Journal Article

A <i>ROSAT</i> survey of Wolf—Rayet galaxies

Ian R. Stevens and David K. Strickland

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 294, issue 4, pages 523-547
Published in print March 1998 | ISSN: 0035-8711
Published online March 1998 | e-ISSN: 1365-2966 | DOI:
A ROSAT survey of Wolf—Rayet galaxies

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We present results from a ROSAT Position Sensitive Proportional Counter (PSPC) survey of the X-ray emission from Wolf-Rayet (WR) galaxies, a class of galaxies believed to be young starbursts (with ages of t∼4–6 Myr), many of which are blue compact dwarf 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, from LX∼4×1038 s−1 to 2 × 1041 erg s−1. 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 far-infrared luminosity Lfir and the number of Lyman continuum photons NLyc. No strong correlation was found with the equivalent width of the WR emission feature around λ4686 Å, the presence of which essentially defines the class of galaxies. There is little evidence of extended X-ray emission.

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 are 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.

Keywords: stars: Wolf-Rayet; ISM: jets and outflows; galaxies: starburst; galaxies: stellar content; X-rays: galaxies

Journal Article.  0 words. 

Subjects: Astronomy and Astrophysics

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