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Wolf Rayet (W-R) Galaxies


Wolf-Rayet (W-R) Galaxies

Wolf-Rayet (W-R) galaxies are a subset of H II galaxies with broad emission lines that are characteristic of W-R stars . Outside the local universe, the broad feature usually detected in W-R galaxies is the so-called W-R bump, a blend of He II and other lines from C III and from N III and N V. Among about 90 known W-R galaxies , a strong feature from WC stars. Indeed, from the current knowledge of stellar evolution, one would expect to detect WC stellar population in about one-third of all W-R galaxies with a metallicity of 0.2–1 . The deficiency of such detection might be caused by the weakness of C IV λ5808 emission, as compared with the W-R bump. Alternatively, uncertainties in our knowledge of the evolution of massive stars could be responsible for such an apparent deficiency. For example, the recent discovery of W-R stars in I Zw 18 seems to indicate enhanced mass-loss rates. These uncertainties also complicate derivations of the upper end of the initial mass function (IMF), which is a fundamental parameter in studies of W-R galaxies . For example, Contini, Davoust, & Considère (1995) report the observations of a new W-R galaxy, Mrk 712, which may require a flat IMF (Contini et al. 1995). Extending the sample of W-R galaxies and studying both their WN and WC content is therefore very useful to constrain the evolution of massive stars and study the process of star formation in starbursts.

We report the discovery of two new W-R galaxies from our systematic search for W-R galaxies. One of them, Mrk 1039, was reported with a classification as an H II galaxy, but the presence of broad emission lines in their spectra was not noticed (de Grijp et al. 1992). W-R signatures were also found in Mrk 35 (Haro 3), previously studied by Steel et al. (1996). However, we observed this source in a different slit position, obtaining different W-R features from those of Steel et al.

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