Matthews, L. D., Greenhill, L. J., Goddi, C., Chandler, C. J., Humphreys, E. M. L., Kunz, M.
We present multi-epoch VLBA imaging of the 28SiO v=1 & v=2, J=1-0 maser emission toward the massive YSO Orion Source I. Both SiO transitions were observed simultaneously with an angular resolution of...
Goddi, C., Greenhill, L. J., Chandler, C. J., Humphreys, E. M. L., Matthews, L. D., Gray, M. D.
We have used the Very Large Array (VLA) at 7 mm wavelength to image five rotational transitions (J=1-0) from three SiO isotopologues towards Orion BN/KL: 28SiO v=0,1,2; and 29SiO and 30SiO v=0. For...
The Megamaser Cosmology Project: I. VLBI observations of UGC 3789 (2008)
Reid, M. J., Braatz, J. A., Condon, J. J., Greenhill, L. J., Henkel, C., Lo, K. Y.
The Megamaser Cosmology Project (MCP) seeks to measure the Hubble Constant (Ho) in order to improve the extragalactic distance scale and constrain the nature of dark energy. We are searching for...
Goddi, C., Greenhill, L. J., Humphreys, E. M. L., Matthews, L. D., Tan, Jonathan C., Chandler, C. J.
We have surveyed molecular line emission from Orion BN/KL from 42.3 to 43.6 GHz with the Green Bank Telescope. Sixty-seven lines were identified and ascribed to 13 different molecular species. The...
Suzaku Observations of the Circinus galaxy (2008)
Yang, Y., Wilson, A. S., Matt, G., Terashima, Y., Greenhill, L. J.
We report Suzaku observations of the active, Compton-thick Circinus galaxy. Observations were obtained with both the X-ray Imaging spectrometer (XIS) and the Hard X-ray Detector (HXD). Below 10 keV,...
Real-Time Calibration of the Murchison Widefield Array (2008)
Mitchell, D. A., Greenhill, L. J., Wayth, R. B., Sault, R. J., Lonsdale, C. J., Cappallo, R. J., ...
The interferometric technique known as peeling addresses many of the challenges faced when observing with low-frequency radio arrays, and is a promising tool for the associated calibration systems....
Humphreys, E. M. L., Reid, M. J., Greenhill, L. J., Moran, J. M., Argon, A. L.
We report measurements of centripetal accelerations of maser spectral components of NGC 4258 for 51 epochs spanning 1994 to 2004. This is the second paper of a series, in which the goal is...
Masers in AGN environments (2007)
Galactic nuclei are well known sources of OH and H2O maser emission. It appears that intense star formation in ultra-luminous infrared galaxies drives most OH sources. In contrast, nuclear activity...
Matthews, L. D., Goddi, C., Greenhill, L. J., Chandler, C. J., Reid, M. J., Humphreys, E. M. L.
A comprehensive picture of high-mass star formation has remained elusive, in part because examples of high-mass YSOs tend to be relatively distant, deeply embedded, and confused with other emission...
Imaging the Ionized Disk of the High-Mass Protostar Orion-I (2007)
Reid, M. J., Menten, K. M., Greenhill, L. J., Chandler, C. J.
We have imaged the enigmatic radio source-I (Orion-I) in the Orion-KL nebula with the VLA at 43 GHz with 34 mas angular resolution. The continuum emission is highly elongated and is consistent with...
Argon, A. L., Greenhill, L. J., Reid, M. J., Moran, J. M., Humphreys, E. M. L.
We report a three year, 18 epoch, VLBI monitoring study of H2O masers in the sub-parsec, warped, accretion disk within the NGC4258 AGN. Our immediate goals are to trace the geometry of the underlying...
Water masers in the Local Group of galaxies (2006)
Brunthaler, A., Henkel, C., Reid, M. J., Greenhill, L. J., Falcke, H.
We compare the number of detected 22 GHz H2O masers in the Local Group galaxies M31, M33, NGC6822, IC10, IC1613, DDO187, GR8, NGC185, and the Magellanic Clouds with the water maser population of the...
Extragalactic H_2O masers and X-ray absorbing column densities (2005)
Zhang, J. S., Henkel, C., Kadler, M., Greenhill, L. J., Nagar, N., Wilson, A. S., ...
Having conducted a search for the 22 GHz water vapor line towards galaxies with nuclear activity, large nuclear column densities or high infrared luminosities, we present H_2O spectra for NGC2273,...
Kondratko, P. T., Greenhill, L. J., Moran, J. M., Lovell, J. E. J., Kuiper, T. B. H., Jauncey, D. L., ...
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...
First Detection of Millimeter/Submillimeter Extragalactic H2O Maser Emission (2005)
Humphreys, E. M. L., Greenhill, L. J., Reid, M. J., Beuther, H., Moran, J. M., Gurwell, M., ...
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...
Submm line imaging of Orion-KL with the Submillimeter Array (2005)
Beuther, H., Zhang, Q., Greenhill, L. J., Reid, M. J., Wilner, D., Keto, E., ...
We present the first submm (865mum) imaging spectral line survey at one arcsecond resolution conducted with the Submillimeter Array toward Orion-KL. Within the 2x2 GHz bandpasses (lower and upper...
The Geometry of and Mass Accretion Rate through the Maser Accretion Disk in NGC 4258 (2005)
Herrnstein, J. R., Moran, J. M., Greenhill, L. J., Trotter, Adam S.
A maximum likelihood analysis of the NGC 4258 maser positions and velocities reveals a ~2 sigma deviation from Keplerian motion in the projected rotation curve of the high-velocity features,...
The Geometric Distance and Proper Motion of the Triangulum Galaxy (M33) (2005)
Brunthaler, A., Reid, M. J., Falcke, H., Greenhill, L. J., Henkel, C.
We measured the angular rotation and proper motion of the Triangulum Galaxy (M33) with the Very Long Baseline Array by observing two H2O masers on opposite sides of the galaxy. By comparing the...
Parsec-scale water maser structure in TXS 2226-184 (2005)
Ball, G. H., Greenhill, L. J., Moran, J. M., Zaw, I., Henkel, C.
The geometric distance and proper motion of the Triangulum Galaxy (M33) (2005)
Brunthaler, A., Reid, M. J., Falcke, H., Greenhill, L. J., Henkel, C.
H2O megamasers : Accretion disks, jet interaction, outflows or massive star formation? (2005)
Henkel, C., Braatz, J. A., Tarchi, A., Peck, A. B., Nagar, N. M., Greenhill, L. J., ...
A Green Bank Telescope Search for Water Masers in Nearby Active Galactic Nuclei (2004)
Braatz, J. A., Henkel, C., Greenhill, L. J., Moran, J. M., Wilson, A. S.
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...
Scintillation in the Circinus Galaxy water megamasers (2004)
McCallum, J. N., Ellingsen, S. P., Jauncey, D. L., Lovell, J. E. J., Greenhill, L. J.
We present observations of the 22 GHz water vapor megamasers in the Circinus galaxy made with the Tidbinbilla 70m telescope. These observations confirm the rapid variability seen earlier by Greenhill...
Disks, Tori, and Cocoons: Emission and Absorption Diagnostics of AGN Environments (2004)
Morganti, R., Greenhill, L. J., Peck, A. B., Jones, D. L., Henkel, C.
One of the most important problems in the study of active galaxies is understanding the detailed geometry, physics, and evolution of the central engines and their environments. The leading models...
Galaxy Evolution and Cosmology with the Square Kilometre Array (2004)
Rawlings, S., Abdalla, F. B., Bridle, S. L., Blake, C. A., Baugh, C. M., Greenhill, L. J., ...
The present-day Universe is seemingly dominated by dark energy and dark matter, but mapping the normal (baryonic) content remains vital for both astrophysics - understanding how galaxies form - and...
Extragalactic Water Masers, Geometric Estimation of H_o and Characterization of Dark Energy (2004)
High precision estimation of the equation of state of dark energy depends on constraints external to analyses of Cosmic Microwave Background fluctuations. A geometric estimation of the local...
The IC133 Water Vapor Maser in the Galaxy M33: A Geometric Distance (2004)
Argon, A. L., Greenhill, L. J., Moran, J. M., Reid, M. J., Menten, K. M., Inoue, M.
We report on the results of a 14 year long VLBI study of proper motions in the IC133 H2O maser source in the galaxy M33. The method of Ordered Motion Parallax was used to model the 3-dimensional...
H2O megamasers: Accretion disks, jet interaction, outflows or massive star formation? (2004)
Henkel, C., Braatz, J. A., Tarchi, A., Peck, A. B., Nagar, N. M., Greenhill, L. J., ...
The 25 years following the serendipitous discovery of megamasers have seen tremendous progress in the study of luminous extragalactic H$_2$O emission. Single-dish monitoring and high resolution...
Sub-arcsecond sub-mm continuum observations of Orion-KL (2004)
Beuther, H., Zhang, Q., Greenhill, L. J., Reid, M. G., Wilner, D., Keto, E., ...
We present the first 865 mu continuum image with sub-arcsecond resolution obtained with the Submillimeter Array. These data resolve the Orion-KL region into the hot core, the nearby radio source I,...
High Angular Resolution Mid-infrared Imaging of Young Stars in Orion BN/KL (2004)
Greenhill, L. J., Gezari, D. Y., Danchi, W. C., Najita, J., Monnier, J. D., Tuthill, P. G.
We present Keck LWS images of the Orion BN/KL star forming region obtained in the first multi-wavelength study to have 0.3-0.5" resolution from 4.7 to 22 microns. The young stellar objects designated...
The IC 133 water vapor maser in the galaxy M33 : a geometric distance (2004)
Argon, A. L., Greenhill, L. J., Moran, J. M., Reid, M. J., Menten, K. M., Inoue, M.
A Green Bank Telescope search for water masers in nearby active galactic nuclei (2004)
Braatz, J. A., Henkel, C., Greenhill, L. J., Moran, J. M., Wilson, A. S.
Disks, Tori, and Cocoons : emission and absorption diagnostics of AGN environments (2004)
Morganti, R., Greenhill, L. J., Peck, A. B., Jones, D. L., Henkel, C.
Galaxy evolution, cosmology and dark energy with the Square Kilometer Array (2004)
Rawlings, S., Abdalla, F. B., Bridle, S. L., Blake, C. A., Baugh, C. M., Greenhill, L. J., ...
The present-day Universe is seemingly dominated by dark energy and dark matter, but mapping the normal (baryonic) content remains vital for both astrophysics – understanding how galaxies form -...
Galaxy evolution, cosmology and dark energy with the Square Kilometer Array (2004)
Rawlings, S., Abdalla, F. B., Bridle, S. L., Blake, C. A., Baugh, C. M., Greenhill, L. J., ...
The present-day Universe is seemingly dominated by dark energy and dark matter, but mapping the normal (baryonic) content remains vital for both astrophysics – understanding how galaxies form -...
The Most Detailed Picture Yet of an Embedded High-mass YSO (2003)
Greenhill, L. J., Reid, M. J., Chandler, C. J., Diamond, P. J., Elitzur, M.
High-mass star formation is not well understood chiefly because examples are deeply embedded, relatively distant, and crowded with sources of emission. Using VLA and VLBA observations of water and...
Recent Progress on a New Geometric Distance to NGC 4258 (2003)
Humphreys, E. M. L., Argon, A. L., Greenhill, L. J., Moran, J. M., Reid, M. J.
We report on our ongoing, high-resolution study of H2O masers in the innermost parsec of NGC 4258. Over thirty epochs of VLBA and VLA data, taken over six years, are being used to monitor the...
A Warped Accretion Disk and Wide Angle Outflow in the Inner Parsec of the Circinus Galaxy (2003)
Greenhill, L. J., Booth, R. S., Ellingsen, S. P., Herrnstein, J. R., Jauncey, D. L., McCulloch, P. M., ...
We present the first VLBI maps of H2O maser emission (lambda 1.3cm) in the nucleus of the Circinus Galaxy, constructed from data obtained with the Australia Telescope Long Baseline Array. The maser...
Greenhill, L. J., Kondratko, P. T., Lovell, J. E. J., Kuiper, T. B. H., Moran, J. M., Jauncey, D. L., ...
We report the discovery of H2O maser emission at 1.35 cm wavelength in seven active galactic nuclei (at distances up to
Discovery of water vapor megamaser emission from Mrk1419 (NGC 2690): An analogue of NGC 4258? (2002)
Henkel, C., Braatz, J. A., Greenhill, L. J., Wilson, A. S.
Water vapor emission at 22 GHz is reported from the nucleus of the LINER galaxy Mrk 1419 (NGC 2960). Single-dish spectra of the maser source show properties that are similar to those seen in NGC...
Recent Globular Cluster Searches with Arecibo and the Green Bank Telescope (2002)
Ransom, S. M., Hessels, J. W. T., Stairs, I. H., Kaspi, V. M., Backer, D. C., Greenhill, L. J., ...
We report the discovery of seven new millisecond pulsars during 20 cm searches of 19 globular clusters using the recently upgraded Arecibo Telescope and the new Green Bank Telescope (GBT). Five of...
Towards Proper Motions in the Local Group (2002)
Brunthaler, A., Reid, M., Falcke, H., Greenhill, L. J., Henkel, C.
Key and still largely missing parameters for measuring the mass content and distribution of the Local Group are the proper motion vectors of its member galaxies. The problem when trying to derive the...
Henkel, C., Braatz, J. A., Greenhill, L. J., Wilson, A. S.
Water vapor emission at 22 GHz is reported from the nucleus of the LINER galaxy Mrk 1419 (NGC 2960). Single-dish spectra of the maser source show properties that are similar to those seen in NGC...
Outflow 20-2000 AU from a high-mass protostar in W51-IRS 2 (2002)
Eisner, J. A., Greenhill, L. J., Herrnstein, J. R., Moran, J. M., Menten, K. M.
Proceedings of the 6th European VLBI Network Symposium (2002)
Ros Porcas Lobanov, A. Brunthaler, M. Reid, H. Falcke, L. J. Greenhill, C. Henkel
Key and still largely missing parameters for measuring the mass content and distribution of the Local Group are the proper motion vectors of its member galaxies. The problem when trying to derive the...
Towards Proper Motions in the Local Group (2002)
Porcas R. W, J. A. (eds, A. Brunthaler, M. Reid, H. Falcke, L.J. Greenhill, ...
Key and still largely missing parameters for measuring the mass content and distribution of the Local Group are the proper motion vectors of its member galaxies. The problem when trying to derive the...
Outflow 20--2000 AU from a High-Mass Protostar in W51-IRS2 (2001)
Eisner, J. A., Greenhill, L. J., Herrnstein, J. R., Moran, J. M., Menten, K. M.
We present the results of the first high angular resolution observations of SiO maser emission towards the star forming region W51-IRS2 made with the Very Large Array (VLA) and Very Long Baseline...
Greenhill, L. J., Ellingsen, S. P., Norris, R. P., McGregor, P. J., Gough, R. G., Sinclair, M. W., ...
We report the cumulative results of five surveys for water maser emission at 1.35 cm wavelength in 131 active galactic nuclei (AGNs) and star-forming galaxies, conducted at the Parkes Observatory...
Radio Properties of Pinwheel Nebulae (2001)
Monnier, J. D., Greenhill, L. J., Tuthill, P. G., Danchi, W. C.
A small number of dusty Wolf-Rayet stars have been resolved into pinwheel nebulae, defined by their ``rotating'' spiral dust shells observed in the infrared. This morphology is naturally explained by...
Extragalactic H2O Masers (2001)
Study of extragalactic H2O masers has progressed significantly in the 25 years since their discovery. Existing in star forming regions and in the accretion disks supermassive black holes, they are...
Radio and Infrared Properties of Dust-Enshrouded Wolf-Rayet Stars (2001)
Monnier, J. D., Greenhill, L. J., Tuthill, P. G., Danchi, W. C.
This paper discusses our ongoing efforts to characterize dust-enshrouded Wolf-Rayet (WR) stars in the radio and infrared. We have used the Very Large Array to measure the broadband radio spectrum of...
Accretion and Outflow Traced by Water Masers in the Circinus AGN (2000)
Greenhill, L. J., Moran, J. M., Booth, R. S., Ellingsen, S. P., McCulloch, P. M., Jauncey, D. L., ...
The first VLBI images of water maser emission in the Circinus Galaxy AGN show both a warped, edge-on accretion disk and an outflow 0.1 to 1 pc from the central engine. The inferred central mass is...
Accretion and Outflow in the Circinus AGN (2000)
The first VLBI images of water maser emission in the Circinus Galaxy AGN show both an accretion disk and outflow 0.1 to 1 pc from the central engine. The maser traces a warped, edge-on accretion disk...
Patel, N. A., Greenhill, L. J., Herrnstein, J., Zhang, Q., Moran, J. M., Ho, P. T. P., ...
We present VLBA observations of water maser emission associated with the star-forming region IRAS 21391+5802, which is embedded in a bright rimmed cometary globule in IC1396. The angular resolution...
Observational Evidence for Massive Black Holes in the Centers of Active Galaxies (2000)
Moran, J. M., Greenhill, L. J., Herrnstein, J. R.
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...
Accelerations of Water Masers in NGC4258 (2000)
Bragg, A. E., Greenhill, L. J., Moran, J. M., Henkel, C.
The water masers in NGC4258 delineate the structure and dynamics of a sub-parsec-diameter accretion disk around a supermassive black hole. We report acceleration measurements for 12 systemic-velocity...
A 4% Geometric Distance to the Galaxy NGC4258 from Orbital Motions in a Nuclear Gas Disk (1999)
Herrnstein, J. R., Moran, J. M., Greenhill, L. J., Diamond, P. J., Inoue, M., Nakai, N., ...
The water maser in the mildly active nucleus in the nearby galaxy NGC4258 traces a thin, nearly edge-on, subparsec-scale Keplerian disk. Using the technique of very long baseline interferometry, we...
Coexisting conical bipolar and equatorial outflows from a high-mass protostar (1998)
Greenhill, L. J., Gwinn, C. R., Schwartz, C., Moran, J. M., Diamond, P. J.
The BN/KL region in the Orion molecular cloud is an archetype in the study of the formation of stars much more massive than the Sun. This region contains luminous young stars and protostars, but it...
Herrnstein, J. R., Moran, J. M., Greenhill, L. J., Blackman, E. G., Diamond, P. J.
We report VLA 1 sigma upper limits of 1.5% and 3% on the intrinsic circular and linear fractional polarizations, respectively, of the water vapor maser emission 0.2 pc from the central engine of NGC...
VLBA Continuum Observations of NGC 4258: Constraints on an Advection-Dominated Accretion Flow (1998)
Herrnstein, J. R., Greenhill, L. J., Moran, J. M., Diamond, P. J., Inoue, M., Nakai, N., ...
We report a 3 sigma upper limit of 220 microJanskys on any 22-GHz continuum emission coincident with the central engine in NGC 4258. If NGC 4258 is powered by an advection-dominated accretion flow,...
VLBA Imaging of the OH Maser in IIIZw35 (1997)
Trotter, A. S., Moran, J. M., Greenhill, L. J., Gwinn, C. R.
We present a parsec-scale image of the OH maser in the nucleus of the active galaxy IIIZw35, made using the Very Long Baseline Array at a wavelength of 18 cm. We detected two distinct components,...
The Distribution of H2O Maser Emission in the Nucleus of NGC 4945 (1997)
Greenhill, L. J., Moran, J. M., Herrnstein, J. R.
We present the first interferometer map of the water maser emission in the active nucleus of NGC 4945. Although the declination of the galaxy is about -49 degrees, we were able to make the...
Lipman Monnier, C. H. Tuthill, T. R. Geballe, L. J. Greenhill, D. Cruzale Bes, Lefe Vre, ...
Visibility observations at 11 km of o Ceti have been made with the University of California (Berkeley) Infrared Spatial Interferometer during the time period 1988È1995. The observed visibilities...
Extremely Rapid Variations of Water Maser Emission from the Circinus Galaxy (1996)
Greenhill, L. J., Ellingsen, S. P., Norris, R. P., Gough, R. G., Sinclair, M. W., Moran, J. M., ...
The water maser lines in the nucleus of the Circinus galaxy vary on time scales as short as a few minutes, at least two orders of magnitude less than for other Galactic or extragalactic water masers....
VLBI Imaging of Water Maser Emission from the Nuclear Torus of NGC 1068 (1996)
Greenhill, L. J., Gwinn, C. R., Antonucci, R., Barvainis, R.
We have made the first VLBI synthesis images of the H2O maser emission associated with the central engine of the Seyfert galaxy NGC 1068. Emission extends about +/-300 km/s from the systemic...
P. G. Tuthill, C. H. Townes, C. G. Degiacomi, T. R. Geballe, L. J. Greenhill, P. Cruzale Bes, ...
Visibility observations at 11 km of o Ceti have been made with the University of California (Berkeley) Infrared Spatial Interferometer during the time period 1988È1995. The observed visibilities...