Antarctic Submillimeter Telescope and Remote Observatory observations of CO J=7 -> 6 and J=4 -> 3 emission toward the Galactic center region

作者：Kim S^*; Martin CL; Stark AA; Lane AP

来源：Astrophysical Journal, 2002, 580(2): 896-903.

DOI：10.1086/343842

• Galaxy : abundances
• Galaxy : center
• ISM : general
• ISM : molecules
• submillimeter

We present position-velocity strip maps of the Galactic center region in the CO J = 7 --> 6 and J = 4 --> 3 transitions observed with the Antarctic Submillimeter Telescope and Remote Observatory located at the Amundsen-Scott South Pole Station. Emission from the two rotational transitions of (CO)-C-12 was mapped at b = 0degrees for 3.degrees5 > l > -1.degrees5 on a 1' grid with a FWHM beam size of 58" at 806 GHz and 105" at 461 GHz. Previous observations of CO J = 4 --> 3 (C. L. Martin et al., in preparation) and of [C I] emission (Ojha et al.) from this region show that these lines are distributed in a manner similar to CO J = 1 --> 0 (Stark et al.); the (CO J = 4 -->3)/(CO J = 1 --> 0) line ratio map is almost featureless across the entire Galactic center region. In contrast, the CO J = 7 --> 6 emission from the Galactic center is strongly peaked toward the Sgr A and Sgr B molecular complexes. A large velocity gradient analysis shows that, aside from the two special regions Sgr A and Sgr B, the photon-dominated regions within a few hundred parsecs of the Galactic center are remarkably uniform in mean density and kinetic temperature at n = 2500-4000 cm(-3) and T = 30-45 K. The (CO J = 7 --> 6)/(CO J = 4 --> 3) line temperature ratios near Sgr B are a factor of 2 higher than those observed in the nuclear region of the starburst galaxy M82 (Mao et al.), while the CO(J = 7 --> 6)/CO(J = 4 --> 3) line temperature ratios around Sgr A are similar to M82. The line ratio on large scales from the Galactic center region is an order of magnitude less than that from M82.

• 出版日期2002-12-1