A survey of the Wolf-Rayet population of the barred, spiral galaxy NGC 1313

TL;DR

This survey of NGC 1313 identifies at least 84 Wolf-Rayet stars, including rare types, and provides insights into the galaxy's star formation rate and metallicity, expanding knowledge of WR populations in spiral galaxies.

Contribution

First comprehensive spectroscopic survey of WR stars in NGC 1313, identifying a diverse population including rare WN/C and WO types, and estimating the total WR count and properties.

Findings

Confirmed 70 WR stars spectroscopically

Detected a WO star beyond the Local Group

Estimated a total WR population of ~115 stars

Abstract

We present a VLT/FORS1 survey of Wolf-Rayet (WR) stars in the spiral galaxy NGC 1313. In total, 94 WR candidate sources have been identified from narrow-band imaging. Of these, 82 have been spectroscopically observed, for which WR emission features are confirmed in 70 cases, one of which also exhibits strong nebular HeII 4686 emission. We also detect strong nebular HeII 4686 emission within two other regions of NGC 1313, one of which is a possible supernova remnant. Nebular properties confirm that NGC 1313 has a metal-content log(O/H)+12=8.23+/-0.06, in good agreement with previous studies. From continuum subtracted Halpha images we infer a global star formation rate of 0.6 Msun/yr. Using template LMC WR stars, spectroscopy reveals that NGC 1313 hosts a minimum of 84 WR stars. Our census comprises 51 WN stars, including a rare WN/C transition star plus 32 WC stars. In addition, we identify one WO star which represents the first such case identified beyond the Local Group. The bright giant HII region PES 1, comparable in Halpha luminosity to NGC 595 in M 33, is found to host a minimum of 17 WR stars. The remaining photometric candidates generally display photometric properties consistent with WN stars, such that we expect a global WR population of ~115 stars with N(WR)/N(O)~0.01 and N(WC)/N(WN)~0.4.