H-alpha velocity fields of giant H II regions in four nearby dwarf irregular galaxies

Details H-alpha velocity fields of giant H II regions in four nearby dwarf irregular galaxies H-alpha velocity fields of giant H II regions in four nearby dwarf irregular galaxies

Oct 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993pasj...45..693t&link_type=abstract

PASJ: Publications of the Astronomical Society of Japan (ISSN 0004-6264), vol. 45, no. 5, p. 693-705

Astronomy and Astrophysics

Astronomy

12

Dwarf Galaxies, H Alpha Line, H Ii Regions, Irregular Galaxies, Local Group (Astronomy), Star Formation, Velocity Distribution, Astronomical Spectroscopy, Charge Coupled Devices, Spectrometers

Scientific paper

We carried out H-alpha spectroscopies of six giant H II regions in four isolated, nearby, face-on dwarf irregular galaxies: I Zw 36, NGC 6822, Sex A, and IC 1613. The H-alpha velocity field maps were obtained for three galaxies, but not for IC 1613. These H-alpha velocity fields have the following common features: (1) At the central parts of the H II regions the velocity fields are rather flat, i.e., the velocity ranges are 5 km/s or less over a scale of 50 to 200 pc. In particular, in the H II region in NGC 6822, observed with a spatial resolution of about 10 pc, the velocity field at the central part is more calm than that expected in gravitationally relaxed systems. (2) The H-alpha velocities at the central parts are nearly the same as the CO velocities, but several km/s larger than the velocities of H I gas surrounding the H II regions. (3) At the outer regions the H-alpha velocities are shifted by 10 to 15 km/s from those at the central parts. By also considering the ages and locations of the H II regions as well as the extent of the H I envelopes, these features seem to be consistent with a model in which the star formation bursts are triggered by the collisions of infalling clouds with the H I disk.

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