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Journal articles on the topic 'Nuclei-quasars'

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Author: Grafiati

Published: 14 March 2023

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1

Kellermann, KI. "Compact Radio Sources, Quasars and Active Galactic Nuclei." Australian Journal of Physics 47, no. 5 (1994): 599. http://dx.doi.org/10.1071/ph940599.

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This paper reviews John G. Bolton's contributions to our understanding of compact radio sources associated with quasars and active galactic nuclei (AGNs), and his work leading to the discovery of quasars. Particular attention is given to the interpretation of the observed properties of quasars and AGNs within the framework of unified models which interpret the wide variety of observed properties as being the result of orientation rather than of any intrinsic differences.

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2

Kembhavi, Ajit K., Jayant V. Narlikar, and Kimberly A. Weaver. "Quasars and Active Galactic Nuclei: An Introduction." Physics Today 53, no. 5 (May 2000): 60–61. http://dx.doi.org/10.1063/1.883085.

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3

Pismis, P., E. Moreno, and A. Garcia-Barreto. "Collimated Bipolar Outflow and the Formation of Nuclear Spirals; Possible Role of Magnetic Fields." Symposium - International Astronomical Union 140 (1990): 447–48. http://dx.doi.org/10.1017/s0074180900190813.

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The existence of non–steady phenomena, namely activity in the form of radial motions (outflow) of matter from the nuclei of galaxies is well established at present. Active Galactic Nuclei (AGN) constitute a topic of great interest and are intensively studied by all existing observational techniques. Conventionally objects classified as AGN span a range from quasars, radio galaxies to Seyferts 1 and 2. It appears, however, that there exist galaxies which exhibit somewhat milder activity which does not qualify their inclusion in the AGN group. The designation of MAGN (M for mildly) was suggested in the past (Pismis, 1986) to cover the less energetic nuclei. It may be reasonable to consider that active nuclei form a sequence, the difference along it being due to the energetics of the nuclei, from the most active quasars and radio galaxies down to the mildest ones like M31 or our Galaxy. The phenomenon underlying the activity may thus be universal, subject to the intrinsic energetics of the nuclei (Pismis, 1987).

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4

Cavaliere, A., E. Giallongo, and F. Vagnetti. "From local active galactic nuclei to early quasars." Astrophysical Journal 296 (September 1985): 402. http://dx.doi.org/10.1086/163459.

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5

Antonucci, Robert. "Unified Models for Active Galactic Nuclei and Quasars." Annual Review of Astronomy and Astrophysics 31, no. 1 (September 1993): 473–521. http://dx.doi.org/10.1146/annurev.aa.31.090193.002353.

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6

Ellingson, E., H. K. C. Yee, and R. F. Green. "Quasars and active galactic nuclei in rich environments. I - Fields surrounding optically faint quasars." Astrophysical Journal Supplement Series 76 (June 1991): 455. http://dx.doi.org/10.1086/191574.

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7

Hough, D. H., and A. C. S. Readhead. "Relativistic Beaming and the Nuclei of Double-lobed Radio Quasars." Symposium - International Astronomical Union 129 (1988): 99–100. http://dx.doi.org/10.1017/s0074180900134114.

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We have defined a complete sample of double-lobed 3CR quasars with minimal orientation bias. Properties of these objects on the >kpc scale are consistent with the simple beaming model for their nuclei. VLBI maps of six nuclei reveal “core-jet” structures. Both nuclei mapped at multiple epochs are modestly superluminal (3C245, 3.1c; 3C263, 1.3c; H0=100 km/s/Mpc, q0=0.5). The distribution of apparent velocities in this sample will provide a stringent test of beaming.

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8

Banks, Michael. "NASA launches X-ray mission." Physics World 35, no. 1 (January 1, 2022): 13ii. http://dx.doi.org/10.1088/2058-7058/35/01/17.

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9

Falcke, H. "11.2. The nature of compact radio cores in galaxies." Symposium - International Astronomical Union 184 (1998): 459–60. http://dx.doi.org/10.1017/s0074180900085569.

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Compact radio cores, which are often assumed to mark the presence of a super-massive black hole, are not only found in the nuclei of powerful quasars but also in nearby galaxies. While in quasars they are typically associated with relativistic jets, the nature of those cores in low-luminosity AGN is less clear. Here, I will briefly mention some of the recent theories (ADAFs or jets) and observations of the latter class of objects.

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10

Akujor, Chidi E., R. W. Porcas, A. R. Patnaik, and A. Ardeberg. "Optically Quiet Quasars – Radio and Optical Investigations." Symposium - International Astronomical Union 159 (1994): 419. http://dx.doi.org/10.1017/s0074180900176041.

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The activity in the nuclei of bright galaxies could arise from a number of sources: they may contain compact variable radio sources, they may be strong IR/optical/X–ray continuum sources, or they may have strong emission lines. Usually but not always these properties go together as in radio loud quasars. However, there appears to exist a class of objects which resemble quasars in radio structure and brightness – have strong flat spectrum cores but appear fainter than would be suggested by their radio brightness – unidentified on sky surveys (Zensus & Porcas, 1985, in J. Dyson, ed, AGN). These are called ‘optically quiet quasars’ (OQQs).

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11

Ellingson, E., H. K. C. Yee, and R. F. Green. "Quasars and active galactic nuclei in rich environments. II - The evolution of radio-loud quasars." Astrophysical Journal 371 (April 1991): 49. http://dx.doi.org/10.1086/169869.

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12

Guo, Sufen, Zhaoxiang Qi, Shilong Liao, Zihuang Cao, Mario G. Lattanzi, Beatrice Bucciarelli, Zhenghong Tang, and Qing-Zeng Yan. "Identifying quasars with astrometric and mid-infrared methods from APOP and ALLWISE." Astronomy & Astrophysics 618 (October 2018): A144. http://dx.doi.org/10.1051/0004-6361/201833135.

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Context. Quasars are spatially stationary, and they are essential objects in astrometry when defining reference frames. However, the census of quasars is far from complete. Mid-infared colors can be used to find quasar candidates because active galactic nuclei (AGNs) show a peculiar appearance in mid-infrared color, but these methods are incapable of separating quasars from AGNs. Aims. The aim of our study is to use astrometric and mid-infrared methods to select quasars and get a reliable quasar candidates catalog. Methods. We used a near-zero proper motion criterion in conjuction with WISE [W1–W2] color to select quasar candidates. The [W1–W2] color criterion is defined by the linear boundary of two samples: LAMOST DR5 quasars, which serve as the quasar sample, and LAMOST DR5 stars and galaxies, which serve as the non-quasar sample. The contamination and completeness are evaluated. Results. We present a catalog of 662 753 quasar candidates, with a completeness of about 75% and a reliability of 77.2%.

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13

Pelletier, G., and H. Sol. "Energetic particle beams in quasars and active galactic nuclei." Monthly Notices of the Royal Astronomical Society 254, no. 4 (February 15, 1992): 635–46. http://dx.doi.org/10.1093/mnras/254.4.635.

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14

Véron-Cetty, M. P., and P. Véron. "A catalogue of quasars and active nuclei: 11th edition." Astronomy & Astrophysics 412, no. 2 (November 28, 2003): 399–403. http://dx.doi.org/10.1051/0004-6361:20034225.

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15

Véron-Cetty, M. P., and P. Véron. "A catalogue of quasars and active nuclei: 13th edition." Astronomy and Astrophysics 518 (July 2010): A10. http://dx.doi.org/10.1051/0004-6361/201014188.

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16

Kellermann, K. I., R. C. Vermeulen, J. A. Zensus, and M. H. Cohen. "Sub-Milliarcsecond Imaging of Quasars and Active Galactic Nuclei." Astronomical Journal 115, no. 4 (April 1998): 1295–318. http://dx.doi.org/10.1086/300308.

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17

Véron-Cetty, M. P., and P. Véron. "A catalogue of quasars and active nuclei: 12th edition." Astronomy & Astrophysics 455, no. 2 (August 2006): 773–77. http://dx.doi.org/10.1051/0004-6361:20065177.

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18

Webb, Wayne, and Matthew Malkan. "Rapid Optical Variability in Active Galactic Nuclei and Quasars." Astrophysical Journal 540, no. 2 (September 10, 2000): 652–77. http://dx.doi.org/10.1086/309341.

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19

Cohen, M. H., and K. I. Kellermann. "Quasars and active galactic nuclei: high resolution radio imaging." Proceedings of the National Academy of Sciences 92, no. 25 (December 5, 1995): 11339–41. http://dx.doi.org/10.1073/pnas.92.25.11339.

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20

Pérez-Fournon, I., and P. Biermann. "A shock model for quasars and active galactic nuclei." Symposium - International Astronomical Union 119 (1986): 405–6. http://dx.doi.org/10.1017/s0074180900153070.

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First order Fermi acceleration is an efficient mechanism to produce relativistic particles in strong astrophysical shocks. We have developed a model using this theory to explain the non-thermal emission from non-relativistic jets in Quasars and AGNs. Fluid dynamical simulations of cosmic jets predict shock formation in them at quasi-periodic intervals. This is also suggested by observations of jets. We identify the shocks as the sites of reacceleration of the energetic particles required to explain the non-thermal emission of the jets. In order to facilitate the comparison with observations, we have done numerical simulations of the expected observational properties at high and low spatial resolution.

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21

Véron-Cetty, M. P., and P. Véron. "A catalogue of quasars and active nuclei: 10th edition." Astronomy & Astrophysics 374, no. 1 (July 2001): 92–94. http://dx.doi.org/10.1051/0004-6361:20010718.

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22

Xin, Chengcheng, Maria Charisi, Zoltán Haiman, and David Schiminovich. "Correlation between optical and UV variability of a large sample of quasars." Monthly Notices of the Royal Astronomical Society 495, no. 1 (May 7, 2020): 1403–13. http://dx.doi.org/10.1093/mnras/staa1258.

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ABSTRACT The variability of quasars across multiple wavelengths is a useful probe of physical conditions in active galactic nuclei. In particular, variable accretion rates, instabilities, and reverberation effects in the accretion disc of a supermassive black hole are expected to produce correlated flux variations in ultraviolet (UV) and optical bands. Recent work has further argued that binary quasars should exhibit strongly correlated UV and optical periodicities. Strong UV–optical correlations have indeed been established in small samples of (N ≲ 30) quasars with well-sampled light curves, and have extended the ‘bluer-when-brighter’ trend previously found within the optical bands. Here, we further test the nature of quasar variability by examining the observed-frame UV–optical correlations among bright quasars extracted from the Half Million Quasars (HMQ) catalogue. We identified a large sample of 1315 quasars in HMQ with overlapping UV and optical light curves from the Galaxy Evolution Explorer and the Catalina Real-time Transient Survey, respectively. We find that strong correlations exist in this much larger sample, but we rule out, at ∼95 per cent confidence, the simple hypothesis that the intrinsic UV and optical variations of all quasars are fully correlated. Our results therefore imply the existence of physical mechanism(s) that can generate uncorrelated optical and UV flux variations.

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23

Fenyves, Ervin J., Stephen N. Balog, David B. Cline, and M. Atac. "Study of the Galactic Center with a High Resolution Gamma Ray Telescope." Symposium - International Astronomical Union 136 (1989): 639–43. http://dx.doi.org/10.1017/s0074180900187145.

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It is generally accepted that massive black holes are the most likely source for the energy radiated from active galactic nuclei, and may explain the enormous amount of energy emitted by quasars, radio galaxies, Seyfert galaxies, and BL Lacertid objects. Although the detailed mechanisms of the black hole formation in galactic nuclei are not clear at present, it seems to be quite possible that the formation of massive black holes is a general outcome of the evolution of galactic nuclei.

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24

Kim, Minjin, Luis C. Ho, Carol J. Lonsdale, Mark Lacy, Andrew W. Blain, and Amy E. Kimball. "Evidence of AGN-driven Outflows in Young Radio Quasars Selected from the Wide-field Infrared Survey Explorer." Proceedings of the International Astronomical Union 9, S304 (October 2013): 347–48. http://dx.doi.org/10.1017/s1743921314004268.

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AbstractWe present near-infrared spectra of young radio quasars selected by cross-correlating the Wide-field Infrared Survey Explorer (WISE) all-sky survey catalog with the radio catalog [Faint Images of the Radio Sky at Twenty cm (FIRST) and NRAO VLA Sky Survey (NVSS)]. The objects have typical redshifts of z ≈ 2 and [O III] luminosities of 107 erg s−1 comparable to those of luminous quasars. The observed flux ratios of narrow emission lines indicate that these objects appear to be powered by active galactic nuclei. The [O III] line is broad, with full width at half maximum ~1300 to 2100 km s−1, significantly larger than that of ordinary quasars. These large line widths might be explained by jet-induced outflows.

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25

Blandford, R. D. "Black Hole Models of Quasars." Symposium - International Astronomical Union 119 (1986): 359–69. http://dx.doi.org/10.1017/s0074180900153021.

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Observations of active galactic nuclei are interpreted in terms of a theoretical model involving accretion onto a massive black hole. Optical quasars and Seyfert galaxies are associated with holes accreting near the Eddington rate and radio galaxies with sub-critical accretion. It is argued that magnetic fields are largely responsible for extracting energy and angular momentum from black holes and disks. Recent studies of electron-positron pair plasmas and their possible role in establishing the emergent X-ray spectrum are reviewed. The main evolutionary properties of active galactic nuclei can be interpreted in terms of a simple model in which black holes accrete gas at a rate dictated by the rate of gas supply which decreases with cosmic time. It may be worth searching for eclipsing binary black holes in lower power Seyferts.

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26

Kardashev, N. S., I. D. Novikov, and B. E. Stern. "The Electron-Positron Cauldron and the Formation of the Hard Radiation of Quasars and AGN." Symposium - International Astronomical Union 119 (1986): 383–93. http://dx.doi.org/10.1017/s0074180900153045.

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Active Galactic Nuclei (AGN) and quasars have unique physical parameters among all the objects in the Universe. Undoubtedly it is the uniqueness of the physical conditions in these systems that gives rise to the peculiar physical processes in them.

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27

Valtaoja, Esko. "Continuum monitoring of bright quasars." Symposium - International Astronomical Union 119 (1986): 79–83. http://dx.doi.org/10.1017/s0074180900152313.

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Beginning in 1980, the fluxes of over 40 bright quasars, BL Lacs and Seyferts have been monitored at radio and optical wavelengths in a Finnish-Soviet collaboration. The chief aims of the program are to provide information about the variability characteristics of active nuclei over a wide range of timescales and to fill a gap in monitoring programs at millimeter wavelengths. The results are also used as a basis for various other investigations.

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28

Gnedin, Yu N., and N. A. Silant'ev. "Magnetic fields of active galactic nuclei and quasars: Redshift dependence." Astronomy Letters 28, no. 7 (July 2002): 438–42. http://dx.doi.org/10.1134/1.1491966.

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29

Wandel, A., and A. Yahil. "Universal mass-luminosity relation for quasars and active galactic nuclei?" Astrophysical Journal 295 (August 1985): L1. http://dx.doi.org/10.1086/184525.

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30

Moncada, Roberto J., Rafael A. Colon, Juan J. Guerra, Matthew J. O'Dowd, and Luis A. Anchordoqui. "Ultrahigh energy cosmic ray nuclei from remnants of dead quasars." Journal of High Energy Astrophysics 13-14 (March 2017): 32–45. http://dx.doi.org/10.1016/j.jheap.2017.04.001.

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31

Gürkan, Gülay, Judith Croston, Martin J. Hardcastle, Vijay Mahatma, Beatriz Mingo, and Wendy L. Williams. "Finding Rare Quasars: VLA Snapshot Continuum Survey of FRI Quasar Candidates Selected from the LOFAR Two-Metre Sky Survey (LoTSS)." Galaxies 10, no. 1 (December 22, 2021): 2. http://dx.doi.org/10.3390/galaxies10010002.

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The radiative and jet power in active galactic nuclei is generated by accretion of material on to supermassive galactic-centre black holes. For quasars, where the radiative power is by definition very high, objects with high radio luminosities form 10 per cent of the population, although it is not clear whether this is a stable phase. Traditionally, quasars with high radio luminosities have been thought to present jets with edge-brightened morphology (Fanaroff-Riley II—FR II) due to the limitations of previous radio surveys (i.e., FRIs were not observed as part of the quasar population). The LOw Frequency ARray (LOFAR) Two-metre Sky Survey (LoTSS) with its unprecedented sensitivity and resolution covering wide sky areas has enabled the first systematic selection and investigation of quasars with core-brightened morphology (Fanaroff-Riley I—FR). We carried out a Very Large Array (VLA) snapshot survey to reveal inner structures of jets in selected quasar candidates; 15 (25 per cent) out of 60 sources show clear inner jet structures that are diagnostic of FRI jets and 13 quasars (∼22 per cent) show extended structures similar to those of FRI jets. Black hole masses and Eddington ratios do not show a clear difference between FRI and FRII quasars. FRII quasars tend to have higher jet powers than FRI quasars. Our results show that the occurrence of FRI jets in powerful radiatively efficient systems is not common, probably mainly due to two factors: galaxy environment and jet power.

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32

Gürkan, Gülay, M. J. Hardcastle, P. N. Best, L. K. Morabito, I. Prandoni, M. J. Jarvis, K. J. Duncan, et al. "LoTSS/HETDEX: Optical quasars." Astronomy & Astrophysics 622 (February 2019): A11. http://dx.doi.org/10.1051/0004-6361/201833892.

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The radio-loud/radio-quiet (RL/RQ) dichotomy in quasars is still an open question. Although it is thought that accretion onto supermassive black holes in the centre the host galaxies of quasars is responsible for some radio continuum emission, there is still a debate as to whether star formation or active galactic nuclei (AGN) activity dominate the radio continuum luminosity. To date, radio emission in quasars has been investigated almost exclusively using high-frequency observations in which the Doppler boosting might have an important effect on the measured radio luminosity, whereas extended structures, best observed at low radio frequencies, are not affected by the Doppler enhancement. We used a sample of quasars selected by their optical spectra in conjunction with sensitive and high-resolution low-frequency radio data provided by the LOw Frequency ARray (LOFAR) as part of the LOFAR Two-Metre Sky Survey (LoTSS) to investigate their radio properties using the radio loudness parameter (R =L144 MHz/Li band). The examination of the radio continuum emission and RL/RQ dichotomy in quasars exhibits that quasars show a wide continuum of radio properties (i.e. no clear bimodality in the distribution of ℛ). Radio continuum emission at low frequencies in low-luminosity quasars is consistent with being dominated by star formation. We see a significant albeit weak dependency of ℛ on the source nuclear parameters. For the first time, we are able to resolve radio morphologies of a considerable number of quasars. All these crucial results highlight the impact of the deep and high-resolution low-frequency radio surveys that foreshadow the compelling science cases for the Square Kilometre Array (SKA).

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33

Surace, J. A., and D. B. Sanders. "High Spatial Resolution Near-IR Tip/Tilt Imaging of “Warm” Ultraluminous Infrared Galaxies." Symposium - International Astronomical Union 186 (1999): 363. http://dx.doi.org/10.1017/s0074180900113105.

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We present results from high spatial resolution (FWHM ≈ 0.3–0.5″) near-IR (1.6 and 2.1μm) imaging of a complete sample of ultraluminous infrared galaxies (ULIGs) chosen to have “warm” mid-IR colors (f25/f60 > 0.2) characteristic of AGN. In conjunction with our WFPC2 imaging program (Surace et al. 1998), we have found that nearly all of these systems are advanced mergers with complex nuclear morphologies. The extended underlying galaxies are detected in each system at H and K′, and are found to have luminosities of a few L∗, similar to quasars (McLeod & Rieke 1994). Many of the circumnuclear star-forming knots seen at optical wavelengths have been detected. Based on model SEDs, their bolometric luminosities appear similar to those of the extended nuclear starbursts seen in other, less-luminous interacting systems (i.e. NGC 4038/9). Each ULIG is increasingly dominated at long wavelengths by a compact source which we identify as a putative active nucleus. The optical/near-IR colors of these putative nuclei are more extreme than the most infrared-active starburst galaxies, yet are identical to “far-IR loud” quasars which are in turn similar to optical quasars with significant hot (800 K) dust emission. Half of the ULIGs have dereddened nuclear near-IR luminosities comparable to those of QSOs, while the others resemble Seyferts; this may be an effect of patchy extinction and scattering. Similarities between the putative ULIG nuclei and QSO nuclei, the underlying host galaxies, and the apparent young age of the ULIGs (as evidenced by their compact star-forming knots) support the evolution of “warm” ULIGs into optical QSOs.

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34

Unwin, S. C., A. E. Wehrle, D. L. Jones, D. L. Meier, and B. G. Piner. "Quasar Astrophysics with the Space Interferometry Mission." Publications of the Astronomical Society of Australia 19, no. 1 (2002): 5–9. http://dx.doi.org/10.1071/as01087.

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AbstractPrecision optical astrometry of quasars and active galaxies can provide important insight into the spatial distribution and variability of emission in compact nuclei. SIM — the Space Interferometry Mission — will be the first optical interferometer capable of precision astrometry on quasars. Although it is not expected to resolve the emission, it will be very sensitive to astrometric shifts, for objects as faint as R magnitude 20. In its wide-angle mode, SIM will yield 4 microarcsecond absolute positions, and proper motions to about 2 microarcsecond/yr. A variety of AGN phenomena are expected to be visible to SIM on these scales, including time and spectral dependence in position offsets between accretion disk and jet emission. SIM should be able to answer the following questions. Does the most compact optical emission from an AGN come from an accretion disk or from a relativistic jet? Do the relative positions of the radio core and optical photocentre of quasars used for the reference frame tie change on the timescales of their photometric variability? Do the cores of galaxies harbour binary supermassive black holes remaining from galaxy mergers? In this paper we briefly describe the operation of SIM and the quasar measurements it will make. We estimate the size of the astrometric signatures which may be expected, and we discuss prospects for using astrometry as a fundamental tool for understanding quasar nuclei.

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35

Liao, Mai, Minfeng Gu, Minhua Zhou, and Liang Chen. "The X-ray emission in young radio active galactic nuclei." Monthly Notices of the Royal Astronomical Society 497, no. 1 (June 4, 2020): 482–97. http://dx.doi.org/10.1093/mnras/staa1559.

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ABSTRACT In this work, we investigated the X-ray emission for a sample of young radio active galactic nuclei (AGNs) by combining data from Chandra/XMM–Newton with data for other wavebands. We find strong correlations between the X-ray luminosity LX at 2–10 keV and the radio luminosities LR at 5 GHz for the VLBI radio-core, VLA radio-core and Faint Images of the Radio Sky at Twenty-Centimeters (FIRST) component, indicating that both parsec- and kiloparsec-scale radio emissions are strongly correlated with X-ray emission in these sources. We find an approximately linear dependence of the radio on the X-ray luminosity in the sources with radiatively efficient accretion flows (i.e. the Eddington ratio Redd ≳ 10−3), with b ∼ 1 ($L_{\rm R}\, \propto \, L_{\rm X} ^{b}$) and $\xi _{\rm RX}\, \sim$ 1 in the fundamental plane using the VLBI data. The dependence is consistent with the re-analysed results of a previous study of Fan and Bai at Redd ≳ 10−3, but is significantly different from the theoretical prediction of accretion flow as the origin of X-ray emission. In contrast to the case for radio-quiet quasars, there is no significant correlation between Γ and the Eddington ratio. Our results seem to indicate that the X-ray emission of high-accretion young radio AGNs may be from the jet. We constructed the spectral energy distributions (SEDs) for 18 sources (most of which are in radiatively efficient accretion), namely nine galaxies and nine quasars with high-quality X-ray data, and find that the X-ray emission of most quasars is more luminous than that of normal radio-quiet quasars. This is clearly seen from the quasar composite SED, in which the X-ray emission is apparently higher than that of radio-quiet quasars, probably supporting jet-related X-ray emission in young radio AGNs. The possibility that the X-ray emission is from self-synchrotron Compton is discussed.

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36

Alighieri, Sperello Di Serego. "The Unification of Quasars and Radio Galaxies." Symposium - International Astronomical Union 175 (1996): 389–90. http://dx.doi.org/10.1017/s0074180900081183.

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The evidence for misdirected quasars in the nuclei of powerful radio galaxies (PRG) is now solid: 1. strong perpendicular polarization of the UV continuum, produced by the scattering of light from the hidden nucleus, has been observed in 10 (out of 11) PRG with z > 0.7 (Cimatti et al. 1993); 2. polarized broad MgII2800 has been seen in 6 PRG (di Serego Alighieri et al. 1994, Antonucci et al. 1994), showing that the hidden nucleus is indeed a quasar. These findings are receiving authoritative confirmation from observations with the Keck telescope (Cimatti, Cohen and van Breugel in these Proceedings). Here I would like to concentrate on recent developments of our understanding of the unification between quasars and PRG.

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37

Li, Jiang-Tao, Feige Wang, Jinyi Yang, Joel N. Bregman, Xiaohui Fan, and Yuchen Zhang. "A Chandra survey of z ≥ 4.5 quasars." Monthly Notices of the Royal Astronomical Society 504, no. 2 (April 15, 2021): 2767–82. http://dx.doi.org/10.1093/mnras/stab1042.

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ABSTRACT X-ray observations provide a unique probe of the accretion disc corona of supermassive black holes (SMBHs). In this paper, we present a uniform Chandra X-ray data analysis of a sample of 152 z ≥ 4.5 quasars. We firmly detect 46 quasars of this sample in 0.5–2 keV above 3σ and calculate the upper limits of the X-ray flux of the remaining. We also estimate the power-law photon index of the X-ray spectrum of 31 quasars. 24 of our sample quasars are detected in the FIRST or NVSS radio surveys; all of them are radio-loud. We statistically compare the X-ray properties of our z ≥ 4.5 quasars to other X-ray samples of active galactic nuclei (AGNs) at different redshifts. The relation between the rest-frame X-ray luminosity and other quasar parameters, such as the bolometric luminosity, UV luminosity, or SMBH mass, shows large scatters. These large scatters can be attributed to the narrow luminosity range at the highest redshift, the large measurement error based on relatively poor X-ray data, and the inclusion of radio-loud quasars in the sample. The LX–LUV relationship is significantly sublinear. We do not find a significant redshift evolution of the LX–LUV relation, expressed either in the slope of this relation, or the departure of individual AGNs from the best-fitting αOX–LUV relation (ΔαOX). The median value of the X-ray photon index is Γ ≈ 1.79, which does not show redshift evolution from z = 0 to z ∼ 7. The X-ray and UV properties of the most distant quasars could potentially be used as a standard candle to constrain cosmological models. The large scatter of our sample on the Hubble diagram highlights the importance of future large unbiased deep X-ray and radio surveys in using quasars in cosmological studies.

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Raffai, P., B. Bécsy, Z. Haiman, and Z. Frei. "A Statistical Method for Detecting Gravitational Recoils of Supermassive Black Holes in Active Galactic Nuclei." Proceedings of the International Astronomical Union 12, S324 (September 2016): 227–30. http://dx.doi.org/10.1017/s1743921317000734.

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AbstractWe propose an observational test for gravitationally recoiling supermassive black holes in active galactic nuclei, based on a positive correlation between the velocities of black holes relative to their host galaxies, |Δv|, and their obscuring dust column densities, Σdust, both measured along the line of sight. Our findings using a set of toy models implemented to a Monte Carlo simulation imply that models of the galactic centre and of recoil dynamics can be tested by future observations of the potential Σdust–|Δv| correlation. We have also found that the fraction of obscured quasars decreases with |Δv|, for which the predicted trend can be compared to the observed fraction of type II quasars, and can further test combinations of models we may implement.

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Singh, Chandra, David Garofalo, and Benjamin Lang. "Powerful Jets from Radiatively Efficient Disks, a Decades-Old Unresolved Problem in High Energy Astrophysics." Galaxies 9, no. 1 (January 26, 2021): 10. http://dx.doi.org/10.3390/galaxies9010010.

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The discovery of 3C 273 in 1963, and the emergence of the Kerr solution shortly thereafter, precipitated the current era in astrophysics focused on using black holes to explain active galactic nuclei (AGN). But while partial success was achieved in separately explaining the bright nuclei of some AGN via thin disks, as well as powerful jets with thick disks, the combination of both powerful jets in an AGN with a bright nucleus, such as in 3C 273, remained elusive. Although numerical simulations have taken center stage in the last 25 years, they have struggled to produce the conditions that explain them. This is because radiatively efficient disks have proved a challenge to simulate. Radio quasars have thus been the least understood objects in high energy astrophysics. But recent simulations have begun to change this. We explore this milestone in light of scale-invariance and show that transitory jets, possibly related to the jets seen in these recent simulations, as some have proposed, cannot explain radio quasars. We then provide a road map for a resolution.

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Ansarinejad, B., T. Shanks, R. M. Bielby, N. Metcalfe, L. Infante, D. N. A. Murphy, D. J. Rosario, and S. M. Stach. "The nature of sub-millimetre galaxies II: an ALMA comparison of SMG dust heating mechanisms." Monthly Notices of the Royal Astronomical Society 510, no. 4 (January 13, 2022): 4976–91. http://dx.doi.org/10.1093/mnras/stac002.

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ABSTRACT We compare the contribution of active galactic nuclei (AGNs) and star formation towards dust heating in sub-mm galaxies (SMGs). We have used ALMA at 0.1-arcsec resolution to image a complete flux-limited sample of seven sub-mm sources previously shown to have spectral energy distributions that were as well-fitted by obscured AGN as star-forming galaxy templates. Indeed, two sub-mm sources were known to be quasars from their absorbed X-ray emission. We find the sub-mm sizes of all SMGs to be small (≈1−2 kpc) and generally ∼3 times smaller than any host detected in the near-infrared (NIR). In all cases, the five SMGs are comparable in sub-mm size to the two known quasars and four z ≈ 6 quasars, also observed with ALMA. We detect no evidence of diffuse spiral arms in this complete sample. We then convert the far-infrared (FIR) luminosities to star formation rate (SFR) surface densities and find that the SMGs occupy the same range as the known quasars in our sample. We conclude that in terms of sub-mm size, extent relative to host and SFR density as well as luminosity and mid-IR (MIR) colour, there is little distinction between the SMGs and sub-mm bright quasars. Finally, we present preliminary evidence that SMGs with higher MIR luminosities and sub-mm loud quasars tend to have dust components that range to hotter temperatures than their less luminous SMG counterparts. In light of these results, we continue to suggest that luminous SMGs may host dust-absorbed quasars that may simultaneously dominate the FIR and hard X-ray backgrounds.

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Xie, Yanxia, and Luis C. Ho. "The Ionization and Destruction of Polycyclic Aromatic Hydrocarbons in Powerful Quasars." Astrophysical Journal 925, no. 2 (February 1, 2022): 218. http://dx.doi.org/10.3847/1538-4357/ac32e2.

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Abstract We reanalyze the mid-infrared (5–40 μm) Spitzer spectra of 86 low-redshift (z < 0.5) Palomar–Green quasars to investigate the nature of polycyclic aromatic hydrocarbon (PAH) emission and its utility as a star formation rate (SFR) indicator for the host galaxies of luminous active galactic nuclei (AGNs). We decompose the spectra with our recently developed template-fitting technique to measure PAH fluxes and upper limits, which we interpret using mock spectra that simulate the effects of AGN dilution. While luminous quasars can severely dilute and affect the detectability of emission lines, PAHs are intrinsically weak in some sources that are otherwise gas-rich and vigorously forming stars, conclusively demonstrating that powerful AGNs destroy PAH molecules. Comparing PAH-based SFRs with independent SFRs derived from the mid-infrared fine-structure neon lines and the total infrared luminosity reveals that PAHs can trace star formation activity in quasars with bolometric luminosities ≲1046 erg s−1, but increasingly underestimate the SFR for more powerful quasars, typically by ∼0.5 dex. Relative to star-forming galaxies and low-luminosity AGNs, quasars have a comparable PAH 11.3 μm/7.7 μm ratio but characteristically lower ratios of 6.2 μm/7.7 μm, 8.6 μm/7.7 μm, and 11.3 μm/17.0 μm. We suggest that these trends indicate that powerful AGNs preferentially destroy small grains and enhance the PAH ionization fraction.

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Kaspi, Shai. "Results from Five Years of Spectrophotometric Monitoring of 28 Palomar-Green Quasars." International Astronomical Union Colloquium 159 (1997): 159–62. http://dx.doi.org/10.1017/s0252921100039877.

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AbstractWe present 5 years of results from a spectrophotometric monitoring program of 28 quasars. The typical sampling intervals are several months. We show the light curves obtained for two quasars, PG 0804+762 and PG 0953+414. Both sources show Balmer emissionline variations which follow those of the continuum with a time lag of order 100 days. This is the first reliable measurement of such a lag in active galactic nuclei with luminosity L > 1045 erg s−1. The broad-line region (BLR) size that is implied is almost an order of magnitude larger than that measured in several Seyfert 1 galaxies and is consistent with the hypothesis that the BLR size grows as L0.5.

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Fricke, K. J., and W. Kollatschny. "Relationships of the Active Nucleus, Galaxy, and Environment." Symposium - International Astronomical Union 134 (1989): 425–44. http://dx.doi.org/10.1017/s0074180900141580.

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35 years ago Baade and Minkowski (1954) suggested that a galaxy collision - diagnosed from the peculiar appearance of the parent object and its strong emission lines - is responsible for the strong radio-source CygA. This was the first time that gravitational interactions between galaxies were suggested to trigger nuclear activity. Over the following decades after the detection of the quasars and the gradual realization that quasars, comparable to the Seyfert phenomenon, are events at the nuclei of seemingly isolated galaxies, the collision hypothesis was abandoned. Efforts concentrated on the understanding of the activity as internal processes in the host galaxies, possibly aided by infall of gas from the intergalactic medium (cf. Rees, 1978; Gunn, 1979).

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Murphy, Edward M., Felix J. Lockman, Ari Laor, and Martin Elvis. "Galactic H i Column Densities toward Quasars and Active Galactic Nuclei." Astrophysical Journal Supplement Series 105 (August 1996): 369. http://dx.doi.org/10.1086/192319.

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Artymowicz, Pawel, D. N. C. Lin, and E. J. Wampler. "Star trapping and metallicity enrichment in quasars and active galactic nuclei." Astrophysical Journal 409 (June 1993): 592. http://dx.doi.org/10.1086/172690.

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Hough, D. H., R. C. Vermeulen, and A. C. S. Readhead. "First VLBA Images of the Nuclei in 3CR Lobe-dominated Quasars." International Astronomical Union Colloquium 164 (1998): 83–84. http://dx.doi.org/10.1017/s025292110004464x.

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AbstractWe report the first VLBA images of the nuclei in eight objects from the 3CR complete sample of 25 lobe-dominated quasars (LDQs): 3C 207, 3C 208, 3C 212, 3C 245, 3C 249.1, 3C 263, 3C 270.1, and 3C 275.1. These images reveal core-jet structures of considerable extent and complexity. In combination with earlier VLBI work on the 3CR LDQ sample, the partial distribution of apparent parsec-scale jet speeds for ten objects is relatively flat up to ~ 5h−1c, or perhaps even ~ 10h−1c. While this is not inconsistent with simple beaming models and quasar-FR II radio galaxy unification, it is crucial to obtain the complete speed distribution for truly definitive tests. Work is in progress on multi-frequency, dual-polarization, and phasereferencing VLBA observations on selected objects in the sample.

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Kacprzak, Glenn G., Christopher W. Churchill, Michael T. Murphy, and Jeff Cooke. "Probing the circumgalactic medium of active galactic nuclei with background quasars." Monthly Notices of the Royal Astronomical Society 446, no. 3 (November 28, 2014): 2861–69. http://dx.doi.org/10.1093/mnras/stu2324.

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48

Mikhailov, Alexander. "Determination of supermassive black hole spins in active galactic nuclei." Acta Astrophysica Taurica 3, no. 1 (March 22, 2022): 44–47. http://dx.doi.org/10.31059/aat.vol3.iss1.pp44-47.

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Abstract Black hole spin is a key to the relativistic jet generation. Existing models are based on the Blandford–Znajek and/or Blandford–Payne mechanisms. The jet power in these models is determined by the spin value, black hole mass, magnetic fields at the event horizon, and the accretion disc. Independent estimates of mass, jet power, and magnetic field give opportunity to constrain the supermassive black hole spin value. We present an application of this approach for supermassive black holes in different samples of active galactic nuclei (AGNs). We found that the assumption about equipartition between magnetic field energy density and accreting matter energy density is reasonable for the systems with thin accretion discs. The “mass-spin” diagrams were constructed for the samples of PG quasars and distant quasars at redshift z ≈ 4.8 and demonstrated the flattening region at masses MBH ≈ 108.5M☉. These diagrams can be used to study accretion onto supermassive black holes.

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Novikov, I. D. "Black Holes in the Universe." Highlights of Astronomy 11, no. 1 (1998): 28–41. http://dx.doi.org/10.1017/s1539299600019936.

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Some 30 years ago very few scientists thought that black holes may really exist. Attention focussed on the black hole hypothesis after neutron stars had been discovered. It was rather surprising that astrophysicists immediately ‘welcomed’ black holes. They found their place not only in the remnants of supernova explosions but also in the nuclei of galaxies and quasars.

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50

Titov, Oleg, Sándor Frey, Alexey Melnikov, Fengchun Shu, Bo Xia, Javier González, Belén Tercero, et al. "Astrometric Apparent Motion of High-redshift Radio Sources." Astronomical Journal 165, no. 2 (January 24, 2023): 69. http://dx.doi.org/10.3847/1538-3881/aca964.

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Abstract Radio-loud quasars at high redshift (z ≥ 4) are rare objects in the universe and rarely observed with Very Long Baseline Interferometry (VLBI). But some of them have flux density sufficiently high for monitoring of their apparent position. The instability of the astrometric positions could be linked to the astrophysical process in the jetted active galactic nuclei in the early universe. Regular observations of the high-redshift quasars are used for estimating their apparent proper motion over several years. We have undertaken regular VLBI observations of several high-redshift quasars at 2.3 GHz (S band) and 8.4 GHz (X band) with a network of five radio telescopes: 40 m Yebes (Spain), 25 m Sheshan (China), and three 32 m telescopes of the Quasar VLBI Network (Russia)—Svetloe, Zelenchukskaya, and Badary. Additional facilities joined this network occasionally. The sources have also been observed in three sessions with the European VLBI Network in 2018–2019 and one Long Baseline Array experiment in 2018. In addition, several experiments conducted with the Very Long Baseline Array in 2017–2018 were used to improve the time sampling and the statistics. Based on these 37 astrometric VLBI experiments between 2017 and 2021, we estimated the apparent proper motions of four quasars: 0901+697, 1428+422, 1508+572, and 2101+600.

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