCOPE/VERY LARGE ARRAY STUDY OF HOLMBERG II
- Astronomy Department, University of Minnesota, Minneapolis, MN 55455 (United States)
- Department of Physics and Astronomy, Macalester College, 1600 Grand Avenue, St. Paul, MN 55125 (United States)
- Raytheon Company, 1151 E Hermans Rd, Tucson, AZ 85756 (United States)
- Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom)
- Observatories of the Carnegie Institution of Washington, 813 Santa Barbara Street, Pasadena, CA 91101 (United States)
- Max-Planck-Institut fuer Astronomie, Koenigstuhl 17, D-69117 Heidelberg (Germany)
We use deep Hubble Space Telescope (HST)/Advanced Camera for Surveys (ACS) F555W and F814W photometry of resolved stars in the M81 Group dwarf irregular galaxy Ho II to study the hypothesis that the holes identified in the neutral interstellar medium (H I) are created by stellar feedback. From the deep photometry, we construct color-magnitude diagrams (CMDs) and measure the star formation histories (SFHs) for stars contained in H I holes from two independent holes catalogs, as well as select control fields, i.e., similar sized regions that span a range of H I column densities. The CMDs reveal young (< 200 Myr) stellar populations inside all H I holes, which contain very few bright OB stars with ages less than 10 Myr, indicating they are not reliable tracers of H I hole locations while the recent SFHs confirm multiple episodes of star formation within most holes. Converting the recent SFHs into stellar feedback energies, we find that enough energy has been generated to have created all holes. However, the required energy is not always produced over a timescale that is less than the estimated kinematic age of the hole. A similar analysis of stars in the control fields finds that the stellar populations of the control fields and H I holes are statistically indistinguishable. However, because we are only sensitive to holes approx100 pc in diameter, we cannot tell if there are smaller holes inside the control fields. The combination of the CMDs, recent SFHs, and locations of young stars shows that the stellar populations inside H I holes are not coherent, single-aged, stellar clusters, as previously suggested, but rather multi-age populations distributed across each hole. From a comparison of the modeled and observed integrated magnitudes, and the locations and energetics of stars inside of H I holes, we propose a potential new model: a viable mechanism for creating the observed H I holes in Ho II is stellar feedback from multiple generations of SF spread out over tens or hundreds of Myr, and thus, the concept of an age for an H I hole is intrinsically ambiguous. For H I holes in the outer parts of Ho II, located beyond the HST/ACS coverage, we use Monte Carlo simulations of expected stellar populations to show that low level SF could provide the energy necessary to form these holes. Applying the same method to the SMC, we find that the holes that appear to be void of stars could have formed via stellar feedback from low level SF. We further find that Halpha and 24 mum emission, tracers of the most recent star formation, do not correlate well with the positions of the H I holes. However, UV emission, which traces star formation over roughly the last 100 Myr, shows a much better correlation with the locations of the H I holes.
- OSTI ID:
- 21367346
- Journal Information:
- Astrophysical Journal, Vol. 704, Issue 2; Other Information: DOI: 10.1088/0004-637X/704/2/1538; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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