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S. Kim, C. L. Martin, A. A. Stark, A. P. Lane (Smithsonian Astrophysical Observatory)
We present a map of the Galactic Center region in the CO J=7-6 transition observed with the Antarctic Submillimeter Telescope and Remote Observatory (AST/RO) located at Amundsen-Scott South Pole Station. Emission from the 809 GHz J=7-6 transition of 12CO was mapped over the region -2.7 < l < 3.6, -1.0 < b < 1.0, on a 1' grid with a spatial resolution of ~ 85''.
The CO J=4-3 and [CI] emissions from this region have been mapped with AST/RO by Martin et al. (2001) and Ojha et al. (2000). These two spectral lines are distributed throughout the Galactic Center region in a manner almost identical to that of CO J=1-0; the CO(4-3)/ CO(1-0) line ratio and the [CI]/CO line ratios are remarkably uniform across a wide variety of Galactic Center features. In contrast, the CO J=7-6 emission from the Galactic Center region is confined to the Sgr A and Sgr B2 complexes. The implication is that the photon-dominated regions surrounding the Galactic Center are remarkably similar in mean density and kinetic temperature at n = 3000 cm-3 and T = 35 K, except for the two special regions Sgr A and Sgr B2, which are denser.
The CO(7-6)/CO(4-3) line temperature ratios near Sgr B2 are similar to those observed in the nuclear region of the starburst galaxy M82 (Mao et al. 2000), while the CO(7-6)/CO(4-3) line temperature ratios around Sgr A are a factor of three lower than those near Sgr B2. The CO(7-6)/CO(4-3) line ratio in the Galactic Center region as a whole is at least an order of magnitude less than that in a comparable region near the center of M82.
This research was supported in part by the National Science Foundation under a cooperative agreement with the Center for Astrophysical Research in Antarctica (CARA), grant number NSF OPP 89-20223. CARA is a National Science Foundation Science and Technology Center.