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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
11

Spectral energy distribution variations of nearby Seyfert galaxies during AGN watch monitoring programs

Kilerci Eser, Ece, Vestergaard, M. 02 1900 (has links)
We present and analyse quasi-simultaneous multi-epoch spectral energy distributions (SEDs) of seven reverberation-mapped active galactic nuclei (AGNs) for which accurate black hole mass measurements and suitable archival data are available from the 'AGNWatch' monitoring programs. We explore the potential of optical-UV and X-ray data, obtained within 2 d, to provide more accurate SED-based measurements of individual AGN and quantify the impact of source variability on key measurements typically used to characterize the black hole accretion process plus on bolometric correction factors at 5100 angstrom, 1350 angstrom and for the 2-10 keV X-ray band, respectively. The largest SED changes occur on long time-scales (greater than or similar to 1 year). For our small sample, the 1 mu m to 10 keV integrated accretion luminosity typically changes by 10 per cent on short time-scales (over 20 d), by similar to 30 per cent over a year, but can change by 100 per cent or more for individual AGN. The extreme ultraviolet (EUV) gap is the most uncertain part of the intrinsic SED, introducing a similar to 25 per cent uncertainty in the accretion-induced luminosity, relative to the model independent interpolation method that we adopt. That aside, our analysis shows that the uncertainty in the accretion-induced luminosity, the Eddington luminosity ratio and the bolometric correction factors can be reduced (by a factor of two or more) by use of the SEDs built from data obtained within 20 d. However, (M) over dot and eta are mostly limited by the unknown EUV emission and the unknown details of the central engine and our aspect angle.
12

The AGN–Star Formation Connection: Future Prospects with JWST

Kirkpatrick, Allison, Alberts, Stacey, Pope, Alexandra, Barro, Guillermo, Bonato, Matteo, Kocevski, Dale D., Pérez-González, Pablo, Rieke, George H., Rodríguez-Muñoz, Lucia, Sajina, Anna, Grogin, Norman A., Mantha, Kameswara Bharadwaj, Pandya, Viraj, Pforr, Janine, Salvato, Mara, Santini, Paola 07 November 2017 (has links)
The bulk of the stellar growth over cosmic time is dominated by IR-luminous galaxies at cosmic noon (z = 1-2), many of which harbor a hidden active galactic nucleus (AGN). We use state-of-the-art infrared color diagnostics, combining Spitzer and Herschel observations, to separate dust-obscured AGNs from dusty star-forming galaxies (SFGs) in the CANDELS and COSMOS surveys. We calculate 24 mu m counts of SFGs, AGN/star-forming "Composites," and AGNs. AGNs and Composites dominate the counts above 0.8 mJy at 24 mu m, and Composites form at least 25% of an IR sample even to faint detection limits. We develop methods to use the Mid-Infrared Instrument (MIRI) on JWST to identify dust-obscured AGNs and Composite galaxies from z similar to 1-2. With the sensitivity and spacing of MIRI filters, we will detect >4 times as many AGN hosts as with Spitzer/IRAC criteria. Any star formation rates based on the 7.7 mu m PAH feature (likely to be applied to MIRI photometry) must be corrected for the contribution of the AGN, or the star formation rate will be overestimated by similar to 35% for cases where the AGN provides half the IR luminosity and similar to 50% when the AGN accounts for 90% of the luminosity. Finally, we demonstrate that our MIRI color technique can select AGNs with an Eddington ratio of lambda(Edd) similar to 0.01 and will identify AGN hosts with a higher specific star formation rate than X-ray techniques alone. JWST/MIRI will enable critical steps forward in identifying and understanding dust-obscured AGNs and the link to their host galaxies.
13

High-redshift Galaxies and Black Holes Detectable with the JWST: A Population Synthesis Model from Infrared to X-Rays

Volonteri, Marta, Reines, Amy E., Atek, Hakim, Stark, Daniel P., Trebitsch, Maxime 10 November 2017 (has links)
The first billion years of the Universe has been a pivotal time: stars, black holes (BHs), and galaxies formed and assembled, sowing the seeds of galaxies as we know them today. Detecting, identifying, and understanding the first galaxies and BHs is one of the current observational and theoretical challenges in galaxy formation. In this paper we present a population synthesis model aimed at galaxies, BHs, and active galactic nuclei (AGNs) at high redshift. The model builds a population based on empirical relations. The spectral energy distribution of galaxies is determined by age and metallicity, and that of AGNs by BH mass and accretion rate. We validate the model against observations, and predict properties of galaxies and AGN in other wavelength and/or luminosity ranges, estimating the contamination of stellar populations (normal stars and high-mass X-ray binaries) for AGN searches from the infrared to X-rays, and vice versa for galaxy searches. For high-redshift galaxies with stellar ages <1 Gyr, we find that disentangling stellar and AGN emission is challenging at restframe UV/optical wavelengths, while high-mass X-ray binaries become more important sources of confusion in X-rays. We propose a color-color selection in the James Webb Space Telescope bands to separate AGN versus star-dominated galaxies in photometric observations. We also estimate the AGN contribution, with respect to massive, hot, and metal-poor stars, at driving high-ionization lines, such as C IV and He II. Finally, we test the influence of the minimum BH mass and occupation fraction of BHs in low-mass galaxies on the restframe UV/near-IR and X-ray AGN luminosity function.
14

A SURVEY OF LUMINOUS HIGH-REDSHIFT QUASARS WITH SDSS AND WISE . II. THE BRIGHT END OF THE QUASAR LUMINOSITY FUNCTION AT z ∼ 5

Yang, Jinyi, Wang, Feige, Wu, Xue-Bing, Fan, Xiaohui, McGreer, Ian D., Bian, Fuyan, Yi, Weimin, Yang, Qian, Ai, Yanli, Dong, Xiaoyi, Zuo, Wenwen, Green, Richard, Jiang, Linhua, Wang, Shu, Wang, Ran, Yue, Minghao 20 September 2016 (has links)
This is the second paper in a series on a new luminous z similar to 5 quasar survey using optical and near-infrared colors. Here we present a new determination of the bright end of the quasar luminosity function (QLF) at z similar to 5. Combining. our 45 new quasars with previously known quasars that satisfy our selections, we construct the largest uniform luminous z similar to 5 quasar sample to date, with 99 quasars in the range of 4.7 <= z < 5.4 and -29 < M-1450 <= -26.8, within the Sloan Digital Sky Survey (SDSS) footprint. We use a modified 1/V-a method including flux limit correction to derive a binned QLF, and we model the parametric QLF using maximum likelihood estimation. With the faint-end slope of the QLF fixed as alpha = -2.03 from previous deeper samples, the best fit of our QLF gives a flatter bright end slope beta = -3.58 +/- 0.24 and a fainter break magnitude M-1450(*) = -26.98 +/- 0.23 than previous studies at similar redshift. Combined with previous work at lower and higher redshifts, our result is consistent with a luminosity evolution and density evolution model. Using the best-fit QLF, the contribution of quasars to the ionizing background at z similar to 5 is found to be 18%-45% with a clumping factor C of 2-5. Our sample suggests an evolution of radio loud fraction with optical luminosity but no obvious evolution with redshift.
15

Discovery of 16 New z ∼ 5.5 Quasars: Filling in the Redshift Gap of Quasar Color Selection

Yang, Jinyi, Fan, Xiaohui, Wu, Xue-Bing, Wang, Feige, Bian, Fuyan, Yang, Qian, McGreer, Ian D., Yi, Weimin, Jiang, Linhua, Green, Richard, Yue, Minghao, Wang, Shu, Li, Zefeng, Ding, Jiani, Dye, Simon, Lawrence, Andy 30 March 2017 (has links)
We present initial results from the first systematic survey of luminous z similar to 5.5 quasars. Quasars at z similar to 5.5, the post-reionization epoch, are crucial tools to explore the evolution of intergalactic medium, quasar evolution, and the early super-massive black hole growth. However, it has been very challenging to select quasars at redshifts 5.3 <= z <= 5.7 using conventional color selections, due to their similar optical colors to late-type stars, especially M dwarfs, resulting in a glaring redshift gap in quasar redshift distributions. We develop a new selection technique for z similar to 5.5 quasars based on optical, near-IR, and mid-IR photometric data from Sloan Digital Sky Survey (SDSS), UKIRT InfraRed Deep Sky Surveys-Large Area Survey (ULAS), VISTA Hemisphere Survey (VHS), and Wide Field Infrared Survey Explorer. From our pilot observations in the SDSS-ULAS/VHS area, we have discovered 15 new quasars at 5.3. z. 5.7 and 6 new lower redshift quasars, with SDSS z band magnitude brighter than 20.5. Including other two z similar to 5.5 quasars already published in our previous work, we now construct a uniform quasar sample at 5.3 <= z <= 5.7, with 17 quasars in a similar to 4800 square degree survey area. For further application in a larger survey area, we apply our selection pipeline to do a test selection by using the new wide field J-band photometric data from a preliminary version of the UKIRT Hemisphere Survey (UHS). We successfully discover the first UHS selected z similar to 5.5 quasar.
16

The evolution of active galactic nuclei in clusters of galaxies from the Dark Energy Survey

Bufanda, E., Hollowood, D., Jeltema, T. E., Rykoff, E. S., Rozo, E., Martini, P., Abbott, T. M. C., Abdalla, F. B., Allam, S., Banerji, M., Benoit-Lévy, A., Bertin, E., Brooks, D., Carnero Rosell, A., Carrasco Kind, M., Carretero, J., Cunha, C. E., da Costa, L. N., Desai, S., Diehl, H. T., Dietrich, J. P., Evrard, A. E., Fausti Neto, A., Flaugher, B., Frieman, J., Gerdes, D. W., Goldstein, D. A., Gruen, D., Gruendl, R. A., Gutierrez, G., Honscheid, K., James, D. J., Kuehn, K., Kuropatkin, N., Lima, M., Maia, M. A. G., Marshall, J. L., Melchior, P., Miquel, R., Mohr, J. J., Ogando, R., Plazas, A. A., Romer, A. K., Rooney, P., Sanchez, E., Santiago, B., Scarpine, V., Sevilla-Noarbe, I., Smith, R. C., Soares-Santos, M., Sobreira, F., Suchyta, E., Tarle, G., Thomas, D., Tucker, D. L., Walker, A. R. 01 March 2017 (has links)
The correlation between active galactic nuclei (AGNs) and environment provides important clues to AGN fuelling and the relationship of black hole growth to galaxy evolution. In this paper, we analyse the fraction of galaxies in clusters hosting AGN as a function of redshift and cluster richness for X-ray-detected AGN associated with clusters of galaxies in Dark Energy Survey (DES) Science Verification data. The present sample includes 33 AGNs with LX > 1043 erg s(-1) in non-central, host galaxies with luminosity greater than 0.5L(*) from a total sample of 432 clusters in the redshift range of 0.1< z <0.95. Analysis of the present sample reveals that the AGN fraction in red-sequence cluster members has a strong positive correlation with redshift such that the AGN fraction increases by a factor of similar to 8 from low to high redshift, and the fraction of cluster galaxies hosting AGN at high redshifts is greater than the low-redshift fraction at 3.6 sigma. In particular, the AGN fraction increases steeply at the highest redshifts in our sample at z > 0.7. This result is in good agreement with previous work and parallels the increase in star formation in cluster galaxies over the same redshift range. However, the AGN fraction in clusters is observed to have no significant correlation with cluster mass. Future analyses with DES Year 1 through Year 3 data will be able to clarify whether AGN activity is correlated to cluster mass and will tightly constrain the relationship between cluster AGN populations and redshift.
17

Alma Observations of Massive Molecular Gas Filaments Encasing Radio Bubbles in the Phoenix Cluster

Russell, H. R., McDonald, M., McNamara, B. R., Fabian, A. C., Nulsen, P. E. J., Bayliss, M. B., Benson, B. A., Brodwin, M., Carlstrom, J. E., Edge, A. C., Hlavacek-Larrondo, J., Marrone, D. P., Reichardt, C. L., Vieira, J. D. 14 February 2017 (has links)
We report new ALMA observations of the CO(3-2) line emission from the 2.1 +/- 0.3*10(10)M(circle dot). molecular gas reservoir in the central galaxy of the Phoenix cluster. The cold molecular gas is fueling a vigorous starburst at a rate of 500-800M(circle dot)yr(-1) and powerful black hole activity in the forms of both intense quasar radiation and radio jets. The radio jets have inflated huge bubbles filled with relativistic plasma into the hot, X-ray atmospheres surrounding the host galaxy. The ALMA observations show that extended filaments of molecular gas, each 10-20 kpc long with a mass of several billion solar masses, are located along the peripheries of the radio bubbles. The smooth velocity gradients and narrow line widths along each filament reveal massive, ordered molecular gas flows around each bubble, which are inconsistent with gravitational free-fall. The molecular clouds have been lifted directly by the radio bubbles, or formed via thermal instabilities induced in low-entropy gas lifted in the updraft of the bubbles. These new data provide compelling evidence for close coupling between the radio bubbles and the cold gas, which is essential to explain the self-regulation of feedback. The very feedback mechanism that heats hot atmospheres and suppresses star formation may also paradoxically stimulate production of the cold gas required to sustain feedback in massive galaxies.
18

VLA AND ALMA IMAGING OF INTENSE GALAXY-WIDE STAR FORMATION IN z ∼ 2 GALAXIES

Rujopakarn, W., Dunlop, J. S., Rieke, G. H., Ivison, R. J., Cibinel, A., Nyland, K., Jagannathan, P., Silverman, J. D., Alexander, D. M., Biggs, A. D., Bhatnagar, S., Ballantyne, D. R., Dickinson, M., Elbaz, D., Geach, J. E., Hayward, C. C., Kirkpatrick, A., McLure, R. J., Michałowski, M. J., Miller, N. A., Narayanan, D., Owen, F. N., Pannella, M., Papovich, C., Pope, A., Rau, U., Robertson, B. E., Scott, D., Swinbank, A. M., Werf, P. van der, Kampen, E. van, Weiner, B. J., Windhorst, R. A. 01 December 2016 (has links)
We present; 0 4 resolution extinction-independent distributions of star formation and dust in 11 star-forming galaxies (SFGs) at z. =. 1.3-3.0. These galaxies are selected from sensitive blank-field surveys of the 2 x 2' Hubble Ultra-Deep Field at gimel = 5 cm and 1.3 mm using the Karl G. Jansky Very Large Array and Atacama Large Millimeter/submillimeter Array. They have star formation rates (SFRs), stellar masses, and dust properties representative of massive main-sequence SFGs at z similar to 2. Morphological classification performed on spatially resolved stellar mass maps indicates a mixture of disk and morphologically disturbed systems; half of the sample harbor X-ray active galactic nuclei (AGNs), thereby representing a diversity of z similar to 2 SFGs undergoing vigorous mass assembly. We find that their intense star formation most frequently occurs at the location of stellar-mass concentration and extends over an area comparable to their stellar-mass distribution, with a median diameter of 4.2 similar to 1.8 kpc. This provides direct evidence of galaxy-wide star formation in distant blank-field-selected main-sequence SFGs. The typical galactic-average SFR surface density is 2.5Me circle dot yr(-1) kpc(-2), sufficiently high to drive outflows. In X-ray-selected AGN where radio emission is enhanced over the level associated with star formation, the radio excess pinpoints the AGNs, which are found to be cospatial with star formation. The median extinctionindependent size of main-sequence SFGs is two times larger than those of bright submillimeter galaxies, whose SFRs are 3-8 times larger, providing a constraint on the characteristic SFR (similar to 300Me yr(-1)) above which a significant population of more compact SFGs appears to emerge.
19

SPACE TELESCOPE AND OPTICAL REVERBERATION MAPPING PROJECT. IV. ANOMALOUS BEHAVIOR OF THE BROAD ULTRAVIOLET EMISSION LINES IN NGC 5548

Goad, M. R., Korista, K. T., Rosa, G. De, Kriss, G. A., Edelson, R., Barth, A. J., Ferland, G. J., Kochanek, C. S., Netzer, H., Peterson, B. M., Bentz, M. C., Bisogni, S., Crenshaw, D. M., Denney, K. D., Ely, J., Fausnaugh, M. M., Grier, C. J., Gupta, A., Horne, K. D., Kaastra, J., Pancoast, A., Pei, L., Pogge, R. W., Skielboe, A., Starkey, D., Vestergaard, M., Zu, Y., Anderson, M. D., Arévalo, P., Bazhaw, C., Borman, G. A., Boroson, T. A., Bottorff, M. C., Brandt, W. N., Breeveld, A. A., Brewer, B. J., Cackett, E. M., Carini, M. T., Croxall, K. V., Bontà, E. Dalla, Lorenzo-Cáceres, A. De, Dietrich, M., Efimova, N. V., Evans, P. A., Filippenko, A. V., Flatland, K., Gehrels, N., Geier, S., Gelbord, J. M., Gonzalez, L., Gorjian, V., Grupe, D., Hall, P. B., Hicks, S., Horenstein, D., Hutchison, T., Im, M., Jensen, J. J., Joner, M. D., Jones, J., Kaspi, S., Kelly, B. C., Kennea, J. A., Kim, M., Kim, S. C., Klimanov, S. A., Lee, J. C., Leonard, D. C., Lira, P., MacInnis, F., Manne-Nicholas, E. R., Mathur, S., McHardy, I. M., Montouri, C., Musso, R., Nazarov, S. V., Norris, R. P., Nousek, J. A., Okhmat, D. N., Papadakis, I., Parks, J. R., Pott, J.-U., Rafter, S. E., Rix, H.-W., Saylor, D. A., Schimoia, J. S., Schnülle, K., Sergeev, S. G., Siegel, M., Spencer, M., Sung, H.-I., Teems, K. G., Treu, T., Turner, C. S., Uttley, P., Villforth, C., Weiss, Y., Woo, J.-H., Yan, H., Young, S., Zheng, W.-K. 03 June 2016 (has links)
During an intensive Hubble Space Telescope (HST) Cosmic Origins Spectrograph (COS) UV monitoring campaign of the Seyfert 1 galaxy NGC 5548 performed from 2014 February to July, the normally highly correlated far UV continuum and broad emission line variations decorrelated for similar to 60-70 days, starting similar to 75 days after the first HST/COS observation. Following this anomalous state, the flux and variability of the broad emission lines returned to a more normal state. This transient behavior, characterized by significant deficits in flux and equivalent width of the strong broad UV emission lines, is the first of its kind to be unambiguously identified in an active galactic nucleus reverberation mapping campaign. The largest corresponding emission line flux deficits occurred for the high ionization, collisionally excited lines C IV and Si IV(+O IV]), and also He II(+O III]), while the anomaly in Ly alpha was substantially smaller. This pattern of behavior indicates a depletion in the flux of photons with E-ph > 54 eV relative to those near 13.6 eV. We suggest two plausible mechanisms for the observed behavior: (i) temporary obscuration of the ionizing continuum incident upon broad line region (BLR) clouds by a moving veil of material lying between the inner accretion disk and inner (BLR), perhaps resulting from an episodic ejection of material from the disk, or (ii) a temporary change in the intrinsic ionizing continuum spectral energy distribution resulting in a deficit of ionizing photons with energies > 54 eV, possibly due to a transient restructuring of the Comptonizing atmosphere above the disk. Current evidence appears to favor the latter explanation.
20

THE WISE DETECTION OF AN INFRARED ECHO IN TIDAL DISRUPTION EVENT ASASSN-14li

Jiang, Ning, Dou, Liming, Wang, Tinggui, Yang, Chenwei, Lyu, Jianwei, Zhou, Hongyan 29 August 2016 (has links)
We report the detection of a significant infrared variability of the nearest tidal disruption event (TDE) ASASSN-14li using Wide-field Infrared Survey Explorer and newly released Near-Earth Object WISE Reactivation data. In comparison with the quiescent state, the infrared flux is brightened by 0.12 and 0.16 mag in the W1 (3.4 mu m) and W2 (4.6 mu m) bands at 36 days after the optical discovery (or similar to 110 days after the peak disruption date). The flux excess is still detectable similar to 170 days later. Assuming that the flare-like infrared emission is from the dust around the black hole, its blackbody temperature is estimated to be similar to 2.1 x 10(3) K, slightly higher than the dust sublimation temperature, indicating that the dust is likely located close to the dust sublimation radius. The equilibrium between the heating and radiation of the dust claims a bolometric luminosity of similar to 10(43) - 10(45) erg s(-1), comparable with the observed peak luminosity. This result has for the first time confirmed the detection of infrared emission from the dust echoes of TDEs.

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