A New Perspective of the Radio Bright Zone at The Galactic Center: Feedback from Nuclear Activities

TL;DR

This study presents high-resolution radio observations of the Galactic Center's Radio Bright Zone, revealing new structures and interactions suggestive of nuclear activity feedback, including radio lobes, shock interactions, and a reflected shock wave from the Sgr A East supernova remnant.

Contribution

It provides the first detailed radio imaging of the central 30 pc at 5.5 GHz, identifying new features and proposing mechanisms for their formation related to nuclear feedback processes.

Findings

Identification of a 14.4 x 7.3 pc radio lobe with X-ray counterpart.

Detection of amorphous radio blobs with Paschen-$eta$ counterparts indicating shock interactions.

Proposal that the Sigma Front is a reflected shock wave from the Sgr A East blast wave.

Abstract

New observations of Sgr A have been carried out with the VLA using the broadband (2 GHz) continuum mode at 5.5 GHz, covering the central 30 pc region of the RBZ at the Galactic center. Using the MS-MFS algorithms in CASA, we have imaged Sgr A with a resolution of 1", achieving an rms 8 $\mu$Jy/beam, and a dynamic range 100,000:1.The radio image is compared with X-ray, CN emission-line and Paschen-$\alpha$ images obtained using Chandra, SMA and HST/NICMOS, respectively. We discuss several prominent radio features. The "Sgr A West Wings" extend 5 pc from the NW and SE tips of the ionized "Mini-spiral" in Sgr A West to positions located 2.9 and 2.4 arc min to the NW and SE of Sgr A*, respectively. The NW wing, along with several other prominent features, including the "NW Streamers", form an elongated radio lobe (NW lobe), oriented nearly perpendicular to the Galactic plane. This radio lobe, with a size of 14.4 pc x 7.3 pc, has a known X-ray counterpart. A row of three thermally emitting rings is observed in the NW lobe. A field containing numerous amorphous radio blobs extends for a distance of ~2 arc min beyond the tip of the SE wing; these features coincide with the SE X-ray lobe. Most of the amorphous radio blobs in the NW and SE lobes have Paschen-$\alpha$ counterparts, suggesting that a shock interaction of ambient gas concentrations with a collimated nuclear wind (outflow) that may be driven by radiation force from the central star cluster within the CND. Finally, we remark on a prominent radio feature located within the shell of the Sgr A East SNR. Because this feature -- the "Sigma Front" -- correlates well in shape and orientation with the nearby edge of the CND, we propose that it is a reflected shock wave resulting from the impact of the Sgr A East blast wave on the CND.