Browsing by Author "Virani, Shanil"
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Item Black Hole Growth and Host Galaxy Morphology(2010) Schawinski, Kevin; Urry, C. Megan; Virani, Shanil; Coppi, Paolo; Bamford, Steven P.; Treister, Ezequiel; Lintott, Chris J.; Sarzi, Marc; Keel, William C.; Kaviraj, Sugata; Cardamone, Carolin N.; Masters, Karen L.; Ross, Nicholas P.; Galaxy Zoo Team; University of Alabama TuscaloosaWe use data from large surveys of the local universe (SDSS+Galaxy Zoo) to show that the galaxy–black hole connection is linked to host morphology at a fundamental level. The fraction of early-type galaxies with actively growing black holes, and therefore the AGN duty cycle, declines significantly with increasing black hole mass. Late-type galaxies exhibit the opposite trend: the fraction of actively growing black holes increases with black hole mass.Item Galaxy Zoo: 'Hanny's Voorwerp', a quasar light echo?(Oxford University Press, 2009) Lintott, Chris J.; Schawinski, Kevin; Keel, William; van Arkel, Hanny; Bennert, Nicola; Edmondson, Edward; Thomas, Daniel; Smith, Daniel J. B.; Herbert, Peter D.; Jarvis, Matt J.; Virani, Shanil; Andreescu, Dan; Bamford, Steven P.; Land, Kate; Murray, Phil; Nichol, Robert C.; Raddick, M. Jordan; Slosar, Anze; Szalay, Alex; Vandenberg, Jan; University of Oxford; Yale University; University of Alabama Tuscaloosa; University of California System; University of California Riverside; University of California Santa Barbara; University of Portsmouth; Liverpool John Moores University; University of Hertfordshire; Johns Hopkins University; United States Department of Energy (DOE); Lawrence Berkeley National Laboratory; University of California BerkeleyWe report the discovery of an unusual object near the spiral galaxy IC 2497, discovered by visual inspection of the Sloan Digital Sky Survey (SDSS) as part of the Galaxy Zoo project. The object, known as Hanny's Voorwerp, is bright in the SDSS g band due to unusually strong [O III]4959, 5007 emission lines. We present the results of the first targeted observations of the object in the optical, ultraviolet and X-ray, which show that the object contains highly ionized Gas. Although the line ratios are similar to extended emission-line regions near luminous active galactic nucleus (AGN), the source of this ionization is not apparent. The emission-fine properties, and lack of X-ray emission from IC 2497, suggest either a highly obscured AGN with a novel geometry arranged to allow photoionization of the object but not the galaxy's own circumnuclear gas, or, as we argue, the first detection of a quasar light echo. In this case, either the luminosity of the central source has decreased dramatically or else the obscuration in the system has increased within 10(5) yr. This object may thus represent the first direct probe of quasar history on these time-scales.Item GALAXY ZOO: THE FUNDAMENTALLY DIFFERENT CO-EVOLUTION OF SUPERMASSIVE BLACK HOLES AND THEIR EARLY-AND LATE-TYPE HOST GALAXIES(IOP Publishing, 2010-03-01) Schawinski, Kevin; Urry, Megan; Virani, Shanil; Coppi, Paolo; Bamford, Steven P.; Treister, Ezequiel; Lintott, Chris J.; Sarzi, Marc; Keel, William C.; Kaviraj, Sugata; Cardamone, Carolin N.; Masters, Karen L.; Ross, Nicholas P.; Andreescu, Dan; Murray, Phil; Nichol, Robert C.; Raddick, M. Jordan; Slosar, Anze; Szalay, Alex S.; Thomas, Daniel; Vandenberg, Jan; Yale University; University of Nottingham; University of Hawaii System; University of Oxford; University of Hertfordshire; University of Alabama Tuscaloosa; Imperial College London; University of Portsmouth; Pennsylvania Commonwealth System of Higher Education (PCSHE); Pennsylvania State University; Pennsylvania State University - University Park; Johns Hopkins University; United States Department of Energy (DOE); Lawrence Berkeley National Laboratory; University of California System; University of California Berkeley; University of LjubljanaWe use data from the Sloan Digital Sky Survey and visual classifications of morphology from the Galaxy Zoo project to study black hole growth in the nearby universe (z 0.05) and to break down the active galactic nucleus (AGN) host galaxy population by color, stellar mass, and morphology. We find that the black hole growth at luminosities L[O III] > 10(40) erg s(-1) in early- and late-type galaxies is fundamentally different. AGN host galaxies as a population have a broad range of stellar masses (10(10)-10(11) M-circle dot), reside in the green valley of the color-mass diagram and their central black holes have median masses around 10(6.5) M-circle dot. However, by comparing early- and late-type AGN host galaxies to their non-active counterparts, we find several key differences: in early-type galaxies, it is preferentially the galaxies with the least massive black holes that are growing, while in late-type galaxies, it is preferentially the most massive black holes that are growing. The duty cycle of AGNs in early-type galaxies is strongly peaked in the green valley below the low-mass end (10(10) M-circle dot) of the red sequence at stellar masses where there is a steady supply of blue cloud progenitors. The duty cycle of AGNs in late-type galaxies on the other hand peaks in massive (10(11) M-circle dot) green and red late-types which generally do not have a corresponding blue cloud population of similar mass. At high-Eddington ratios (L/L-Edd > 0.1), the only population with a substantial fraction of AGNs are the low-mass green valley early-type galaxies. Finally, the Milky Way likely resides in the "sweet spot" on the color-mass diagram where the AGN duty cycle of late-type galaxies is highest. We discuss the implications of these results for our understanding of the role of AGNs in the evolution of galaxies.Item Probing Quasar Shutdown Timescales with Hanny's Voorwerp(2012) Evans, Daniel A.; Schawinski, Kevin; Virani, Shanil; Urry, C. Megan; Keel, William C.; Natarajan, Priyamvada; Lintott, Chris J.; Manning, Anna; Coppi, Paolo; Kaviraj, Sugata; Bamford, Steven P.; Jozsa, Gyula I. G.; van Arkel, Hanny; Gay, Pamela; Fortson, Lucy; Garrett, Michael; University of Alabama TuscaloosaGalaxy formation is significantly modulated by energy output from supermassive black holes at the centers of galaxies which grow in highly efficient luminous quasar phases. The timescale on which black holes transition into and out of such phases is, however, unknown. We present the first measurement of the shutdown timescale for an individual quasar using Suzaku and XMM-Newton X-ray observations of the nearby galaxy IC 2497, which hosted a luminous quasar no more than ∼230,000 years ago that is still seen as a light echo in 'Hanny's Voorwerp', but whose presentday radiative output is lower by at least 2 and more likely by over 4 orders of magnitude. This extremely rapid shutdown provides new insights into the physics of accretion in supermassive black holes, and may signal a transition of the accretion disk to a radiatively inefficient state. These results were first presented by [1]. © 2012 American Institute of Physics.Item THE SUDDEN DEATH OF THE NEAREST QUASAR(IOP Publishing, 2010-11-20) Schawinski, Kevin; Evans, Daniel A.; Virani, Shanil; Urry, C. Megan; Keel, William C.; Natarajan, Priyamvada; Lintott, Chris J.; Manning, Anna; Coppi, Paolo; Kaviraj, Sugata; Bamford, Steven P.; Jozsa, Gyula I. G.; Garrett, Michael; van Arkel, Hanny; Gay, Pamela; Fortson, Lucy; Yale University; Massachusetts Institute of Technology (MIT); Harvard University; Smithsonian Astrophysical Observatory; Smithsonian Institution; Elon University; University of Alabama Tuscaloosa; University of Oxford; Imperial College London; University of Nottingham; University of Bonn; Leiden University; Leiden University - Excl LUMC; Swinburne University of Technology; Southern Illinois University System; Southern Illinois University Edwardsville; University of Minnesota System; University of Minnesota Twin CitiesGalaxy formation is significantly modulated by energy output from supermassive black holes at the centers of galaxies which grow in highly efficient luminous quasar phases. The timescale on which black holes transition into and out of such phases is, however, unknown. We present the first measurement of the shutdown timescale for an individual quasar using X-ray observations of the nearby galaxy IC 2497, which hosted a luminous quasar no more than 70,000 years ago that is still seen as a light echo in "Hanny's Voorwerp," but whose present-day radiative output is lower by at least two, and more likely by over four, orders of magnitude. This extremely rapid shutdown provides new insight into the physics of accretion in supermassive black holes and may signal a transition of the accretion disk to a radiatively inefficient state.