THE Pa{alpha} LUMINOSITY FUNCTION OF H II REGIONS IN NEARBY GALAXIES FROM HST/NICMOS
- Astronomy Department, University of Massachusetts, Amherst, MA 01003 (United States)
- Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom)
- MPI for Astronomy, Koenigstuhl 17, D-69117 Heidelberg (Germany)
- Department of Physics, Meisei University, 2-1-1 Hodokubo, Hino, Tokyo 191-8506 (Japan)
- Joint ALMA Office, Alonso de Cordova 3107, Vitacura, Santiago 763-0355 (Chile)
- Institute of Space and Aeronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshino-dai, Chuo-ku, Sagamihara, Kanagawa 252-5210 (Japan)
The H II region luminosity function (LF) is an important tool for deriving the birthrates and mass distribution of OB associations and is an excellent tracer of the newly formed massive stars and associations. To date, extensive work (predominantly in H{alpha}) has been done from the ground, which is hindered by dust extinction and the severe blending of adjacent (spatially or in projection) H II regions. Reliably measuring the properties of H II regions requires a linear resolution <40 pc, but analyses satisfying this requirement have been done only in a handful of galaxies, so far. As the first space-based work using a galaxy sample, we have selected 12 galaxies from our HST/NICMOS Pa{alpha} survey and studied the LF and size distribution of H II regions both in individual galaxies and cumulatively, using a virtually extinction-free tracer of the ionizing photon rate. The high angular resolution and low sensitivity to diffuse emission of NICMOS also offer an advantage over ground-based imaging by enabling a higher degree of de-blending of the H II regions. We do not confirm the broken power-law LFs found in ground-based studies. Instead, we find that the LFs, both individual and co-added, follow a single power law dN(L)/dln L{proportional_to}L {sup -1}, are consistent with the mass function of star clusters in nearby galaxies, and are in agreement with the results of the existing analyses with Hubble Space Telescope (HST) data. The individual and co-added size distributions of H II regions are both roughly consistent with dN(D)/dln D{proportional_to}D {sup -3}, but the power-law scaling is probably contaminated by blended regions or complexes.
- OSTI ID:
- 22121884
- Journal Information:
- Astrophysical Journal, Vol. 772, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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