Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992aas...181.4009l&link_type=abstract
American Astronomical Society, 181st AAS Meeting, #40.09; Bulletin of the American Astronomical Society, Vol. 24, p.1182
Astronomy and Astrophysics
Astronomy
Scientific paper
We present results from a recently completed survey of fine-structure lines, [C\II.] 158 microns, [O\I.] 63 microns, [Si\II.] 35 microns, [S\III.] 19, 33 microns, and [O\III.] 52, 88 microns in galaxies. The galaxies span a wide range of morphologies (irregular to grand design), have varying metalicities, and include mergers, AGNs, and many starburst systems. The observations were made beginning in 1987 with the facility Cooled Grating Spectrometer onboard the Kuiper Airborne Observatory at a typical resolution of ~ 80-170 km/s and with a 35-42'' beam. One or more of these lines was detected in each of the galaxies. The [O\I.] line was detected in eight galaxies, the [Si\II.] line was detected in ten. We interpret the [C\II.] and [O\I.] fluxes, along with previous measurements of the IR continuum fluxes, in the context of photodissociation region (PDR) models (Tielens & Hollenbach 1985; Wolfire et al. 1990). With these models, we obtain estimates of the typical interstellar UV field incident on the line emitting regions (10(2) --10(3) times the local interstellar radiation field) and the total mass (10(7) --10(8) M_{mathordsun }), density (10(3) --10(4) cm(-3) ), and temperature (100--200 K) of the warm atomic gas. The [O\III.] and [S\III.] line flux ratios constrain the densities and elemental abundances within the H\II. regions of these galactic nuclei, and provide estimates of the effective temperature of the ionizing stars. Such measurements imply gas pressures of nT ~ 10(6) cm(-3) K and a typical cutoff to the upper mass limit of the IMF of about 20 M_{mathordsun }. The [C\II.]/[Si\II.] ratio is generally comparable to that seen in M82, sugesting that [Si\II.] emission is uniformly strong. One explanation is that silicon is relatively undepleted in these galaxies and [Si\II.] emission originates in H\II. regions. The low-metalicity systems show high [CII]/CO and [OI]/CO flux ratios, 3-5 times the Milky Way value, indicating that they contain a larger fraction of photodissociated gas. A search in two AGNs for [O\IV.] 26 microns and [Ne\V.] 24 microns emission from regions of high ionization yielded only upper limits. Finally, we report observations of M82 that have yielded the first extragalactic detection of the PDR cooling line [Fe\II.] 26 microns.
Carral Patricia
Colgan Sean J. W.
Erickson Edwin F.
Haas Michael R.
Hollenbach David J.
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