The AST/RO survey of the galactic center region. I. The inner 3 degrees

We present fully sampled maps of 461 GHz CO J = 4 → 3, 807 GHz CO J = 7 → 6, and 492 GHz [C _I] ³P ₁ → ³P ₀ emission from the inner 3 degrees of the Galactic center region taken with the Antarctic Submillimeter Telescope and Remote Observatory (AST/RO) in 2001-2002. The data cover -1°.3 < l < 2°, -0°.3 < b < 0°.2 with 0.′5 spacing, resulting in spectra in three transitions at over 24,000 positions on the sky. The CO J = 4 → 3 emission is found to be essentially coextensive with lower J transitions of CO. The CO J = 7 → 6 emission is spatially confined to a far smaller region than the lower J CO lines. The [C _I] ³P ₁ → ³P ₀ emission has a spatial extent similar to the low-J CO emission but is more diffuse. Bright CO J = 7 → 6 emission is detected in the well-known Galactic center clouds Sgr A and Sgr B. We also detect CO J = 4 → 3 and CO J = 7 → 6 absorption from spiral arms in the Galactic disk at velocities near 0 km s ^-1 along the line of sight to the Galactic center. Analyzing our CO J = 7 → 6 and CO J = 4 → 3 data in conjunction with J = 1 → 0 ¹²CO and ¹³CO data previously observed with the Bell Laboratories 7 m antenna, we apply a large velocity gradient (LVG) model to estimate the kinetic temperature and density of molecular gas in the inner 200 pc of the Galactic center region. We show maps of the derived distribution of gas density and kinetic temperature as a function of position and velocity for the entire region. Kinetic temperature was found to decrease from relatively high values (>70 K) at cloud edges to low values (<50 K) in the interiors. Typical gas pressures in the Galactic center gas are n(H ₂) ∼ 10 ^5.2 K cm ^-3. We present an (l,b] map of molecular hydrogen column density derived from our LVG results.