Evidence for a jet and outflow from Sgr A*: a continuum and spectral line study

TL;DR

This study provides evidence for a collimated jet and possible outflow from Sgr A* through spectral line and continuum radio observations, revealing high-velocity gas and elongated structures aligned with the Galactic plane.

Contribution

First detection of a collimated jet and outflow from Sgr A* using ALMA and VLA data, characterizing their structure, velocity, and orientation.

Findings

Detection of high-velocity emission near -2500 and 4000 km/s.

Identification of a collimated jet with an opening angle of ~30 degrees.

Observation of elongated continuum structures aligned with the Galactic plane.

Abstract

We study the environment of Sgr A* using spectral and continuum observations with the ALMA and VLA. Our analysis of sub-arcsecond H30alpha, H39alpha, H52alpha and H56alpha line emission towards Sgr A* confirm the recently published broad peak ~500 km/s~spectrum toward Sgr~A*. We also detect emission at more extreme radial velocities peaking near -2500 and 4000 km/s, within 0.2''. We then present broad band radio continuum images at multiple frequencies on scales from arcseconds to arcminutes. A number of elongated continuum structures lie parallel to the Galactic plane, extending from ~0.4'' to 10'. We note a nonthermal elongated structure on an arcminute scale emanating from Sgr A* at low frequencies between 1 and 1.4 GHz where thermal emission from the mini-spiral is depressed by optical depth effects. The position angle of this elongated structure and the sense of motion of ionized features with respect to Sgr A* suggest a symmetric, collimated jet emerging from Sgr A* with an opening angle of ~30deg and a position angle of ~60deg punching through the medium before accelerating a significant fraction of the orbiting ionized gas to high velocities. The jet with estimated mass flow rate ~1.4x10^{-5} solar mass/yr emerges perpendicular to the equatorial plane of the accretion flow near the event horizon of Sgr A* and runs along the Galactic plane. To explain a number of east-west features near Sgr A*, we also consider the possibility of an outflow component with a wider-angle launched from the accretion flow at larger radii.