Browsing by Author "Ichikawa, K."

Now showing 1 - 4 of 4
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    BASS. XLII. The Relation between the Covering Factor of Dusty Gas and the Eddington Ratio in Nearby Active Galactic Nuclei
    Ricci, C.; Ichikawa, K.; Stalevski, M.; Kawamuro, T.; Yamada, S.; Ueda, Y.; Mushotzky, R.; Privon, G. C.; Koss, M. J.; Trakhtenbrot, B.; Fabian, A. C.; Ho, L. C.; Asmus, D.; Bauer, Franz Erik; Chang, C. S.; Gupta, K. K.; Oh, K.; Powell, M.; Pfeifle, R. W.; Rojas, A.; Ricci, F.; Temple, M. J.; Toba, Y.; Tortosa, A.; Treister, Ezequiel; Harrison, F.; Stern, D.; Urry, C. M.
    Accreting supermassive black holes (SMBHs) located at the centers of galaxies are typically surrounded by large quantities of gas and dust. The structure and evolution of this circumnuclear material can be studied at different wavelengths, from the submillimeter to the X-ray. Recent X-ray studies have shown that the covering factor of the obscuring material tends to decrease with increasing Eddington ratio, likely due to radiative feedback on dusty gas. Here we study a sample of 549 nearby (z less than or similar to 0.1) hard X-ray (14-195 keV) selected nonblazar active galactic nuclei (AGN) and use the ratio between the AGN infrared and bolometric luminosity as a proxy of the covering factor. We find that, in agreement with what has been found by X-ray studies of the same sample, the covering factor decreases with increasing Eddington ratio. We also confirm previous findings that showed that obscured AGN typically have larger covering factors than unobscured sources. Finally, we find that the median covering factors of AGN located in different regions of the column density-Eddington ratio diagram are in good agreement with what would be expected from a radiation-regulated growth of SMBHs.
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    Infrared polarimetry of Mrk 231: scattering off hot dust grains in the central core
    (OXFORD UNIV PRESS, 2017) Lopez Rodriguez, E.; Packham, C.; Jones, T. J.; Siebenmorgen, R.; Roche, P. F.; Levenson, N. A.; Alonso Herrero, A.; Perlman, E.; Ichikawa, K.; Ramos Almeida, C.; Gonzalez Martin, O.; Nikutta, R.; Martinez Paredez, M.; Shenoy, D.; Gordon, M. S.; Telesco, C. M.
    We present high-angular (0.17-0.35 arcsec) resolution imaging polarimetric observations of Mrk 231 in the 3.1 mu m filter using MMT-Pol on the 6.5-m MMT, and in the 8.7, 10.3, and 11.6 mu m filters using CanariCam on the 10.4-m Gran Telescopio CANARIAS. In combination with already published observations, we compile the 1-12 mu m total and polarized nuclear spectral energy distribution (SED). The total flux SED in the central 400 pc is explained as the combination of (1) a hot (731 +/- 4 K) dusty structure, directly irradiated by the central engine, which is at 1.6 +/- 0.1 pc away and attributed to be in the pc-scale polar region, (2) an optically-thick, smooth and disc-like dusty structure ('torus') with an inclination of 48 degrees +/- 23 degrees surrounding the central engine, and (3) an extinguished (A(V) = 36 +/- 5 mag) starburst component. The polarized SED decreases from 0.77 +/- 0.14 per cent at 1.2 mu m to 0.31 +/- 0.15 per cent at 11.6 mu m and follows a power-law function, lambda(similar to 0.57). The polarization angle remains constant (similar to 108 degrees) in the 1-12 mu m wavelength range. The dominant polarization mechanism is explained as scattering-off hot dust grains in the pc-scale polar regions.
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    [O iii] lambda5007 and X-ray properties of a complete sample of hard X-ray selected AGNs in the local Universe
    (2015) Ueda, Y.; Hashimoto, Y.; Ichikawa, K.; Ishino, Y.; Kniazev, A.; Vaeisaenen, P.; Ricci, Claudio; Berney, S.; Gandhi, P.; Koss, M.
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    The BAT AGN Spectroscopic Survey. XVIII. Searching for Supermassive Black Hole Binaries in X-Rays
    (2020) Liu, T. T.; Koss, M.; Blecha, L.; Ricci, Claudio; Trakhtenbrot, B.; Mushotzky, R.; Harrison, F.; Ichikawa, K.; Kakkad, D.; Treister, Ezequiel; Oh, K.; Powell, M.; Privon, G. C.; Schawinski, K.; Shimizu, T. T.; Smith, K. L.; Stern, D.; Urry, C. M.