The Tokyo-Onsala-ESO-Calán Galactic CO J=2-1 Survey. I. The Galactic Center Region

Details The Tokyo-Onsala-ESO-Calán Galactic CO J=2-1 Survey. I. The Galactic Center Region The Tokyo-Onsala-ESO-Calán Galactic CO J=2-1 Survey. I. The Galactic Center Region

Sep 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001apjs..136..189s&link_type=abstract

The Astrophysical Journal Supplement Series, Volume 136, Issue 1, pp. 189-219.

Astronomy and Astrophysics

Astronomy

34

Galaxy: Center, Ism: Clouds, Ism: Molecules, Radio Lines: Ism, Surveys

Scientific paper

As a part of the Tokyo-Onsala-ESO-Calán Galactic CO survey, we have made large-scale mapping observations of the Galactic center in the CO J=2-1 line using the 60 cm survey telescope in Chile. The data were taken with the same beam size (9') and sampling grid (7.5′) as the CO J=1-0 Columbia survey, so that the two data sets can be compared directly. Velocity channel maps and longitude-velocity diagrams of the 12CO J=2-1 line, covering -6deg<=l<=6deg, -2deg<=b<=2deg, -300<=vLSR<=300 km s-1, are presented, along with the corresponding maps of the 12CO J=2-1/J=1-0 intensity ratio [R2-1/1-0(12CO)]. A longitude-velocity diagram of the 13CO J=2-1 line intensity and corresponding 13CO J=2-1/12CO J=2-1 intensity ratio [R13/12(J=2-1)] is also presented at b=0deg. The overall R2-1/1-0(12CO) in the central 900 pc of the Galaxy is 0.96+/-0.01, which is higher than the typical value in the Galactic disk, 0.6-0.7. The isotopic intensity ratio R13/12(J=2-1) is 0.10+/-0.01. The two observed intensity ratios [R2-1/1-0(12CO) and R13/12(J=2-1)] indicate that the optical depth of the 12CO J=1-0 line is ~1 or smaller in the Galactic center molecular clouds, much smaller than those of the giant molecular clouds (GMCs) in the Galactic disk. Longitude-velocity distributions of physical properties of molecular gas are derived using a large velocity gradient analysis. Molecular gas in the Galactic center generally shows a high pressure. In particular, there is a high-pressure region in the central ~100 pc where the pressure is an order of magnitude higher than that in GMCs in the Galactic disk. This region is dominated by high-density gas and contains star-forming regions.

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