AST/RO Observations of CO J = 7 → 6 and J = 4 → 3 Emission toward the Galactic Center Region

• Main Authors: Sunguen Kim, Christopher L. Martin, Antony A. Stark, Adair P. Lane
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 2002
• Subjects: Subject headings; Galaxy; abundances — Galaxy; center — ISM; general —; Antarctic; The Antarctic; South Pole; Amundsen-Scott; Amundsen Scott South Pole Station; Amundsen-Scott South Pole Station; Antarc*; South pole
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.338.2835; http://arxiv.org/pdf/astro-ph/0207586v1.pdf

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 (AST/RO) located at Amundsen-Scott South Pole Station. Emission from the two rotational transitions of 12CO was mapped at b = 0 ◦ for 3.5 ◦> ℓ> −1.5 ◦ , on a 1 ′ grid with a FWHM beamsize of 58 ′ ′ at 806 GHz and 105 ′ ′ at 461 GHz. Previous observations of CO J = 4 → 3 (Martin et al., in preparation) and [CI] (Ojha et al. 2001) emission from this region show that these lines are distributed in a manner similar to CO J = 1 → 0 (Stark et al. 1987); 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 (LVG) 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 to 4000 cm−3 and T = 30 to 45 K. The (CO J = 7 → 6)/(CO J = 4 → 3) line temperature ratios near Sgr B are a factor of two higher than those observed in the nuclear region of the starburst galaxy M82 (Mao et al. 2000), 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.