Browsing FAS Scholarly Articles by Keyword "galaxies: nuclei"

Now showing items 1-16 of 16

    • Accelerations of Water Masers in NGC 4258 

      Bragg, Ann E.; Greenhill, Lincoln Jared; Moran, James M.; Henkel, Christian (IOP Publishing, 2000)
      The water masers in NGC4258 delineate the structure and dynamics of a sub-parsec-diameter accretion disk around a supermassive black hole. VLBA observations provide precise information about the positions in the plane of ...

    • Black Hole Spin and the Radio Loud/Quiet Dichotomy of Active Galactic Nuclei 

      Tchekhovskoy, Alexander; Narayan, Ramesh; McKinney, Jonathan C. (IOP Publishing, 2010)
      Radio loud active galactic nuclei (AGNs) are on average 1000 times brighter in the radio band compared to radio quiet AGNs. We investigate whether this radio loud/quiet dichotomy can be due to differences in the spin of ...

    • Bondi Flow from a Slowly Rotating Hot Atmosphere 

      Narayan, Ramesh; Fabian, Andrew C. (Oxford University Press (OUP), 2011)
      A supermassive black hole in the nucleus of an elliptical galaxy at the centre of a cool-core group or cluster of galaxies is immersed in hot gas. Bondi accretion should occur at a rate determined by the properties of the ...

    • The Cambridge-Cambridge ROSAT Serendipity Survey - III. VLA observations and the evolution of radio-quiet and radio-loud objects 

      Ciliegi, P.; Elvis, Martin S.; Wilkes, Belinda Jane; Boyle, B. J.; McMahon, R. G.; Maccacaro, T. (Oxford University Press (OUP), 1995)
      We present the results of the VLA radio observations at 1.475 GHz (20 cm) of the active galactic nuclei (AGN) in the Cambridge-Cambridge ROSAT Serendipity Survey (CRSS), a sample of 123 faint X-ray sources with ...

    • Discovery of an Outflow from Radio Observations of the Tidal Disruption event ASASSN-14li 

      Alexander, K. D.; Berger, Edo; Guillochon, J.; Zauderer, B. A.; Williams, Peter Kelsey George (American Astronomical Society, 2016)
      We report the discovery of transient radio emission from the nearby optically-discovered TDE ASASSN-14li (distance of 90 Mpc), making it the first typical TDE detected in the radio, and unambiguously pointing to the formation ...

    • Double-peaked narrow-line signatures of dual supermassive black holes in galaxy merger simulations 

      Blecha, L.; Loeb, A.; Narayan, Ramesh (Oxford University Press (OUP), 2013)
      We present a first attempt to model the narrow-line (NL) region of active galactic nuclei (AGN) in hydrodynamic simulations of galaxy mergers, using a novel physical prescription. This model is used to determine the origin ...

    • First Detection of Millimeter/Submillimeter Extragalactic H2O Maser Emission 

      Humphreys, E. M. L.; Greenhill, L. J.; Reid, M. J.; Beuther, H.; Moran, James M.; Gurwell, Mark Andrew; Wilner, David J.; Kondratko, P. T. (IOP Publishing, 2005)
      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 GALEX Time Domain Survey. II. Wavelength-Dependent Variability of Active Galactic Nuclei in the Pan-STARRS1 Medium Deep Survey 

      Hung, T; Gezari, S; Jones, D.O.; Kirshner, Robert P.; Chornock, R; Berger, Edo; Rest, A.; Huber, M.; Narayan, G.; Scolnic, D.; Waters, C.; Wainscoat, R.; Martin, D.C.; Forster, K.; Neill, J.D. (American Astronomical Society, 2016)
      We analyze the wavelength-dependent variability of a sample of spectroscopically confirmed active galactic nuclei (AGN) selected from near-UV (NUV) variable sources in the GALEX Time Domain Survey that have a large amplitude ...

    • The Geometry of and Mass Accretion Rate through the Maser Accretion Disk in NGC 4258 

      Herrnstein, J. R.; Moran, James M.; Greenhill, Lincoln Jared; Trotter, Adam S. (IOP Publishing, 2005)
      A maximum likelihood analysis of the NGC 4258 maser positions and velocities reveals a ∼ 2 σ deviation from Keplerian motion in the projected rotation curve of the high-velocity features, corresponding to a ∼ 9 km s−1, or ...

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

      Braatz, J. A.; Henkel, C.; Greenhill, Lincoln Jared; Moran, James M.; Wilson, A. S. (IOP Publishing, 2004)
      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, ...

    • Ps1-10jh Continues to Follow the Fallback Accretion Rate of a Tidally Disrupted Star 

      Gezari, S.; Chornock, R.; Lawrence, A.; Rest, A.; Jones, D. O.; Berger, Edo; Challis, P. M.; Narayan, G. (IOP Publishing, 2015)
      We present late-time observations of the tidal disruption event candidate PS1-10jh. UV and optical imaging with HST/WFC3 localize the transient to be coincident with the host galaxy nucleus to an accuracy of 0.023 arcsec, ...

    • A Simplified Global Solution for an Advection‐dominated Accretion Flow 

      Yuan, Feng; Ma, Renyi; Narayan, Ramesh (IOP Publishing, 2008)
      When we model black hole accretion sources such as active galactic nuclei and black hole X-ray binaries as advection dominated accretion flows (ADAFs), it is necessary to use the global solution to the equations rather ...

    • Steps toward determination of the size and structure of the broad-line region in active nuclei. 7: Variability of the optical spectrum of NGC 5548 over years 

      Peterson, B. M.; Berlind, Perry; Bertram, R.; Bochkarev, N. G.; Bond, D.; Brotherton, M. S.; Busler, J. R.; Chuvaev, K. K.; Cohen, R. D.; Dietrich, M.; Elvis, Martin S.; Filippenko, A. V.; Foltz, C. B.; Garnavich, P. M.; Ho, L. C.; Horine, E.; Horne, K.; Huchra, J; Kollatschny, W.; Korista, K. T.; Malkan, M. A.; Matheson, T.; Mignoli, M.; Morris, S. L.; Nazarova, L.; Penfold, J.; Peters, J.; Pogge, R. W.; Pronik, V. I.; Rush, B.; Sergeev, S. G.; Shapovalova, A. I.; Shields, J. C.; Stirpe, G. M.; Tokarz, S.; Wagner, Rudolf; Weymann, R. J.; White, R. J.; Wilkes, Belinda Jane; Wills, D.; Wills, B. J.; Winge, C.; Younger, P. F. (IOP Publishing, 1994)
      We report on the results of a continuation of a large monitoring program of optical spectroscopy of the Seyfert 1 galaxy NGC 5548. The new observations presented here were obtained between 1990 December and 1992 October, ...

    • Swift J1112.2-8238: A Candidate Relativistic Tidal Disruption Flare 

      Brown, G. C.; Levan, A. J.; Stanway, E. R.; Tanvir, N. R.; Cenko, S. B.; Berger, Edo; Chornock, R.; Cucchiaria, A. (Oxford University Press (OUP), 2015)
      We present observations of Swift J1112.2-8238, and identify it as a candidate relativistic tidal disruption flare (rTDF). The outburst was first detected by Swift/BAT in June 2011 as an unknown, long-lived (order of days) ...

    • Toward a New Geometric Distance to the Active Galaxy NGC 4258. I. VLBI Monitoring of Water Maser Emission 

      Argon, A; Greenhill, Lincoln Jared; Reid, Mark Jonathan; Moran, James M.; Humphreys, E. M. L. (IOP Publishing, 2007)
      We report a three year, 18 epoch, VLBI monitoring study of H 2O masers in the sub-parsec, warped, accretion disk within the NGC 4258 AGN. Our immediate goals are to trace the geometry of the underlying disk, track rotation ...

    • Toward a New Geometric Distance To the Active Galaxy NGC 4258. III. Final Results and The Hubble Constant 

      Humphreys, E. M. L.; Reid, Mark Jonathan; Moran, James M.; Greenhill, Lincoln Jared; Argon, Alice L. (American Astronomical Society, 2013)
      We report a new geometric maser distance estimate to the active galaxy NGC 4258. The data for the new model are maser line-of-sight (LOS) velocities and sky positions from 18 epochs of very long baseline interferometry ...