VLA observations of OH in galaxies. I - NGC 253 and its nuclear plume

Details VLA observations of OH in galaxies. I - NGC 253 and its nuclear plume VLA observations of OH in galaxies. I - NGC 253 and its nuclear plume

Dec 1985

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1985apj...299..312t&link_type=abstract

Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 299, Dec. 1, 1985, p. 312-333.

Astronomy and Astrophysics

Astronomy

52

Galactic Nuclei, Galactic Radiation, Hydroxyl Emission, Interstellar Matter, Radio Astronomy, Absorbers (Materials), Astronomical Maps, Centimeter Waves, Ejecta, Plumes

Scientific paper

The distribution of emission and absorption has been mapped in all four 18 cm lines of OH in the nuclear regions of NGC 253, using the VLA with a resolution of 17.7 x 9.5 arcsec. A steep rotation curve is found over the inner 150 pc radius, yielding a nuclear mass of about 5 x 10 to the 8th solar mass, the same as found from IR observations. The absorb ing gas covers a range of 60-550 km/s, wider than seen optically or as yet in H I. Clumping of the absorbing gas implies individual entities about 20 pc in size, suggestive of giant molecular clouds in the Milky Way. The absorbing gas appears to be distributed in a toroid of mean radius 170 pc centered on the nucleus. Anomalous OH emission is observed in three of the four 18 cm lines in the form of a spectacular plume ejected from the nucleus, and extending 1.5 kpc above the equatorial plane. The plume has a dynamical lifetime of 7.6 million yr, over which a few percent of the total nuclear mass has been ejected into it. The relative intensities of the anomalous emission lines differ markedly from those of Milky Way OH masers, and have proved difficult to understand in terms of pumping models devised to explain various types of Milky Way OH masers. Pumping involving collisions, near-IR, or UV radiation are ruled out on grounds of inadequate rates. Only far-IR pumping has sufficient rate, and may also explain two of the three lines seen in emission.

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