Astronomy and Astrophysics – Astrophysics
Scientific paper
2006-02-27
Mon.Not.Roy.Astron.Soc.368:1822-1832,2006
Astronomy and Astrophysics
Astrophysics
12 pages, 8 figures, accepted for MNRAS (fixes previous error in Table 2)
Scientific paper
10.1111/j.1365-2966.2006.10245.x
We reinvestigate the massive stellar content of NGC3125 (Tol3) using VLT/FORS1 imaging & spectroscopy, plus archival VLT/ISAAC, HST/FOC and HST/STIS datasets. Narrow-band imaging confirms that A and B knots represent the primary sites of Wolf-Rayet (WR) stars, whilst HST imaging reveals that both regions host multiple clusters. Clusters A1 + A2 within region A host WR stars. altough is not clear which cluster within region B hosts WR stars. Nebular properties infer an LMC-like metallicity. LMC template WN5-6 & WC4 spectra are matched to the observed optical WR bumps of A1 and B, permitting the contribution of WC stars to the blue bump to be quantified. We obtain N(WN5-6:WC4)=105:20, 55:0, 40:20 for clusters A1, A2 and B1+B2, a factor of 3 lower than optical studies, as a result of a lower E(B-V). Using Starburst99 models to estimate O star populations for individual clusters, we find N(WR)/N(O)=0.2 for A1 and 0.1 for A2 and B1+B2. From Halpha imaging, the O star content of the Giant HII regions A and B is found to be a factor of 5-10 times higher than that derived spectroscopically for the UV/optically bright clusters, suggesting that NGC3125 hosts optically obscured young massive clusters, further supported by VLT/ISAAC K band imaging. Archival HST/STIS UV spectroscopy confirms the low E(B-V) towards A1, for which we have determined an SMC extinction law, in preference to an LMC or starburst law. We obtain N(WN5-6)=110 from the slit-loss corrected HeII 1640 line flux, in excellent agreement with optical result. However, this is a factor of 35 times lower than that inferred from the same dataset by Chandar et al. due to their use of a starburst extinction law. Highly discrepant stellar populations may result in spatially resolved star forming regions from UV and optical studies through use of different extinction laws.
Crowther Paul A.
Hadfield Lucy J.
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