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

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  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  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.