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

Abstract

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  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.

Do Wolf-Rayet stars have similar locations in hosts as type Ib/c supernovae and long gamma-ray bursts?

“…Hadfield et al (2005) and Hadfield & Crowther (2007) give estimates for the numbers or WR stars contained in each region, as well as for the corresponding errors. The number of stars per region is simply taken into account by, e.g., including the fractional flux value of the pixel that hosts 5 WR stars 5 times in the corresponding distribution.…”

“…Their spectral type (WN, WC, early, late) is determined, and the number of WR stars is estimated by fitting template spectra to the flux-calibrated, integrated spectrum of the WR-star region. By excluding galaxies where the survey did not cover the entire galaxy (Schild et al 2003;Hadfield & Crowther 2006), we decided to rely on the following two galaxies: M 83 (Hadfield et al 2005) and NGC 1313 (Hadfield & Crowther 2007). …”

“…To study how the errors in the number of WR stars can affect the results above, we have followed an MC approach. Multiple realizations of the distributions were generated where the numbers of WR stars per region were drawn randomly from Gaussian distributions with the mean and standard deviation specified by the number of WR stars and the associated errors provided by Hadfield et al (2005). While this causes the p-values to fluctuate around their central values in Table 3, none of the qualitative conclusions above are affected.…”

Studying the YMC population of M83: how long clusters remain embedded, their interaction with the ISM and implications for GC formation theories

“…Bastian et al (2006) previously used the same technique to age date clusters in the Antennae galaxies. Hadfield et al (2005) carried out a survey searching for WR stars in regions within M83, discovering 132 sources. We crossreferenced the coordinates of the regions they identified as containing these objects with the coordinates of our cluster sample, examining images of the position of the features to confirm that the features originated from the cluster.…”

Massive Stars in the Nuclei and Arms of Spirals

“…A clear example of the effect of metallicity on the W-R star content is given by Hadfield et al (2005), who detected W-R features in a large fraction of H ii regions in M83, a nearby metal-rich galaxy (Bresolin & Kennicutt 2002), with WC8-9 stars being the dominant types. The WC/WN number ratio has been shown by many authors to increase with gas-phase metallicity (see Crowther 2007 for a recent review), in rough agreement with predictions by Eldridge & Vink (2006).…”