The Galactic Center Molecular Cloud Survey. I. A Steep Linewidth-Size Relation & Suppression of Star Formation

Abstract: The Central Molecular Zone (CMZ; inner $\sim{}200~\rm{}pc$) of the Milky Way is a star formation (SF) environment with very extreme physical properties. Exploration of SF in this region is important because (i) this region allows us to test models of star formation under exceptional conditions, and (ii) the CMZ clouds might be suitable to serve as templates to understand the physics of starburst galaxies in the nearby and the distant universe. For this reason we launched the Galactic Center Molecular Cloud Survey (GCMS), the first systematic study that resolves all major CMZ clouds at interferometer angular resolution (i.e., a few arc seconds). Here we present initial results based on observations with the Submillimeter Array (SMA) and the Atacama Pathfinder Experiment (APEX). Our study is complemented by dust emission data from the Herschel Space Telescope and a comprehensive literature survey of CMZ star formation activity. Our research reveals (i) an unusually steep linewidth-size relation, $\sigma(v)\propto{}r_{\rm{}eff}^{0.66\pm{}0.18}$, down to velocity dispersions $\sim{}0.6~\rm{}km\,s^{-1}$ at 0.1 pc scale. This scaling law potentially results from the decay of gas motions to transonic velocities in strong shocks. The data also show that, relative to dense gas in the solar neighborhood, (ii) star formation is suppressed by factors $\gtrsim{}10$ in individual CMZ clouds. This observation encourages exploration of processes that can suppress SF inside dense clouds for a significant period of time.