Browsing by Author "Pfeifle, R. W."

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    A hard X-ray view of luminous and ultra-luminous infrared galaxies in GOALS - I. AGN obscuration along the merger sequence
    (2021) Ricci, C.; Privon, G. C.; Pfeifle, R. W.; Armus, L.; Iwasawa, K.; Torres-Albà, N.; Satyapal, S.; Bauer, F. E.; Treister, E.; Ho, L. C.; Aalto, S.; Arévalo, P.; Barcos-Muñoz, L.; Charmandaris, V.; Diaz-Santos, T.; Evans, A. S.; Gao, T.; Inami, H.; Koss, M. J.; Lansbury, G.; Linden, S. T.; Medling, A.; Sanders, D. B.; Song, Y.; Stern, D.; U, V.; Ueda, Y.; Yamada, S.
    The merger of two or more galaxies can enhance the inflow of material from galactic scales into the close environments of active galactic nuclei (AGNs), obscuring and feeding the supermassive black hole (SMBH). Both recent simulations and observations of AGN in mergers have confirmed that mergers are related to strong nuclear obscuration. However, it is still unclear how AGN obscuration evolves in the last phases of the merger process. We study a sample of 60 luminous and ultra-luminous IR galaxies (U/LIRGs) from the GOALS sample observed by NuSTAR. We find that the fraction of AGNs that are Compton thick (CT;N-H >= 10(24)cm(-2) ) peaks at at a late merger stage, prior to coalescence, when the nuclei have projected separations (d(sep)) of 0.4-6 kpc. A similar peak is also observed in the median N-H [[(1.6 +/- 0.5) x 10(24) cm(-2)].]. The vast majority (85(-9)(+7) per cent)) of the AGNs in the final merger stages (d(sep) less than or similar to 10 kpc) are heavily obscured (N-H = 10(23) cm(-2)), and the median N-H of the accreting SMBHs in our sample is systematically higher than that of local hard X-ray-selected AGN, regardless of the merger stage. This implies that these objects have very obscured nuclear environments, with the gas almost completely covering the AGN in late mergers. CT AGNs tend to have systematically higher absorption-corrected X-ray luminosities than less obscured sources. This could either be due to an evolutionary effect, with more obscured sources accreting more rapidly because they have more gas available in their surroundings, or to a selection bias. The latter scenario would imply that we are still missing a large fraction of heavily obscured, lower luminosity (L2-10 less than or similar to 10(43) erg s(-1)) AGNs in U/LIRGs.
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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.