J. L. Bibby, P. A. Crowther
We present a narrow-band VLT/FORS1 imaging survey of the SAB(rs)cd spiral
galaxy NGC 5068, located at a distance of 5.45Mpc, from which 160 candidate
Wolf-Rayet sources have been identified, of which 59 cases possess
statistically significant 4686 excesses. Follow-up Gemini/GMOS spectroscopy of
64 candidates, representing 40% of the complete photometric catalogue, confirms
Wolf-Rayet signatures in 30 instances, corresponding to a 47% success rate. 21
out of 22 statistically significant photometric sources are spectroscopically
confirmed. Nebular emission detected in 30% of the Wolf-Rayet candidates
spectrally observed, which enable a re-assessment of the metallicity gradient
in NGC 5068. A central metallicity of log(O/H)+12 ~ 8.74 is obtained, declining
to 8.23 at R_25. We combine our spectroscopy with archival Halpha images of NGC
5068 to estimate a current star formation rate of 0.63(+0.11/-0.13)Msun/yr, and
provide a catalogue of the 28 brightest HII regions from our own continuum
subtracted Halpha images, of which ~17 qualify as giant HII regions.
Spectroscopically, we identify 24 WC and 18 WN-type Wolf-Rayet stars within 30
sources since emission line fluxes indicate multiple Wolf-Rayet stars in
several cases. We estimate an additional ~66 Wolf-Rayet stars from the
remaining photometric candidates, although sensitivity limits will lead to an
incomplete census of visually faint WN stars, from which we estimate a global
population of ~170 Wolf-Rayet stars. Based on the Halpha-derived O star
population of NGC 5068 and N(WR)/N(O)~0.03, representative of the LMC, we would
expect a larger Wolf-Rayet population of 270 stars. Finally, we have compared
the spatial distribution of spectroscopically confirmed WN and WC stars with
SDSS-derived supernovae, and find both WN and WC stars to be most consistent
with the parent population of Type Ib SNe.
View original:
http://arxiv.org/abs/1111.0958
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