Expansive components in H II regions

Free access article

Issue		A&A Volume 430, Number 3, February II 2005


Page(s)		911 - 926
Section		Extragalactic astronomy
DOI		http://dx.doi.org/10.1051/0004-6361:20041708

A&A 430, 911-926 (2005)
DOI: 10.1051/0004-6361:20041708

Expansive components in H II regions

M. Relaño¹ and J. E. Beckman^{1, 2}

¹ Instituto de Astrofísica de Canarias, C. Vía Láctea s/n, 38200, La Laguna, Tenerife, Spain
e-mail: mpastor@ll.iac.es
² Consejo Superior de Investigaciones Científicas (CSIC), Spain
e-mail: jeb@ll.iac.es

(Received 22 July 2004 / Accepted 5 October 2004 )

Abstract
We study the presence of low intensity high velocity components, which we have termed wing features in the integrated H $\alpha$ emission line profiles of the $\ion{H}{ii}$ region populations of the spiral barred galaxies NGC 1530, NGC 3359 and NGC 6951. We find that more than a third of the $\ion{H}{ii}$ region line profiles in each galaxy show these components. The highest fraction is obtained in the galaxy whose line profiles show the best S:N, which suggests that wing features of this type may well exist in most, if not all, $\ion{H}{ii}$ region line profiles. Applying selection criteria to the wing features, we obtain a sample of $\ion{H}{ii}$ regions with clearly defined high velocity components in their profiles. Deconvolution of a representative sample of the line profiles eliminates any doubt that the wing features could possibly be due to instrumental effects. We present an analysis of the high velocity low intensity features fitting them with Gaussian functions; the emission measures, central velocities and velocity dispersions for the red and blue features take similar values. We interpret the features as signatures of expanding shells inside the $\ion{H}{ii}$ regions. Up to a shell radius of $R_{{\rm shell}}\sim 0.2~R_{{\rm reg}}$ , the stellar winds from the central ionizing stars appear to satisfy the energy and momentum requirements for the formation and driving the shell. Several examples of the most luminous $\ion{H}{ii}$ regions show that the shells appear to have larger radii; in these cases additional mechanisms may well be needed to explain the kinetic energies and momenta of the shells.

Key words: ISM: H II regions -- ISM: kinematics and dynamics -- galaxies: individual: NGC 1530 -- galaxies: individual: NGC 6951 -- galaxies: individual: NGC 3359 -- galaxies: ISM

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