Browsing by Author "Urry, C. Megan"
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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 CHANDRA OBSERVATIONS OF GALAXY ZOO MERGERS: FREQUENCY OF BINARY ACTIVE NUCLEI IN MASSIVE MERGERS(IOP Publishing, 2012-07-10) Teng, Stacy H.; Schawinski, Kevin; Urry, C. Megan; Darg, Dan W.; Kaviraj, Sugata; Oh, Kyuseok; Bonning, Erin W.; Cardamone, Carolin N.; Keel, William C.; Lintott, Chris J.; Simmons, Brooke D.; Treister, Ezequiel; National Aeronautics & Space Administration (NASA); NASA Goddard Space Flight Center; University System of Maryland; University of Maryland College Park; Yale University; University of Oxford; Yonsei University; Brown University; University of Alabama Tuscaloosa; Universidad de ConcepcionWe present the results from a Chandra pilot study of 12 massive galaxy mergers selected from Galaxy Zoo. The sample includes major mergers down to a host galaxy mass of 10(11) M-circle dot that already have optical active galactic nucleus (AGN) signatures in at least one of the progenitors. We find that the coincidences of optically selected active nuclei with mildly obscured (N-H less than or similar to 1.1 x 10(22) cm(-2)) X-ray nuclei are relatively common (8/12), but the detections are too faint (<40 counts per nucleus; f(2-10 keV) less than or similar to 1.2 x 10(-13) erg s(-1) cm(-2)) to reliably separate starburst and nuclear activity as the origin of the X-ray emission. Only one merger is found to have confirmed binary X-ray nuclei, though the X-ray emission from its southern nucleus could be due solely to star formation. Thus, the occurrences of binary AGNs in these mergers are rare (0%-8%), unless most merger-induced active nuclei are very heavily obscured or Compton thick.Item Extended X-ray emission in the IC 2497-Hanny's Voorwerp system: energy injection in the gas around a fading AGN(Oxford University Press, 2016-01-29) Sartori, Lia F.; Schawinski, Kevin; Koss, Michael; Treister, Ezequiel; Maksym, W. Peter; Keel, William C.; Urry, C. Megan; Lintott, Chris J.; Wong, O. Ivy; Swiss Federal Institutes of Technology Domain; ETH Zurich; Universidad de Concepcion; Harvard University; Smithsonian Astrophysical Observatory; Smithsonian Institution; University of Alabama Tuscaloosa; Yale University; University of Oxford; University of Western AustraliaWe present deep Chandra X-ray observations of the core of IC 2497, the galaxy associated with Hanny's Voorwerp and hosting a fading AGN. We find extended soft X-ray emission from hot gas around the low intrinsic luminosity (unobscured) AGN (L-bol similar to 10(42)-10(44) erg s(-1)). The temperature structure in the hot gas suggests the presence of a bubble or cavity around the fading AGN (E-bub similar to 10(54)-10(55) erg). A possible scenario is that this bubble is inflated by the fading AGN, which after changing accretion state is now in a kinetic mode. Other possibilities are that the bubble has been inflated by the past luminous quasar (L-bol similar to 10(46) erg s(-1)), or that the temperature gradient is an indication of a shock front from a superwind driven by the AGN. We discuss the possible scenarios and the implications for the AGN-host galaxy interaction, as well as an analogy between AGN and X-ray binaries lifecycles. We conclude that the AGN could inject mechanical energy into the host galaxy at the end of its lifecycle, and thus provide a source for mechanical feedback, in a similar way as observed for X-ray binaries.Item Fading AGN Candidates: AGN Histories and Outflow Signatures(IOP Publishing, 2017-02-01) Keel, William C.; Lintott, Chris J.; Maksym, W. Peter; Bennert, Vardha N.; Chojnowski, S. Drew; Moiseev, Alexei; Smirnova, Aleksandrina; Schawinski, Kevin; Sartori, Lia F.; Urry, C. Megan; Pancoast, Anna; Schirmer, Mischa; Scott, Bryan; Showley, Charles; Flatland, Kelsi; University of Alabama Tuscaloosa; University of Oxford; California State University System; California Polytechnic State University San Luis Obispo; New Mexico State University; Russian Academy of Sciences; Special Astrophysics Observatory of the Russian Academy of Sciences; Swiss Federal Institutes of Technology Domain; ETH Zurich; Yale UniversityWe consider the energy budgets and radiative history of eight fading active galactic nuclei (AGNs), identified from an energy shortfall between the requirements to ionize very extended (radius > 10 kpc) ionized clouds and the luminosity of the nucleus as we view it directly. All show evidence of significant fading on timescales of approximate to 50,000 yr. We explore the use of minimum ionizing luminosity Q(ion) derived from photoionization balance in the brightest pixels in H alpha at each projected radius. Tests using presumably constant Palomar-Green QSOs, and one of our targets with detailed photoionization modeling, suggest that we can derive useful histories of individual AGNs, with the caveat that the minimum ionizing luminosity is always an underestimate and subject to uncertainties about fine structure in the ionized material. These consistency tests suggest that the degree of underestimation from the upper envelope of reconstructed Q(ion) values is roughly constant for a given object and therefore does not prevent such derivation. The AGNs in our sample show a range of behaviors, with rapid drops and standstills; the common feature is a rapid drop in the last approximate to 2 x 10(4) yr before the direct view of the nucleus. The e-folding timescales for ionizing luminosity are mostly in the thousands of years, with a few episodes as short as 400 yr. In the limit of largely obscured AGNs, we find additional evidence for fading from the shortfall between even the lower limits from recombination balance and the maximum luminosities derived from far-infrared fluxes. We compare these long-term light curves, and the occurrence of these fading objects among all optically identified AGNs, to simulations of AGN accretion; the strongest variations over these timespans are seen in models with strong and local (parsec-scale) feedback. We present Gemini integral-field optical spectroscopy, which shows a very limited role for outflows in these ionized structures. While rings and loops of emission, morphologically suggestive of outflow, are common, their kinematic structure shows some to be in regular rotation. UGC 7342 exhibits local signatures of outflows <300 km s(-1), largely associated with very diffuse emission, and possibly entraining gas in one of the clouds seen in Hubble Space Telescope images. Only in the Teacup AGN do we see outflow signatures of the order of 1000 km s(-1). In contrast to the extended emission regions around many radio-loud AGNs, the clouds around these fading AGNs consist largely of tidal debris being externally illuminated but not displaced by AGN outflows.Item The green valley is a red herring: Galaxy Zoo reveals two evolutionary pathways towards quenching of star formation in early- and late-type galaxies star(Oxford University Press, 2014-03-15) Schawinski, Kevin; Urry, C. Megan; Simmons, Brooke D.; Fortson, Lucy; Kaviraj, Sugata; Keel, William C.; Lintott, Chris J.; Masters, Karen L.; Nichol, Robert C.; Sarzi, Marc; Skibba, Ramin; Treister, Ezequiel; Willett, Kyle W.; Wong, O. Ivy; Yi, Sukyoung K.; Swiss Federal Institutes of Technology Domain; ETH Zurich; Yale University; University of Oxford; University of Minnesota System; University of Minnesota Twin Cities; University of Hertfordshire; University of Alabama Tuscaloosa; University of Portsmouth; University of California System; University of California San Diego; Universidad de Concepcion; Commonwealth Scientific & Industrial Research Organisation (CSIRO); Yonsei UniversityWe use SDSS+GALEX+Galaxy Zoo data to study the quenching of star formation in low-redshift galaxies. We show that the green valley between the blue cloud of star-forming galaxies and the red sequence of quiescent galaxies in the colour-mass diagram is not a single transitional state through which most blue galaxies evolve into red galaxies. Rather, an analysis that takes morphology into account makes clear that only a small population of blue early-type galaxies move rapidly across the green valley after the morphologies are transformed from disc to spheroid and star formation is quenched rapidly. In contrast, the majority of blue star-forming galaxies have significant discs, and they retain their late-type morphologies as their star formation rates decline very slowly. We summarize a range of observations that lead to these conclusions, including UV-optical colours and halo masses, which both show a striking dependence on morphological type. We interpret these results in terms of the evolution of cosmic gas supply and gas reservoirs. We conclude that late-type galaxies are consistent with a scenario where the cosmic supply of gas is shut off, perhaps at a critical halo mass, followed by a slow exhaustion of the remaining gas over several Gyr, driven by secular and/or environmental processes. In contrast, early-type galaxies require a scenario where the gas supply and gas reservoir are destroyed virtually instantaneously, with rapid quenching accompanied by a morphological transformation from disc to spheroid. This gas reservoir destruction could be the consequence of a major merger, which in most cases transforms galaxies from disc to elliptical morphology, and mergers could play a role in inducing black hole accretion and possibly active galactic nuclei feedback.Item HST IMAGING OF FADING AGN CANDIDATES. I. HOST-GALAXY PROPERTIES AND ORIGIN OF THE EXTENDED GAS(IOP Publishing, 2015-05) Keel, William C.; Maksym, W. Peter; Bennert, Vardha N.; Lintott, Chris J.; Chojnowski, S. Drew; Moiseev, Alexei; Smirnova, Aleksandrina; Schawinski, Kevin; Urry, C. Megan; Evans, Daniel A.; Pancoast, Anna; Scott, Bryan; Showley, Charles; Flatland, Kelsi; University of Alabama Tuscaloosa; California State University System; California Polytechnic State University San Luis Obispo; New Mexico State University; Russian Academy of Sciences; Special Astrophysics Observatory of the Russian Academy of Sciences; Swiss Federal Institutes of Technology Domain; ETH Zurich; Yale University; Harvard University; Smithsonian Astrophysical Observatory; Smithsonian Institution; University of California System; University of California Santa Barbara; California Institute of Technology; National Aeronautics & Space Administration (NASA); NASA Jet Propulsion Laboratory (JPL); San Francisco State UniversityWe present narrow- and medium-band Hubble Space Telescope imaging, with additional supporting ground-based imaging, spectrophotometry, and Fabry-Perot interferometric data, for eight galaxies identified as hosting a fading active galactic nucleus (AGN). These are selected to have AGN-ionized gas projected > 10 kpc from the nucleus and energy budgets with a significant shortfall of ionizing radiation between the requirement to ionize the distant gas and the AGN as observed directly, indicating fading of the AGN on approximate to 50,000 yr timescales. This paper focuses on the host-galaxy properties and origin of the gas. In every galaxy, we identify evidence of ongoing or past interactions, including tidal tails, shells, and warped or chaotic dust structures; a similarly selected sample of obscured AGNs with extended ionized clouds shares this high incidence of disturbed morphologies. Several systems show multiple dust lanes in different orientations, broadly fit by differentially precessing disks of accreted material viewed similar to 1.5 Gyr after its initial arrival. The host systems are of early Hubble type; most show nearly pure de Vaucouleurs surface brightness profiles and Sersic indices appropriate for classical bulges, with one S0 and one SB0 galaxy. The gas has a systematically lower metallicity than the nuclei; three systems have abundances uniformly well below solar, consistent with an origin in tidally disrupted low-luminosity galaxies, while some systems have more nearly solar abundances (accompanied by such signatures as multiple Doppler components), which may suggest redistribution of gas by outflows within the host galaxies themselves. These aspects are consistent with a tidal origin for the extended gas in most systems, although the ionized gas and stellar tidal features do not always match closely. Unlike extended emission regions around many radio-loud AGNs, these clouds are kinematically dominated by rotation, in some cases in warped disks. Outflows can play important kinematic roles only in localized regions near some of the AGNs. We find only a few sets of young star clusters potentially triggered by AGN outflows. In UGC 7342 and UGC 11185, multiple luminous star clusters are seen just within the projected ionization cones, potentially marking star formation triggered by outflows. As in the discovery example, Hanny's Voorwerp/IC 2497, there are regions in these clouds where the lack of a strong correlation between Ha surface brightness and ionization parameter indicates that there is unresolved fine structure in the clouds. Together with thin coherent filaments spanning several kpc, persistence of these structures over their orbital lifetimes may require a role for magnetic confinement. Overall, we find that the sample of fading AGNs occur in interacting and merging systems, that the very extended ionized gas is composed of tidal debris rather than galactic winds, and that these host systems are bulge-dominated and show no strong evidence of triggered star formation in luminous clusters.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.