On the origin of the central 1" hole in the stellar disk of Sgr A* and the Fermi gamma-ray bubbles

The supermassive black hole Sgr A* at the center of the Galaxy is surrounded by two misaligned disks of young, massive stars extending from ~0.04 to 0.4 pc. The stellar surface density increases as ~ r^-2 towards Sgr A* but is truncated within 1" (0.04pc). We explore the origin of this annulus using a model in which star formation occurs in a disk of gas created through the partial capture of a gas cloud as it sweeps through the inner few parsecs of the galaxy and temporarily engulfs Sgr A*. We identify the locations within which star formation and/or accretion onto Sgr A* take place. Within 0.04 pc the disk is magnetically active and the associated heating and enhanced pressure prevents the disk from becoming self gravitating. Instead, it forms a magneto-turbulent disk that drains onto Sgr A* within 3 Myr. Meanwhile, fragmentation of the gas beyond the central 0.04 pc hole creates the observed young stellar disk. The two large scale bubbles of gamma-ray emission extending perpendicular to the Galactic plane may be created by a burst of accretion of ~10^5 Msun of gas lying between 0.01 and 0.03 pc. The observed stellar ages imply that this capture event occurred ~10^6.5 yr ago, thus such events occurring over the life time of the Galaxy could have significantly contributed to the current mass of Sgr A* and to the inner few parsec of the nuclear star cluster. We suggest that these events also occur in extragalactic systems.Comment: ApJL accepted; eq 1 for surface density profile generalised from previous version plus minor change

The Origin of Keplerian Megamaser Disks

Several examples of thin, Keplerian, sub-parsec megamaser disks have been discovered in the nuclei of active galaxies and used to precisely determine the mass of their host black holes. We show that there is an empirical linear correlation between the disk radius and black hole mass and that such disks are naturally formed as molecular clouds pass through the galactic nucleus and temporarily engulf the central supermassive black hole. For initial cloud column densities below about 10^{23.5} cm^{-2} the disk is non-self gravitating, but for higher cloud columns the disk would fragment and produce a compact stellar disk similar to that observed around Sgr A* at the galactic centre.Comment: 2 pages, to appear in Proc IAU Symp 287, Cosmic Masers: from OH to H_0, R. Booth, E. Humphries & W. Vlemmings, ed

THE INTERACTION OF COSMIC RAYS WITH GALACTIC CENTER MOLECULAR CLOUDS

Recent observations indicate that the cosmic rate ionization rate in the Galactic center is higher than elsewhere in the Galaxy by one to two orders of magnitudes. These measurements are based on infrared H3+ molecular spectroscopy studies. This interaction explains the ubiquitous warm molecular gas observed throughout the Galactic center as well as the unusual chemistry of molecular gas, as indicated by the high abundance of methanol, SiO and HCO+/HCN intensity ratios. I will present preliminary results of two molecular line surveys of the Galactic center that we have carried out using the CSO and ALMA. In particular, we discuss the intensity ratios of several molecular lines in the context of cosmic ray driven gas chemistry

SIO EMISSION FROM THE INNER PC OF SGR A*

A critical question regarding star formation near supermassive black holes (SMBHs) is whether tidal shear completely_x000d_ suppresses star formation or whether it induces star formation. The circumnuclear molecular ring orbiting the 4_x000d_ million solar mass black hole Sgr A* in the inner few parsecs of the Galactic center is an excellent testing ground to_x000d_ study star formation in extreme tidal environments. We have carried out ALMA observations of SiO (5-4) line emission_x000d_ to resolve protostellar outflow candidates in the molecular ring and its interior. We will describe preliminary_x000d_ results of these observations. In addition, we will present _x000d_ ALMA and VLA observations of continuum sources that show bow-shock structures. The characteristics of these mm sources suggest _x000d_ the presence of protoplanetary disks._x000d_ These continuum measurements suggest on-going low-mass star formation_x000d_ with the implication that gas clouds can survive near the strong tidal and radiation fields of the Galactic center._x000d_ _x000d_ _x000d_ _x000d

Discovery of New Interacting Supernova Remnants in the Inner Galaxy

OH(1720 MHz) masers are excellent signposts of interaction between supernova remnants(SNRs) and molecular clouds. Using the GBT and VLA we have surveyed 75 SNRs and six candidates for maser emission. Four new interacting SNRs are detected with OH masers: G5.4-1.2, G5.7-0.0, G8.7-0.1 and G9.7-0.0. The newly detected interacting SNRs G5.7-0.0 and G8.7-0.1 have TeV gamma-ray counterparts which may indicate a local cosmic ray enhancement. It has been noted that maser-emitting SNRs are preferentially distributed in the Molecular Ring and Nuclear Disk. We use the present and existing surveys to demonstrate that masers are strongly confined to within 50 degrees Galactic longitude at a rate of 15 percent of the total SNR population. All new detections are within 10 degrees Galactic longitude emphasizing this trend. Additionally, a substantial number of SNR masers have peak fluxes at or below the detection threshold of existing surveys. This calls into question whether maser surveys of Galactic SNRs can be considered complete and how many maser-emitting remnants remain to be detected in the Galaxy.Comment: Accepted to ApJ Letters, with 2 figures and 2 table