Density Bounding in the H II Regions of Galactic Disks: Evidence and Consequences

Details Density Bounding in the H II Regions of Galactic Disks: Evidence and Consequences Density Bounding in the H II Regions of Galactic Disks: Evidence and Consequences

Feb 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002rmxac..12..213b&link_type=abstract

Ionized Gaseous Nebulae, a Conference to Celebrate the 60th Birthdays of Silvia Torres-Peimbert and Manuel Peimbert, Mexico City

Astronomy and Astrophysics

Astronomy

2

Galaxies: Ism, Galaxies: Spiral, Ism: General, Ism: H Ii Regions

Scientific paper

We present four lines of evidence leading to the conclusion that a notable fraction of the ionizing photon emission from the stars within H II regions in the disks of normal galaxies escapes from the regions into the surrounding galaxy and beyond. These are: (1) The surface brightness intensity distribution of the diffuse ensuremath {{Hα }} emitted by a disk galaxy is well modeled by assuming that the Lyman continuum producing it leaks from the H II regions. (2) The relation of the central ensuremath {{Hα }} surface brightness to total luminosity of an H II region departs from the predictions of uniform ionization bounded systems. (3) The ensuremath {{Hα }} luminosity function of complete H II region populations shows a break whose parameters are explicable using the density bounding hypothesis, but not via competing hypotheses. (4) The relation between the ensuremath {{Hα }} internal velocity half-width and luminosity for H II regions is naturally explained via density bounding. A fractally clumpy cloud structure, and a simple law relating the mass of the most luminous star in a young cluster to the mass of its placental gas cloud give model parameters which can account for the observations. We show how the fraction of the Lyc escaping from leaky H II regions which finally completely escapes the galactic disks can ionize large volumes of the ultra-low density intracluster gas around galaxies.

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