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Astron. Astrophys. 338, 15-26 (1998)

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Internal turbulence, viriality, and density bounding of the most luminous H II regions in the spiral galaxy M 100

M. Rozas 1, N. Sabalisck 1, J.E. Beckman 1 and J.H. Knapen 2

1 Instituto de Astrofísica de Canarias, E-38200 La Laguna, Tenerife, Canarias, Spain (mrozas, nss, jeb@iac.es)
2 University of Hertfordshire, Department of Physical Sciences, College Lane, Hatfield, Herts AL10 9AB, UK (knapen@star.herts.ac.uk)

Received 20 May 1998 / Accepted 2 July 1998


We present TAURUS Fabry-Perot velocity data in [FORMULA] emission of the disc of the grand design spiral M 100 (NGC 4321). We have studied the emission spectra of the 200 [FORMULA] regions most luminous in [FORMULA], calibrated in luminosity using photometric [FORMULA] imaging from the literature. The emission spectra of individual [FORMULA] regions were fitted using one or more Gaussian functions, and analyzed in terms of their velocity dispersion. We concentrate on the question of whether the emission lines show values of their internal velocity dispersions of [FORMULA] regions which would be predicted from the virial theorem, and find that in general this is not the case. There is a systematic trend to super-virial line widths, characteristic of the non-equilibrium effects of powerful OB stellar winds, and supernovae. We propose that the lower envelope in velocity dispersion [FORMULA], in the plot of [FORMULA] luminosity v. [FORMULA] represents the virialized regions, and give a tentative theoretical explanation for its slope of 2.6 in the log-log plane, in terms of density bounding for the regions of highest luminosity.

Key words: ISM: HII regions – galaxies: individual: M100 – galaxies: spiral – galaxies: structure – galaxies: ISM

Send offprint requests to: J.E. Beckman

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© European Southern Observatory (ESO) 1998

Online publication: September 8, 1998