Astron. Astrophys. 315, L125-L128 (1996)
SWS spectroscopy of the starburst galaxy NGC 3256*
D. Rigopoulou1, D. Lutz1, R. Genzel1, E. Egami1, D. Kunze1, E. Sturm1, H. Feuchtgruber1,2, S. Schaeidt1,2, O.H. Bauer1, A. Sternberg3, H. Netzer3, A.F.M. Moorwood4, and Th. de Graauw5
1 Max-Planck-Institut fuer Extraterrestrische Physik,
Postfach 1603, D-85740 Garching bei München, Germany
Received 17 July 1996 / Accepted 13 August 1996
Abstract. We present 2.5-40 m ISO SWS spectra of the starburst galaxy NGC 3256. We have observed many fine-structure lines of various atomic species as well as three rotational transitions of molecular hydrogen. From the [SIII] 18 m/33 m line ratio we infer low electron densities of 300 cm-3 in the HII regions. The observed [NeIII]/[NeII] (15 m/12 m), [ArIII]/[ArII] (8.9 m/6.9 m), and [SIV]/[SIII] (10.5 m/18.7 m) line ratios are consistent with an ionizing radiation field with an effective temperature of 41000 K. Comparison of the observed fine-structure line ratios with theoretical models of nebular emission from evolving starbursts shows that stars with masses 50 M have been forming recently in NGC 3256. The H2 observations reveal the presence of warm molecular gas. We estimate that 109 M of H2 gas is present at temperatures close to 150 K. This mass corresponds to a few percent of the total cold molecular mass as estimated from CO studies.
Key words: galaxies: individual (NGC 3256) - galaxies: interactions - galaxies: starburst - infrared: galaxies
* Based on observations 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.
Last change: December 16, 1996