STAR FORMATION RATES IN RESOLVED GALAXIES: CALIBRATIONS WITH NEAR- AND FAR-INFRARED DATA FOR NGC 5055 AND NGC 6946
- Department of Astronomy, University of Massachusetts, Amherst, MA 01003 (United States)
- Department of Physics and Astronomy, McMaster University, Hamilton, Ontario L8S 4M1 (Canada)
- Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom)
- Observatories of the Carnegie Institution for Science, 813 Santa Barbara Street, Pasadena, CA 91101 (United States)
- Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden (Netherlands)
- Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 (United States)
- Institut d'Astrophysique de Paris, UMR7095 CNRS, Universite Pierre and Marie Curie, 98 bis Boulevard Arago, F-75014 Paris (France)
- Spitzer Science Center, California Institute of Technology, MC 314-6, Pasadena, CA 91125 (United States)
- Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)
- Department of Physics and Astronomy, University of Toledo, Toledo, OH 43606 (United States)
- Department of Physics and Astronomy, University of Wyoming, Laramie, WY 82071 (United States)
- Steward Observatory, University of Arizona, Tucson, AZ 85721 (United States)
- Tianjin Astrophysics Center, Tianjin Normal University, Tianjin 300387 (China)
- NASA Herschel Science Center, IPAC, California Institute of Technology, Pasadena, CA 91125 (United States)
We use the near-infrared Br{gamma} hydrogen recombination line as a reference star formation rate (SFR) indicator to test the validity and establish the calibration of the Herschel/PACS 70 {mu}m emission as a SFR tracer for sub-galactic regions in external galaxies. Br{gamma} offers the double advantage of directly tracing ionizing photons and of being relatively insensitive to the effects of dust attenuation. For our first experiment, we use archival Canada-France-Hawaii Telescope Br{gamma} and Ks images of two nearby galaxies: NGC 5055 and NGC 6946, which are also part of the Herschel program KINGFISH (Key Insights on Nearby Galaxies: a Far-Infrared Survey with Herschel). We use the extinction corrected Br{gamma} emission to derive the SFR(70) calibration for H II regions in these two galaxies. A comparison of the SFR(70) calibrations at different spatial scales, from 200 pc to the size of the whole galaxy, reveals that about 50% of the total 70 {mu}m emission is due to dust heated by stellar populations that are unrelated to the current star formation. We use a simple model to qualitatively relate the increase of the SFR(70) calibration coefficient with decreasing region size to the star formation timescale. We provide a calibration for an unbiased SFR indicator that combines the observed H{alpha} with the 70 {mu}m emission, also for use in H II regions. We briefly analyze the PACS 100 and 160 {mu}m maps and find that longer wavelengths are not as good SFR indicators as 70 {mu}m, in agreement with previous results. We find that the calibrations show about 50% difference between the two galaxies, possibly due to effects of inclination.
- OSTI ID:
- 22126685
- Journal Information:
- Astrophysical Journal, Vol. 768, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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