Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 1986
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1986aj.....91..107c&link_type=abstract
Astronomical Journal (ISSN 0004-6256), vol. 91, Jan. 1986, p. 107-112. Research supported by the National Astronomy and Ionosphe
Astronomy and Astrophysics
Astronomy
12
Absorption Spectra, Extragalactic Radio Sources, Formaldehyde, Molecular Clouds, Abundance, Interstellar Gas, Optical Thickness, Radial Velocity, Spectral Line Width
Scientific paper
Absorption by galactic H2CO has been observed with the λ6 cm system at Arecibo towards the extragalactic sources 3C 123 and 3C 154. Towards 3C 123, which lies behind part of the Taurus cloud complex, there is both a broad and a remarkably narrow spectral component. The narrow component is at a velocity of 4.40 km s-1. It has a fitted width of only 0.12 km s-1. There is no evidence for H2CO at a velocity of 5.5 km s-1, where other molecules have been observed. A VLA synthesis map of the H2CO absorption has been obtained towards 3C 123. This map shows that the optical depth across 3C 123 varies less than 15% on angular scales of 3arcsec - 20arcsec. At the estimated distance of the molecular cloud, these correspond to 0.003 - 0.02 pc. The velocity peak and width are constant to 0.15 km s-1 over the extent of 3C 123. Upper limits are given for H2CO absorption towards 3C 75, 3C 138, 3C 348, 3C 390, 3C 410, and 3C 454.3.
Colgan Sean J. W.
Salpeter Edwin E.
Terzian Ye.
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