THE ADVANCED CAMERA FOR SURVEYS NEARBY GALAXY SURVEY TREASURY. IV. THE STAR FORMATION HISTORY OF NGC 2976
- Department of Astronomy, Box 351580, University of Washington, Seattle, WA 98195 (United States)
- CfA Fellow, Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)
- Department of Astronomy, University of Minnesota, 116 Church St. SE, Minneapolis, MN 55455 (United States)
- Raytheon, 1151 E. Hermans Road, Tucson, AZ 85706 (United States)
- Department of Astronomy, New Mexico State University, Box 30001, 1320 Frenger St., Las Cruces, NM 88003 (United States)
We present resolved stellar photometry of NGC 2976 obtained with the Advanced Camera for Surveys (ACS) as part of the ACS Nearby Galaxy Survey Treasury (ANGST) program. The data cover the radial extent of the major axis of the disk out to 6 kpc, or approx6 scale lengths. The outer disk was imaged to a depth of M{sub F606W} approx 1, and an inner field was imaged to the crowding limit at a depth of M{sub F606W} approx -1. Through detailed analysis and modeling of the resulting color-magnitude diagrams, we have reconstructed the star formation history (SFH) of the stellar populations currently residing in these portions of the galaxy, finding similar ancient populations at all radii but significantly different young populations at increasing radii. In particular, outside of the well-measured break in the disk surface brightness profile, the age of the youngest population increases with distance from the galaxy center, suggesting that star formation is shutting down from the outside-in. We use our measured SFH, along with H I surface density measurements, to reconstruct the surface density profile of the disk during previous epochs. Comparisons between the recovered star formation rates and reconstructed gas densities at previous epochs are consistent with star formation following the Schmidt law during the past 0.5 Gyr, but with a drop in star formation efficiency at low gas densities, as seen in local galaxies at the present day. The current rate and gas density suggest that rapid star formation in NGC 2976 is currently in the process of ceasing from the outside-in due to gas depletion. This process of outer disk gas depletion and inner disk star formation was likely triggered by an interaction with the core of the M81 group approx>1 Gyr ago that stripped the gas from the galaxy halo and/or triggered gas inflow from the outer disk toward the galaxy center.
- OSTI ID:
- 21392349
- Journal Information:
- Astrophysical Journal, Vol. 709, Issue 1; Other Information: DOI: 10.1088/0004-637X/709/1/135; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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