Modelling the Pan-Spectral Energy Distribution of Starburst Galaxies: II. Control of the H II Region Parameters

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We examine from a theoretical viewpoint how the physical parameters of H II regions are controlled both in normal galaxies and in starburst environments. These parameters are the H II region luminosity function, the time-dependent size, the covering fraction of molecular clouds, the pressure in the ionized gas and the ionization parameter. The factors which control them are the initial mass function of the exciting stars, the cluster mass function, the metallicity and the mean pressure in the surrounding interstellar medium. We investigate the sensitivity of the H{alpha} luminosity to the IMF, and find that this can translate to about ... continued below

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Dopita, M A; Fischera, J; Sutherland, R S; Kewley, L J; Tuffs, R J; Popescu, C C et al. March 1, 2006.

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We examine from a theoretical viewpoint how the physical parameters of H II regions are controlled both in normal galaxies and in starburst environments. These parameters are the H II region luminosity function, the time-dependent size, the covering fraction of molecular clouds, the pressure in the ionized gas and the ionization parameter. The factors which control them are the initial mass function of the exciting stars, the cluster mass function, the metallicity and the mean pressure in the surrounding interstellar medium. We investigate the sensitivity of the H{alpha} luminosity to the IMF, and find that this can translate to about 30% variation in derived star formation rates. The molecular cloud dissipation timescale is estimated from a case study of M17 to be {approx} 1 Myr. Based upon H II luminosity function fitting for nearby galaxies, we propose that the cluster mass function has a log-normal form peaking at {approx} 185M{sub {circle_dot}}. This suggests that the cluster mass function is the continuation of the stellar IMF to higher mass. The pressure in the H II regions is controlled by the mechanical luminosity flux from the central cluster. Since this is closely related to the ionizing photon flux, we show that the ionization parameter is not a free variable, and that the diffuse ionized medium may be composed of many large, faint and old H II regions. Finally, we derive theoretical probability distributions for the ionization parameter as a function of metallicity and compare these to those derived for SDSS galaxies.

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PDF-file: 39 pages; size: 0.3 Mbytes

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  • Journal Name: Astrophysical Journal, vol. 647, no. 1, August 1, 2006, pp. 244-255

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  • Report No.: UCRL-JRNL-220864
  • Grant Number: W-7405-ENG-48
  • Office of Scientific & Technical Information Report Number: 899108
  • Archival Resource Key: ark:/67531/metadc890978

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  • March 1, 2006

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  • Sept. 22, 2016, 2:13 a.m.

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  • Nov. 29, 2016, 8:26 p.m.

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Dopita, M A; Fischera, J; Sutherland, R S; Kewley, L J; Tuffs, R J; Popescu, C C et al. Modelling the Pan-Spectral Energy Distribution of Starburst Galaxies: II. Control of the H II Region Parameters, article, March 1, 2006; Livermore, California. (digital.library.unt.edu/ark:/67531/metadc890978/: accessed May 24, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.