Prescott, Moire K. M. and Kennicutt, Robert C., Jr. and Bendo, George J. and Buckalew, Brent A. and Calzetti, Daniela and Engelbracht, Charles W. and Gordon, Karl D. and Hollenbach, David J. and Lee, Janice C. and Moustakas, John and Dale, Daniel A. and Helou, George and Jarrett, Thomas H. and Murphy, Eric J. and Smith, John-David T. and Akiyama, Sanae and Sosey, Megan L. (2007) The incidence of highly obscured star-forming regions in SINGS galaxies. Astrophysical Journal, 668 (1). pp. 182-202. ISSN 0004-637X http://resolver.caltech.edu/CaltechAUTHORS:20090414-111750090
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Using the new capabilities of Spitzer and extensive multiwavelength data from SINGS, it is now possible to study the infrared properties of star formation in nearby galaxies down to scales equivalent to large H II regions. We are therefore able to determine what fraction of large, infrared-selected star-forming regions in normal galaxies are highly obscured and address how much of the star formation we miss by relying solely on the optical portion of the spectrum. Employing a new empirical method for deriving attenuations of infrared-selected star-forming regions, we investigate the statistics of obscured star formation on 500 pc scales in a sample of 38 nearby galaxies. We find that the median attenuation is 1.4 mag in Hα and that there is no evidence for a substantial subpopulation of uniformly highly obscured star-forming regions. The regions in the highly obscured tail of the attenuation distribution (AHα ≳ 3) make up only ~4% of the sample of nearly 1800 regions, although very embedded infrared sources on the much smaller scales and lower luminosities of compact and ultracompact H II regions are almost certainly present in greater numbers. The highly obscured cases in our sample are generally the bright, central regions of galaxies with high overall attenuation but are not otherwise remarkable. We also find that a majority of the galaxies show decreasing radial trends in Hα attenuation. The small fraction of highly obscured regions seen in this sample of normal, star-forming galaxies suggests that on 500 pc scales the timescale for significant dispersal or breakup of nearby, optically thick dust clouds is short relative to the lifetime of a typical star-forming region.
|Additional Information:||© 2007 American Astronomical Society. Print publication: Issue 1 (2007 October 10); received 2007 February 18; accepted for publication 2007 June 21. We are grateful to Kristian Finlator and Christy Tremonti for many thoughtful discussions. M. P. was supported by an NSF Graduate Research Fellowship. This work is based in part on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. Support for this work was provided by NASA through an award issued by JPL/Caltech. This research has made use of 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. This publication makes use of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation.|
|Subject Keywords:||galaxies: ISM; galaxies: photometry; H II regions; stars: formation|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Jason Perez|
|Deposited On:||06 Aug 2009 20:29|
|Last Modified:||26 Dec 2012 10:57|
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