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Title:
Gas kinematics and the structure of extragalactic giant and supergiant H II regions
Authors:
Gallagher, J. S.; Hunter, D. A.
Affiliation:
AA(Illinois, University, Urbana, IL)
Publication:
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 274, Nov. 1, 1983, p. 141-151. (ApJ Homepage)
Publication Date:
11/1983
Category:
Astrophysics
Origin:
STI
NASA/STI Keywords:
GALACTIC STRUCTURE, GAS FLOW, H II REGIONS, INTERSTELLAR GAS, MOLECULAR CLOUDS, NEBULAE, B STARS, GALACTIC RADIATION, H ALPHA LINE, IONIZED GASES, MILKY WAY GALAXY, O STARS
DOI:
10.1086/161432
Bibliographic Code:
1983ApJ...274..141G

Abstract

We examine the hypothesis of Terlevich and Melnick that velocity widths of emission lines in luminous H II regions reflect the gravitationally bound state of these systems. Observational data to test this concept are taken from our homogeneous sets of flux calibrated Halpha images and high-resolution echelle Hoc intensity line velocity profiles for nearby irregular galaxies. Giant H II regions with diameters in the range 50-500 pc show well-known supersonic gas velocities, but no convincing evidence is found to associate these motions with gravitational binding of the H II complexes. Large-scale gas flows induced by embedded OB stellar populations provide a more plausible explanation for observed velocity line widths in the giant H II regions. Supergiant H II complexes with diameters of more than 500 pc have some features which are consistent with self-gravitating models and are in any case kinematically distinct from more common giant H II regions. Since supergiant H II complexes extend over significant fractions of their parent galaxies, observed velocities in the ionized gas are likely to be substantially influenced by kinematic properties of the galaxian environment. It thus is unlikely that pressure supported, bound self-gravitating models can provide a complete explanation for the gas kinematics of supergiant H II regions.

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