Other
Scientific paper
Dec 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999aas...195.5310d&link_type=abstract
American Astronomical Society, 195th AAS Meeting, #53.10; Bulletin of the American Astronomical Society, Vol. 31, p.1455
Other
Scientific paper
We report observations with the Infrared Space Observatory's Long Wavelength Spectrometer (LWS) of several positions in the disk of the luminous nearby Sc galaxy M 101 (NGC 5457), including the galaxy nucleus and three giant spiral-arm H II regions: NGC 5447, NGC 5461, and NGC 5471. These H II regions span nearly a factor of three in galactocentric distance in a galaxy which is well known for its prominent radial abundance gradient. The emission contained with the 75" ISO LWS beam at positions centered on the giant H II regions is dominated by their emission plus that of the associated photodissociation regions and giant molecular clouds, with little contribution from extended diffuse disk emission. Both the [C II] 158 μ m and [O I] 63 μ m lines are detected from all three H II regions and the galaxy nucleus; [O III] 88 μ m is detected in NGC 5447 and 5461, with [N II] 122 μ m marginally detected or below our detection limit. The [C II]/[O I] line ratios are indicative of warm, dense gas, as expected if the fine-structure lines originate from the photodissociated surfaces of giant molecular clouds in these active star-forming regions. The power in the [C II] and [O I] lines relative to the infrared continuum is consistent with grain photoelectric heating of photodissociation regions. These two diagnostic ratios do not appear to correlate strongly with metallicity within our limited sample. We also examine ratios of the far-infrared lines with other measured properties of the H II regions such as CO emission; some of these ratios, for example, [C II]/CO, are expected to be sensitive to metallicity effects. This research was supported by NASA through data analysis grants to the ISO Key Project Team on ``The Interstellar Medium of Normal Galaxies'' and subcontracts to the institutions of the Co-Investigators.
Brauher James
Dale Daniel
Dinerstein Harriet L.
Helou George
Hollenbach David
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