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Astron. Astrophys. 315, L101-L104 (1996)

SWS spectroscopy of the colliding galaxies NGC4038/39*

D. Kunze1, D. Rigopoulou1, D. Lutz1, E. Egami1, H. Feuchtgruber1,2, R. Genzel1, H.W.W. Spoon1, E. Sturm1, A. Sternberg3, A.F.M. Moorwood4, and Th. de Graauw5

1 Max-Planck-Institut für Extraterrestrische Physik, Postfach 1603, D-85740 Garching, Germany
2 ISO Science Operations Centre, Astrophysics Division of ESA, Apdo. 50727, E-28080 Villafranca/Madrid, Spain
3 School of Physics and Astronomy and The Wise Observatory, Tel Aviv University, Tel Aviv 69978, Israel
4 European Southern Observatory, Karl-Schwarzschild-Str. 2, D-85748 Garching, Germany
5 Space Research Organization of the Netherlands and Kapteyn Institute, P.O. Box 800, 9700 AV Groningen, The Netherlands

Received 17 July 1996 / Accepted 13 August 1996

Abstract. We present mid-infrared spectroscopy of the prototypical interacting galaxies NGC 4038/39 (the `Antennae') obtained with the ISO Short Wavelength Spectrometer (SWS). Our observations focus on the interaction zone where the two galaxies overlap, providing new constraints on the properties of the young and vigorous extranuclear starburst triggered by the recent interaction of the two galaxies. We use hydrogen recombination lines to derive an extinction of img1.gif to the starburst region, concluding that a model where emitting gas and absorbing dust are mixed best fits the data. We discuss the use of mid-infrared fine structure line ratios for determining the average effective temperature of the stellar ionizing radiation field, and derive an average temperature of 44000K from the extinction-corrected [NeIII]15.6 img2.gifm/[NeII]12.8 img2.gifm line ratio. The observations are well described by starburst models for a recent starburst with an initial mass function extending up to 100 Mimg3.gif . Observations of the pure rotational (0-0) S(1) and S(2) lines of molecular hydrogen are used to constrain the fraction of molecular gas that is at temperatures of a few hundred Kelvin.

Key words: galaxies: starburst - galaxies: interactions - galaxies: individual: NGC 4038/39 - infrared: galaxies

* Based on observations made with ISO, an ESA project with instruments funded by ESA member states (especially the PI countries: France, Germany, the Netherlands and the United Kingdom) and with the participation of ISAS and NASA. The SWS is a joint project of SRON and MPE

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Last change: December 16, 1996
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