Articles de revues : « Radio-quiet AGN »

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Young, S., J. H. Hough, D. J. Axon et J. A. Bailey. « Beaming in Radio-Quiet AGN ». International Astronomical Union Colloquium 163 (1997) : 837–38. http://dx.doi.org/10.1017/s0252921100044262.

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AbstractWe have obtained new optical spectropolarimetric data for the radio-quiet Seyfert NGC 1068, taken through apertures on the nucleus and at two positions within the ionization/scattering cone. The equivalent width of scattered broad-Hβ at these positions, is consistent with the presence of intrinsically beamed continuum radiation.

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O'Brien, Paul T., et Karen M. Leighly. « AGN Watch continuum monitoring of radio-quiet and radio-loud AGN ». Advances in Space Research 21, n^o 1-2 (janvier 1998) : 67–76. http://dx.doi.org/10.1016/s0273-1177(97)00615-7.

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Sasikumar, Silpa, et Preeti Kharb. « Looking at radio-quiet AGN with radio polarimetry ». Acta Astrophysica Taurica 3, n^o 1 (14 mars 2022) : 17–22. http://dx.doi.org/10.31059/aat.vol3.iss1.pp17-22.

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The dominant radio emission mechanism in radio-quiet quasars (RQQs) is an open question. Primary contenders include: low-power radio jets, winds, star-formation and coronal emission. Our work suggests that radio polarization and emission-line studies can help to distinguish between these scenarios and determine the primary contributor. Our multi-frequency, multi-scale radio polarization study has revealed a composite jet and "wind" radio outflow in the radio-intermediate quasar, III Zw 2, as well as in the BALQSO, Mrk 231. Our radio polarization study in conjunction with the [O III] emission-line study of five type 2 RQQs have provided insights on the interplay of jets/winds and emission-line gas. These sources reveal an anti-correlation between polarized radio emission and [O III] emission. This is similar to that observed in some radio-loud active galactic nuclei (AGN) in the literature and suggests that the radio emission could be depolarized by the emission-line gas. Overall, our work suggests that a close interaction between the radio outflow and the surrounding gaseous environment is likely to be responsible for their stunted form in RQ and RI AGN.

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Matt, G. « BeppoSAX Observations of Radio-quiet AGN ». Physica Scripta T77 (1 janvier 1998) : 62–64. http://dx.doi.org/10.1088/0031-8949/1998/t77/016.

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Matt, G. « X-Rays from radio-quiet AGN ». Astronomical & ; Astrophysical Transactions 20, n^o 2 (août 2001) : 253–61. http://dx.doi.org/10.1080/10556790108229706.

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Padovani, P., M. Bonzini, N. Miller, K. I. Kellermann, V. Mainieri, P. Rosati, P. Tozzi et S. Vattakunnel. « The AGN content of deep radio surveys and radio emission in radio-quiet AGN. Why every astronomer should care about deep radio fields ». Proceedings of the International Astronomical Union 9, S304 (octobre 2013) : 79–85. http://dx.doi.org/10.1017/s1743921314003391.

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AbstractWe present our very recent results on the sub-mJy radio source populations at 1.4 GHz based on the Extended Chandra Deep Field South VLA survey, which reaches ~ 30 μJy, with details on their number counts, evolution, and luminosity functions. The sub-mJy radio sky turns out to be a complex mix of star-forming galaxies and radio-quiet AGN evolving at a similar, strong rate and declining radio-loud AGN. While the well-known flattening of the radio number counts below 1 mJy is mostly due to star-forming galaxies, these sources and AGN make up an approximately equal fraction of the sub-mJy sky. Our results shed also light on a fifty-year-old issue, namely radio emission from radio-quiet AGN, and suggest that it is closely related to star formation, at least at z ~ 1.5 − 2. The implications of our findings for future, deeper radio surveys, including those with the Square Kilometre Array, are also discussed. One of the main messages, especially to non-radio astronomers, is that radio surveys are reaching such faint limits that, while previously they were mainly useful for radio quasars and radio galaxies, they are now detecting mostly star-forming galaxies and radio-quiet AGN, i.e., the bulk of the extragalactic sources studied in the infrared, optical, and X-ray bands.

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Kukula, M. J., J. S. Dunlop, G. L. Taylor et D. H. Hughes. « Host Galaxies of Radio-Loud & ; Radio-Quiet AGN ». Symposium - International Astronomical Union 175 (1996) : 248–49. http://dx.doi.org/10.1017/s0074180900080682.

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A clear understanding of both the differences and similarities between the host galaxies of the three main classes of powerful active galaxy – radio-quiet quasars (RQQs), radio-loud quasars (RLQs) and radio galaxies (RGs) – is vital in any attempt to unify or relate the various manifestations of the AGN phenomenon. The unification of RLQs and RGs via orientation effects requires that the hosts of the two types be derived from the same population of galaxies. Meanwhile, the correlation between radio power and host morphology in nearby AGN, with radio-quiet objects (Seyferts) occurring in disc systems and radio-loud sources in ellipticals, is generally assumed to persist at higher redshifts and nuclear luminosities. However, in both cases the evidence remains ambiguous and, moreover, many previous studies have been based on poorly selected samples.

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Kharb, Preeti, et Sasikumar Silpa. « Looking for Signatures of AGN Feedback in Radio-Quiet AGN ». Galaxies 11, n^o 1 (8 février 2023) : 27. http://dx.doi.org/10.3390/galaxies11010027.

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In this article, we discuss the state of “AGN feedback” in radio-quiet (RQ) AGN. This study involves heterogeneous samples of nearby Seyfert and LINER galaxies as well as quasi-stellar objects (QSOs) that have been observed at low radio frequencies (few ∼100 MHz) with the upgraded Giant Meterwave Radio Telescope (GMRT) and ∼GHz frequencies with the Karl G. Jansky Very Large Array (VLA) and Very Long Baseline Array (VLBA). These multi-frequency, multi-resolution observations detect a range of arcsecond-scale radio spectral indices that are consistent with the presence of multiple contributors including starburst winds and AGN jets or winds; steep spectrum “relic” emission is observed as well. Polarization-sensitive data from the VLA and GMRT suggest that the radio outflows are stratified (e.g., in IIIZw2, Mrk231); distinct polarization signatures suggest that there could either be a “spine + sheath” structure in the radio outflow, or there could be a “jet + wind” structure. Similar nested biconical outflows can also explain the VLBA and SDSS emission-line data in the KISSR sample of double-peaked emission-line Seyfert and LINER galaxies. Furthermore, the modeling of the emission-lines with plasma modeling codes such as MAPPINGS indicates that parsec-scale jets and winds in these sources can disturb or move the narrow-line region (NLR) gas clouds via the “shock + precursor” mechanism. Apart from the presence of “relic” emission, several Seyfert and LINER galaxies show clear morphological signatures of episodic jet activity. In one such source, NGC2639, at least four distinct episodes of jets are observed, the largest one of which was only detectable at 735 MHz with the GMRT. Additionally, a ∼6 kpc hole in the CO molecular gas along with a dearth of young stars in the center of its host galaxy is observed. Multiple jet episodes on the 10–100 parsec scales and a ∼10 parsec hole in the molecular gas is also observed in the Seyfert galaxy NGC4051. This suggests a link between episodic jet activity in RQ AGN and “AGN feedback” influencing the evolution of their host galaxies. However, a similar simple relationship between radio outflows and molecular gas mass is not observed in the Palomar–Green (PG) QSO sample, indicating that “AGN feedback” is a complex phenomenon in RQ AGN. “AGN feedback” must occur through the local impact of recurring multi-component outflows in RQ AGN. However, global feedback signatures on their host galaxy properties are not always readily evident.

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Marziani, P., M. Calvani et J. W. Sulentic. « On the Difference Between Radio Quiet and Radio Loud AGN ». International Astronomical Union Colloquium 163 (1997) : 761–62. http://dx.doi.org/10.1017/s0252921100043840.

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AbstractA systematic difference in alignment between the central black hole spin and the angular momentum of the accreting gas may help to explain several differences found in the optical and UV HST spectra of radio loud and radio quiet AGN.

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Villforth, Carolin, Kari Nilsson, Roy Østensen, Jochen Heidt, Sami-Matias Niemi et Janine Pforr. « Intranight polarization variability in radio-loud and radio-quiet AGN ». Monthly Notices of the Royal Astronomical Society 397, n^o 4 (21 août 2009) : 1893–908. http://dx.doi.org/10.1111/j.1365-2966.2009.14886.x.

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Mannheim, Karl. « On the Difference Between Radio Loud and Radio Quiet AGN ». Symposium - International Astronomical Union 159 (1994) : 285–88. http://dx.doi.org/10.1017/s0074180900175175.

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Nuclear jets containing relativistic “hot” particles close to the central engine cool dramatically by producing high energy radiation. The radiative dissipation is similar to the famous Compton drag acting upon “cold” thermal particles in a relativistic bulk flow. Highly relativistic protons induce anisotropic showers raining electromagnetic power down onto the putative accretion disk. Thus, the radiative signature of hot hadronic jets is x-ray irradiation of cold thermal matter. The synchrotron radio emission of the accelerated electrons is self-absorbed due to the strong magnetic fields close to the magnetic nozzle.

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Robinson, A. « Extended Emission-Line Regions Around AGN ». International Astronomical Union Colloquium 159 (1997) : 280–87. http://dx.doi.org/10.1017/s0252921100040288.

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AbstractHigh-excitation extended emission-line nebulae around active galactic nuclei probably result either from photoionization of the interstellar medium by beamed continuum radiation, or dynamical interactions between radio sources and the ambient gas, or both. Here I discuss the models based on these mechanisms, and their relative importance in radio-quiet and radio-loud active galaxies.

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E. Smith, Harding, Carol J. Lonsdale, Colin J. Lonsdale et Philip J. Diamond. « VLBI Imaging of Luminous Infrared Galaxies : Starbursts & ; AGN ». Symposium - International Astronomical Union 194 (1999) : 60–65. http://dx.doi.org/10.1017/s0074180900161728.

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Luminous Infrared Galaxies (LIGs) are locally more numerous than normal galaxies, AGN, and QSOs above L ˜ 1011L⊙ and may be the evolutionary precursors of classical radio-quiet quasars. VLBI observations of a complete sample show that high-Tb radio cores are common, perhaps universal among LIGs. VLBI imaging shows that these radio cores may be produced by intense starbursts which generate luminous radio supernovae, as in the case of Arp 220 (Smith et al. 1998), or by a classical AGN core, as in the case of Mrk 231, which we interpret as a newly formed QSO emerging from a starburst. Compact OH 1667MHz maser emission appears to be common in LIGs and may be related to AGN activity. These results lend further support to the scenario suggested by Sanders et al (1988) in which mergers of gas-rich galaxies lead first to luminous starbursts which evolve into radio-quiet quasars.

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Gupta, Maitrayee, Marek Sikora et Katarzyna Rusinek. « Comparison of SEDs of very massive radio-loud and radio-quiet AGN ». Monthly Notices of the Royal Astronomical Society 492, n^o 1 (4 décembre 2019) : 315–25. http://dx.doi.org/10.1093/mnras/stz3384.

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ABSTRACT The main objective of this work is to establish and interpret the dominant spectral components and their differences in radio-loud (RL) and radio-quiet (RQ) AGN with very massive black holes, and accreting at moderate rates. Such a sample is selected from the Swift/BAT catalogue of AGN having determined optical spectra types and hosting black holes with masses $\rm \gt 10^{8.5}\, M_{\odot }$. We confirm our previous results, that radio loudness distribution of Swift/BAT AGN is bimodal and that radio galaxies are about two times X-ray louder than their RQ counterparts. We show that the average X-ray loudness (defined as a ratio of luminosity in the 14–195 keV band to that at 12 μm) of Type 1 and Type 2 AGN is very similar. This similarity holds for both RL and RQ subsamples and indicates negligible dependence of the observed X-ray luminosities on the inclination angle in both populations. In both the radiative output is dominated by mid-IR and hard X-ray components, and relatively weak UV luminosities indicate large amounts of dust in polar regions.

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Abrahamyan, Hayk V., et Areg M. Mickaelian. « Radio Properties of AGN ». Proceedings of the International Astronomical Union 9, S304 (octobre 2013) : 102–3. http://dx.doi.org/10.1017/s1743921314003469.

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AbstractTo study the radio properties of AGN, we cross-correlate and investigate Veron-Cetty & Veron catalog of QSOs and Active Galaxies (v.13, 2010) with a number of radio catalogs: NVSS, FIRST, GB6, 87GB, SUMSS, WISH, WENSS, and 7C. This catalog contains 168,940 objects with positional accuracy of mostly 1 arcsec, though many positions have larger errors. We use new cross-correlation software based on accuracy of each object independently. In this software we take into account errors for each source and take identifications with errors within 3 sigma. Altogether, we find ~16,000 AGN having radio detection in any of the listed catalogs. Using all data from radio catalogs, we derive a homogeneous sample of radio AGN. The sample allows accomplish several tasks, including study of the distribution of radio sources by activity types, differences in physical properties of radio-loud and radio-quiet AGN, luminosity functions for various types of radio AGN, study of the q parameter by AGN types and its evolution, etc.

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White, Sarah V., Matt J. Jarvis, Eleni Kalfountzou, Martin J. Hardcastle, Aprajita Verma, José M. Cao Orjales et Jason Stevens. « Accretion and star formation in ‘radio-quiet’ quasars ». Proceedings of the International Astronomical Union 15, S356 (octobre 2019) : 204–8. http://dx.doi.org/10.1017/s1743921320002914.

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AbstractRadio observations allow us to identify a wide range of active galactic nuclei (AGN), which play a significant role in the evolution of galaxies. Amongst AGN at low radio-luminosities is the ‘radio-quiet’ quasar (RQQ) population, but how they contribute to the total radio emission is under debate, with previous studies arguing that it is predominantly through star formation. In this talk, SVW summarised the results of recent papers on RQQs, including the use of far-infrared data to disentangle the radio emission from the AGN and that from star formation. This provides evidence that black-hole accretion, instead, dominates the radio emission in RQQs. In addition, we find that this accretion-related emission is correlated with the optical luminosity of the quasar, whilst a weaker luminosity-dependence is evident for the radio emission connected with star formation. What remains unclear is the process by which this accretion-related emission is produced. Understanding this for RQQs will then allow us to investigate how this type of AGN influences its surroundings. Such studies have important implications for modelling AGN feedback, and for determining the accretion and star-formation histories of the Universe.

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Calvani, M., J. W. Sulentic, P. Marziani, D. Dultzin-Hacyan et M. Moles. « A Possible Fundamental Difference Between Radio Loud and Radio Quiet AGN ». Symposium - International Astronomical Union 175 (1996) : 250–51. http://dx.doi.org/10.1017/s0074180900080694.

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We report on some striking differences between radio loud and quiet emitters that we found in a comparative analysis of the high and low ionization lines for 52 low redshift AGN (31 loud; 21 quiet).The broad components of Civλ1549 and Hβ were chosen as representative of the high and low ionization lines respectively. CIVλ1549 observations were obtained with the Faint Object Spectrograph on the HST. They were retrieved from the HST data archive and matching optical spectra for the region of Hβ were obtained at several ground based observatories. Details on observations, narrow/broad component deconvolution and profile cleaning from satellite lines (especially FeII) can be found in Marziani et al. (1995). The rest frame for each quasar was determined from the radial velocity of strong narrow lines, typically [Oiii]λλ4959,5007.

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Miraghaei, Halime. « A Statistical Analysis on the Morphology and Color of Galaxies Hosting Radio-loud Active Galactic Nuclei ». Astronomical Journal 164, n^o 6 (14 novembre 2022) : 246. http://dx.doi.org/10.3847/1538-3881/ac9b13.

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Abstract The properties of galaxies hosting radio-loud active galactic nuclei (AGN) have been investigated in order to find out the relation between morphology and color of galaxies and radio loudness. The concentration index is used to map the morphology of galaxies as early or late type. 4000 Å break strength and star-formation rate are used to quantify the state of galaxies as blue star forming or red quenched. Due to the environmental dependence of these properties, galaxies with the same environment have been considered. The results show that the prevalence of radio-loud AGN in early-type galaxies is independent of environment. This is confirmed by comparing a sample of galaxies hosting radio-loud AGN with a sample of galaxies hosting radio-quiet AGN or with a randomly selected galaxy sample from the total population of galaxies used in this study. In addition, it is shown that galaxies hosting radio-loud AGN are bluer indicating the role of cold gas in triggering AGN activity. Finally, the optically-selected radio-loud AGN show to have higher [O iii] luminosities compared with their radio-quiet counterparts. We argue the relation between radio size and luminosity with the [O iii] luminosity.

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Stacey, H. R., J. P. McKean, N. J. Jackson, P. N. Best, G. Calistro Rivera, J. R. Callingham, K. J. Duncan et al. « LoTSS/HETDEX : Disentangling star formation and AGN activity in gravitationally lensed radio-quiet quasars ». Astronomy & ; Astrophysics 622 (février 2019) : A18. http://dx.doi.org/10.1051/0004-6361/201833967.

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Determining the star-forming properties of radio-quiet quasars is important for understanding the co-evolution of star formation and black hole accretion. We present the detection of the gravitationally lensed radio-quiet quasars SDSS J1055+4628, SDSS J1313+5151, and SBS 1520+530 at 144 MHz, which fall in the HETDEX Spring Field targeted in the LOFAR Two-metre Sky Survey (LoTSS) first full data release. We compare their radio and far-infrared luminosities relative to the radio–infrared correlation and find that their radio luminosities can be explained by star formation. The implied star formation rates derived from their radio and infrared luminosities are between 20 and 300 M ⊙ yr−1. These detections represent the first study of gravitationally lensed sources with LOFAR, opening a new frequency window for investigating the star-forming properties of high-redshift quasars at radio wavelengths. We consider the implications for future data releases and estimate that many of the objects in our parent sample will be detected during LoTSS, significantly increasing the fraction of gravitationally lensed radio-quiet quasars with radio detections.

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Karouzos, Marios, Myungshin Im et Markos Trichas. « Where the active galaxies live : a panchromatic view of radio-AGN in the AKARI-NEP field ». Proceedings of the International Astronomical Union 8, S295 (août 2012) : 270. http://dx.doi.org/10.1017/s1743921313005036.

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AbstractWe study the host galaxy properties of radio sources in the AKARI-North Ecliptic Pole (NEP) field, using an ensemble of multi-wavelength datasets. We identify both radio-loud and radio-quiet AGN and study their host galaxy properties by means of SED fitting. We investigate the relative importance of nuclear and star-formation activity in radio-AGN and assess the role of radio-AGN as efficient quenchers of star-formation in their host galaxies.

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Macchetto, Ferdinando D., et Marco Chiaberge. « Radiatively inefficient accretion disks in low-luminosity AGN† ». Proceedings of the International Astronomical Union 2, S238 (août 2006) : 273–76. http://dx.doi.org/10.1017/s1743921307005121.

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AbstractWe study a complete and distance-limited sample of 25 LINERs, 21 of which have been imaged with the Hubble Space Telescope to study their physical properties and to compare their radio and optical properties with those of other samples of local AGNs, namely Seyfert galaxies and low-luminosity radio galaxies (LLRG). Our results show that the LINERs population is not homogeneous, as there are two subclasses: i) the first class is similar to LLRG, as it extends the population of radio-loud nuclei to lower luminosities; ii) the second is similar to Seyferts, and extends the properties of radio-quiet nuclei towards the lowest luminosities. The different nature of the various classes of local AGN are best understood when the fraction of the Eddington luminosity they irradiate, Lo/LEdd, is plotted against the nuclear radio-loudness parameter: Seyferts are associated with relatively high radiative efficiencies Lo/LEdd ≳ 104 (and high accretion rates onto low mass black holes); LLRG are associated with low radiative efficiencies (and low accretion rates onto high black hole masses); all LINERs have low radiative efficiency (and accretion rates), and can be radio-loud or radio quiet depending on their black hole mass.

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Bonzini, M., V. Mainieri, P. Padovani, K. I. Kellermann, N. Miller, P. Rosati, P. Tozzi et S. Vattakunnel. « Host galaxy properties of radio selected AGN ». Proceedings of the International Astronomical Union 9, S304 (octobre 2013) : 343–44. http://dx.doi.org/10.1017/s1743921314004244.

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AbstractWith the goal of investigating the link between black hole (BH) and star formation (SF) activity, we study a deep sample of radio selected star forming galaxies (SFGs) and active galactic nuclei (AGNs). Using a multi-wavelength approach we characterize their host galaxies properties (stellar masses, optical colors, and morphology). Moreover, comparing the star formation rate derived from the radio and far-infrared luminosity, we found evidences that the main contribution to the radio emission in the radio-quiet AGNs is star-formation activity in their host galaxy.

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Sbarrato, Tullia, Massimo Dotti, Giancarlo Ghirlanda et Fabrizio Tavecchio. « Study of the orientation of narrow-line Seyfert I ». Astronomy & ; Astrophysics 616 (août 2018) : A43. http://dx.doi.org/10.1051/0004-6361/201732451.

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We study a sample of narrow-line Seyfert 1 galaxies (NLS1) in their optical and radio features to understand the differences between their radio silent, radio-loud, and radio-quiet subclasses. We first show that the different redshift and mass distributions of radio-loud and radio-quiet NLS1s could be ascribed to observational biases. We then present a geometrical model according to which most of the different observational features of radio-loud and radio-quiet NLS1s are ascribed to the orientation of an intrinsically structured jet. We estimate the fraction of intrinsically jetted sources among NLS1s that justifies the observed radio-detected population. Noticeably, under the assumptions of the geometrical model, we derive a fraction of jetted sources significantly larger than in standard AGN.

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Bianchi, S., M. Guainazzi, G. Matt et N. Fonseca Bonilla. « On the Iwasawa-Taniguchi effect of radio-quiet AGN ». Astronomy & ; Astrophysics 467, n^o 1 (19 mars 2007) : L19—L22. http://dx.doi.org/10.1051/0004-6361:20077331.

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Nyland, Kristina, Dillon Dong, Pallavi Patil, Mark Lacy, Amy Kimball, Gregg Hallinan, Sumit Sarbadhicary et al. « Variable radio AGN at high redshift identified in the VLA Sky Survey ». Proceedings of the International Astronomical Union 15, S359 (mars 2020) : 27–32. http://dx.doi.org/10.1017/s1743921320001921.

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AbstractAs part of an on-going study of radio transients in Epoch 1 (2017–2019) of the Very Large Array Sky Survey (VLASS), we have discovered a sample of 0.2 < z < 3.2 active galactic nuclei (AGN) selected in the optical/infrared that have recently brightened dramatically in the radio. These sources would have previously been classified as radio-quiet based on upper limits from the Faint Images of the Radio Sky at Twenty-centimeters (FIRST; 1993-2011) survey; however, they are now consistent with radio-loud quasars. We present a quasi-simultaneous, multi-band (1–18 GHz) VLA follow-up campaign of our sample of AGN with extreme radio variability. We conclude that the radio properties are most consistent with AGN that have recently launched jets within the past few decades, potentially making them among the youngest radio AGN known.

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Gupta, Maitrayee, Marek Sikora et Katarzyna Rusinek. « Erratum : Comparison of SEDs of very massive radio-loud and radio-quiet AGN ». Monthly Notices of the Royal Astronomical Society 499, n^o 3 (30 octobre 2020) : 4024–25. http://dx.doi.org/10.1093/mnras/staa2974.

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Padovani, Paolo, Ken Kellermann, Edward Fomalont, Neal Miller, Paolo Tozzi, Vincenzo Mainieri et Piero Rosati. « Submillijansky Radio-Quiet and Radio-Loud AGN in the Chandra Deep Field South ». Proceedings of the International Astronomical Union 5, S267 (août 2009) : 130. http://dx.doi.org/10.1017/s1743921310005910.

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Retana-Montenegro, E., et H. J. A. Röttgering. « Probing the radio loud/quiet AGN dichotomy with quasar clustering ». Astronomy & ; Astrophysics 600 (avril 2017) : A97. http://dx.doi.org/10.1051/0004-6361/201526433.

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Dultzin-Hacyan, D., J. Sulentic, P. Marziani, M. Calvani et M. Moles. « A Correlation Analysis for Emission Lines in 52 AGN ». International Astronomical Union Colloquium 159 (1997) : 262–63. http://dx.doi.org/10.1017/s0252921100040264.

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AbstractWe recently completed the first comparison of high- and low-ionization broad lines in a sample of 52 AGN. We summarize here the principal results of a correlation analysis for this sample. We then briefly outline a model for the broad-line structure in radio-quiet AGN that is suggested by the correlation analysis.

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Akujor, Chidi E., R. W. Porcas, A. R. Patnaik et 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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Dopita, Michael A. « Towards a Truly Unified Model of AGN : Aspect, Accretion and Evolution ». Publications of the Astronomical Society of Australia 14, n^o 3 (1997) : 230–45. http://dx.doi.org/10.1071/as97230.

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AbstractThe Unified Model holds that the aspect-dependent effects primarily determine the nature of the active galactic nucleus that we observe. In this paper, I argue that three parameters; aspect, accretion rate into the nuclear regions, and the evolutionary status of the central black hole hold the key to unification. The mystery of why the epoch of quasar formation occurred so early in the evolution of the Universe, why radio-loud QSOs represent only a small fraction of the general population of QSOs, and why ellipticals are invariably the hosts of radio-loud active galaxies could be explained if (a) the most rapid growth of black holes occurred in galactic merger events, and if (b) an excess in the rate of nuclear feeding was able to choke off the radio jets, producing radio quiet QSOs. In this paper, I develop the idea that rate of nuclear feeding plays a dominant role and that feeding at super-Eddington rates into the broad-line region (BLR) during merger events is the means whereby massive black holes are grown. In particular, I develop a toy model for the radio-loud, radio-quiet dichotomy based on the rate of nuclear feeding, suggest an electron scattering model for the ‘big blue bump’ and its relation to the BLR, and emphasise the important diagnostic capabilities offered by analyses of the narrow line regions based on shock excitation models.

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Ciliegi, P., M. Elvis, B. J. Wilkes, B. J. Boyle, R. G. Mcmahon et T. Maccacaro. « VLA Observations of the Cambridge-Cambridge Rosat Survey ». Symposium - International Astronomical Union 175 (1996) : 543–44. http://dx.doi.org/10.1017/s0074180900081791.

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We report the result of the VLA observations of all the 80 AGN in the Cambridge-Cambridge ROSAT Serendipity Survey (CRSS, Boyle et al. 1995), a new well defined sample of 80 X-ray selected AGN with fx(0.5-2.0keV)≥ 2 × 10–14 erg s–1 cm–2. Our aim was to obtain a complete classification of the sample members as Radio-loud (RL) or Radio-quiet (RQ) in order to determine well-constrained X-ray luminosity function (XLF) for X-ray selected RQ and RL AGN separately.

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White, Sarah V., Matt J. Jarvis, Eleni Kalfountzou, Martin J. Hardcastle, Aprajita Verma, José M. Cao Orjales et Jason Stevens. « Evidence that the AGN dominates the radio emission in z ∼ 1 radio-quiet quasars ». Monthly Notices of the Royal Astronomical Society 468, n^o 1 (2 février 2017) : 217–38. http://dx.doi.org/10.1093/mnras/stx284.

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Radcliffe, J. F., P. D. Barthel, M. A. Garrett, R. J. Beswick, A. P. Thomson et T. W. B. Muxlow. « The radio emission from active galactic nuclei ». Astronomy & ; Astrophysics 649 (mai 2021) : L9. http://dx.doi.org/10.1051/0004-6361/202140791.

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Context. For nearly seven decades, astronomers have been studying active galaxies, that is to say, galaxies with actively accreting central supermassive black holes: active galactic nuclei (AGN). A small fraction are characterized by luminous, powerful radio emission: This class is known as radio-loud AGN. A substantial fraction, the so-called radio-quiet AGN population, display intermediate or weak radio emission. However, an appreciable fraction of strong X-ray-emitting AGN are characterized by the absence of radio emission, down to an upper limit of about 10−7 times the luminosity of the most powerful radio-loud AGN. Aims. We wish to address the nature of these – seemingly radio-silent – X-ray-luminous AGN and their host galaxies to determine if there is any radio emission, and, if so, where it originates. Methods. Focusing on the GOODS-N field, we examine the nature of these objects, employing stacking techniques on ultra-deep radio data obtained with the JVLA. We combine these radio data with Spitzer far-infrared data. Results. We establish the absence, or totally insignificant contribution, of jet-driven radio emission in roughly half of the otherwise normal population of X-ray-luminous AGN, which appear to reside in normal star-forming galaxies. Conclusions. AGN- or jet-driven radio emission is simply a mechanism that may be at work or may be dormant in galaxies with actively accreting black holes. The latter cases can be classified as radio-silent AGN.

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Roy, A. L., J. M. Wrobel, A. S. Wilson, J. S. Ulvestad, R. P. Norris, C. G. Mundell, T. P. Krichbaum, H. Falcke et E. J. M. Colbert. « Parsec-Scale Jets and Tori in Seyfert Galaxies ». Symposium - International Astronomical Union 205 (2001) : 70–71. http://dx.doi.org/10.1017/s0074180900220457.

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What causes the dichotomy between very powerful and very weak radio emission from AGNs? Perhaps the engines are the same but the jets get disrupted by dense ISM in radio-quiet objects, or else the engines are intrinsically different with jet power scaling with, say, black hole spin. To distinguish, one can look for interaction between the jets and the NLR and measure the jet speed close to the core using VLBI, before environmental effects become important. We find that in radio-quiet AGN, the jets appear slower and have a greater tendency to bend, and that one-sidedness and flat-spectrum cores are probably due to obscuration.

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Alhosani, Abdulla, Joseph D. Gelfand, Ingyin Zaw, Ari Laor, Ehud Behar, Sina Chen et Ramon Wrzosek. « Dependence of the Radio Emission on the Eddington Ratio of Radio-quiet Quasars ». Astrophysical Journal 936, n^o 1 (31 août 2022) : 73. http://dx.doi.org/10.3847/1538-4357/ac8665.

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Abstract Roughly 10% of quasars are “radio-loud,” producing copious radio emission in large jets. The origin of the low-level radio emission seen from the remaining 90% of quasars is unclear. Observing a sample of eight radio-quiet quasars with the Very Long Baseline Array, we discovered that their radio properties depend strongly on their Eddington ratio r Edd ≡ L AGN/L Edd. At lower Eddington ratios r Edd ≲ 0.3, the total radio emission of the AGN predominately originates from an extremely compact region, possibly as small as the accretion disk. At higher Eddington ratios (r Edd ≳ 0.3), the relative contribution of this compact region decreases significantly, and though the total radio power remains about the same, the emission now originates from regions ≳100 pc in size. The change in the physical origin of the radio-emitting plasma region with r Edd is unexpected, as the properties of radio-loud quasars show no dependence with Eddington ratio. Our results suggest that at lower Eddington ratios the magnetized plasma is likely confined by the accretion disk corona and only at higher Eddington ratios escapes to larger scales. Stellar-mass black holes show a similar dependence of their radio properties on the accretion rate, supporting the paradigm that unifies the accretion onto black holes across the mass range.

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TORRESI, ELEONORA, PAOLA GRANDI, ELISA COSTANTINI et GIORGIO G. C. PALUMBO. « JETS AND OUTFLOWS IN RADIO GALAXIES : IMPLICATIONS FOR AGN FEEDBACK ». International Journal of Modern Physics : Conference Series 08 (janvier 2012) : 396–99. http://dx.doi.org/10.1142/s2010194512004989.

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One of the main debated astrophysical problems is the role of the AGN feedback in galaxy formation. It is known that massive black holes have a profound effect on the formation and evolution of galaxies, but how black holes and galaxies communicate is still an unsolved problem. For Radio Galaxies, feedback studies have mainly focused on jet/cavity systems in the most massive and X–ray luminous galaxy clusters. The recent high–resolution detection of warm absorbers in some Broad Line Radio Galaxies allow us to investigate the interplay between the nuclear engine and the surrounding medium from a different perspective. We report on the detection of warm absorbers in two Broad Line Radio Galaxies, 3C 382 and 3C 390.3, and discuss the physical and energetic properties of the absorbing gas. Finally, we attempt a comparison between radio–loud and radio–quiet outflows.

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Hirst, Paul, Duncan Law-Green et Martin Ward. « Multiwavelength Properties of Narrow-line Seyfert 1's : Studying One Extreme of the AGN Primary Eigenvector ». Symposium - International Astronomical Union 194 (1999) : 77–78. http://dx.doi.org/10.1017/s0074180900161765.

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Narrow Line Seyfert 1 galaxies (NLS1s) are an important subclass of radio quiet AGN having extreme optical and X-ray spectroscopic properties. Their relationship to other types of Seyferts remains unclear. NLS1s exhibit many characteristics of Seyfert 1 AGN, but their optical spectra show narrow permitted lines, and some high ionization species. This may result from us viewing them close to ‘pole-on' orientation with respect to an inner torus geometry. We present comparisons of the radio and X-ray properties of NLS1s with those of the 12μm and CfA Seyfert samples.

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Fawcett, V. A., D. M. Alexander, D. J. Rosario, L. Klindt, S. Fotopoulou, E. Lusso, L. K. Morabito et G. Calistro Rivera. « Fundamental differences in the radio properties of red and blue quasars : enhanced compact AGN emission in red quasars ». Monthly Notices of the Royal Astronomical Society 494, n^o 4 (11 avril 2020) : 4802–18. http://dx.doi.org/10.1093/mnras/staa954.

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ABSTRACT We have recently used the Faint Images of the Radio Sky at Twenty-centimeters (FIRST) survey to show that red quasars have fundamentally different radio properties to typical blue quasars: a significant (factor ≈3) enhancement in the radio-detection fraction, which arises from systems around the radio-quiet threshold with compact (<5 arcsec) radio morphologies. To gain greater insight into these physical differences, here we use the DR14 Sloan Digital Sky Survey (SDSS) and more sensitive, higher resolution radio data from the Very Large Array (VLA) Stripe 82 (S82) and VLA-COSMOS 3 GHz (C3GHz) surveys. With the S82 data, we perform morphological analyses at a resolution and depth three times that of the FIRST radio survey, and confirm an enhancement in radio-faint and compact red quasars over typical quasars; we now also find tentative evidence for an enhancement in red quasars with slightly extended radio structures (16–43 kpc at z = 1.5). These analyses are complemented by C3GHz, which is deep enough to detect radio emission from star-formation processes. From our data we find that the radio enhancement from red quasars is due to AGN activity on compact scales (≲43 kpc) for radio-intermediate–radio-quiet sources (−5 < $\mathcal {R}$ < −3.4, where $\mathcal {R}$ = $L_{\rm{1.4\,GHz}}/L_{6\mu\text{m}}$), which decreases at $\mathcal {R}$ < −5 as the radio emission from star-formation starts to dilute the AGN component. Overall our results argue against a simple orientation scenario and are consistent with red quasars representing a younger, earlier phase in the overall evolution of quasars.

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M. Sambruna, Rita. « Blazars : Clues to Jet Physics ». Symposium - International Astronomical Union 194 (1999) : 113–22. http://dx.doi.org/10.1017/s0074180900161844.

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Being dominated by non-thermal emission from aligned relativistic jets, blazars allow us to elucidate the physics of extragalactic jets, and, ultimately, how energy is extracted from the central black hole. Crucial information about jet structure is provided by the spectral energy distributions from radio to γ-rays, their trends with luminosity, and correlated multifrequency variability. Since blazar jets have broad implications for all radio-loud (and possibly radio-quiet) AGNs, we also need to understand their circumnuclear structure, especially the details of the physical and dynamical conditions of the highly ionized gas on sub-pc scales, which could be directly related to jet formation and radiative power. Eventually, the bulk of information provided by blazars will help us clarify the origin of the radio-loud/radio-quiet AGN dichotomy, one of the most outstanding open issues of extragalactic astrophysics.

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BALLANTYNE, D. R. « THE ACCRETION GEOMETRY IN RADIO-LOUD ACTIVE GALAXIES ». Modern Physics Letters A 22, n^o 32 (20 octobre 2007) : 2397–411. http://dx.doi.org/10.1142/s0217732307024322.

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We review the latest attempts to determine the accretion geometry in radio-loud active galactic nuclei (AGN). These objects, which comprise ~ 10–20% of the AGN population, produce powerful collimated radio jets that can extend thousands of parsecs from the center of the host galaxy. Recent multiwavelength surveys have shown that radio-loudness is more common in low-luminosity AGN than in higher luminosity Seyfert galaxies or quasars. These low-luminosity AGN have small enough accretion rates that they are most likely accreting via a geometrically thick and radiatively inefficient accretion flow. In contrast, X-ray spectroscopic observations of three higher luminosity broad-line radio galaxies (3C 120, 4C+74.26 and PG 1425+267) have found evidence for an untruncated thin disk extending very close to the black hole. These tentative detections indicate that, for this class of radio-loud AGN, the accretion geometry is very similar to their radio-quiet counterparts. These observations suggest that there are three conditions to jet formation that must be satisfied: the presence of a rapidly spinning black hole, an accretion flow with a large H/r ratio, and a favorable magnetic field geometry.

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Hartley, P., N. Jackson, S. Badole, J. P. McKean, D. Sluse et H. Vives-Arias. « Using strong lensing to understand the microJy radio emission in two radio quiet quasars at redshift 1.7 ». Monthly Notices of the Royal Astronomical Society 508, n^o 3 (18 octobre 2021) : 4625–38. http://dx.doi.org/10.1093/mnras/stab2758.

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ABSTRACT The radio quasar luminosity function exhibits an upturn around $L_{6\rm \:GHz}=10^{23}$ W Hz−1 that is well-modelled by a star-forming host galaxy population. This distribution leads some authors to cite star formation as the main radio emission mechanism in so-called radio-quiet quasars (RQQs). Understanding the origin of RQQ radio emission is crucial for our understanding of quasar feedback mechanisms – responsible for the regulation of star formation in the host galaxy – and for understanding galaxy evolution as a whole. By observing RQQs that have been magnified by strong gravitational lensing, we have direct access to the RQQ population out to cosmic noon, where evidence for twin mini-jets has recently been found in a sub-$\mu$Jy RQQ. Here we present radio observations of two lensed RQQs using the VLA at 5 GHz, the latest objects to be observed in a sample of quadruply-imaged RQQs above −30°. In SDSS J1004+4112 we find strong evidence for AGN-related radio emission in the variability of the source. In PG 1115+080 we find tentative evidence for AGN-related emission, determined by comparing the radio luminosity with modelled dust components. If confirmed in the case of PG 1115+080, which lies on the radio–FIR correlation, the result would reinforce the need for caution when applying the correlation to rule out jet activity and when assuming no AGN heating of FIR-emitting dust when calculating star formation rates. Our programme so far has shown that the two of the faintest radio sources ever imaged show strong evidence for AGN-dominated radio emission.

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Marziani, Paola, Marco Berton, Swayamtrupta Panda et Edi Bon. « Optical Singly-Ionized Iron Emission in Radio-Quiet and Relativistically Jetted Active Galactic Nuclei ». Universe 7, n^o 12 (8 décembre 2021) : 484. http://dx.doi.org/10.3390/universe7120484.

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The issue of the difference between optical and UV properties of radio-quiet and radio-loud (relativistically “jetted”) active galactic nuclei (AGN) is a long standing one, related to the fundamental question of why a minority of powerful AGN possess strong radio emission due to relativistic ejections. This paper examines a particular aspect: the singly-ionized iron emission in the spectral range 4400–5600 Å, where the prominent HI Hβ and [Oiii]λλ4959,5007 lines are also observed. We present a detailed comparison of the relative intensity of Feii multiplets in the spectral types of the quasar main sequence where most jetted sources are found, and afterwards discuss radio-loud narrow-line Seyfert 1 (NLSy1) nuclei with γ-ray detection and with prominent Feii emission. An Feii template based on I Zw 1 provides an accurate representation of the optical Feii emission for RQ and, with some caveats, also for RL sources. CLOUDY photoionization simulations indicate that the observed spectral energy distribution can account for the modest Feii emission observed in composite radio-loud spectra. However, spectral energy differences alone cannot account for the stronger Feii emission observed in radio-quiet sources, for similar physical parameters. As for RL NLSy1s, they do not seem to behave like other RL sources, likely because of their different physical properties, that could be ultimately associated with a higher Eddington ratio.

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B. Sanders, D. « Infrared Emission from AGN ». Symposium - International Astronomical Union 194 (1999) : 25–38. http://dx.doi.org/10.1017/s0074180900161686.

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Infrared observations of complete samples of active galactic nuclei (AGN) have shown that a substantial fraction of their bolometric luminosity is emitted at wavelengths ˜8–1000μm. In radio-loud and Blazar-like objects much of this emission appears to be direct non-thermal synchrotron radiation. However, in the much larger numbers of radio-quiet AGN it is now clear that thermal dust emission is responsible for the bulk of radiation from the near-infrared through submillimeter wavelengths. Luminous infrared-selected AGN are often surrounded by powerful nuclear starbursts, both of which appear to be fueled by enormous supplies of molecular gas and dust funneled into the nuclear region during the strong interaction/merger of gas rich disks. All-sky surveys in the infrared show that luminous infrared AGN are at least as numerous as optically-selected AGN of comparable bolometric luminosity, suggesting that AGN may spend a substantial fraction of their lifetime in a dust-enshrouded phase. The space density of luminous infrared AGN at high redshift may be sufficient to account for much of the X-Ray background, and for a substantial fraction of the far-infrared background as well. These objects plausibly represent a major epoch in the formation of spheroids and massive black holes (MBH).

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Sadler, Elaine M., Scott M. Croom, John H. Y. Ching, Helen M. Johnston, Russell D. Cannon et Tom Mauch. « Radio-Mode Feedback in Massive Galaxies at Redshift 0 < ; z < ; 1 ». Proceedings of the International Astronomical Union 5, S267 (août 2009) : 377–82. http://dx.doi.org/10.1017/s1743921310006745.

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AbstractWe have carried out a large observational study of the radio luminosities, stellar populations, and environments of massive galaxies over the redshift range 0 < z < 1. Radio jets powered by an accreting central black hole are common in massive galaxies, and there is a large class of “optically quiet AGN,” with radio emission but no optical/IR signature of black-hole accretion. The central black holes in these galaxies are probably accreting in a radiatively inefficient mode, and our results suggest that “radio-mode feedback” as described by Croton et al. is likely to occur in all masssive early-type galaxies at z < 0.8. While it appears that radio-loud AGN occur episodically in all massive early-type galaxies, we also identify a sub-population of galaxies with powerful radio sources and a prominent younger (~ 108 yr) stellar population that may have undergone recent mergers.

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Ocran, E. F., A. R. Taylor, M. Vaccari, C. H. Ishwara-Chandra, I. Prandoni, M. Prescott et C. Mancuso. « The evolution of the low-frequency radio AGN population to z ≃ 1.5 in the ELAIS N1 field ». Monthly Notices of the Royal Astronomical Society 500, n^o 4 (13 novembre 2020) : 4685–702. http://dx.doi.org/10.1093/mnras/staa3538.

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ABSTRACT We study the cosmic evolution of radio sources out to z ≃ 1.5 using a GMRT 610 MHz survey covering ∼1.86 deg2 of the ELAIS N1 field with a minimum/median rms noise 7.1/19.5 μJy beam−1 and an angular resolution of 6 arcsec. We classify sources as star forming galaxies (SFGs), radio-quiet (RQ) and radio-loud (RL) Active Galactic Nuclei (AGNs) using a combination of multiwavelength diagnostics and find evidence in support of the radio emission in SFGs and RQ AGN arising from star formation, rather than AGN-related processes. At high luminosities, however, both SFGs and RQ AGN display a radio excess when comparing radio and infrared star formation rates. The vast majority of our sample lie along the $\rm {SFR - \mathit{ M}_{\star }}$ ‘main sequence’ at all redshifts when using infrared star formation rates. We derive the 610 MHz radio luminosity function for the total AGN population, constraining its evolution via continuous models of pure density and pure luminosity evolution with $\rm {\Phi ^{\star }\, \propto \, (\, 1+\, \mathit{ z})^{(2.25\pm 0.38)-(0.63\pm 0.35)z}}$ and $\rm {\mathit{ L}_{610\, MHz}\, \propto \, (\, 1+\, \mathit{ z})^{(3.45\pm 0.53)-(0.55\pm 0.29)\mathit{ z}}}$, respectively. For our RQ and RL AGN, we find a fairly mild evolution with redshift best fitted by pure luminosity evolution with $\rm {\mathit{ L}_{610\, MHz}\, \propto \, (\, 1+\, \mathit{ z})^{(2.81\pm 0.43)-(0.57\pm 0.30)\mathit{ z}}}$ for RQ AGN and $\rm {\mathit{ L}_{610\, MHz}\, \propto \, (\, 1+\, \mathit{ z})^{(3.58\pm 0.54)-(0.56\pm 0.29)\mathit{ z}}}$ for RL AGN. The 610 MHz radio AGN population thus comprises two differently evolving populations whose radio emission is mostly SF-driven or AGN-driven, respectively.

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Smith, Krista Lynne, Michael Koss, Richard Mushotzky, O. Ivy Wong, T. Taro Shimizu, Claudio Ricci et Federica Ricci. « Significant Suppression of Star Formation in Radio-quiet AGN Host Galaxies with Kiloparsec-scale Radio Structures ». Astrophysical Journal 904, n^o 2 (24 novembre 2020) : 83. http://dx.doi.org/10.3847/1538-4357/abc3c4.

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Sebastian, Biny, P. Kharb, C. P. O’Dea, J. F. Gallimore et S. A. Baum. « A radio polarimetric study to disentangle AGN activity and star formation in Seyfert galaxies ». Monthly Notices of the Royal Astronomical Society 499, n^o 1 (19 août 2020) : 334–54. http://dx.doi.org/10.1093/mnras/staa2473.

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ABSTRACT To understand the origin of radio emission in radio-quiet active galactic nucleus (AGN) and differentiate between the contributions from star formation, AGN accretion, and jets, we have observed a nearby sample of Seyfert galaxies along with a comparison sample of starburst galaxies using the Expanded Very Large Array (EVLA) in full-polarization mode in the B-array configuration. The radio morphologies of the Seyfert galaxies show lobe/bubble-like features or prominent cores in radio emission, whereas the starburst galaxies show radio emission spatially coincident with the star-forming regions seen in optical images. There is tentative evidence that Seyferts tend to show more polarized structures than starburst galaxies at the resolution of our observations. We find that unlike a sample of Seyfert galaxies hosting kilo-parsec scale radio (KSR) emission, starburst galaxies with superwinds do not show radio-excess compared to the radio–FIR correlation. This suggests that shock acceleration is not adequate to explain the excess radio emission seen in Seyferts and hence most likely have a jet-related origin. We also find that the [O iii] luminosity of the Seyferts is correlated with the off-nuclear radio emission from the lobes, whereas it is not well correlated with the total emission which also includes the core. This suggests strong jet–medium interaction, which in turn limits the jet/lobe extents in Seyferts. We find that the power contribution of AGN jet, AGN accretion, and star formation is more or less comparable in our sample of Seyfert galaxies. We also find indications of episodic AGN activity in many of our Seyfert galaxies.

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Li, Shuang-Liang. « A nearby luminous AGN sample optically selected from Hubble Space Telescope ». Monthly Notices of the Royal Astronomical Society 490, n^o 3 (12 octobre 2019) : 3793–98. http://dx.doi.org/10.1093/mnras/stz2864.

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ABSTRACT In this work, a nearby luminous active galactic nucleus (AGN) sample is selected from Hubble Space Telescope(HST), where only sources with both X-ray emission observed by Chandra/XMM–Newton and radio flux detected by Very Large Array (VLA)/Very Long Baseline Array (VLBA)/very long baseline interferometry (VLBI)/Multi-Element Radio Linked Interferometer Network (MERLIN) are adopted to keep high precision. Finally, we get a sample of 30 luminous AGNs, which consists of 11 radio-loud AGNs (RLAGN) and 19 radio-quiet AGNs (RQAGN). It is found that the relationship between RUV and αox, which was first reported by Li & Xie in low-luminosity AGNs (LLAGN), and other relationships are all absent in RLAGN, probably due to the complex physical process therein. Our results indicate that the X-ray emission from jet should play an important role in RLAGN and further support the transition of accretion mode between LLAGN and RLAGN. On the other hand, the traditional relationships in RQAGN, such as αox and λ, Γ and λ, are found to be well consistent with previous works.

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Cid Fernandes, R., R. Terlevich, G. Tenorio-Tagle, J. Franco et M. Rozyczka. « Supernova Fragments and the Origin of the Rapid X-ray Variability ». Symposium - International Astronomical Union 159 (1994) : 371. http://dx.doi.org/10.1017/s0074180900175643.

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The Starburst model for Radio Quiet Active Galactic Nuclei proved able to explain the origin of the broad line region, the variability characteristics of line and continuum in Seyfert galaxies, X-ray spectra, the luminosity function of QSOs and etc. But can we understand the rapid X-ray variability observed in several AGN with supernovae?

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