The SWS survey for rotational H2 lines in late-type galaxies
نویسندگان
چکیده
We report the first extragalactic detection of the pure rotational H2 S(0) and S(1) lines at 28.2 and 17.0 m in the central 130 pc molecular complex of the nearby Scd galaxy NGC 6946. We deduce a temperature of this gas component of 170 K and a mass of 5 106 M for an ortho/para ratio of 3, corresponding to the ratio of statistical weights. The warm gas is confined to a 500 (135 pc) diameter region where a moderate nuclear starburst accounts for the elevated temperature. Depending on the assumed CO/H2 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/H2 conversion factor for the 12CO J = 1!0 line is not strongly affected by the presence of the warm component.
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