A spectroscopic search for the non-nuclear Wolf-Rayet population of the metal-rich spiral galaxy M 83

¹ Department of Physics & Astronomy, University of Sheffield, Hicks Building, Hounsfield Rd, Sheffield, S3 7RH, UK e-mail: L.Hadfield@sheffield.ac.uk
² Institut für Astronomie, ETH-Zentrum, 8092 Zürich, Switzerland
³ Physikalisch-Meteorologisches Observatorium, 7260 Davos, Switzerland

Received: 27 October 2004
Accepted: 26 April 2005

Abstract

We present a catalogue of non-nuclear regions containing Wolf-Rayet stars in the metal-rich spiral galaxy M 83 (NGC 5236). From a total of 283 candidate regions identified using He ii λ4686 imaging with VLT-FORS2, Multi Object Spectroscopy of 198 regions was carried out, confirming 132 WR sources. From this sub-sample, an exceptional content of ~1035 ± 300 WR stars is inferred, with N(WC)/N(WN) ~ 1.2, continuing the trend to larger values at higher metallicity amongst Local Group galaxies, and greatly exceeding current evolutionary predictions at high metallicity. Late-type stars dominate the WC population of M 83, with N(WC8–9)/N(WC4–7) = 9 and WO subtypes absent, consistent with metallicity dependent WC winds. Equal numbers of late to early WN stars are observed, again in contrast to current evolutionary predictions. Several sources contain large numbers of WR stars. In particular, #74 (alias region 35 from de Vaucouleurs et al.) contains ~230 WR stars, and is identified as a Super Star Cluster from inspection of archival HST/ACS images. Omitting this starburst cluster would result in revised statistics of N(WC)/N(WN) ~ 1 and N(WC8–9)/N(WC4–7) ~ 6 for the “quiescent” disk population. Including recent results for the nucleus and accounting for incompleteness in our spectroscopic sample, we suspect the total WR population of M 83 may exceed 3000 stars.