Browsing by Author "Hickox, R. C."

Now showing 1 - 10 of 10
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    Accretion History of AGNs. II. Constraints on AGN Spectral Parameters Using the Cosmic X-Ray Background
    (2020) Ananna, Tonima; Treister, Ezequiel; Urry, C. Megan; Ricci, Claudio; Hickox, R. C.; Padmanabhan, Nikhil; Marchesi, Stefano; Kirkpatrick, Allison
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    Accretion history of AGNs. III. Radiative efficiency and AGN contribution to reionization
    (2020) Ananna, T. T.; Urry, C. M.; Treister, Ezequiel; Hickox, R. C.; Shankar, F.; Ricci, Claudio; Cappelluti, N.; Marchesi, S.; Turner, T. J.
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    Determining the covering factor of compton-thick active galactic nuclei with NuSTAR
    (2015) Brightman, M.; Balokovic, M.; Stern, D.; Arevalo, P.; Ballantyne, D. R.; Bauer, Franz Erik; Bogg, S. E.; Craig, W. W.; Christensen, F. E.; Comastri, A.; Gandhi, P.; Hailey, C. J.; Harrison, F. A.; Hickox, R. C.; Koss, M.; Lamassa, S.; Fuerst, F.; Puccetti, S.; Rivers, E.; Vasudevan, R.; Walton, D. J.; Zhang, W. W.
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    GOODS-Herschel: the far-infrared view of star formation in active galactic nucleus host galaxies since z ∼ 3
    (2012) Mullaney, J. R.; Pannella, M.; Daddi, E.; Alexander, D. M.; Elbaz, D.; Hickox, R. C.; Bournaud, F.; Altieri, B.; Aussel, H.; Coia, D.; Dannerbauer, H.; Dasyra, K.; Dickinson, M.; Hwang, H. S.; Kartaltepe, J.; Leiton, R.; Magdis, G.; Magnelli, B.; Popesso, P.; Valtchanov, I.; Bauer, F. E.; Brandt, W. N.; Del Moro, A.; Hanish, D. J.; Ivison, R. J.; Juneau, S.; Luo, B.; Lutz, D.; Sargent, M. T.; Scott, D.; Xue, Y. Q.
    We present a study of the infrared properties of X-ray selected, moderate-luminosity (i.e. L-X = 10(42)-10(44) erg s(-1)) active galactic nuclei (AGNs) up to z approximate to 3, in order to explore the links between star formation in galaxies and accretion on to their central black holes. We use 100 and 160 mu m fluxes from GOODS-Herschel - the deepest survey yet undertaken by the Herschel telescope - and show that in the vast majority of cases (i.e. > 94 per cent) these fluxes are dominated by emission from the host galaxy. As such, these far-infrared bands provide an uncontaminated view of star formation in the AGN host galaxies. We find no evidence of any correlation between the X-ray and infrared luminosities of moderate AGNs at any redshift, suggesting that global star formation is decoupled from nuclear (i.e. AGN) activity in these galaxies. On the other hand, we confirm that the star formation rates of AGN hosts increase strongly with redshift, by a factor of 43(-18)(+27) from z < 0.1 to z = 2-3 for AGNs with the same range of X-ray luminosities. This increase is entirely consistent with the factor of 25-50 increase in the specific star formation rates (SSFRs) of normal, star-forming (i.e. main-sequence) galaxies over the same redshift range. Indeed, the average SSFRs of AGN hosts are only marginally (i.e. approximate to 20 per cent) lower than those of main-sequence galaxies at all surveyed redshifts, with this small deficit being due to a fraction of AGNs residing in quiescent (i.e. low SSFR) galaxies. We estimate that 79 +/- 10 per cent of moderate-luminosity AGNs are hosted in main-sequence galaxies, 15 +/- 7 per cent in quiescent galaxies and < 10 per cent in strongly starbursting galaxies. We derive the fractions of all main-sequence galaxies at z < 2 that are experiencing a period of moderate nuclear activity, noting that it is strongly dependent on galaxy stellar mass (M-stars), rising from just a few per cent at M-stars similar to 10(10) M-circle dot to greater than or similar to 20 per cent at M-stars >= 10(11) M-circle dot. Our results indicate that it is galaxy stellar mass that is most important in dictating whether a galaxy hosts a moderate-luminosity AGN. We argue that the majority of moderate nuclear activity is fuelled by internal mechanisms rather than violent mergers, which suggests that high-redshift disc instabilities could be an important AGN feeding mechanism.
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    Hard X-Ray-selected AGNs in Low-mass Galaxies from the NuSTAR Serendipitous Survey
    (2017) Chen, C. T. J.; Brandt, W. N.; Reines, A. E.; Lansbury, G.; Stern, D.; Alexander, D. M.; Bauer, Franz Erik; Ricci, Claudio; Del Moro, A.; Gandhi, P.; Harrison, F. A.; Hickox, R. C.; Koss, M. J.; Lanz, L.; Koss, M. J.; Lanz, L.; Luo, B.; Ricci, Claudio
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    Hot Dust-obscured Galaxies with Excess Blue Light
    (2020) Assef, R. J.; Brightman, M.; Walton, D. J.; Stern, D.; Bauer, F. E.; Blain, A. W.; Diaz-Santos, T.; Eisenhardt, P. R. M.; Hickox, R. C.; Jun, H. D.; Psychogyios, A.; Tsai, C-W; Wu, J. W.
    Hot dust-obscured galaxies (Hot DOGs) are among the most luminous galaxies in the universe. Powered by highly obscured, possibly Compton-thick, active galactic nuclei (AGNs), Hot DOGs are characterized by spectral energy distributions that are very red in the mid-infrared yet dominated by the host galaxy stellar emission in the UV and optical. An earlier study identified a subsample of Hot DOGs with significantly enhanced UV emission. One target, W0204-0506, was studied in detail and, based on Chandra observations, it was concluded that the enhanced emission was most likely due to either extreme unobscured star formation (star formation rate > 1000Myr(-1)) or to light from the highly obscured AGN scattered by gas or dust into our line of sight. Here, we present a follow-up study of W0204-0506 as well as two more Hot DOGs with excess UV emission. For the two new objects we obtained Chandra/ACIS-S observations, and for all three targets we obtained Hubble Space Telescope/WFC3 F555W and F160W imaging. The analysis of these observations, combined with multiwavelength photometry and UV/optical spectroscopy suggests that UV emission is most likely dominated by light from the central highly obscured, hyperluminous AGN that has been scattered into our line of sight, by either gas or dust. We cannot decisively rule out, however, that star formation or a second AGN in the system may significantly contribute to the UV excess of these targets.
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    THE NuSTAR EXTRAGALACTIC SURVEY: A FIRST SENSITIVE LOOK AT THE HIGH-ENERGY COSMIC X-RAY BACKGROUND POPULATION
    (2013) Alexander, D. M.; Stern, D.; Del Moro, A.; Lansbury, G. B.; Assef, R. J.; Aird, J.; Ajello, M.; Ballantyne, D. R.; Bauer, F. E.; Boggs, S. E.; Brandt, W. N.; Christensen, F. E.; Civano, F.; Comastri, A.; Craig, W. W.; Elvis, M.; Grefenstette, B. W.; Hailey, C. J.; Harrison, F. A.; Hickox, R. C.; Luo, B.; Madsen, K. K.; Mullaney, J. R.; Perri, M.; Puccetti, S.; Saez, C.; Treister, E.; Urry, C. M.; Zhang, W. W.; Bridge, C. R.; Eisenhardt, P. R. M.; Gonzalez, A. H.; Miller, S. H.; Tsai, C. W.
    We report on the first 10 identifications of sources serendipitously detected by the Nuclear Spectroscopic Telescope Array (NuSTAR) to provide the first sensitive census of the cosmic X-ray background source population at greater than or similar to 10 keV. We find that these NuSTAR-detected sources are approximate to 100 times fainter than those previously detected at greater than or similar to 10 keV and have a broad range in redshift and luminosity (z = 0.020-2.923 and L10-40 keV approximate to 4 x 10(41)-5 x 10(45) erg s(-1)); the median redshift and luminosity are z approximate to 0.7 and L10-40 keV approximate to 3 x 10(44) erg s(-1), respectively. We characterize these sources on the basis of broad-band approximate to 0.5-32 keV spectroscopy, optical spectroscopy, and broad-band ultraviolet-to-mid-infrared spectral energy distribution analyses. We find that the dominant source population is quasars with L10-40 keV > 10(44) erg s(-1), of which approximate to 50% are obscured with N-H greater than or similar to 10(22) cm(-2). However, none of the 10 NuSTAR sources are Compton thick (N-H greater than or similar to 10(24) cm(-2)) and we place a 90% confidence upper limit on the fraction of Compton-thick quasars (L10-40 keV > 10(44) erg s(-1)) selected at greater than or similar to 10 keV of less than or similar to 33% over the redshift range z = 0.5-1.1. We jointly fitted the rest-frame approximate to 10-40 keV data for all of the non-beamed sources with L10-40 keV > 10(43) erg s(-1) to constrain the average strength of reflection; we find R < 1.4 for Gamma = 1.8, broadly consistent with that found for local active galactic nuclei (AGNs) observed at greater than or similar to 10 keV. We also constrain the host-galaxy masses and find a median stellar mass of approximate to 10(11) M-circle dot, a factor approximate to 5 times higher than the median stellar mass of nearby high-energy selected AGNs, which may be at least partially driven by the order of magnitude higher X-ray luminosities of the NuSTAR sources. Within the low source-statistic limitations of our study, our results suggest that the overall properties of the NuSTAR sources are broadly similar to those of nearby high-energy selected AGNs but scaled up in luminosity and mass.
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    The NuSTAR Extragalactic Survey : First Direct Measurements of the Greater Than Or Similar To 10 Kev X-Ray Luminosity Function For Active Galactic Nuclei At z > 0.1
    (2015) Aird, J.; Alexander, D. M.; Ballantyne, D. R.; Civano, F.; Moro, A. Del; Hickox, R. C.; Lansbury, G. B.; Mullaney, J. R.; Bauer, Franz Erik; Brandt, W. N.
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    The NuSTAR Extragalactic Surveys: Initial Results and Catalog from the Extended Chandra Deep Field South
    (2015) Mullaney, J.; Bauer, Franz Erik; Treister, Ezequiel; Del Moro, A.; Aird, J. A.; Alexander, D. M.; Civano, Francesca; Hickox, R. C.; Lansbury, George B.; Ajello, Marco; Assef, R.
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    The Nustar Extragalactic Surveys: Overview and Catalog from the COSMOS Field
    (2015) Civano, Francesca; Bauer, Franz Erik; Luo, B.; Saez, C.; Treister, Ezequiel; Hickox, R. C.; Puccetti, S.; Comastri, A.; Mullaney, J.; Zappacosta, L.; LaMassa, Stephanie M.