On the geometrical evolution of the ionized gas in HII galaxies

Free access article

Issue		A&A Volume 455, Number 3, September I 2006


Page(s)		825 - 834
Section		Extragalactic astronomy
DOI		http://dx.doi.org/10.1051/0004-6361:20054637

A&A 455, 825-834 (2006)
DOI: 10.1051/0004-6361:20054637

On the geometrical evolution of the ionized gas in HII galaxies

F. Cuisinier¹, P. Westera², E. Telles³ and R. Buser²

¹ GEMAC - Departamento de Astronomia / Observatório do Valongo, Universidade Federal do Rio de Janeiro, Ladeira do Pedro Antonio 43, 20080-090 Rio de Janeiro RJ, Brazil
    e-mail: francois@ov.ufrj.br
² Department of Physics and Astronomy, University of Basel, Venusstr. 7, 4102 Binningen, Switzerland
    e-mail: [westera;buser]@astro.unibas.ch
³ Observatório Nacional/MCT, Rua José Cristino, 77 Rio de Janeiro RJ, 20921-400, Brazil
    e-mail: etelles@on.br

(Received 2 December 2005 / Accepted 28 March 2006)

Abstract
Aims.In this paper, we investigate the behaviour of the number of Lyman continuum ionizing photons as compared to the actual number of hydrogen recombinations in HII galaxies.
Methods.We evaluate the number of ionizing photons from the population synthesis of spectra observed in the visible, extrapolating the spectra to the extreme ultraviolet (EUV), beyond the Lyman limit. We check for possible systematic deviations of the predicted ionizing spectra in the EUV by comparing the ratio of the predicted number of ionizing photons to the number of recombinations, as measured in H $\beta$ , ${\Delta \log Q\rm (H^0)}$ , with the metallicity. We find that, as far as the number of ionizing photons is concerned, no systematic tendency can be detected.

The ${\rm H\beta}$ equivalent width can be understood as a nebular age indicator, decreasing with age, although the observed ${\rm H\beta}$ equivalent width can also be affected by the contribution to the continuum by the accumulation of previous, non-ionizing stellar populations.
Results.We attribute the increase of ${\Delta \log Q\rm (H^0)}$ with the age of the burst to the fact that more and more ionizing photons escape the nebulae when the nebulae get older, because of their increasing, expansion-induced subfragmentation.

Key words: galaxies: starburst -- galaxies: ISM -- ISM: HII regions -- line: formation

What is OpenURL?

The OpenURL standard is a protocol for transmission of metadata describing the resource that you wish to access. An OpenURL link contains article metadata and directs it to the OpenURL server of your choice. The OpenURL server can provide access to the resource and also offer complementary services (specific search engine, export of references...). The OpenURL link can be generated by different means.

If your librarian has set up your subscription with an OpenURL resolver, OpenURL links appear automatically on the abstract pages.
You can define your own OpenURL resolver with your EDPS Account. In this case your choice will be given priority over that of your library.
You can use an add-on for your browser (Firefox or I.E.) to display OpenURL links on a page (see http://www.openly.com/openurlref/). You should disable this module if you wish to use the OpenURL server that you or your library have defined.