Browsing by Author "Xue, Y. Q."

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    Does black hole growth depend fundamentally on host-galaxy compactness?
    (2019) Ni, Q.; Yang, G.; Brandt, W. N.; Alexander, D. M.; Chen, C-T J.; Luo, B.; Vito, F.; Xue, Y. Q.
    Possible connections between central black hole (BH) growth and host-galaxy compactness have been found observationally, which may provide insight into BH-galaxy coevolution: compact galaxies might have large amounts of gas in their centres due to their high mass-to-size ratios, and simulations predict that high central gas density can boost BH accretion. However, it is not yet clear if BH growth is fundamentally related to the compactness of the host galaxy, due to observational degeneracies between compactness, stellar mass (M-star) and star formation rate (SFR). To break these degeneracies, we carry out systematic partial-correlation studies to investigate the dependence of sample-averaged BH accretion rate ((BHAR) over bar) on the compactness of host galaxies, represented by the surface-mass density, Sigma(e), or the projected central surface-mass density within 1 kpc, Sigma(1). We utilize 8842 galaxies with H < 24.5 in the five CANDELS fields at z = 0.5-3. We find that <(BHAR)over bar> does not significantly depend on compactness when controlling for SFR or M-star among bulge-dominated galaxies and galaxies that are not dominated by bulges, respectively. However, when testing is confined to star-forming galaxies at z = 0.5-1.5, we find that the (BHAR) over bar-Sigma(1) relation is not simply a secondary manifestation of a primary (BHAR) over bar -M-star relation, which may indicate a link between BH growth and the gas density within the central 1 kpc of galaxies.
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    Extragalactic fast X-ray transient candidates discovered by Chandra (2000-2014)
    (2022) Quirola-Vasquez, J.; Bauer, F. E.; Jonker, P. G.; Brandt, W. N.; Yang, G.; Levan, A. J.; Xue, Y. Q.; Eappachen, D.; Zheng, X. C.; Luo, B.
    Context. Extragalactic fast X-ray transients (FXRTs) are short flashes of X-ray photons of unknown origin that last a few seconds to hours.
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    Extragalactic fast X-ray transient candidates discovered by Chandra (2014-2022)
    (2023) Quirola-Vasquez, J.; Bauer, F. E.; Jonker, P. G.; Brandt, W. N.; Yang, G.; Levan, A. J.; Xue, Y. Q.; Eappachen, D.; Camacho, E.; Ravasio, M. E.; Zheng, X. C.; Luo, B.
    Context. Extragalactic fast X-ray transients (FXTs) are short flashes of X-ray photons of unknown origin that last a few minutes to hours.
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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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    Long-term x-ray variability of typical active galactic nuclei in the distant universe.
    (2016) Yang, G.; Kim, Sam; Brandt, W N.; Bauer, Franz Erik; Schulze, Steve.; Luo, B.; Xue, Y. Q.; Sun, M. Y.; Zheng, X. C.; Paolillo, M.; Shemmer, O.
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    Mid-infrared luminous quasars in the GOODS–Herschel fields: a large population of heavily obscured, Compton-thick quasars at z ≈ 2
    (2016) Del Moro, A.; Alexander, D. M.; Bauer, Franz Erik; Daddi, E.; Kocevski, D. D.; McIntosh, D. H.; Stanley, F.; Brandt, W. N.; Elbaz, D.; Harrison, C. M.; Luo, B.; Mullaney, J. R.; Xue, Y. Q.
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    Probing a magnetar origin for the population of extragalactic fast X-ray transients detected by Chandra
    (2024) Quirola-Vasquez, J.; Bauer, F. E.; Jonker, P. G.; Brandt, W. N.; Eappachen, D.; Levan, A. J.; Lopez, E.; Luo, B.; Ravasio, M. E.; Sun, H.; Xue, Y. Q.; Yang, G.; Zheng, X. C.
    Context. Twenty-two extragalactic fast X-ray transients (FXTs) have now been discovered from two decades of Chandra data (analyzing similar to 259 Ms of data), with 17 associated with distant galaxies (greater than or similar to 100 Mpc). Different mechanisms and progenitors have been proposed to explain their properties; nevertheless, after analyzing their timing, spectral parameters, host -galaxy properties, luminosity function, and volumetric rates, their nature remains uncertain. Aims. We interpret a sub -sample of nine FXTs that show a plateau or a fast -rise light curve within the framework of a binary neutron star (BNS) merger magnetar model. Methods. We fit their light curves and derive magnetar (magnetic field and initial rotational period) and ejecta (ejecta mass and opacity) parameters. This model predicts two zones: an orientation -dependent free zone (where the magnetar spin -down X-ray photons escape freely to the observer) and a trapped zone (where the X-ray photons are initially obscured and only escape freely once the ejecta material becomes optically thin). We argue that six FXTs show properties consistent with the free zone and three FXTs with the trapped zone. Results. This sub -sample of FXTs has a similar distribution of magnetic fields and initial rotation periods to those inferred for short gamma -ray bursts, suggesting a possible association. We compare the predicted ejecta emission fed by the magnetar emission (called merger -nova) to the optical and near -infrared upper limits of two FXTs, XRT 141001 and XRT 210423 where contemporaneous optical observations are available. The non -detections place lower limits on the redshifts of XRT 141001 and XRT 210423 of z greater than or similar to 1.5 and greater than or similar to 0.1, respectively. Conclusions. If the magnetar remnants lose energy via gravitational waves (GWs), it should be possible to detect similar objects with the current advanced LIGO detectors out to a redshift z less than or similar to 0.03, while future GW detectors will be able to detect them out to z approximate to 0.5.
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    Radiation pressure, absorption and AGN feedback in the Chandra Deep Fields
    (2010) Raimundo, S. I.; Fabian, A. C.; Bauer, F. E.; Alexander, D. M.; Brandt, W. N.; Luo, B.; Vasudevan, R. V.; Xue, Y. Q.
    The presence of absorbing gas around the central engine of active galactic nuclei (AGN) is a common feature of these objects. Recent work has looked at the effect of the dust component of the gas, and how it enhances radiation pressure such that dusty gas can have a lower effective Eddington limit than ionized gas. In this work, we use multiwavelength data and X-ray spectra from the 2 Ms exposures of the Chandra Deep Field-North and Chandra Deep Field-South surveys to characterize the AGN in terms of their Eddington ratio (lambda) and hydrogen column density (N-H). Their distributions are then compared with what is predicted when considering the coupling between dust and gas. Our final sample consists of 234 objects from both fields, the largest and deepest sample of AGN for which this comparison has been made up to date. We find that most of the AGN in our sample tend to be found at low Eddington ratios (typically 10-4 < lambda < 10-1) and high N-H (> 1022 cm-2), with black hole masses in the range similar to(108-109) M-circle dot. Their distribution is in agreement with that expected from the enhanced radiation pressure model, avoiding the area where we would predict the presence of outflows. We also investigate how the balance between AGN radiation pressure and gravitational potential influences the behaviour of clouds in the Galactic bulge, and describe a scenario where an enhanced radiation pressure can lead to the Fundamental Plane of black hole/galaxy scaling relations.
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    REVEALING A POPULATION OF HEAVILY OBSCURED ACTIVE GALACTIC NUCLEI AT z ≈ 0.5-1 IN THE CHANDRA DEEP FIELD-SOUTH
    (2011) Luo, B.; Brandt, W. N.; Xue, Y. Q.; Alexander, D. M.; Brusa, M.; Bauer, F. E.; Comastri, A.; Fabian, A. C.; Gilli, R.; Lehmer, B. D.; Rafferty, D. A.; Schneider, D. P.; Vignali, C.
    Heavily obscured (NH greater than or similar to 3 x 10(23) cm(-2)) active galactic nuclei (AGNs) not detected even in the deepest X-ray surveys are often considered to be comparably numerous to the unobscured and moderately obscured AGNs. Such sources are required to fit the cosmic X-ray background (XRB) emission in the 10-30 keV band. We identify a numerically significant population of heavily obscured AGNs at z approximate to 0.5-1 in the Chandra Deep Field-South (CDF-S) and Extended Chandra Deep Field-South by selecting 242 X-ray undetected objects with infrared-based star-formation rates (SFRs) substantially higher (a factor of 3.2 or more) than their SFRs determined from the UV after correcting for dust extinction. An X-ray stacking analysis of 23 candidates in the central CDF-S region using the 4 Ms Chandra data reveals a hard X-ray signal with an effective power-law photon index of Gamma = 0.6(-0.4)(+ 0.3), indicating a significant contribution from obscured AGNs. Based on Monte Carlo simulations, we conclude that 74% +/- 25% of the selected galaxies host obscured AGNs, within which approximate to 95% are heavily obscured and approximate to 80% are Compton-thick (CT; N-H > 1.5 x 10(24) cm(-2)). The heavily obscured objects in our sample are of moderate intrinsic X-ray luminosity (approximate to(0.9-4) x 10(42) erg s(-1) in the 2-10 keV band). The space density of the CT AGNs is (1.6 +/- 0.5) x 10(-4) Mpc(-3). The z approximate to 0.5-1 CT objects studied here are expected to contribute approximate to 1% of the total XRB flux in the 10-30 keV band, and they account for approximate to 5%-15% of the emission in this energy band expected from all CT AGNs according to population-synthesis models. In the 6-8 keV band, the stacked signal of the 23 heavily obscured candidates accounts for <5% of the unresolved XRB flux, while the unresolved approximate to 25% of the XRB in this band can probably be explained by a stacking analysis of the X-ray undetected optical galaxies in the CDF-S (a 2.5 sigma stacked signal). We discuss prospects to identify such heavily obscured objects using future hard X-ray observatories.
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    Revealing the relation between black hole growth and host-galaxy compactness among star-forming galaxies
    (2021) Ni, Q.; Brandt, W. N.; Yang, G.; Leja, J.; Chen, C-T J.; Luo, B.; Matharu, J.; Sun, M.; Vito, F.; Xue, Y. Q.; Zhang, K.
    Recent studies show that a universal relation between black hole (BH) growth and stellar mass (M-*) or star formation rate (SFR) is an oversimplification of BH-galaxy coevolution, and that morphological and structural properties of host galaxies must also be considered. Particularly, a possible connection between BH growth and host-galaxy compactness was identified among star-forming (SF) galaxies. Utilizing approximate to 6300 massive galaxies with I-814W < 24 at z < 1.2 in the Cosmic Evolution Survey (COSMOS) field, we perform systematic partial correlation analyses to investigate how sample-averaged BH accretion rate (BHAR) depends on host-galaxy compactness among SF galaxies, when controlling for morphology and M-* (or SFR). The projected central surface mass density within 1 kpc, Sigma(1), is utilized to represent host-galaxy compactness in our study. We find that the BHAR-Sigma(1) relation is stronger than either the BHAR-M-* or BHAR-SFR relation among SF galaxies, and this BHAR-Sigma(1) relation applies to both bulge-dominated galaxies and galaxies that are not dominated by bulges. This BHAR-Sigma(1) relation among SF galaxies suggests a link between BH growth and the central gas density of host galaxies on the kpc scale, which may further imply a common origin of the gas in the vicinity of the BH and in the central similar to kpc of the galaxy. This BHAR-Sigma(1) relation can also be interpreted as the relation between BH growth and the central velocity dispersion of host galaxies at a given gas content (i.e. gas mass fraction), indicating the role of the host-galaxy potential well in regulating accretion on to the BH.
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    Searching for fast extragalactic X-ray transients in Chandra surveys
    (2019) Yang, G.; Brandt, W. N.; Zhu, S. F.; Bauer, Franz Erik; Luo, B.; Xue, Y. Q.; Zheng, X. C.
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    SUPERMASSIVE BLACK HOLE GROWTH IN STARBURST GALAXIES OVER COSMIC TIME: CONSTRAINTS FROM THE DEEPEST CHANDRA FIELDS
    (2011) Rafferty, D. A.; Brandt, W. N.; Alexander, D. M.; Xue, Y. Q.; Bauer, F. E.; Lehmer, B. D.; Luo, B.; Papovich, C.
    We present an analysis of deep multiwavelength data for z approximate to 0.3-3 starburst galaxies selected by their 70 mu m emission in the Extended-Chandra Deep Field-South and Extended Groth Strip. We identify active galactic nuclei (AGNs) in these infrared sources through their X-ray emission and quantify the fraction that host an AGN. We find that the fraction depends strongly on both the mid-infrared color and rest-frame mid-infrared luminosity of the source, rising to similar to 50%-70% at the warmest colors (F-24 (mu m)/F-70 (mu m) less than or similar to 0.2) and highest mid-infrared luminosities (corresponding to ultraluminous infrared galaxies), similar to the trends found locally. Additionally, we find that the AGN fraction depends strongly on the star formation rate (SFR) of the host galaxy (inferred from the observed-frame 70 mu m luminosity after subtracting the estimated AGN contribution), particularly for more luminous AGNs (L0.5-8.0keV greater than or similar to 10(43) erg s(-1)). At the highest SFRs (similar to 1000 M-circle dot yr(-1)), the fraction of galaxies with an X-ray detected AGN rises to approximate to 30%, roughly consistent with that found in high-redshift submillimeter galaxies. Assuming that the AGN fraction is driven by the SFR (rather than stellar mass or redshift, for which our sample is largely degenerate), this result implies that the duty cycle of luminous AGN activity increases with the SFR of the host galaxy: specifically, we find that luminous X-ray detected AGNs are at least similar to 5-10 times more common in systems with high SFRs (greater than or similar to 300 M-circle dot yr(-1)) than in systems with lower SFRs (less than or similar to 30 M-circle dot yr(-1)). Lastly, we investigate the ratio between the supermassive black hole accretion rate (inferred from the AGN X-ray luminosity) and the bulge growth rate of the host galaxy (approximated as the SFR) and find that, for sources with detected AGNs and star formation (and neglecting systems with low star formation rates to which our data are insensitive), this ratio in distant starbursts agrees well with that expected from the local scaling relation assuming the black holes and bulges grew at the same epoch. These results imply that black holes and bulges grow together during periods of vigorous star formation and AGN activity.
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    The 2 Ms Chandra Deep Field-North Survey and the 250 ks Extended Chandra Deep Field-South Survey : Improved Point-Source Catalogs
    (2016) Xue, Y. Q.; Luo, B.; Brandt, W. N.; Alexander, D. M.; Bauer, Franz Erik; Lehmer, B. D.; Yang, G.
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    THE 4 Ms CHANDRA DEEP FIELD-SOUTH NUMBER COUNTS APPORTIONED BY SOURCE CLASS: PERVASIVE ACTIVE GALACTIC NUCLEI AND THE ASCENT OF NORMAL GALAXIES
    (2012) Lehmer, B. D.; Xue, Y. Q.; Brandt, W. N.; Alexander, D. M.; Bauer, F. E.; Brusa, M.; Comastri, A.; Gilli, R.; Hornschemeier, A. E.; Luo, B.; Paolillo, M.; Ptak, A.; Shemmer, O.; Schneider, D. P.; Tozzi, P.; Vignali, C.
    We present 0.5-2 keV, 2-8 keV, 4-8 keV, and 0.5-8 keV (hereafter soft, hard, ultra-hard, and full bands, respectively) cumulative and differential number-count (log N-log S) measurements for the recently completed approximate to 4 Ms Chandra Deep Field-South (CDF-S) survey, the deepest X-ray survey to date. We implement a new Bayesian approach, which allows reliable calculation of number counts down to flux limits that are factors of approximate to 1.9-4.3 times fainter than the previously deepest number-count investigations. In the soft band (SB), the most sensitive bandpass in our analysis, the approximate to 4 Ms CDF-S reaches a maximum source density of approximate to 27,800 deg(-2). By virtue of the exquisite X-ray and multiwavelength data available in the CDF-S, we are able to measure the number counts from a variety of source populations (active galactic nuclei (AGNs), normal galaxies, and Galactic stars) and subpopulations (as a function of redshift, AGN absorption, luminosity, and galaxy morphology) and test models that describe their evolution. We find that AGNs still dominate the X-ray number counts down to the faintest flux levels for all bands and reach a limiting SB source density of approximate to 14,900 deg(-2), the highest reliable AGN source density measured at any wavelength. We find that the normal-galaxy counts rise rapidly near the flux limits and, at the limiting SB flux, reach source densities of approximate to 12,700 deg(-2) and make up 46% +/- 5% of the total number counts. The rapid rise of the galaxy counts toward faint fluxes, as well as significant normal-galaxy contributions to the overall number counts, indicates that normal galaxies will overtake AGNs just below the approximate to 4 Ms SB flux limit and will provide a numerically significant new X-ray source population in future surveys that reach below the approximate to 4 Ms sensitivity limit. We show that a future approximate to 10 Ms CDF-S would allow for a significant increase in X-ray-detected sources, with many of the new sources being cosmologically distant (z greater than or similar to 0.6) normal galaxies.
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    The chandra deep field-south survey: 4 Ms source catalogs
    (2011) Xue, Y. Q.; Bauer, Franz Erik
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    THE CHANDRA DEEP FIELD-SOUTH SURVEY: 7 MS SOURCE CATALOGS
    (2017) Luo, B.; Brandt, W. N.; Xue, Y. Q.; Lehmer, B.; Alexander, D. M.; Bauer, Franz Erik; Vito, F.; Yang, G.; Basu-Zych, A. R.; Comastri, A.
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    THE EVOLUTION OF NORMAL GALAXY X-RAY EMISSION THROUGH COSMIC HISTORY: CONSTRAINTS FROM THE 6 MS CHANDRA DEEP FIELD-SOUTH
    (2016) Lehmer, B. D.; Basu-Zych, A. R.; Mineo, S.; Brandt, W. N.; Eufrasio, R. T.; Fragos, T.; Hornschemeier, A. E.; Luo, B.; Xue, Y. Q.; Bauer, Franz Erik
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    The universal shape of the X-ray variability power spectrum of AGN up to z ∼ 3
    (2023) Paolillo, M.; Papadakis, I. E.; Brandt, W. N.; Bauer, F. E.; Lanzuisi, G.; Allevato, V.; Shemmer, O.; Zheng, X. C.; De Cicco, D.; Gilli, R.; Luo, B.; Thomas, M.; Tozzi, P.; Vito, F.; Xue, Y. Q.
    Aims. We study the ensemble X-ray variability properties of active galactic nuclei (AGN) over large ranges of timescale (20 ks <= T <= 14 yr), redshift (0 <= z less than or similar to 3), luminosity (10(40) erg s(-1) <= L-X <= 10(46) erg s(-1)), and black hole (BH) mass (10(6) <= M-circle dot <= 10(9)).
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    Tracing the accretion history of supermassive black holes through X-ray variability: results from the Chandra Deep Field-South
    (2017) Paolillo, M.; Papadakis, I.; Brandt, W. N.; Luo, B.; Xue, Y. Q.; Tozzi, P.; Shemmer, O.; Allevato, V.; Bauer, Franz Erik; Comastri, A.