A NEW CATALOG OF H II REGIONS IN M31
- Department of Physics and Astronomy, University of Western Ontario, 1151 Richmond St., London, ON N6A 3K7 (Canada)
We present a new catalog of H II regions in M31. The full disk of the galaxy ({approx}24 kpc from the galaxy center) is covered in a 2.2 deg{sup 2} mosaic of 10 fields observed with the Mosaic Camera on the Mayall 4 m telescope as part of the Local Group Galaxies survey. We used HIIphot, a code for automated photometry of H II regions, to identify the regions and measure their fluxes and sizes. A 10{sigma} detection level was used to exclude diffuse gas fluctuations and star residuals after continuum subtraction. That selection limit may result in missing some faint H II regions, but our catalog of 3691 H II regions is still complete to a luminosity of L{sub H{alpha}} = 10{sup 34} erg s{sup -1}. This is five times fainter than the only previous CCD-based study which contained 967 objects in the NE half of M31. We determined the H{alpha} luminosity function (LF) by fitting a power law to luminosities larger than L{sub H{alpha}} = 10{sup 36.7} and determined a slope of 2.52 {+-} 0.07. The in-arm and inter-arm LFs peak at different luminosities but they have similar bright-end slopes. The inter-arm regions are less populated (40% of total detected regions) and constitute only 14% of the total luminosity of L{sub H{alpha}} = 5.6 x 10{sup 40} erg s{sup -1} (after extinction correction and considering 65% contribution from diffused ionized gas). A star formation rate of 0.44 M{sub sun} yr{sup -1} was estimated from the H{alpha} total luminosity; this value is consistent with the determination from the Spitzer 8 {mu}m image. We removed all known and potential planetary nebulae, yet we found a double-peaked LF. The inter-arm older population suggests a starburst between 15 and 20 million years ago. This result is in agreement with UV studies of the star formation history in M31 which found a star formation rate decrease in the recent past. We found a fair spatial correlation between the H II regions and stellar clusters in selected star-forming regions. Most of the matched regions lie within the arm regions.
- OSTI ID:
- 21582815
- Journal Information:
- Astronomical Journal (New York, N.Y. Online), Vol. 142, Issue 4; Other Information: DOI: 10.1088/0004-6256/142/4/139; ISSN 1538-3881
- Country of Publication:
- United States
- Language:
- English
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