The stellar content of the WR galaxy NGC5253 from ISOSWS spectroscopy

1. Why mid-IR spectroscopy of WR galaxies? Wolf-Rayet (WR) galaxies are a subset of blue emission-line galaxies whose spectra show the signature of large numbers of WR stars with ages in the range

The stellar content of the WR galaxy NGC5253 from ISO/SWS spectroscopy Paul A. Crowther Dept of Physics& Astronomy, UCL, Gower St. London, UK Sara C. Beck School of Physics& Astronomy, Tel Aviv University, Israel Allan J. Willis Dept of Physics& Astronomy, UCL, Gower St. London, UK Peter S. Conti JILA, University of Colorado, Boulder, CO 80309, USA Patrick W. Morris SRON, Sorbonnelaan 2, CA 3584 Utrecht, The Netherlands Ralph S. Sutherland MSSSO, ANU, Canberra, ACT 0200, Australia

1. Why mid-IR spectroscopy of WR galaxies? Wolf-Rayet (WR) galaxies are a subset of blue emission-line galaxies whose spectra show the signature of large numbers of WR stars with ages in the range 1{10 106 yr. Mid infra-red (IR) observations are well suited to the study of their hot, massive stars since this spectral region contains many ne-structure nebular lines which depend very sensitively on stellar content. The launch of the Infrared Space Observatory (ISO) has opened up this window, which we are exploiting through a Guest Observer program with the Short Wavelength Spectrometer (SWS), that includes NGC 5253, a nearby (4Mpc) WR galaxy. NGC 5253 contains several young super-star clusters, no older than a few million years and has been the focus of many recent studies which have shown that the extinction is very high and patchy in the UV and optical. ISO observations of NGC 5253 are particularly important since the interstellar extinction at mid-IR wavelengths is low and because of its remarkably hot and young stellar population.

2. Hot clusters embedded in cooler emission Our approach di ers from previous investigations in that we are able to distinguish between the regions in which di erent infrared ne-structure lines form, us1

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