The OH-streamer in Sagittarius A revisited: analysis of hydroxyl absorption within 10 pc from the Galactic centre

Abstract

Aims. We study the structure and kinematics of the OH-streamer and the +80 km s −1 cloud and their interactions with the circumnuclear disk (CND) and with other molecular clouds in the vicinity of the Galactic centre (GC), and we map OH absorption at about 6 resolution at R ≤ 10 pc from the GC, with about 9 km s −1 of velocity resolution. Methods. The VLA was used to map OH line absorption at the 1665 and 1667 MHz lambda doublet main lines of the 2 Π 3/2 state towards the Sagittarius A complex. Results. Strong OH absorption was found in the OH-streamer, the southern streamer (SS), the +20, +50, and +80 km s −1 molecular clouds, the molecular belt, the CND, the expanding molecular ring (EMR), and the high negative velocity gas (HNVG). The OHstreamer was found to comprise three parts, head, mid, and tail, and to interact with the SS/+20, +80 km s −1 clouds and the CND. Optical depths and column densities divided by excitation temperatures have been calculated for the OH-streamer and the +80 km s −1 cloud. Conclusions. The OH-streamer, the SS, the +20 and +80 km s −1 clouds, and the CND are intimately related in position and velocity space. The OH-streamer was found to be a clumpy object stretching in projection from the inner radius of the CND at about 1.8 pc from Sgr A * towards and partly engulfing Sgr A * . As a side result of our data, a possible link between the near side of the EMR and the CND's southwest lobe was found. Additionally, we found OH absorption against all four of the previously known compact H  regions A−D, located east of Sgr A East, indicating their close association with the +50 km s −1 cloud.

High-speed molecular cloudlets around the Galactic center’s supermassive black hole

“…In particular, the emission structure emitting at v LSR ≃+40 to +100 km s −1 (P.A.≃300-315° in Figures 3 and 8). This component may be related to the +80 km s −1 OH-absorption streamer detected by Karlsson et al (2015) and that likely follows a specific trajectory. In addition, Figure 8 shows the contribution of the diffuse H 13 CN emission component that spreads around the inner edge of the CND-S (gray color shaded areas in Fig.…”

“…The feature has a considerable absorption depth, τ abs,CO 3−2 ≃−ln( T / T c )≃0.8, equivalent to N ( CO )≈2·10 17 cm −2 (or N (H 2 )≈5·10 21 cm −2 ) for the absorbing material (see below). VLA observations show an OH absorption feature at v LSR ≃−73 km s −1 as well, but only toward the CND-S lobe (Karlsson et al 2015). The fact that we detect it toward Sgr A* implies that it is more extended around the CND.…”

Odinobservations of ammonia in the Sgr A +50 km s-1cloud and circumnuclear disk

“…However, with appropriate centering of the observing frequency and many frequency calibrations, performed using a nearby telluric ozone line, it is possible to correct for this lack of phase lock. This short paper now reports on new successful Odin NH 3 observations in the Sgr A +50 km s −1 Cloud, and in the southwestern region of the CND which is a complex shocked region containing a number of interacting components (Karlsson et al 2015).…”

Tidal Distortion of the Envelope of an AGB Star IRS 3 near Sgr A*

“…Recent OH, CN, CS, HCN and SiO observations suggest that molecular gas is able to survive within 5 (0.2 pc) of Sgr A* (Montero-Castano et al 2009;Martin et al 2009;Yusef-Zadeh et al 2013;Moser et al 2016;Karlsson et al 2015). One key question is how this gas finds its way so close to Sgr A*.…”