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For refcode 1996A&A...315L.145V:
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Copyright by European Southern Observatory (ESO). Reproduced by permission
1996A&A...315L.145V The SWS survey for rotational H2 lines in late-type galaxies. Observations of the central regions of NGC 6946. Valentijn E.A., van der Werf P.P., de Graauw T., de Jong T. Space Research Organization of The Netherlands P. O. Box 800, 9700 AV Groningen, The Netherlands Leiden Observatory, P. O. Box 9513, 2300 RA Leiden, The Netherlands Astronomical Institute "Anton Pannekoek", Kruislaan 403,1098 SJ Amsterdam, The Netherlands Received 15 July 1996/Accepted 6 August 1996 Abstract. We report the first extragalactic detection of the pure rotational H_2_ S(0) and S(1) lines at 28.2 and 17.0 microns in the central 130 pc molecular complex of the nearby Scd galaxy NGC 6946. We deduce a temperature of this gas component of 170K and a mass of 5 x 10^6^M_sun for an ortho/para ratio of 3, corresponding to the ratio of statistical weights. The warm gas is confined to a ~5" (135pc) diameter region where a moderate nuclear starburst accounts for the elevated temperature. Depending on the assumed CO/H_2_ conversion factor, the warm component contains of the order of 5-10% (with formal lower and upper limits of 2 and 20%) of the total molecular mass in this region. CO data had indicated the presence of this warm gas, but did not provide a mass measurement. The ISO results can fully account for the warm component indicated by the CO data. The CO/H_2_ conversion factor for the 12_CO_ J=1-0 line is not strongly affected by the presence of the warm component. Keywords: galaxies: individual: NGC 6946 - galaxies: ISM
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