Oral Presentation

The circumnuclear disk revealed by ALMA - environments of star formation in the inner 10 pc of the Galaxy

Author(s): Hsieh, Pei-Ying (NAOJ)

Presenter: Pei-Ying Hsieh (NAOJ)

The molecular 2-pc circumnuclear disk (CND) immediately around the Milky Way supermassive black hole (SMBH), SgrA*, resembles the "molecular torus" in AGNs, providing a unique opportunity to study SMBH accretion and nuclear star formation at sub-parsec scales. In recent years, we have been studying the key question of how much of the available gas can actually form stars in the environment around Sgr A*, and how material is being moved around and accreted in this region. The lifetime of the CND has been a long-standing debate over the past decade. The CND can not live longer than 10^5 years if the gas density is under the tidal threshold of SgrA*/nuclear star clusters, thus depleting the source of fuel and star formation. Utilizing the ALMA and various single-dish telescopes, we present CS line maps toward the CND of the Galactic Center. Our primary goal is to resolve the compact structures within the CND and the streamers, in order to understand the stability conditions of molecular cores in the vicinity of Sgr A*. Our data provide the first homogeneous high-resolution (1.3" = 0.05 pc) observations aiming at resolving density and temperature structures. A stability analysis based on the unmagnetized virial theorem including tidal force shows that 84 (+16/-37) % of the total gas mass (2.5X10^4 Msun) is tidally stable, which accounts for the majority of gas mass. Turbulence dominates the internal energy and thereby sets the threshold densities 10-100 times higher than the tidal limit at distance >1.5 pc to Sgr A*, and therefore, inhibits the clouds from collapsing to form stars near the SMBH.