A Survey for H2O Megamasers III. Monitoring Water Vapor Masers in Active Galaxies

We present single-dish monitoring of the spectra of 13 extragalactic water megamasers taken over a period of 9 years and a single epoch of sensitive spectra for 7 others. Our data include the first K-band science observations taken with the new 100 m Green Bank Telescope (GBT). In the context of a circumnuclear, molecular disk model, our results suggest that either (a) the maser lines seen are systemic features subject to a much smaller acceleration than present in NGC 4258, presumably because the gas is farther from the nuclear black hole, or (b) we are detecting ``satellite'' lines for which the acceleration is in the plane of the sky. We also report a search for water vapor masers towards the nuclei of 58 highly inclined, nearby galaxies.Comment: accepted by ApJ

Class I methanol masers in low-mass star formation regions

Four Class I maser sources were detected at 44, 84, and 95 GHz toward chemically rich outflows in the regions of low-mass star formation NGC 1333I4A, NGC 1333I2A, HH25, and L1157. One more maser was found at 36 GHz toward a similar outflow, NGC 2023. Flux densities of the newly detected masers are no more than 18 Jy, being much lower than those of strong masers in regions of high-mass star formation. The brightness temperatures of the strongest peaks in NGC 1333I4A, HH25, and L1157 at 44 GHz are higher than 2000 K, whereas that of the peak in NGC 1333I2A is only 176 K. However, rotational diagram analysis showed that the latter source is also a maser. The main properties of the newly detected masers are similar to those of Class I methanol masers in regions of massive star formation. The former masers are likely to be an extension of the latter maser population toward low luminosities of both the masers and the corresponding YSOs.Comment: 5 pages, 1 figure, Proc. IAU Symp. 287 "Cosmic Masers: from OH to H0". LSR velocities of the HH25 masers, which are presented in Table 1, are correcte

Microwave and Millimeter Wave Techniques

Contains reports on three research projects.Joint Services Electronics Program (Contract DAAB07-75-C-1346

Radio Astronomy

Contains reports on twelve research projects.National Science Foundation (Grant AST77-06052)Joint Services Electronics Program (Contract DAAB07-76-C-1400)National Aeronautics and Space Administration (Contract NAS5-21980)U.S. Air Force - Electronic Systems Division (Contract F19628-75-C-0122)U.S. Department of Commerce - National Oceanic Atmospheric Administration (Grant 04-8-M01-1)National Aeronautics and Space Administration (Contract NAS5-22929)National Aeronautics and Space Administration (Contract NAS5-23677)National Science Foundation (Grant AST73-05042-A03)National Science Foundation (Grant AST76-20376

Microwave and Millimeter Wave Techniques

Contains research objectives and summary of research on four research projects.Joint Services Electronics Program (Contract DAAB07-74-C-0630)National Science Foundation (Grant GP-40485X)National Science Foundation (Grant MPS73-05043-A01

Radio Astronomy

Contains research objectives and summary of research on seven research projects.M.I.T. Sloan Fund for Basic ResearchNational Aeronautics and Space Administration (Contract NAS5-21980)National Aeronautics and Space Administration (Contract NAS5-22485)National Aeronautics and Space Administration (Contract NAS5-23677)National Aeronautics and Space Administration (Contract NAS5-22929)U. S. Air Force - Electronic Systems Division (Contract F19628-75-C-0122)National Science Foundation (Grant AST73-05043-A02)National Science Foundation (Grant AST73-05042-A03

The Detection of New Methanol Masers in the 5_{-1}-4_0E Line

Fifty-one objects in the 5_{-1}-4_0E methanol line at 84.5 GHz were detected during a survey of Class I maser sources. Narrow maser features were found in 17 of these. Broad quasi-thermal lines were detected towards other sources. One of the objects with narrow features, the young bipolar outflow L 1157 was also observed in the 8_0-7_1A+ line at 95.2 GHz; a narrow line was detected at this frequency. Analysis showed that the broad lines are usually inverted. The quasi-thermal profiles imply that the line opacities are not larger than several units. These results confirm the plausibility of models in which compact Class I masers appear in extended sources as a result of an appropriate velocity field. Measurements of linear polarization at 84.5 GHz in 13 sources were made. No polarization was found except a tentative detection of a weak polarization in M 8E

Observational Evidence for Massive Black Holes in the Centers of Active Galaxies

Naturally occurring water vapor maser emission at 1.35 cm wavelength provides an accurate probe for the study of accretion disks around highly compact objects, thought to be black holes, in the centers of active galaxies. Because of the exceptionally fine angular resolution, 200 microarcseconds, obtainable with very long baseline interferometry, accompanied by high spectral resolution, < 0.1 km/s, the dynamics and structures of these disks can be probed with exceptional clarity. The data on the galaxy NGC4258 are discussed here in detail. The mass of the black hole binding the accretion disk is 3.9 times 10^7 solar masses. Although the accretion disk has a rotational period of about 800 years, the physical motions of the masers have been directly measured with VLBI over a period of a few years. These measurements also allow the distance from the earth to the black hole to be estimated to an accuracy of 4 percent. The status of the search for other maser/black hole candidates is also discussed.Comment: 24 pages, 11 figures, latex, uses aaspp4 style file. To be published in the Journal of Astronomy and Astrophysics (India), proceedings of the Discussion Meeting on the Physics of Black Holes, Bangalore, India: December 199

Supermassive Black Holes in Galactic Nuclei: Past, Present and Future Research

This review discusses the current status of supermassive black hole research, as seen from a purely observational standpoint. Since the early '90s, rapid technological advances, most notably the launch of the Hubble Space Telescope, the commissioning of the VLBA and improvements in near-infrared speckle imaging techniques, have not only given us incontrovertible proof of the existence of supermassive black holes, but have unveiled fundamental connections between the mass of the central singularity and the global properties of the host galaxy. It is thanks to these observations that we are now, for the first time, in a position to understand the origin, evolution and cosmic relevance of these fascinating objects.Comment: Invited Review, 114 pages. Because of space requirements, this version contains low resolution figures. The full resolution version can be downloaded from http://www.physics.rutgers.edu/~lff/publications.htm

A radio study of the double-double radio galaxy 3C293

We present radio continuum observations at frequencies ranging from $\sim$150 to 5000 MHz of the misaligned double-double radio galaxy, DDRG, 3C293 (J1352+3126) using the Giant Metrewave Radio Telescope (GMRT) and the Very Large Array (VLA). The spectra of the outer lobes and the central source are consistent with being straight, indicating spectral ages of \lapp17-23 Myr for the outer lobes, and \lapp0.1 Myr for the central source. The north-western lobe has a prominent hotspot suggesting that the interruption of jet activity is \lapp0.1 Myr, consistent with the age of the inner double. The time scale of interruption of jet activity appears significantly smaller than observed in most other DDRGs which are often associated with giant radio sources. These observations suggest that there is a wide range of time scales of interruption of jet activity in active galaxies.Comment: 11 pages, 5 figures, Accepted for publication in MNRA