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

Abstract

We study the environment of Sgr A* using spectral and continuum observations with the ALMA and VLA. Our analysis of sub-arcsecond H30α, H39α, H52α and H56α line emission towards Sgr A* confirm the recently published broad peak ∼ 500 km s −1 spectrum toward Sgr A*. We also detect emission at more extreme radial velocities peaking near −2500 and 4000 km s −1 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 ∼ 30 • and a position angle of ∼60 • punching through the medium before accelerating a significant fraction of the orbiting ionized gas to high velocities. The jet with estimated mass flow rate ∼ 1.4 × 10 −5 M yr −1 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.

Missing bright red giants in the Galactic center: A fingerprint of its once active state?

“…1 for illustration. Even in the current quiescent state of Sgr A*, there is evidence for the interaction of wind-blowing stellar objects with the ambient wind or even a low surfacebrightness jet (Yusef-Zadeh et al, 2020). Clear examples are comet-shaped sources X3, X7 (Mužić et al, 2010), and the bow-shock source X8 (Peißker et al, 2019) located in the so-called mini-cavity.…”

Depletion of bright red giants in the Galactic center during its active phases

“…The presence of bow-shock sources X3 and X7 (Mužić et al 2010) as well as X8 (Peißker et al 2019) in the mini-cavity implies the interaction of these sources with a nuclear outflow in the current state of activity of Sgr A*. The present nuclear outflow could be a signature of a low surfacebrightness jet (Yusef-Zadeh et al 2020), which was much more luminous a few million years ago. The infrared-excess sources X3, X7, and X8 thus directly reveal the interaction of a nuclear outflow/jet with stars at the scale of ∼ 0.2 pc.…”

“…In a similar way as we discussed in point (vi) in terms of the non-spherical stellar distribution, the jet interaction with the surrounding gas could also be revealed via the nonisotropic distribution of ionization tracers. In particular, the shock-tracer line [FeIII] seems to be preferentially located in the direction of the minicavity (Peißker et al 2020), which suggests either the current or the past interaction of the gas with the high-velocity outflow/jet (Yusef-Zadeh et al 2020). On the scales larger than one parsec, the non-isotropic distribution is manifested by bipolar radio lobes (Heywood et al 2019) and X-ray (Ponti et al 2019) and γ-ray bubbles (Su et al 2010;Ackermann et al 2014).…”