Molecular Gas Toward The Supermassive Black Hole Sgr A*

Analyzing the chemistry and kinematics of the molecular gas along the line of sight to Sgr A* will improve our overall understanding of the physical conditions of the ISM throughout the Galaxy’s disk and center. We obtained 218-264 GHz (1mm) and 330-346 GHz (0.8mm) ALMA observations of absorption at several velocities along this line of sight, which allows us to explore how the physical conditions of molecular gas vary with Galactocentric radius. We analyze the kinematics, chemistry, excitation, and CO isotopologues at these velocities to place several components in either the spiral arms, bar, or Galactic Center (GC). The chemical richness of these clouds is probed by clear detections of H₂CO(3-2), CS(7-6), CH₃OH(2-1), SO(7-6), and C₂H(7/5-5/2). We determine excitation by taking a ¹²CO(3-2)/¹²CO(2-1) ratio, whereas ¹²CO(2-1)/¹⁸CO(2-1) and ¹²CO(3-2)/¹³CO(3-2) probe Galactocentric distance. Using these indicators of location in the Galaxy, we place features in the Central Molecular Zone (CMZ), or the inner ~500 pc of the Galactic Center, perhaps in the 100 pc ring and possibly related to the well-studied 20 km/s and 50 km/s molecular clouds. We also derive the placements of other velocity features in the inner Galactic Disk, perhaps near the 3 kpc arm of the bar. To unveil new components, we plan to add ~80GHz (3mm) ALMA archival data to our study.