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Universe
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Focus on Active Galactic Nuclei
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Focus on Active Galactic Nuclei

A special issue of Universe (ISSN 2218-1997). This special issue belongs to the section "Galaxies and Clusters".

Deadline for manuscript submissions: closed (30 June 2024) | Viewed by 5879

Special Issue Editors

Prof. Dr. Li Zhang

E-Mail Website
Guest Editor
School of Physics and Astronomy, Yunnan University, Kunming 650091, China
Interests: high-energy astrophysics; gamma-ray astronomy; cosmic rays; pulsar; pulsar wind nebula; supernova remnants; active galactic nuclei
Dr. Dahai Yan

E-Mail Website
Guest Editor
School of Physics and Astronomy, Yunnan University, Kunming 650091, China
Interests: time-domain astronomy; high-energy astrophysics; gamma-ray astronomy; active galactic nuclei; black hole

Special Issue Information

Dear Colleagues,

This Special Issue of Universe undertakes a scholarly journey into the core facets of Active Galactic Nuclei (AGN), directing focused attention on critical topics, such as jet physics, accretion disk dynamics, the nuanced interplay between jets and accretion disks, the enigmatic radiance of diffuse extragalactic gamma-ray emissions, and the gravitational ballet of supermassive black hole binaries.

Prof. Dr. Li Zhang
Dr. Dahai Yan
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Universe is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • active galactic nuclei
  • supermassive black hole binaries
  • extragalactic gamma-ray astronomy
  • gamma-ray instrumentation
  • probabilistic models for astrophysical data

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Published Papers (4 papers)

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Research

13 pages, 3218 KiB  
Article
Source Count Distribution of Fermi LAT Gamma-Ray Blazars Using Novel Nonparametric Methods
by Xuhang Yin and Houdun Zeng
Universe 2024, 10(9), 340; https://doi.org/10.3390/universe10090340 - 26 Aug 2024
Viewed by 689
Abstract
We utilized a sample from the Fermi-LAT 14-year Source Catalog by adjusting the flux detection threshold, enabling us to derive the intrinsic source count distribution dN/dF25 of extragalactic blazars using nonparametric, unbinned methods developed by Efron and Petrosian [...] Read more.
We utilized a sample from the Fermi-LAT 14-year Source Catalog by adjusting the flux detection threshold, enabling us to derive the intrinsic source count distribution dN/dF25 of extragalactic blazars using nonparametric, unbinned methods developed by Efron and Petrosian and Lynden-Bell. Subsequently, we evaluated the contribution of blazars to the extragalactic gamma-ray background. Our findings are summarized as follows: (1) There is no significant correlation between flux and spectral index values among blazars and their subclasses FSRQs and BL Lacs. (2) The intrinsic differential distributions of flux values exhibit a broken-power-law form, with parameters that closely match previous findings. The intrinsic photon index distributions are well described by a Gaussian form for FSRQs and BL Lacs individually, while a dual-Gaussian model provides a more appropriate fit for blazars as a whole. (3) Blazars contribute 34.5% to the extragalactic gamma-ray background and 16.8% to the extragalactic diffuse gamma-ray background. When examined separately, FSRQs and BL Lacs contribute 19.6% and 13% to the extragalactic gamma-ray background, respectively. Full article
(This article belongs to the Special Issue Focus on Active Galactic Nuclei)
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13 pages, 586 KiB  
Article
The Host Galaxy Fluxes of Active Galaxy Nuclei Are Generally Overestimated by the Flux Variation Gradient Method
by Minxuan Cai, Zhen Wan, Zhenyi Cai, Lulu Fan and Junxian Wang
Universe 2024, 10(7), 282; https://doi.org/10.3390/universe10070282 - 28 Jun 2024
Cited by 1 | Viewed by 772
Abstract
In terms of the variable nature of normal active galaxy nuclei (AGN) and luminous quasars, a so-called flux variation gradient (FVG) method has been widely utilized to estimate the underlying non-variable host galaxy fluxes. The FVG method assumes an invariable AGN color, but [...] Read more.
In terms of the variable nature of normal active galaxy nuclei (AGN) and luminous quasars, a so-called flux variation gradient (FVG) method has been widely utilized to estimate the underlying non-variable host galaxy fluxes. The FVG method assumes an invariable AGN color, but this assumption has been questioned by the intrinsic color variation of quasars and local Seyfert galaxies. Here, using an up-to-date thermal fluctuation model to simulate multi-wavelength AGN variability, we theoretically demonstrate that the FVG method generally overestimates the host galaxy flux; that is, it is more significant for brighter AGN/quasars. Furthermore, we observationally confirm that the FVG method indeed overestimates the host galaxy flux by comparing it to that estimated through other independent methods. We thus caution that applying the FVG method should be performed carefully in the era of time-domain astronomy. Full article
(This article belongs to the Special Issue Focus on Active Galactic Nuclei)
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17 pages, 1754 KiB  
Article
Revisiting a Core–Jet Laboratory at High Redshift: Analysis of the Radio Jet in the Quasar PKS 2215+020 at z = 3.572
by Sándor Frey, Judit Fogasy, Krisztina Perger, Kateryna Kulish, Petra Benke, Dávid Koller and Krisztina Éva Gabányi
Universe 2024, 10(2), 97; https://doi.org/10.3390/universe10020097 - 17 Feb 2024
Viewed by 2638
Abstract
The prominent radio quasar PKS 2215+020 (J2217+0220) was once labelled as a new laboratory for core–jet physics at redshift z=3.572 because of its exceptionally extended jet structure traceable with very long baseline interferometric (VLBI) observations up to a ∼600 pc projected [...] Read more.
The prominent radio quasar PKS 2215+020 (J2217+0220) was once labelled as a new laboratory for core–jet physics at redshift z=3.572 because of its exceptionally extended jet structure traceable with very long baseline interferometric (VLBI) observations up to a ∼600 pc projected distance from the compact core and a hint of an arcsec-scale radio and an X-ray jet. While the presence of an X-ray jet could not be confirmed later, this active galactic nucleus is still unique at high redshift with its long VLBI jet. Here, we analyse archival multi-epoch VLBI imaging data at five frequency bands from 1.7 to 15.4 GHz covering a period of more than 25 years from 1995 to 2020. We constrain apparent proper motions of jet components in PKS 2215+020 for the first time. Brightness distribution modeling at 8 GHz reveals a nearly 0.02 mas yr−1 proper motion (moderately superluminal with apparently two times the speed of light), and provides δ=11.5 for the Doppler-boosting factor in the inner relativistic jet that is inclined within 2∘ to the line of sight and has a Γ=6 bulk Lorentz factor. These values qualify PKS 2215+020 as a blazar, with rather typical jet properties in a small sample of only about 20 objects at z>3.5 that have similar measurements to date. According to the 2-GHz VLBI data, the diffuse and extended outer emission feature at ∼60 mas from the core, probably a place where the jet interacts with and decelerated by the ambient galactic medium, is consistent with being stationary, albeit slow motion cannot be excluded based on the presently available data. Full article
(This article belongs to the Special Issue Focus on Active Galactic Nuclei)
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11 pages, 465 KiB  
Article
Covering Factor of the Dust-Driven Broad-Line Region Clouds
by Mohammad-Hassan Naddaf and Bożena Czerny
Universe 2024, 10(1), 29; https://doi.org/10.3390/universe10010029 - 10 Jan 2024
Cited by 2 | Viewed by 1222
Abstract
The origin of the broad-line region (BLR) clouds in active galactic nuclei is still under discussion. We develop a scenario in which the clouds in the outer, less ionized part of the BLR are launched by the radiation pressure acting on dust. Most [...] Read more.
The origin of the broad-line region (BLR) clouds in active galactic nuclei is still under discussion. We develop a scenario in which the clouds in the outer, less ionized part of the BLR are launched by the radiation pressure acting on dust. Most of the outflow forms a failed wind, so we refer to it as failed radiatively accelerated dusty outflow (FRADO), but, for a certain parameter range, actual outflow also takes place. We aim to test the model predictions. In this paper, we present the calculation of the angular distribution of clouds and the net covering factor as this affects the fraction of radiation that can be intercepted and reprocessed in the form of the Hβ or Mg II emission line. The results reveal that the covering factor is intricately linked to the mass, accretion rate, and metallicity of the clouds. Notably, as these parameters increase, so does the covering factor, shedding light on the dynamic interplay between the central engine and the surrounding material in AGNs. Full article
(This article belongs to the Special Issue Focus on Active Galactic Nuclei)
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