The Galactic center chimneys: the base of the multiphase outflow of the Milky Way

Abstract

Context. Outflows and feedback are key ingredients of galaxy evolution. Evidence for an outflow arising from the Galactic center (GC) – the so-called GC chimneys – has recently been discovered at radio, infrared, and X-ray bands. Aims. We undertake a detailed examination of the spatial relationships between the emission in the different bands in order to place constraints on the nature and history of the chimneys and to better understand their impact on the GC environment and their relation with Galactic scale outflows. Methods. We compare X-ray, radio, and infrared maps of the central few square degrees. Results. The X-ray, radio, and infrared emissions are deeply interconnected, affecting one another and forming coherent features on scales of hundreds of parsecs, therefore indicating a common physical link associated with the GC outflow. We debate the location of the northern chimney and suggest that it might be located on the front side of the GC because of a significant tilt of the chimneys toward us. We report the presence of strong shocks at the interface between the chimneys and the interstellar medium, which are traced by radio and warm dust emission. We observe entrained molecular gas outflowing within the chimneys, revealing the multiphase nature of the outflow. In particular, the molecular outflow produces a long, strong, and structured shock along the northwestern wall of the chimney. Because of the different dynamical times of the various components of the outflow, the chimneys appear to be shaped by directed large-scale winds launched at different epochs. The data support the idea that the chimneys are embedded in an (often dominant) vertical magnetic field, which likely diverges with increasing latitude. We observe that the thermal pressure associated with the hot plasma appears to be smaller than the ram pressure of the molecular outflow and the magnetic pressure. This leaves open the possibility that either the main driver of the outflow is more powerful than the observed hot plasma, or the chimneys represent a “relic” of past and more powerful activity. Conclusions. These multiwavelength observations corroborate the idea that the chimneys represent the channel connecting the quasi-continuous, but intermittent, activity at the GC with the base of the Fermi bubbles. In particular, the prominent edges and shocks observed in the radio and mid-infrared bands testify to the most powerful, more recent outflows from the central parsecs of the Milky Way.

New Constraints on Cosmic Particle Populations at the Galactic Center using X-ray Observations of the Molecular Cloud Sagittarius B2

“…In addition to non-thermal photons, evidence for CRs at the GC comes from observations that could be explained by pressure from CR-driven winds (Heywood et al 2019;Nakashima et al 2019;Ponti et al 2019;Yusef-Zadeh & Wardle 2019;Ponti et al 2021). Similar winds could be responsible for the Fermi Bubbles, and could explain the observed blue-shifted atomic hydrogen lines from the CMZ (Oka et al 2019) and high-velocity clouds moving away from the disk (McClure-Griffiths et al 2013).…”

Analyzing the Intrinsic Magnetic Field in the Galactic Center Radio Arc

“…Heywood et al (2019) revealed the presence of large-scale synchrotron 'chimneys' that are possible outflows from Sgr A * . The Radio Arc NTFs are located precisely at the northeastern edge of the chimney as can be seen in Heywood et al (2019) and Ponti et al (2021). The chimney is an edge-brightened synchro1tron source, and so could be the source of the internal rotation detected along these lines-of-sight.…”

“…Their synchrotron nature indicates the presence of relativistic, free electrons (Yusef-Zadeh et al 1984). The source and mechanism causing the electrons to accelerate to relativistic velocities, however, remain a topic of active debate with many hypotheses (see references in Ponti et al 2021).…”

Tracing the Milky Way's Vestigial Nuclear Jet

“…2) are enveloped by ever larger radio and X-ray arcs inclined by ∼ 15 • toward the north-west to end in similar prows at similar radius; this tilt persists to the largest scale of radio emission (purple dashed line in Figure 2). To the north, the X-ray pattern offsets east of similar radio continuum emission (Heywood et al 2019;Ponti et al 2021). The enigmatic, vertical bundle of flux tubes (Guan et al 2021) at 15 radius east may confine the X-ray emission, which at least in the north protrudes farther eastward once the filaments end.…”

“…To the south, radio synchrotron 1-2 Myr old appears to envelop the X-rays (Nakashima et al 2013;Ponti et al 2013). Just those electrons attest to an eruption of 7 × 10 52 erg (Ponti et al 2021;Heywood et al 2019), but certainly orders of magnitude more energetic than that because the entrained ions and dust, being inefficient radiators, retain much more kinetic energy.…”