SGR A* and Its Environment: Low-Mass Star Formation, the Origin of X-Ray Gas and Collimated Outflow

Abstract

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 K s 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  M 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°.

ALMA and VLA observations of emission from the environment of Sgr A*

“…The magnetar has a relatively flat spectrum with α = −0.21. The mm emission from the magnetar could be due to the combination of pulsed and diffuse shocked emission produced by the interaction of the pulsar outburst with the ISM (Yusef-Zadeh et al 2016). The remaining eight sources are stellar, six of which have spectra consistent with ionized winds.…”

“…In this model, a fraction of the gaseous material accretes onto Sgr A* and the rest is driven as an outflow from Sgr A* (e.g., Quataert 2004;Shcherbakov and Baganoff 2010;Wang et al 2013). Alternatively, the diffuse X-ray emission associated with Sgr A* is interpreted as 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 ∼ 10 −6 M yr −1 (Yusef-Zadeh et al 2016). The new millimeter halo emission and a dust cavity provide additional constraints on the origin of the gas in the inner 1 of Sgr A*.…”

A Nonthermal Radio Filament Connected to the Galactic Black Hole?

“…Both jets and broadly collimated winds have been considered, but the nature of the outflow remains to be observationally determined. Morphological clues that there is an outflow from the vicinity of Sgr A * abound in deep IR and radio maps (Yusef-Zadeh & Morris 1991;Muzić et al 2010;Yusef-Zadeh et al 2016;Zhao et al 2016), but direct dynamical evidence has not yet emerged. Such observationally implied outflows tend not to be highly collimated (although see Muzić et al 2010;Li et al 2013;Yusef-Zadeh et al 2016) and can be ascribed equally well in most cases to the collective stellar winds from the central cluster of young, massive stars.…”

“…However, they were not able to demonstrate that the filament is a nonthermal feature because of the difficulty of obtaining its spectral index in this complex region. Yusef-Zadeh et al (2016) noted that the bent filament extends toward Sgr A * , but could not be followed closer to Sgr A * than about 5 arcsec. In this Letter, we examine the radio filament near Sgr A * with an independent data set.…”

“…Until recently, no NTF had yet been found within the central parsec, but Yusef-Zadeh et al (2016) recently presented radio images of a bent filament located 0.25-0.75 pc north of Sgr A * , and one of the suggestions they made for the nature of this feature was that it might be a member of the NTF population. However, they were not able to demonstrate that the filament is a nonthermal feature because of the difficulty of obtaining its spectral index in this complex region.…”