A ROSAT survey of Wolf-Rayet galaxies

Astronomy and Astrophysics – Astronomy

Scientific paper

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Starburst Galaxies, Sky Surveys (Astronomy), Rosat Mission, X Ray Sources, Cosmic X Rays, Proportional Counters, Dwarf Galaxies, X Ray Stars

Scientific paper

We present results from a ROSAT Position Sensitive Proportional Counter (PSPC) survey of the X-ray emission from Wolf-Rayet (WR) galaxies. Of the 36 WR galaxies listed in the catalogue of Conti, a total of 14 have been observed deliberately or serendipitously with the ROSAT PSPC, and of these, seven have been detected. The derived X-ray luminosities of WR galaxies range over nearly three orders of magnitude. The X-ray spectra of the WR galaxies can typically be well-fitted with a single temperature Raymond-Smith spectral model, with a temperature in the range kT = 0.3-1.0 keV, with the general trend that the more X-ray-luminous WR galaxies have hotter spectra. WR galaxies are significantly X-ray-overluminous for their blue luminosity, compared with a sample of nearby spiral and starburst galaxies. In addition, the X-ray luminosity of WR galaxies correlates well with the FIR luminosity and the number of Lyman continuum photons. No strong correlation was found with the equivalent width of the WR emission feature around 4686 A the presence of which essentially defines the class of galaxies. Various explanations for the observed properties of WR galaxies are explored, and we conclude that the X-ray emission provides strong evidence that a large fraction of the observed X-rays is coming from a hot superbubble formed by the combined action of stellar winds from massive early-type stars in the central starburst cluster. These results are consistent with, and add weight to, the view that WR galaxies are young starbursts, in which the duration of the star-forming epoch was very short, and that we are viewing them a few Myr after the initiation of the starburst. As such, WR galaxies represent an important epoch in the evolution of starburst galaxies.

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