The AST/RO Survey of the Galactic Center Region. I. The Inner 3 Degrees

Abstract

We present fully-sampled maps of 461 GHz CO (4-3), 807 GHz CO (7-6), and 492 GHz [CI] (3P1-3P0) 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 arcmin spacing, resulting in spectra in 3 transitions at over 24,000 positions on the sky. The CO (4-3) emission is found to be essentially coextensive with lower-J transitions of CO. The CO (7-6) emission is spatially confined to a far smaller region than the lower-J CO lines. The [CI] (3P1-3P0) emission has a spatial extent similar to the low-J CO emission, but is more diffuse. Bright CO (7-6) emission is detected in the well-known Galactic Center clouds Sgr A and Sgr B. We also detect CO (4-3) and CO (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 (7-6) and CO (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 (>70K) at cloud edges to low values (<50K) in the interiors. Typical gas pressures in the Galactic Center gas are n(H_2) T_kin approx 10^5.2 K cm^-3. We also present an (l,b) map of molecular hydrogen column density derived from our LVG results.Comment: 41 pages, 29 figures reduced to low resolution for astro-ph, for high resolution figures please go to http://cfa-www.harvard.edu/ASTRO/galcen_1.pdf this version incorporates changes due to accepted erratum (to appear in ApJS 153

The Milky Way as a Star Formation Engine

“…Indeed, Huettemeister et al (1998) found extensive SiO emission from the CMZ clouds, indicating the presence of shocks sufficiently strong to sputter dust grains to produce a significant gas-phase abundance of SiO. Molecular gas in the CMZ is not only dense, but also warm, and able to excite high-J transitions of CO, as well as a variety of high dipole-moment molecules (Martin et al, 2004).…”

Star Formation in the Central 400 Pc of the Milky Way: Evidence for a Population of Massive Young Stellar Objects

“…This important region of the Galaxy hosts several sources of energetic activity, and is the site of massive molecular clouds with pockets of past and present massive star formation. On a larger scale, the distribution of molecular clouds is asymmetric in the so-called "central molecular zone" showing 2/3 of the molecular gas on the positive longitude side of the Galactic center region (Bania 1977;Bally et al 1988;Oka et al 2005;Tsuboi et al 1999;Martin et al 2004;Morris & Serabyn 1996). The nature of this asymmetry in the context of gasdynamics is not understood.…”

The nature of nonthermal X-ray filaments near the galactic center

“…Here we investigate this possibility on a local scale and examine the application of ICS in three nonthermal filaments that are detected in both radio and X-ray wavelengths. All the filaments lie in the vicinity of molecular clouds characterized by their high density ≈ 10 4 − 10 5 cm −3 and high temperature ≈ 70 K (e.g., Morris and Serabyn 1996;Martin et al 2004). …”