SWS Spectroscopy of the Starburst Galaxy NGC 3256

D. Rigopoulou - D. Lutz - R. Genzel - E. Egami - D. Kunze - E. Sturm - H. Feuchtgruber - S. Schaeidt - O.H. Bauer - A. Sternberg - H. Netzer - A.F.M. Moorwood - Th. de Graauw

Abstract:

We present 2.5-40 tex2html_wrap_inline276 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 tex2html_wrap_inline276 m/33 tex2html_wrap_inline276 m line ratio we infer low electron densities of tex2html_wrap_inline284 300 cm-3 in the HII regions. The observed [NeIII]/[NeII] (15 tex2html_wrap_inline276 m/12 tex2html_wrap_inline276 m), [ArIII]/[ArII] (8.9 tex2html_wrap_inline276 m/6.9 tex2html_wrap_inline276 m), and [SIV]/[SIII] (10.5 tex2html_wrap_inline276 m/18.7 tex2html_wrap_inline276 m) line ratios are consistent with an ionizing radiation field with an effective temperature of tex2html_wrap_inline284 41000 K. Comparison of the observed fine-structure line ratios with theoretical models of nebular emission from evolving starbursts shows that stars with masses tex2html_wrap_inline314 50 M tex2html_wrap_inline316 have been forming recently in NGC 3256. The H tex2html_wrap_inline274 observations reveal the presence of warm molecular gas. We estimate that tex2html_wrap_inline284 109 M tex2html_wrap_inline316 of H tex2html_wrap_inline274 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.

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