SGR A* AND ITS ENVIRONMENT: LOW-MASS STAR FORMATION, THE ORIGIN OF X-RAY GAS AND COLLIMATED OUTFLOW

摘要

We present high-resolution multiwavelength radio continuum images of the region within 150'' of Sgr?A*, revealing a number of new extended features and stellar sources in this region. First, we detect a continuous 2'' east–west ridge of radio emission, linking Sgr?A* and a cluster of stars associated with IRS 13 N and IRS 13E. The ridge suggests that an outflow of east–west blob-like structures is emerging from Sgr?A*. In particular, we find arc-like radio structures within the ridge with morphologies suggestive of photoevaporative protoplanetary disks. We use infrared Ks and L' fluxes to show that the emission has similar characteristics to those of a protoplanetary disk irradiated by the intense radiation field at the Galactic center. This suggests that star formation has taken place within the S-cluster 2'' from Sgr?A*. We suggest that the diffuse X-ray emission associated with Sgr A* is due to an expanding hot wind produced by the mass loss from B-type main sequence stars, and/or the disks of photoevaporation of low mass young stellar objects (YSOs) at a rate of ~10?6 yr?1. The proposed model naturally reduces the inferred accretion rate and is an alternative to the inflow–outflow style models to explain the underluminous nature of Sgr A*. Second, on a scale of 5'' from Sgr A*, we detect new cometary radio and infrared sources at a position angle PA?~?50° which is similar to that of two other cometary sources X3 and X7, all of which face Sgr A*. In addition, we detect a striking tower of radio emission at a PA?~?50°–60° along the major axis of the Sgr A East supernova remnant shell on a scale of 150'' from Sgr A*. We suggest that the cometary sources and the tower feature are tracing interaction sites of a mildly relativistic jet from Sgr A* with the atmosphere of stars and the nonthermal Sgr A East shell at a PA?~?50°–60° with , and opening angle 10°. Lastly, we suggest that the east–west ridge of radio emission traces an outflow that is potentially associated with past flaring activity from Sgr A*. The position angle of the outflow driven by flaring activity is close to ?90°.