First Detection of Millimeter/Submillimeter Extragalactic H2O Maser Emission

We report the first detection of an extragalactic millimeter wavelength H2O maser at 183 GHz towards NGC 3079 using the Submillimeter Array (SMA), and a tentative submillimeter wave detection of the 439 GHz maser towards the same source using the James Clerk Maxwell Telescope (JCMT). These H2O transitions are known to exhibit maser emission in star-forming regions and evolved stars. NGC 3079 is a well-studied nuclear H2O maser source at 22 GHz with a time-variable peak flux density in the range 3 -- 12 Jy. The 183 GHz H2O maser emission, with peak flux density $\sim$0.5 Jy (7$\sigma$ detection), also originates from the nuclear region of NGC 3079 and is spatially coincident with the dust continuum peak at 193 GHz (53 mJy integrated). Peak emission at both 183 and 439 GHz occurs in the same range of velocity as that covered by the 22 GHz spectrum. We estimate the gas to dust ratio of the nucleus of NGC 3079 to be $\approx$150, comparable to the Galactic value of 160. Discovery of maser emission in an active galactic nucleus beyond the long-known 22 GHz transition opens the possibility of future position-resolved radiative transfer modeling of accretion disks and outflows $<1$ pc from massive black holes.Comment: 12 pages, 3 figures, ApJ Letters accepte

Evidence for a Geometrically Thick Self-Gravitating Accretion Disk in NGC 3079

We have mapped, for the first time, the full velocity extent of the water maser emission in NGC 3079. The largely north-south distribution of emission, aligned with a kpc-scale molecular disk, and the segregation of blue- and red-shifted emission on the sky are suggestive of a nearly edge-on molecular disk on pc-scales. Positions and line-of-sight velocities of blue- and red-shifted maser emission are consistent with a central mass of ~2 x 10^6 Msun enclosed within a radius of ~0.4 pc. The corresponding mean mass density of 10^6.8 Msun pc^-3 is suggestive of a central black hole, which is consistent with the detection of hard X-ray excess (20-100 keV) and an Fe Kalpha line from the nucleus. Because the rotation curve traced by the maser emission is flat, the mass of the pc-scale disk is significant with respect to the central mass. Since the velocity dispersion of the maser features does not decrease with radius and constitutes a large fraction of the orbital velocity, the disk is probably thick and flared. The rotation curve and the physical conditions necessary to support maser emission imply a Toomre Q-parameter that is << 1. Thus, the disk is most likely clumpy, and we argue that it is probably forming stars. Overall, the accretion disk in NGC 3079 stands in contrast to the compact, thin, warped, differentially rotating disk in the archetypal maser galaxy NGC 4258 (abridged).Comment: 41 pages, 13 figures, to appear in the 2005 January 10 issue of the Astrophysical Journal. High resolution versions of the figures and of the paper are available at http://cfa-www.harvard.edu/~pkondratko/publications/NGC3079

Discovery of Water Maser Emission in Five AGN and a Possible Correlation Between Water Maser and Nuclear 2-10 keV Luminosities

We report the discovery of water maser emission in five active galactic nuclei (AGN) with the 100-m Green Bank Telescope (GBT). The positions of the newly discovered masers, measured with the VLA, are consistent with the optical positions of the host nuclei to within 1 sigma (0.3 arcsec radio and 1.3 arcsec optical) and most likely mark the locations of the embedded central engines. The spectra of three sources, 2MASX J08362280+3327383, NGC 6264, and UGC 09618 NED02, display the characteristic spectral signature of emission from an edge-on accretion disk with maximum orbital velocity of ~700, ~800, and ~1300 km s^-1, respectively. We also present a GBT spectrum of a previously known source MRK 0034 and interpret the narrow Doppler components reported here as indirect evidence that the emission originates in an edge-on accretion disk with orbital velocity of ~500 km s^-1. We obtained a detection rate of 12 percent (5 out of 41) among Seyfert 2 and LINER systems with 10000 km s^-1 < v_sys < 15000 km s^-1. For the 30 nuclear water masers with available hard X-ray data, we report a possible relationship between unabsorbed X-ray luminosity (2-10 keV) and total isotropic water maser luminosity, L_{2-10} proportional to L_{H2O}^{0.5+-0.1}, consistent with the model proposed by Neufeld and Maloney in which X-ray irradiation and heating of molecular accretion disk gas by the central engine excites the maser emission.Comment: 16 pages, 5 tables, 3 figures, to appear in the November 10, 2006, v651n2 issue of the Astrophysical Journa

A Green Bank Telescope Search for Water Masers in Nearby Active Galactic Nuclei

Using the Green Bank Telescope, we have conducted a survey for 1.3 cm water maser emission toward the nuclei of nearby active galaxies, the most sensitive large survey for H2O masers to date. Among 145 galaxies observed, maser emission was newly detected in eleven sources and confirmed in one other. Our survey targeted nearby (v < 12,000 km/s, mainly type 2 AGNs north of declination -20 degrees, and includes a few additional sources as well. We find that more than a third of Seyfert 2 galaxies have strong maser emission, though the detection rate declines beyond v about 5000 km/s due to sensitivity limits. Two of the masers discovered during this survey are found in unexpected hosts: NGC 4151 (Seyfert 1.5) and NGC 2782 (starburst). We discuss the possible relations between the large X-ray column to NGC 4151 and a possible hidden AGN in NGC 2782 to the detected masers. Four of the masers discovered here, NGC 591, NGC 4388, NGC 5728 and NGC 6323, have high-velocity lines symmetrically spaced about the systemic velocity, a likely signature of molecular gas in a nuclear accretion disk. The maser source in NGC 6323, in particular, reveals the classic spectrum of a "disk maser" represented by three distinct groups of Doppler components. Future single-dish and VLBI observations of these four galaxies could provide a measurement of the distance to each galaxy, and of the Hubble constant, independent of standard candle calibrations.Comment: published in ApJ Letter

The Discovery of H2O Maser Emission in Seven AGN and at High Velocities in the Circinus Galaxy

We report the discovery of H2O maser emission at 1.35 cm wavelength in seven active galactic nuclei (at distances up to < 80 Mpc) during a survey conducted at the 70-m diameter antenna of the NASA Deep Space Network near Canberra, Australia. The detection rate was ∼ 4%. Two of the maser sources are particularly interesting because they display satellite high-velocity emission lines, which are a signature of emission from the accretion disks of supermassive black holes when seen edge on. Three of the masers are coincident, to within uncertainties of 0.′′2, with continuum emission sources we observed at about λ1.3 cm. We also report the discovery of new spectral features in the Circinus galaxy H2O maser that broaden the known velocity range of emission therein by a factor of ∼ 1.7. If the new spectral features originate in the Circinus accretion disk, then molecular material must survive at radii ∼ 3 times smaller than had been believed previously (∼ 0.03 pc or ∼ 2 × 105 Schwarzschild radii).AstronomyPhysic

The Discovery of H2O Maser Emission in Seven AGN and at High Velocities in the Circinus Galaxy

We report the discovery of H2O maser emission at 1.35 cm wavelength in seven active galactic nuclei (at distances up to <80 Mpc) during a survey conducted at the 70-m diameter antenna of the NASA Deep Space Network near Canberra, Australia. The detection rate was (approx.) 4%. Two of the maser sources are particularly interesting because they display satellite high-velocity emission lines, which are a signature of emission from the accretion disks of supermassive black holes when seen edge on. Three of the masers are coincident, to within uncertainties of 0.''2, with continuum emission sources we observed at about (lamda)1.3 cm. We also report the discovery of new spectral features in the Circinus galaxy H2O maser that broaden the known velocity range of emission therein by a factor of (approx.) 1.7. If the new spectral features originate in the Circinus accretion disk, then molecular material must survive at radii (approx.) 3 times smaller than had been believed previously [(approx.) 0.03 pc or (approx.) 2 x 105 Schwarzschild radii].Comment: 4 pages, including 2 figures. To appear in ApJ Letters Jan. 1, 2003 editio

Using VLBI to Probe the Orion-KL Outflow on AU Scales

We present the first contemporaneous 43GHz and 86GHz VLBI images of the v=1 J=2-1 and J=1-0 SiO masers in the Orion-KL nebula. Both maser species exhibit the same general morphology of earlier J=1-0 maser images which appear to trace the edges of a bi-polar conical outflow. Surprisingly, the J=2-1 masers form further from the central protostar than the J=1-0 masers, a fact not readily explained by current SiO maser pumping models. The average magnitude of offsets between corresponding regions of the two masing transitions is approximately 14% of the total radial extent of the SiO maser emission. This offset indicates that each transition must trace different physical conditions.Comment: 20 pages, 4 figure

21cm Absorption by Compact Hydrogen Disks Around Black Holes in Radio-Loud Nuclei of Galaxies

The clumpy maser disks observed in some galactic nuclei mark the outskirts of the accretion disk that fuels the central black hole and provide a potential site of nuclear star formation. Unfortunately, most of the gas in maser disks is currently not being probed; large maser gains favor paths that are characterized by a small velocity gradient and require rare edge-on orientations of the disk. Here we propose a method for mapping the atomic hydrogen distribution in nuclear disks through its 21cm absorption against the radio continuum glow around the central black hole. In NGC 4258, the 21cm optical depth may approach unity for high angular-resolution (VLBI) imaging of coherent clumps which are dominated by thermal broadening and have the column density inferred from X-ray absorption data, ~10^{23}/cm^2. Spreading the 21cm absorption over the full rotation velocity width of the material in front of the narrow radio jets gives a mean optical depth of ~0.1. Spectroscopic searches for the 21cm absorption feature in other galaxies can be used to identify the large population of inclined gaseous disks which are not masing in our direction. Follow-up imaging of 21cm silhouettes of accelerating clumps within these disks can in turn be used to measure cosmological distances.Comment: 4 page

Angular Momentum and the Formation of Stars and Black Holes

The formation of compact objects like stars and black holes is strongly constrained by the requirement that nearly all of the initial angular momentum of the diffuse material from which they form must be removed or redistributed during the formation process. The mechanisms that may be involved and their implications are discussed for (1) low-mass stars, most of which probably form in binary or multiple systems; (2) massive stars, which typically form in clusters; and (3) supermassive black holes that form in galactic nuclei. It is suggested that in all cases, gravitational interactions with other stars or mass concentrations in a forming system play an important role in redistributing angular momentum and thereby enabling the formation of a compact object. If this is true, the formation of stars and black holes must be a more complex, dynamic, and chaotic process than in standard models. The gravitational interactions that redistribute angular momentum tend to couple the mass of a forming object to the mass of the system, and this may have important implications for mass ratios in binaries, the upper stellar IMF in clusters, and the masses of supermassive black holes in galaxies.Comment: Accepted by Reports on Progress in Physic

Discovery of Water Maser Emission in Eight AGN with 70-m Antennas of NASA's Deep Space Network

We report the discovery of water maser emission in eight active galactic nuclei (AGN) with the 70-m NASA Deep Space Network (DSN) antennas at Tidbinbilla, Australia and Robledo, Spain. The positions of the newly discovered masers, measured with the VLA, are consistent with the optical positions of the host nuclei to within 1 sigma (0.3 arcsec radio and 1.3 arcsec optical) and most likely mark the locations of the embedded central engines. The spectra of two sources, NGC 3393 and NGC 5495, display the characteristic spectral signature of emission from an edge-on accretion disk, with orbital velocities of ~600 and ~400 km s^-1, respectively. In a survey with DSN facilities of 630 AGN selected from the NASA Extragalactic Database, we have discovered a total of 15 water maser sources. The resulting incidence rate of maser emission among nearby (v_sys < 7000 km s^-1) Seyfert 1.8-2.0 and LINER systems is ~10 percent for a typical rms noise level of ~14 mJy over 1.3 km s^-1 spectral channels. As a result of this work, the number of nearby AGN (v_sys < 7000 km s^-1) observed with <20 mJy rms noise has increased from 130 to 449.Comment: 7 pages, 1 figure, 2 tables, to appear in the 2006 February 10 issue of the Astrophysical Journal, uses twocolumns.cl