Browsing by Author "Hickox, Ryan C."

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    Chandra Observations of Excess Fe Kα Line Emission in Galaxies with High Star Formation Rates: X-Ray Reflection on Galaxy Scales?
    (2021) Yan, Wei; Hickox, Ryan C.; Chen, Chien-Ting J.; Ricci, Claudio; Masini, Alberto; Bauer, Franz E.; Alexander, David M.
    In active galactic nuclei (AGNs), fluorescent Fe K alpha (iron) line emission is generally interpreted as originating from obscuring material around a supermassive black hole on the scale of a few parsecs. However, recent Chandra studies indicate the existence of iron line emission extending to kiloparsec scales in the host galaxy. The connection between iron line emission and large-scale material can be spatially resolved directly only in nearby galaxies, but could be inferred in more distant AGNs by a connection between line emission and star-forming gas and dust that is more extended than the parsec-scale torus. Here we present the results from a stacking analysis and X-ray spectral fitting performed on sources in the Chandra Deep Field South (CDFS) 7 Ms observations. From the deep stacked spectra, we select sources with stellar mass log(M-*/M-circle dot) > 10 at 0.5 < z < 2, obtaining 25 sources with high-infrared (IR) luminosity (star formation rate, SFRFIR >= 17 M-circle dot yr(-1)) and 32 sources below this threshold. We find that the equivalent width (EW) of the iron line EW(Fe) is a factor of three higher with 3 sigma significance for high-IR luminosity measured from Herschel observations, indicating a connection between iron line emission and star-forming material on galaxy scales. We show that there is no significant dependence of the EW(Fe) on M-* or X-ray luminosity, suggesting that the reflection of AGN X-ray emission over large scales in their host galaxies may be widespread.
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    Probing the Structure and Evolution of BASS Active Galactic Nuclei through Eddington Ratios
    (2022) Ananna, Tonima Tasnim; Urry, C. Megan; Ricci, Claudio; Natarajan, Priyamvada; Hickox, Ryan C.; Trakhtenbrot, Benny; Treister, Ezequiel; Weigel, Anna K.; Ueda, Yoshihiro; Koss, Michael J.; Bauer, F. E.; Temple, Matthew J.; Balokovic, Mislav; Mushotzky, Richard; Auge, Connor; Sanders, David B.; Kakkad, Darshan; Sartori, Lia F.; Marchesi, Stefano; Harrison, Fiona; Stern, Daniel; Oh, Kyuseok; Caglar, Turgay; Powell, Meredith C.; Podjed, Stephanie A.; Mejia-Restrepo, Julian E.
    We constrain the intrinsic Eddington ratio (lambda(Edd)) distribution function for local active galactic nuclei (AGN) in bins of low and high obscuration [log(N-H/cm(-2)) <= 22 and 22 < log(N-H/cm(-2)) < 25], using the Swift Burst Alert Telescope 70 month/BASS DR2 survey. We interpret the fraction of obscured AGN in terms of circumnuclear geometry and temporal evolution. Specifically, at low Eddington ratios (log lambda(Edd) < -2), obscured AGN outnumber unobscured ones by a factor of similar to 4, reflecting the covering factor of the circumnuclear material (0.8, or a torus opening angle of similar to 34 degrees). At high Eddington ratios (log lambda(Edd) > - 1), the trend is reversed, with <30% of AGN having log(N-H/cm(-2)) > 22, which we suggest is mainly due to the small fraction of time spent in a highly obscured state. Considering the Eddington ratio distribution function of narrow-line and broad-line AGN from our prior work, we see a qualitatively similar picture. To disentangle temporal and geometric effects at high lambda(Edd), we explore plausible clearing scenarios such that the time-weighted covering factors agree with the observed population ratio. We find that the low fraction of obscured AGN at high lambda(Edd) is primarily due to the fact that the covering factor drops very rapidly, with more than half the time spent with <10% covering factor. We also find that nearly all obscured AGN at high-lambda(Edd) exhibit some broad lines. We suggest that this is because the height of the depleted torus falls below the height of the broad-line region, making the latter visible from all lines of sight.
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    The Most Obscured AGNs in the XMM-SERVS Fields
    (2023) Yan, Wei; Brandt, W. N.; Zou, Fan; Zhu, Shifu; Chen, Chien-Ting J.; Hickox, Ryan C.; Luo, Bin; Ni, Qingling; Alexander, David M.; Bauer, Franz E.; Vignali, Cristian; Vito, Fabio
    We perform X-ray spectral analyses to derive the characteristics (e.g., column density, X-ray luminosity) of & AP;10,200 active galactic nuclei (AGNs) in the XMM-Spitzer Extragalactic Representative Volume Survey, which was designed to investigate the growth of supermassive black holes across a wide dynamic range of cosmic environments. Using physical torus models (e.g., Borus02) and a Bayesian approach, we uncover 22 representative Compton-thick (CT; N (H) > 1.5 x 10(24) cm(-2)) AGN candidates with good signal-to-noise ratios as well as a large sample of 136 heavily obscured AGNs. We also find an increasing CT fraction (f (CT)) from low (z < 0.75) to high (z > 0.75) redshift. Our CT candidates tend to show hard X-ray spectral shapes and dust extinction in their spectral energy distribution fits, which may shed light on the connection between AGN obscuration and host-galaxy evolution.