Volume 485, Number 3, July III 2008
|Page(s)||657 - 677|
|Published online||15 May 2008|
Galaxies with Wolf-Rayet signatures in the low-redshift Universe*
A survey using the Sloan Digital Sky Survey
Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands e-mail: firstname.lastname@example.org
2 Centro de Astrofísica da Universidade do Porto, Rua das Estrelas S/N, 4150-762 Porto, Portugal
3 Institut d'Astrophysique de Paris, UMR 7095 CNRS, Université Pierre & Marie Curie, 98 bis boulevard Arago, 75014 Paris, France
Accepted: 10 April 2008
Context. The availability of large spectroscopic datasets has opened up the possibility of constructing large samples of rare objects in a systematic manner.
Aims. The goal of this study is to analyse the properties of galaxies showing Wolf-Rayet features in their optical spectrum using spectra from the Sloan Digital Sky Survey Release 6. With this unprecedentedly large sample we aim to constrain the properties of the Wolf-Rayet phase and its impact on the surrounding interstellar medium.
Methods. We carried out very careful continuum subtraction on all galaxies with equivalent widths of H Å in emission and identify Wolf-Rayet features using a mixture of automatic and visual classification. We combined this with spectroscopic and photometric information from the SDSS and derive metal abundances using a number of methods.
Results. We find a total of 570 galaxies with significant Wolf-Rayet (WR) features and a further 1115 potential candidates, several times more than even the largest heterogeneously assembled catalogues. We discuss in detail the properties of galaxies showing Wolf-Rayet features with a focus on their empirical properties. We are able to accurately quantify the incidence of Wolf-Rayet galaxies with metal abundance and show that the likelihood of otherwise similar galaxies showing Wolf-Rayet features increases with increasing metallicity, but that WR features are found in galaxies of a wide range in morphology. The large sample allows us to show explicitly that there are systematic differences in the metal abundances of WR and non-WR galaxies. The most striking result is that, below EW() = 100 Å, Wolf-Rayet galaxies show an elevated N/O relative to non-WR galaxies. We interpret this as a rapid enrichment of the ISM from WR winds. We also show that the model predictions for WR features strongly disagree with the observations at low metallicity; while they do agree quite well with the data at solar abundances. We discuss possible reasons for this and show that models incorporating binary evolution reproduce the low-metallicity results reasonably well. Finally we combine the WR sample with a sample of galaxies with nebular He ii to show that, at , the main sources of He ii ionising photons appears to be O stars, arguing for a less dense stellar wind at these metallicities, while at higher abundances WN stars might increasingly dominate the ionisation budget.
Key words: stars: Wolf-Rayet / galaxies: abundances / galaxies: evolution / galaxies: starburst / galaxies: fundamental parameters
© ESO, 2008
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.