Ammonia absorption toward NGC 7538 IRS 1: 2 ARC second observations in the (3,3) line

Journal Article · Sun Jul 15 04:00:00 EDT 1984 · Astrophys. J., Lett. Ed.; (United States)

DOI:https://doi.org/10.1086/184313· OSTI ID:6176036

Henkel, C; Wilson, T L; Johnston, K J

Absorption from the (3,3) line of NH/sub 3/ has been detected at -60.0 km s/sup -1/ toward the ultracompact H II region IRS 1 in NGC 7538 with the VLA. In single-dish spectra, the line is blended with an emission component at -56.5 km s/sup -1/. With the 2.5 x 2.2 beam, however, line emission is resolved out. This corresponds to a spatial extent of more than 10''. The measured width of the absorption line is 8.5 km s/sup -1/ (FWHP). Accounting for the total optical depth of approximately 25 (estimated from hyperfine ratios), we obtain an intrinsic unsaturated line width of approximately 3.5 km s/sup -1/. The line shape appears not to be compatible with a single Gaussian-shaped velocity component of high optical depth. The molecular cloud covers at least 60% of the continuum source; this is approximately 1'', corresponding to 0.017 pc. From the line shape, the cloud may consist of several clumps of size less than 0.01 pc, each with a different radial velocity and smaller line width. In addition to the spectral line measurements, a 23.87 GHz continuum map of IRS 1, 2, 3 is presented. The electron density in IRS 1 is found to be roughly 2 x 10/sup 5/ cm/sup -3/. It is suggested that IRS 1 and IRS 2 may be similar objects at a different state of their evolution.

• Research Organization: Max-Planck-Institut fuer Radioastronomie, Bonn, Federal Republic of Germany
• OSTI ID: 6176036
• Journal Information: Astrophys. J., Lett. Ed.; (United States), Journal Name: Astrophys. J., Lett. Ed.; (United States) Vol. 282:2; ISSN AJLEA
• Country of Publication: United States
• Language: English

Related Subjects

640105* -- Astrophysics & Cosmology-- Galaxies
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ABSORPTION SPECTRA
AMMONIA
CHEMISTRY
COSMIC RADIO SOURCES
COSMOCHEMISTRY
ELECTROMAGNETIC RADIATION
ELECTRON DENSITY
ELECTRON TEMPERATURE
H2 REGIONS
HYDRIDES
HYDROGEN COMPOUNDS
INFRARED RADIATION
INTERSTELLAR SPACE
MICROWAVE SPECTRA
MOLECULES
NITROGEN COMPOUNDS
NITROGEN HYDRIDES
RADIAL VELOCITY
RADIATIONS
SPACE
SPECTRA
VELOCITY