Letter to the Editor

An exceptional population of late-type WC stars in the metal-rich spiral galaxy M 83^*

¹ Department of Physics and Astronomy, University of Sheffield, Hicks Building, Hounsfield Rd, Shefffield, S3 7RH, UK
² Institut für Astronomie, ETH-Zentrum, 8092 Zürich, Switzerland
³ Physikalisch-Meteorologisches Observatorium, 7260 Davos, Switzerland

Corresponding author: P. A. Crowther, Paul.Crowther@sheffield.ac.uk

Received: 27 February 2004
Accepted: 4 April 2004

Abstract

We have surveyed the metal-rich spiral galaxy M 83 (NGC 5236) for its Wolf-Rayet population using VLT-FORS2 narrow-band imaging and follow-up spectroscopy. From a total of 280 candidates identified using He ii λ4686 imaging, Multi Object Spectroscopy of 198 sources was carried out, revealing 132 objects containing bona-fide Wolf-Rayet features. From this sample, an exceptional W-R content of ~1030 is inferred, with N(WC)/N(WN) ~ 1.3, continuing the trend to larger values at higher metallicity amongst Local Group galaxies. More dramatic is the dominance of late-type WC stars in M 83 with N(WC8-9)/N(WC4-7) = 9 which we attribute to the sensitivity of the classification line C iii λ5696 to mass-loss, providing the strength of WC winds scale with metallicity. One young massive compact cluster, #74 in our catalogue, hosts 20% of the entire galactic population, namely ~180 late WC stars and ~50 late WN stars.