Hα line profiles for a sample of supergiant HII regions

I. The main spectral component

¹ Instituto de Astronomía, Universidad Nacional Autónoma de México, Ensenada, México e-mail: maite@astrosen.unam.mx
² Facultad de Facultad de Física Teórica y del Cosmos, Universidad de Granada, Spain e-mail: mrelano@ugr.es
³ Instituto de Astrofísica de Canarias, La Laguna, Tenerife, Spain e-mail: jeb@iac.es
⁴ Consejo Superior de Investigaciones Cientificas, Spain

Received: 20 October 2005
Accepted: 26 April 2006

Abstract

We present an analysis of the Hα emission line profiles of a sample of giant extragalactic HII regions, selected from among the brightest and most isolated in a group of spiral galaxies for which we have photometric and spectroscopic data: NGC 157, NGC 3631, NGC 6764, NGC 3344, NGC 4321, NGC  5364, NGC 5055, NGC 5985, NGC 7479. Our study confirms that the majority of the line profiles are composed of a bright, main component and two fainter, high velocity components that we denominate wings. Here, we analyze the kinematics of the principal components, finding a relation between the Hα luminosity, L_H\alpha, and the turbulent velocity dispersion, . A linear fit to the relation between these quantities yields log , in agreement with previous studies. We compute the mass of each HII region using both the virial theorem and the Hα luminosity, confirming that, though these estimates do not coincide exactly, they are comparable within the uncertainties and consequently that the HII regions in our sample are approximately virialized.