Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992aas...181.9305m&link_type=abstract
American Astronomical Society, 181st AAS Meeting, #93.05; Bulletin of the American Astronomical Society, Vol. 24, p.1268
Astronomy and Astrophysics
Astronomy
1
Scientific paper
We have mapped the 158 microns [CII] line in the low metallicity galaxies IC10 and LMC and in the normal metallicity galaxies NGC 6946, NGC 891, M83 and Cen A using the MPE-UCB Far-infrared Imaging Fabry-Perot Interferometer (FIFI) on the Kuiper Airborne Observatory (KAO). The peak [CII] emission arising from the nuclear regions we attribute to dense (n_H>=10(3) cm(-3) ) PDRs as seen in previous [CII] surveys of extragalactic nuclei. We find the [CII] emission to be extended in the galaxies, beyond the optical and molecular components and interpret this extended, low brightness [CII] component as originating in the diffuse atomic medium, representing the first detection of far-infrared line emission from atomic interstellar gas. We analyze the [CII] emission in the extended regions of the normal metallicity galaxies and find that the [CII] emission probably originates mainly in cold (T ~ 100 K), neutral atomic hydrogen clouds having pressures between 6.0times 10(3) and 1.0times 10(4) cm(-3) K, similar to HI clouds in our Galaxy. We find that low density HII regions can also contribute up to 50% to the observed [CII] emission. Hot (T ~ 8000K) diffuse HI gas can only significantly contribute to the observed [CII] emission if it is clumped with a filling factor of about 10%, thereby violating the concept of pressure equilibrium, or has a high ionization fraction (>10%). In the low metallicity galaxies we find [CII] to CO ratios enhanced relative to ratios observed in star formation regions in our Galaxy. Photodissociation regions constitute a much larger fraction of the mass of these galaxies compared to our Galaxy. This can be explained by low metallicity effects: increased penetration depth of UV photons into the molecular gas leads to smaller CO emitting regions while the C(+) is not affected much since the lower carbon abundance is compensated by greater photodissociated layers.
Geis Norbert
Genzel Reinhard
Herrmann Fabian
Madden Suzanne C.
Poglitsch Albrecht
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