Browsing by Author "Alexander, David M."

Now showing 1 - 9 of 9
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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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    Identification and Characterization of a Large Sample of Distant Active Dwarf Galaxies in XMM-SERVS
    (2023) Zou, Fan; Brandt, W. N.; Ni, Qingling; Zhu, Shifu; Alexander, David M.; Bauer, Franz E.; Chen, Chien-Ting J.; Luo, Bin; Sun, Mouyuan; Vignali, Cristian; Vito, Fabio; Xue, Yongquan; Yan, Wei
    Active dwarf galaxies are important because they contribute to the evolution of dwarf galaxies and can reveal their hosted massive black holes. However, the sample size of such sources beyond the local universe is still highly limited. In this work, we search for active dwarf galaxies in the recently completed XMM-Spitzer Extragalactic Representative Volume Survey (XMM-SERVS). XMM-SERVS is currently the largest medium-depth X-ray survey covering 13 deg(2) in three extragalactic fields, which all have well-characterized multiwavelength information. After considering several factors that may lead to misidentifications, we identify 73 active dwarf galaxies at z < 1, which constitutes the currently largest X-ray-selected sample beyond the local universe. Our sources are generally less obscured than predictions based on the massive-AGN (active galactic nucleus) X-ray luminosity function and have a low radio-excess fraction. We find that our sources reside in environments similar to those of inactive dwarf galaxies. We further quantify the accretion distribution of the dwarf-galaxy population after considering various selection effects and find that it decreases with X-ray luminosity, but redshift evolution cannot be statistically confirmed. Depending on how we define an AGN, the active fraction may or may not show a strong dependence on stellar mass. Their Eddington ratios and X-ray bolometric corrections significantly deviate from the expected relation, which is likely caused by several large underlying systematic biases when estimating the relevant parameters for dwarf galaxies. Throughout this work, we also highlight problems in reliably measuring photometric redshifts and overcoming strong selection effects for distant active dwarf galaxies.
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    Localizing narrow Fe Kα emission within bright AGN
    (2022) Andonie, Carolina; Bauer, Franz E.; Carraro, Rosamaria; Arevalo, Patricia; Alexander, David M.; Brandt, William N.; Buchner, Johannes; He, Adam; Koss, Michael J.; Ricci, Claudio; Salinas, Vicente; Solimano, Manuel; Tortosa, Alessia; Treister, Ezequiel
    Context. The 6.4 keV Fe K alpha emission line is a ubiquitous feature in X-ray spectra of active galactic nuclei (AGN), and its properties track the interaction between the variable primary X-ray continuum and the surrounding structure from which it arises.
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    Probing black hole accretion tracks, scaling relations, and radiative efficiencies from stacked X-ray active galactic nuclei
    (2020) Shankar, Francesco; Weinberg, David H.; Marsden, Christopher; Grylls, Philip J.; Bernardi, Mariangela; Yang, Guang; Moster, Benjamin; Fu, Hao; Carraro, Rosamaria; Alexander, David M.; Allevato, Viola; Ananna, Tonima T.; Bongiorno, Angela; Calderone, Giorgio; Civano, Francesca; Daddi, Emanuele; Delvecchio, Ivan; Duras, Federica; La Franca, Fabio; Lapi, Andrea; Lu, Youjun; Menci, Nicola; Mezcua, Mar; Ricci, Federica; Rodighiero, Giulia; Sheth, Ravi K.; Suh, Hyewon; Villforth, Carolin; Zanisi, Lorenzo
    The masses of supermassive black holes at the centres of local galaxies appear to be tightly correlated with the mass and velocity dispersions of their galactic hosts. However, the local M-bh-M-star relation inferred from dynamically measured inactive black holes is up to an order-of-magnitude higher than some estimates from active black holes, and recent work suggests that this discrepancy arises from selection bias on the sample of dynamical black hole mass measurements. In this work, we combine X-ray measurements of the mean black hole accretion luminosity as a function of stellar mass and redshift with empirical models of galaxy stellar mass growth, integrating over time to predict the evolving M-bh-M-star relation. The implied relation is nearly independent of redshift, indicating that stellar and black hole masses grow, on average, at similar rates. Matching the de-biased local M-bh-M-star relation requires a mean radiative efficiency epsilon greater than or similar to 0.15, in line with theoretical expectations for accretion on to spinning black holes. However, matching the 'raw' observed relation for inactive black holes requires epsilon similar to 0.02, far below theoretical expectations. This result provides independent evidence for selection bias in dynamically estimated black hole masses, a conclusion that is robust to uncertainties in bolometric corrections, obscured active black hole fractions, and kinetic accretion efficiency. For our fiducial assumptions, they favour moderate-to-rapid spins of typical supermassive black holes, to achieve epsilon similar to 0.12-0.20. Our approach has similarities to the classic Soltan analysis, but by using galaxy-based data instead of integrated quantities we are able to focus on regimes where observational uncertainties are minimized.
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    The Black Hole-Galaxy Connection: Interplay between Feedback, Obscuration, and Host Galaxy Substructure
    (2022) Juneau, Stephanie; Goulding, Andy D.; Banfield, Julie; Bianchi, Stefano; Duc, Pierre-Alain; Ho, I-Ting; Dopita, Michael A.; Scharwaechter, Julia; Bauer, Franz E.; Groves, Brent; Alexander, David M.; Davies, Rebecca L.; Elbaz, David; Freeland, Emily; Hampton, Elise; Kewley, Lisa J.; Nikutta, Robert; Shastri, Prajval; Shu, Xinwen; Vogt, Frederic P. A.; Wang, Tao; Wong, O. Ivy; Woo, Jong-Hak
    There is growing evidence for physical influence between supermassive black holes and their host galaxies. We present a case study of the nearby galaxy NGC 7582, for which we find evidence that galactic substructure plays an important role in affecting the collimation of ionized outflows as well as contributing to the heavy active galactic nucleus (AGN) obscuration. This result contrasts with a simple, small-scale AGN torus model, according to which AGN-wind collimation may take place inside the torus itself, at subparsec scales. Using 3D spectroscopy with the Multi Unit Spectroscopic Explorer instrument, we probe the kinematics of the stellar and ionized gas components as well as the ionization state of the gas from a combination of emission-line ratios. We report for the first time a kinematically distinct core (KDC) in NGC 7582, on a scale of similar to 600 pc. This KDC coincides spatially with dust lanes and starbursting complexes previously observed. We interpret it as a circumnuclear ring of stars and dusty, gas-rich material. We obtain a clear view of the outflowing cones over kiloparsec scales and demonstrate that they are predominantly photoionized by the central engine. We detect the back cone (behind the galaxy) and confirm previous results of a large nuclear obscuration of both the stellar continuum and H ii regions. While we tentatively associate the presence of the KDC with a large-scale bar and/or a minor galaxy merger, we stress the importance of gaining a better understanding of the role of galaxy substructure in controlling the fueling, feedback, and obscuration of AGNs.
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    THE GEOMETRY OF THE INFRARED AND X-RAY OBSCURER IN A DUSTY HYPERLUMINOUS QUASAR
    (2016) Farrah, Duncan; Balokovic, Mislav; Stern, Daniel; Harris, Kathryn; Kunimoto, Michelle; Walton, Dominic J.; Alexander, David M.; Arévalo, Patricia; Bauer, Franz Erik; Claudio Ricci
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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.
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    The NuSTAR Serendipitous Survey: The 80 Month Catalog and Source Properties of the High-energy Emitting Active Galactic Nucleus and Quasar Population
    (2024) Greenwell, Claire L.; Klindt, Lizelke; Lansbury, George B.; Rosario, David J.; Alexander, David M.; Aird, James; Stern, Daniel; Forster, Karl; Koss, Michael J.; Bauer, Franz E.; Ricci, Claudio; Tomsick, John; Brandt, William N.; Connor, Thomas; Boorman, Peter G.; Annuar, Adlyka; Ballantyne, David R.; Chen, Chien-Ting; Civano, Francesca; Comastri, Andrea; Fawcett, Victoria A.; Fornasini, Francesca M.; Gandhi, Poshak; Harrison, Fiona; Heida, Marianne; Hickox, Ryan; Kammoun, Elias S.; Lanz, Lauranne; Marchesi, Stefano; Noirot, Gael; Romero-Colmenero, Encarni; Treister, Ezequiel; Urry, C. Megan; Vaisanen, Petri; van Soelen, Brian
    We present a catalog of hard X-ray serendipitous sources detected in the first 80 months of observations by the Nuclear Spectroscopic Telescope Array (NuSTAR). The NuSTAR serendipitous survey 80 month (NSS80) catalog has an unprecedented similar to 62 Ms of effective exposure time over 894 unique fields (a factor of 3 increase over the 40 month catalog, NSS40), with an areal coverage of similar to 36 deg(2), larger than all NuSTAR extragalactic surveys. NSS80 provides 1274 hard X-ray sources in the 3-24 keV band (822 new detections compared to the previous NSS40). Approximately 76% of the NuSTAR sources have lower-energy (<10 keV) X-ray counterparts from Chandra, XMM-Newton, and Swift-XRT. We have undertaken an extensive campaign of ground-based spectroscopic follow-up to obtain new source redshifts and classifications for 427 sources. Combining these with existing archival spectroscopy provides redshifts for 550 NSS80 sources, of which 547 are classified. The sample is primarily composed of active galactic nuclei (AGNs), detected over a large range in redshift (z = 0.012-3.43), but also includes 58 spectroscopically confirmed Galactic sources. In addition, five AGN-galaxy pairs, one dual AGN system, one BL Lac candidate, and a hotspot of 4C 74.26 (radio quasar) have been identified. The median rest-frame 10-40 keV luminosity and redshift of NSS80 are < L10-40 keV > = 1.2 x 10(44) erg s(-1) and < z > = 0.56. We investigate the optical properties and construct composite optical spectra to search for subtle signatures not present in the individual spectra, finding an excess of redder BL AGNs compared to optical quasar surveys, predominantly due to the presence of the host galaxy and, at least in part, due to dust obscuration.
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    The XMM-SERVS Survey: XMM-Newton Point-source Catalogs for the W-CDF-S and ELAIS-S1 Fields
    (2021) Ni, Qingling; Brandt, W. N.; Chen, Chien-Ting; Luo, Bin; Nyland, Kristina; Yang, Guang; Zou, Fan; Aird, James; Alexander, David M.; Bauer, Franz Erik; Lacy, Mark; Lehmer, Bret D.; Mallick, Labani; Salvato, Mara; Schneider, Donald P.; Tozzi, Paolo; Traulsen, Iris; Vaccari, Mattia; Vignali, Cristian; Vito, Fabio; Xue, Yongquan; Banerji, Manda; Chow, Kate; Comastri, Andrea; Del Moro, Agnese; Gilli, Roberto; Mullaney, James; Paolillo, Maurizio; Schwope, Axel; Shemmer, Ohad; Sun, Mouyuan; Timlin III, John D.; Trump, Jonathan R.
    We present the X-ray point-source catalogs in two of the XMM-Spitzer Extragalactic Representative Volume Survey (XMM-SERVS) fields, W-CDF-S (4.6 deg(2)) and ELAIS-S1 (3.2 deg(2)), aiming to fill the gap between deep pencil-beam X-ray surveys and shallow X-ray surveys over large areas. The W-CDF-S and ELAIS-S1 regions were targeted with 2.3 and 1.0 Ms of XMM-Newton observations, respectively; 1.8 and 0.9 Ms exposures remain after flare filtering. The survey in W-CDF-S has a flux limit of 1.0 x 10(-14) erg cm(-2) s(-1) over 90% of its area in the 0.5-10 keV band; 4053 sources are detected in total. The survey in ELAIS-S1 has a flux limit of 1.3 x 10(-14) erg cm(-2) s(-1) over 90% of its area in the 0.5-10 keV band; 2630 sources are detected in total. Reliable optical-to-IR multiwavelength counterpart candidates are identified for approximate to 89% of the sources in W-CDF-S and approximate to 87% of the sources in ELAIS-S1. A total of 3129 sources in W-CDF-S and 1957 sources in ELAIS-S1 are classified as active galactic nuclei (AGNs). We also provide photometric redshifts for X-ray sources; approximate to 84% of the 3319/2001 sources in W-CDF-S/ELAIS-S1 with optical-to-near-IR forced photometry available have either spectroscopic redshifts or high-quality photometric redshifts. The completion of the XMM-Newton observations in the W-CDF-S and ELAIS-S1 fields marks the end of the XMM-SERVS survey data gathering. The approximate to 12,000 pointlike X-ray sources detected in the whole approximate to 13 deg(2) XMM-SERVS survey will benefit future large-sample AGN studies.