A Very Large Telescope imaging and spectroscopic survey of the Wolf-Rayet population in NGC 7793

作者：Bibby J L^*; Crowther P A

来源：Monthly Notices of the Royal Astronomical Society, 2010, 405(4): 2737-2753.

DOI：10.1111/j.1365-2966.2010.16659.x

• stars: Wolf-Rayet
• ISM: H ii regions
• galaxies: individual: NGC 7793
• galaxies: stellar content
• galaxies: ISM

We present a Very Large Telescope/Focal Reducer and Low Dispersion Spectrograph #1 (VLT/FORS1) imaging and spectroscopic survey of the Wolf-Rayet (WR) population in the Sculptor group spiral galaxy NGC 7793. We identify 74 emission-line candidates from archival narrow-band imaging, from which 39 were observed with the Multi Object Spectroscopy mode of FORS1. 85 per cent of these sources displayed WR features. Additional slits were used to observe H ii regions, enabling an estimate of the metallicity gradient of NGC 7793 using strong line calibrations, from which a central oxygen content of log (O/H) + 12 = 8.6 was obtained, falling to 8.25 at R-25. We have estimated WR populations using a calibration of line luminosities of Large Magellanic Cloud stars, revealing similar to 27 WN and similar to 25 WC stars from 29 sources spectroscopically observed. Photometric properties of the remaining candidates suggest an additional similar to 27 WN and similar to 8 WC stars. A comparison with the WR census of the LMC suggests that our imaging survey has identified similar to 80 per cent of WN stars and similar to 90 per cent for the WC subclass. Allowing for incompleteness, NGC 7793 hosts similar to 105 WR stars for which N(WC)/N(WN) similar to 0.5. From our spectroscopy of H ii regions in NGC 7793, we revise the global H alpha star formation rate of Kennicutt et al. upward by 50 per cent to 0.45 M-circle dot yr-1. This allows us to obtain N(WR)/N(O) similar to 0.018, which is somewhat lower than that resulting from the WR census by Schild et al. of another Sculptor group spiral NGC 300, whose global physical properties are similar to NGC 7793. Finally, we also report the fortuitous detection of a bright (m(V) = 20.8 mag) background quasar Q2358-32 at z similar to 2.02 resulting from C iv lambda 1548-51 redshifted to the lambda 4684 passband.

• 出版日期2010-7-11