Astronomy and Astrophysics – Astronomy
Scientific paper
Feb 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994apj...421..505u&link_type=abstract
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 421, no. 2, p. 505-516
Astronomy and Astrophysics
Astronomy
21
Carbon Monoxide, Emission Spectra, Galactic Nuclei, Gas Ionization, Interstellar Gas, Molecular Spectra, Radio Astronomy, Shock Heating, Astronomical Spectroscopy, Infrared Astronomy Satellite, Shock Waves, Submillimeter Waves
Scientific paper
We present observations of (12)CO J = 2 goes to emission in a 15 min x 15 min region around AFGL 5376 (l = 359.5 deg, b = 0.43 deg), an unusually warm (Tc = 100 K) and extended Infrared Astronomy Satellite (IRAS) source located near the Galactic center. The new spatial maps made with the Caltech Submillimeter Observatory (CSO) confirm that (1) there is a clear association of high-velocity CO emission with the infrared source-the CO emission nearly completely surrounds the infrared peak at a radius of about 4 min, and (2) AFGL 5376 defines the most prominent portion of a strong (approximately 50 km/s), large-scale (90 pc) shock front. Contour maps produced from the Bell Labs (12)CO J = 1 goes to 0 Galactic center database are also presented; they show that the forbidden velocity emission surrounding AFGL 5376 forms a well-defined tongue of gas that extends perpendicularly from the Galactic plane out to b approximately 0.9 deg. The shape and location of the CO tongue lead us to suggest that it is the molecular counterpart of the western limb of a prominent radio continuum feature, the Galactic center lobe (GCL). Its total H2 mass is approximately 106 solar mass. The distributions of relatively low velocity (50-115 km/s) and high velocity (115-160 km/s) gas are separated across a remarkably well defined and narrow fit which extends latitudinally through the CO tongue for about 0.6 deg (about 90 pc, assuming dgc = 8.5 kpc), making it perhaps the largest continuous shock observed near the Galactic center. We hypothesize that the rift bisecting the western edge of the GCL marks the location where a system of gas in noncircular motion about the Galactic center is colliding with ambient material above the Galactic plane. The absence of CO emission directly toward the peak of AFGL 5376 and along other portions of the shock front is attributed to the shock-induced dissociation or heating of CO; only the shock-heated dust grains have survived to manifest themselves as the infrared source AFGL 5376. The western edge of the radio continuum GCL is evidence of shock ionization along a line parallel to the dissociation front. The noncircular gas motions characterizing the gas associated with AFGL 5376 are linked to the large-scale kinematical feature known as the expanding molecular ring (EMR). The observations presented here are used to contrast compeing theories for the EMR: an explosion-induced ring of expanding gas versus the reaction or orbiting gas to a bar potential.
Bally John
Morris Mark R.
Serabyn Eugen
Uchida Keven Isao
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