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  • 1
    Electronic Resource
    Electronic Resource
    Rapid growth of black holes in massive star-forming galaxies (2005)
    [s.l.] : Macmillian Magazines Ltd.
    Nature 434 (2005), S. 738-740 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The tight relationship between the masses of black holes and galaxy spheroids in nearby galaxies implies a causal connection between the growth of these two components. Optically luminous quasars host the most prodigious accreting black holes in the Universe, and can account for s30 ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/nature03473
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  • 2
    Electronic Resource
    Electronic Resource
    Rapid X-ray flaring from the direction of the supermassive black hole at the Galactic Centre (2001)
    [s.l.] : Macmillian Magazines Ltd.
    Nature 413 (2001), S. 45-48 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The nuclei of most galaxies are now believed to harbour supermassive black holes. The motions of stars in the central few light years of our Milky Way Galaxy indicate the presence of a dark object with a mass of about 2.6 × 106 solar masses (refs 2, ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/35092510
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  • 3
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    Chandra reveals a luminous Compton-thick QSO powering a Lyα blob in a z = 4 starbursting protocluster (2020)
    EDP Sciences
    Details
    Publication Date: 2020-10-01
    Description: Context. Galaxy clusters in the local universe descend from high-redshift overdense regions known as protoclusters. The large gas reservoirs and high rate of galaxy interaction in protoclusters are expected to enhance star-formation activity and trigger luminous supermassive black-hole accretion in the nuclear regions of the host galaxies. Aims. We investigated the active galactic nucleus (AGN) content of a gas-rich and starbursting protocluster at z = 4.002, known as the Distant Red Core (DRC). In particular, we search for luminous and possibly obscured AGN in 13 identified members of the structure, and compare the results with protoclusters at lower redshifts. We also test whether a hidden AGN can power the Lyα blob (LAB) detected with VLT/MUSE in the DRC. Methods. We observed all of the identified members of the structure with 139 ks of Chandra ACIS-S imaging. Being less affected by absorption than optical and IR bands, even in the presence of large column densities of obscuring material, X-ray observations are the best tools to detect ongoing nuclear activity in the DRC galaxies. Results. We detect obscured X-ray emission from the two most gas-rich members of the DRC, named DRC-1 and DRC-2. Both of them are resolved into multiple interacting clumps in high-resolution Atacama Large Millimeter Array and Hubble Space Telescope observations. In particular, DRC-2 is found to host a luminous (L2−10 keV ≈ 3 × 1045 erg s−1 ) Compton-thick (NH ≳ 1024 cm−2) quasar (QSO) candidate, comparable to the most luminous QSOs known at all cosmic times. The AGN fraction among DRC members is consistent with results found for lower redshift protoclusters. However, X-ray stacking analysis reveals that supermassive black hole (SMBH) accretion is likely also taking place in other DRC galaxies that are not detected individually by Chandra. Conclusions. The luminous AGN detected in the most gas-rich galaxies in the DRC and the widespread SMBH accretion in the other members, which is suggested by stacking analysis, point toward the presence of a strong link between large gas reservoirs, galaxy interactions, and luminous and obscured nuclear activity in protocluster members. The powerful and obscured QSO detected in DRC-2 is likely powering the nearby LAB detected with VLT/MUSE, possibly through photoionization; however, we propose that the diffuse Lyα emission may be due to gas shocked by a massive outflow launched by DRC-2 over a ≈10 kpc scale.
    Print ISSN: 0004-6361
    Electronic ISSN: 1432-0746
    Topics: Physics
    Published by EDP Sciences
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  • 4
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    Extremely red quasars from SDSS, BOSS and WISE: classification of optical spectra (2015)
    Oxford University Press
    Details
    Publication Date: 2015-09-16
    Description: Quasars with extremely red infrared-to-optical colours are an interesting population that can test ideas about quasar evolution as well as orientation, obscuration and geometric effects in the so-called AGN unified model. To identify such a population, we match the quasar catalogues of the Sloan Digital Sky Survey (SDSS), the Baryon Oscillation Spectroscopic Survey (BOSS) to the Wide-Field Infrared Survey Explorer ( WISE ) to identify quasars with extremely high infrared-to-optical ratios. We identify 65 objects with r AB – W 4 Vega  〉 14 mag (i.e. F (22 μm)/ F ( r ) 1000). This sample spans a redshift range of 0.28 〈  z  〈 4.36 and has a bimodal distribution, with peaks at z  ~ 0.8 and z  ~ 2.5. It includes three z  〉 2.6 objects that are detected in the W 4 band but not W 1 or W 2 (i.e. ‘ W 1 W 2 dropouts'). The SDSS/BOSS spectra show that the majority of the objects are reddened type 1 quasars, type 2 quasars (both at low and high redshift) or objects with deep low-ionization broad absorption lines (BALs) that suppress the observed r -band flux. In addition, we identify a class of type 1 permitted broad emission-line objects at z ~= 2–3 which are characterized by emission line rest-frame equivalent widths (REWs) of 150 Å, much larger than those of typical quasars. In particular, 55 per cent (45 per cent) of the non-BAL type 1s with measurable C iv in our sample have REW(C iv ) 〉 100 (150) Å, compared to only 5.8 per cent (1.3 per cent) for non-BAL quasars in BOSS. These objects often also have unusual line ratios, such as very high N v /Ly α ratios. These large REWs might be caused by suppressed continuum emission analogous to type 2 quasars; however, there is no obvious mechanism in standard unified models to suppress the continuum without also obscuring the broad emission lines.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 5
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    Extremely red quasars from SDSS, BOSS and WISE: classification of optical spectra (2015)
    Oxford University Press
    Details
    Publication Date: 2015-09-27
    Description: Quasars with extremely red infrared-to-optical colours are an interesting population that can test ideas about quasar evolution as well as orientation, obscuration and geometric effects in the so-called AGN unified model. To identify such a population, we match the quasar catalogues of the Sloan Digital Sky Survey (SDSS), the Baryon Oscillation Spectroscopic Survey (BOSS) to the Wide-Field Infrared Survey Explorer ( WISE ) to identify quasars with extremely high infrared-to-optical ratios. We identify 65 objects with r AB – W 4 Vega  〉 14 mag (i.e. F (22 μm)/ F ( r ) 1000). This sample spans a redshift range of 0.28 〈  z  〈 4.36 and has a bimodal distribution, with peaks at z  ~ 0.8 and z  ~ 2.5. It includes three z  〉 2.6 objects that are detected in the W 4 band but not W 1 or W 2 (i.e. ‘ W 1 W 2 dropouts'). The SDSS/BOSS spectra show that the majority of the objects are reddened type 1 quasars, type 2 quasars (both at low and high redshift) or objects with deep low-ionization broad absorption lines (BALs) that suppress the observed r -band flux. In addition, we identify a class of type 1 permitted broad emission-line objects at z ~= 2–3 which are characterized by emission line rest-frame equivalent widths (REWs) of 150 Å, much larger than those of typical quasars. In particular, 55 per cent (45 per cent) of the non-BAL type 1s with measurable C iv in our sample have REW(C iv ) 〉 100 (150) Å, compared to only 5.8 per cent (1.3 per cent) for non-BAL quasars in BOSS. These objects often also have unusual line ratios, such as very high N v /Ly α ratios. These large REWs might be caused by suppressed continuum emission analogous to type 2 quasars; however, there is no obvious mechanism in standard unified models to suppress the continuum without also obscuring the broad emission lines.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 6
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    Discovery of extreme [O III] {lambda}5007 outflows in high-redshift red quasars (2016)
    Oxford University Press
    Details
    Publication Date: 2016-05-12
    Description: Black hole feedback is now a standard component of galaxy formation models. These models predict that the impact of black hole activity on its host galaxy likely peaked at z  = 2–3, the epoch of strongest star formation activity and black hole accretion activity in the Universe. We used XS hooter on the Very Large Telescope to measure rest-frame optical spectra of four z  ~ 2.5 extremely red quasars with infrared luminosities ~10 47  erg s –1 . We present the discovery of very broad (full width at half max = 2600–5000 km s –1 ), strongly blueshifted (by up to 1500 km s –1 ) [O iii ] 5007 Å emission lines in these objects. In a large sample of type 2 and red quasars, [O iii ] kinematics are positively correlated with infrared luminosity, and the four objects in our sample are on the extreme end in both [O iii ] kinematics and infrared luminosity. We estimate that at least 3 per cent of the bolometric luminosity in these objects is being converted into the kinetic power of the observed wind. Photo-ionization estimates suggest that the [O iii ] emission might be extended on a few kpc scales, which would suggest that the extreme outflow is affecting the entire host galaxy of the quasar. These sources may be the signposts of the most extreme form of quasar feedback at the peak epoch of galaxy formation, and may represent an active ‘blow-out’ phase of quasar evolution.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 7
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    Mid-infrared luminous quasars in the GOODS-Herschel fields: a large population of heavily obscured, Compton-thick quasars at z {approx} 2 (2016)
    Oxford University Press
    Details
    Publication Date: 2016-01-01
    Description: We present the infrared (IR) and X-ray properties of a sample of 33 mid-IR luminous quasars ( L 6 μm ≥ 6 x 10 44 erg s –1 ) at redshift z 1–3, identified through detailed spectral energy distribution analyses of distant star-forming galaxies, using the deepest IR data from Spitzer and Herschel in the GOODS– Herschel fields. The aim is to constrain the fraction of obscured, and Compton-thick (CT, N H 〉 1.5 x 10 24 cm –2 ) quasars at the peak era of nuclear and star formation activities. Despite being very bright in the mid-IR band, 30 per cent of these quasars are not detected in the extremely deep 2 and 4 Ms Chandra X-ray data available in these fields. X-ray spectral analysis of the detected sources reveals that the majority (67 per cent) are obscured by column densities N H 〉 10 22 cm –2 ; this fraction reaches 80 per cent when including the X-ray-undetected sources (9 out of 33), which are likely to be the most heavily obscured, CT quasars. We constrain the fraction of CT quasars in our sample to be 24–48 per cent, and their space density to be = (6.7 ± 2.2) x 10 –6 Mpc –3 . From the investigation of the quasar host galaxies in terms of star formation rates (SFRs) and morphological distortions, as a sign of galaxy mergers/interactions, we do not find any direct relation between SFRs and quasar luminosity or X-ray obscuration. On the other hand, there is tentative evidence that the most heavily obscured quasars have, on average, more disturbed morphologies than the unobscured/moderately obscured quasar hosts, which preferentially live in undisturbed systems. However, the fraction of quasars with disturbed morphology amongst the whole sample is 40 per cent, suggesting that galaxy mergers are not the main fuelling mechanism of quasars at z 2.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 8
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    Supermassive black-hole growth over cosmic time: Active galaxy demography, physics, and ecology from Chandra surveys (2010)
    National Academy of Sciences
    Details
    Publication Date: 2010-04-19
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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  • 9
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    Constraining FeLoBAL outflows from absorption line variability (2015)
    Oxford University Press
    Details
    Publication Date: 2015-08-27
    Description: Iron low-ionization broad absorption lines (FeLoBALs) trace a rare class of quasar outflows with large column densities and potentially large kinetic energies that might be important for ‘feedback’ to galaxy evolution. In order to probe the physical properties of these outflows, we conducted a multiple-epoch, absorption line variability study of 12 FeLoBAL quasars spanning a redshift range of 0.7 ≤  z  ≤ 1.9 over rest-frame time-scales of ~10 d to 7.6 yr. We detect absorption line variability with ≥8 confidence in 3 out of the 12 sources in our sample over time-scales of ~0.6 to 7.6 yr. Variable wavelength intervals are associated with ground- and excited-state Fe  ii multiplets, the Mg  ii 2796, 2803 doublet, Mg  i 2852, and excited-state Ni  ii multiplets. The observed variability along with evidence of saturation in the absorption lines favours transverse motions of gas across the line of sight as the preferred scenario, and allows us to constrain the outflow distance from the supermassive black hole to be 69, 7, and 60 pc for our three variable sources. In combination with other studies, these results suggest that the outflowing gas in FeLoBAL quasars resides on a range of scales and includes matter within tens of parsecs of the central source.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 10
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    The nature of the torus in the heavily obscured AGN Markarian 3: an X-ray study (2016)
    Oxford University Press
    Details
    Publication Date: 2016-06-10
    Description: In this paper, we report the results of an X-ray monitoring campaign on the heavily obscured Seyfert galaxy, Markarian 3, carried out between the fall of 2014 and the spring of 2015 with NuSTAR , Suzaku and XMM–Newton . The hard X-ray spectrum of Markarian 3 is variable on all the time-scales probed by our campaign, down to a few days. The observed continuum variability is due to an intrinsically variable primary continuum seen in transmission through a large, but still Compton-thin column density ( N H ~ 0.8–1.1 x 10 24  cm –2 ). If arranged in a spherical-toroidal geometry, the Compton scattering matter has an opening angle ~=66°, and is seen at a grazing angle through its upper rim (inclination angle ~=70°). We report a possible occultation event during the 2014 campaign. If the torus is constituted by a system of clouds sharing the same column density, this event allows us to constrain their number (17 ± 5) and individual column density, [~= (4.9 ± 1.5) x 10 22  cm –2 ]. The comparison of IR and X-ray spectroscopic results with state-of-the art ‘torus’ models suggests that at least two-thirds of the X-ray obscuring gas volume might be located within the dust sublimation radius. We report also the discovery of an ionized absorber, characterized by variable resonant absorption lines due to He- and H-like iron. This discovery lends support to the idea that moderate column density absorbers could be due to clouds evaporated at the outer surface of the torus, possibly accelerated by the radiation pressure due to the central AGN emission leaking through the patchy absorber.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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