scholarly journals Theoretical Models of Active Galactic Nuclei

1984 ◽  
pp. 215-225 ◽  
Author(s):  
R. D. Blandford
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Theoretical Models

scholarly journals Constraining photoionization models with a reprojected optical diagnostic diagram

2020 ◽  
Vol 499 (4) ◽  
pp. 5749-5764 ◽  
Author(s):  
Xihan Ji ◽  
Renbin Yan
Keyword(s):  
Star Formation ◽  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Theoretical Models ◽  
Line Ratio ◽  
Star Forming ◽  
Optical Diagnostic ◽  
Diagnostic Diagram ◽  
Upper Limits ◽  
Nitrogen Abundance

ABSTRACT Optical diagnostic diagrams are powerful tools to separate different ionizing sources in galaxies. However, the model-constraining power of the most widely used diagrams is very limited and challenging to visualize. In addition, there have always been classification inconsistencies between diagrams based on different line ratios, and ambiguities between regions purely ionized by active galactic nuclei (AGNs) and composite regions. We present a simple reprojection of the 3D line ratio space composed of [N ii]λ6583/H α, [S ii]λλ6716, 6731/H α, and [O iii]λ5007/H β, which reveals its model-constraining power and removes the ambiguity for the true composite objects. It highlights the discrepancy between many theoretical models and the data loci. With this reprojection, we can put strong constraints on the photoionization models and the secondary nitrogen abundance prescription. We find that a single nitrogen prescription cannot fit both the star-forming locus and AGN locus simultaneously, with the latter requiring higher N/O ratios. The true composite regions stand separately from both models. We can compute the fractional AGN contributions for the composite regions, and define demarcations with specific upper limits on contamination from AGN or star formation. When the discrepancy about nitrogen prescriptions gets resolved in the future, it would also be possible to make robust metallicity measurements for composite regions and AGNs.

scholarly journals Numerical Simulations of Jets from Active Galactic Nuclei

Galaxies ◽  
2019 ◽  
Vol 7 (1) ◽  
pp. 24 ◽  
Author(s):  
José-María Martí
Keyword(s):  
Numerical Simulations ◽  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Theoretical Models ◽  
The Status ◽  
Hydrodynamical Description ◽  
Jet Plasma ◽  
The Impact ◽  
Continuous Injection ◽  
Double Radio Galaxies

Numerical simulations have been playing a crucial role in the understanding of jets from active galactic nuclei (AGN) since the advent of the first theoretical models for the inflation of giant double radio galaxies by continuous injection in the late 1970s. In the almost four decades of numerical jet research, the complexity and physical detail of simulations, based mainly on a hydrodynamical/magneto-hydrodynamical description of the jet plasma, have been increasing with the pace of the advance in theoretical models, computational tools and numerical methods. The present review summarizes the status of the numerical simulations of jets from AGNs, from the formation region in the neighborhood of the supermassive central black hole up to the impact point well beyond the galactic scales. Special attention is paid to discuss the achievements of present simulations in interpreting the phenomenology of jets as well as their current limitations and challenges.

scholarly journals Galaxy-scale ionised winds driven by ultra-fast outflows in two nearby quasars

2020 ◽  
Vol 644 ◽  
pp. A15
Author(s):  
A. Marasco ◽  
G. Cresci ◽  
E. Nardini ◽  
F. Mannucci ◽  
A. Marconi ◽  
...  
Keyword(s):  
Active Galactic Nuclei ◽  
Adaptive Optics ◽  
Velocity Dispersion ◽  
Galactic Nuclei ◽  
Optical Emission ◽  
Theoretical Models ◽  
Small Sample ◽  
Mean Velocity ◽  
Field Mode ◽  
Mass Outflow

We used MUSE adaptive optics data in narrow field mode to study the properties of the ionised gas in MR 2251−178 and PG 1126−041, two nearby (z ≃ 0.06) bright quasars (QSOs) hosting sub-pc scale ultra-fast outflows (UFOs) detected in the X-ray band. We decomposed the optical emission from diffuse gas into a low- and a high-velocity components. The former is characterised by a clean, regular velocity field and a low (∼80 km s−1) velocity dispersion. It traces regularly rotating gas in PG 1126−041, while in MR 2251−178 it is possibly associated with tidal debris from a recent merger or flyby. The other component is found to be extended up to a few kpc from the nuclei, and shows a high (∼800 km s−1) velocity dispersion and a blue-shifted mean velocity, as is expected from outflows driven by active galactic nuclei (AGN). We estimate mass outflow rates up to a few M⊙ yr−1 and kinetic efficiencies LKIN/LBOL between 1−4 × 10−4, in line with those of galaxies hosting AGN of similar luminosities. The momentum rates of these ionised outflows are comparable to those measured for the UFOs at sub-pc scales, which is consistent with a momentum-driven wind propagation. Pure energy-driven winds are excluded unless about 100× additional momentum is locked in massive molecular winds. In comparing the outflow properties of our sources with those of a small sample of well-studied QSOs hosting UFOs from the literature, we find that winds seem to systematically lie either in a momentum-driven or an energy-driven regime, indicating that these two theoretical models bracket the physics of AGN-driven winds very well.

scholarly journals Mock catalogs for the extragalactic X-ray sky: Simulating AGN surveys with ATHENA and with the AXIS probe

2020 ◽  
Vol 642 ◽  
pp. A184
Author(s):  
S. Marchesi ◽  
R. Gilli ◽  
G. Lanzuisi ◽  
T. Dauser ◽  
S. Ettori ◽  
...  
Keyword(s):  
Active Galactic Nuclei ◽  
Cosmic Time ◽  
Galactic Nuclei ◽  
Theoretical Models ◽  
X Rays ◽  
X Ray ◽  
Flux Limit ◽  
Order Of Magnitude ◽  
Deep Fields ◽  
First Time

We present a series of new, publicly available mock catalogs of X-ray selected active galactic nuclei (AGNs), nonactive galaxies, and clusters of galaxies. These mocks are based on up-to-date observational results on the demographic of extragalactic X-ray sources and their extrapolations. They reach fluxes below 10−20 erg cm−2 s−1 in the 0.5–2 keV band, that is, more than an order of magnitude below the predicted limits of future deep fields, and they therefore represent an important tool for simulating extragalactic X-ray surveys with both current and future telescopes. We used our mocks to perform a set of end-to-end simulations of X-ray surveys with the forthcoming ATHENA mission and with the AXIS probe, a subarcsecond resolution X-ray mission concept proposed to the Astro 2020 Decadal Survey. We find that these proposed, next generation surveys may transform our knowledge of the deep X-ray Universe. As an example, in a total observing time of 15 Ms, AXIS would detect ∼225 000 AGNs and ∼50 000 nonactive galaxies, reaching a flux limit of f0.5−2 ∼ 5 × 10−19 erg cm−2 s−1 in the 0.5–2 keV band, with an improvement of over an order of magnitude with respect to surveys with current X-ray facilities. Consequently, 90% of these sources would be detected for the first time in the X-rays. Furthermore, we show that deep and wide X-ray surveys with instruments such as AXIS and ATHENA are expected to detect ∼20 000 z > 3 AGNs and ∼250 sources at redshift z > 6, thus opening a new window of knowledge on the evolution of AGNs over cosmic time and putting strong constraints on the predictions of theoretical models of black hole seed accretion in the early universe.

scholarly journals Variability in Active Galactic Nuclei

2011 ◽  
Vol 7 (S285) ◽  
pp. 109-110
Author(s):  
Erin Wells Bonning
Keyword(s):  
Active Galactic Nuclei ◽  
Time Domain ◽  
Galactic Nuclei ◽  
Periodic Oscillation ◽  
Theoretical Models ◽  
Quasi Periodic Oscillation ◽  
Complex Processes ◽  
Central Engine ◽  
The Rich ◽  
The Time Domain

AbstractThis talk explored variability in active galactic nuclei (AGN) for a variety of scales across the time domain. From billion-year-scale intermittency to a quasi-periodic oscillation signal with a period of one hour, time-varying signals offer insights into a myriad of complex processes driven by the AGN central engine. Athough the era of time-domain observations of AGN across the spectrum has but just begun, already observations reveal the rich detail of phenomena associated with actively accreting black holes which challenge theoretical models.

scholarly journals Theoretical Models of Active Galactic Nuclei

1984 ◽  
Vol 110 ◽  
pp. 215-225
Author(s):  
R. D. Blandford
Keyword(s):  
Active Galactic Nuclei ◽  
Accretion Rate ◽  
Galactic Nuclei ◽  
Theoretical Models ◽  
Source Model ◽  
Massive Black Hole ◽  
Bl Lac Objects ◽  
Accretion Rates ◽  
Compact Sources

We review attempts to incorporate radio sources within the context of general models of active galactic nuclei. The behaviour of gas accreting onto a massive black hole depends upon its angular momentum and accretion rate. It is argued that radio galaxies, QSR's and QSO's (and Seyfert 1 galaxies) be associated with increasing mass accretion rates The classification of an active galaxy appears to be aspect-dependent. In particular BL Lac objects, OVV quasars and the superluminally expanding compact sources appear to be beamed towards us. We show how the choice of source model can influence the statistics of beaming.

scholarly journals Feedback from Active Galactic Nuclei in Galaxy Groups

Universe ◽  
2021 ◽  
Vol 7 (5) ◽  
pp. 142
Author(s):  
Dominique Eckert ◽  
Massimo Gaspari ◽  
Fabio Gastaldello ◽  
Amandine M. C. Le Brun ◽  
Ewan O’Sullivan
Keyword(s):  
Active Galactic Nuclei ◽  
Galaxy Evolution ◽  
Large Scale ◽  
Galactic Nuclei ◽  
Theoretical Models ◽  
Feedback Process ◽  
Galaxy Groups ◽  
Heating Source ◽  
Massive Halos ◽  
Halo Gas

The co-evolution between supermassive black holes and their environment is most directly traced by the hot atmospheres of dark matter halos. The cooling of the hot atmosphere supplies the central regions with fresh gas, igniting active galactic nuclei (AGN) with long duty cycles. Outflows from the central engine tightly couple with the surrounding gaseous medium and provide the dominant heating source preventing runaway cooling by carving cavities and driving shocks across the medium. The AGN feedback loop is a key feature of all modern galaxy evolution models. Here, we review our knowledge of the AGN feedback process in the specific context of galaxy groups. Galaxy groups are uniquely suited to constrain the mechanisms governing the cooling–heating balance. Unlike in more massive halos, the energy that is supplied by the central AGN to the hot intragroup medium can exceed the gravitational binding energy of halo gas particles. We report on the state-of-the-art in observations of the feedback phenomenon and in theoretical models of the heating-cooling balance in galaxy groups. We also describe how our knowledge of the AGN feedback process impacts galaxy evolution models and large-scale baryon distributions. Finally, we discuss how new instrumentation will answer key open questions on the topic.

scholarly journals Inherent and Local Magnetic Field Structures in Jets from Active Galactic Nuclei

Galaxies ◽  
2021 ◽  
Vol 9 (3) ◽  
pp. 58
Author(s):  
Denise C. Gabuzda
Keyword(s):  
Black Hole ◽  
Active Galactic Nuclei ◽  
Accretion Disk ◽  
Field Component ◽  
Galactic Nuclei ◽  
Intrinsic Property ◽  
Theoretical Models ◽  
Local Magnetic Field ◽  
Astrophysical Jets ◽  
Wide Range

In theoretical models for the electromagnetic launching of astrophysical jets, a helical magnetic (B)-field component is generated through the winding up of an initial longitudinal field component by the rotation of the cental black hole and accretion disk. This helical field component travels outward with the jet plasma. There is now abundant evidence that the jets of active galactic nuclei carry helical B fields, and the presence of such fields has been invoked to explain a wide range of phenomena observed in these jets. However, distinguishing between features associated with this inherent jet B field and with B fields generated by local phenomena such as shocks and shear can be challenging. There is now evidence that the field that is accreted is dipolar like, giving rise to a current distribution with inward currents along both jet axes and outward currents in a more extended region around the jets. Striking limb brightening has been observed for several relatively nearby active galactic nuclei; it is argued that this must be due to some intrinsic property of the jet, which is independent of the viewing angle, such as its helical B field, or mass loading and/or particle acceleration at the jet edges. Circular-polarization observations may make it possible to reconstruct the full three-dimensional B field of jets carrying a helical B-field component, and to correctly infer the direction of rotation of the central black hole and its accretion disk.

scholarly journals Obscured Active Galactic Nuclei

2018 ◽  
Vol 56 (1) ◽  
pp. 625-671 ◽  
Author(s):  
Ryan C. Hickox ◽  
David M. Alexander
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Theoretical Models ◽  
Observational Cosmology ◽  
Supermassive Black Hole ◽  
Cosmic Evolution ◽  
Radiative Power ◽  
Important Challenge ◽  
Luminous Objects ◽  
The Universe

Active galactic nuclei (AGN) are powered by the accretion of material onto a supermassive black hole (SMBH) and are among the most luminous objects in the Universe. However, the huge radiative power of most AGN cannot be seen directly, as the accretion is hidden behind gas and dust that absorb many of the characteristic observational signatures. This obscuration presents an important challenge for uncovering the complete AGN population and understanding the cosmic evolution of SMBHs. In this review, we describe a broad range of multiwavelength techniques that are currently being employed to identify obscured AGN, and we assess the reliability and completeness of each technique. We follow with a discussion of the demographics of obscured AGN activity, explore the nature and physical scales of the obscuring material, and assess the implications of obscured AGN for observational cosmology. We conclude with an outline of the prospects for future progress from both observations and theoretical models, and we highlight some of the key outstanding questions.

scholarly journals PEV COSMIC NEUTRINOS FROM THE MOUNTAINS

2004 ◽  
Vol 19 (13n16) ◽  
pp. 1117-1124 ◽  
Author(s):  
◽  
P. YEH ◽  
H. ATHAR ◽  
N. LA BARBERA ◽  
S. BOUAISSI ◽  
...  
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Center ◽  
Galactic Nuclei ◽  
Primary Source ◽  
Theoretical Models ◽  
Wide Field ◽  
Air Showers ◽  
Tau Neutrinos ◽  
Wide Field Of View ◽  
First Time

The NuTel collaboration is building a wide field-of-view Čerenkov telescope to be installed on a mountain site for observing near horizontal air showers emerging from another mountain. Cosmic tau neutrinos is the primary source of such showers. This technique will be realized for the first time in the ντ energy range of 2 PeV to 1000 PeV. The telescope has enough sensitivity to observe cosmic neutrinos from sources like Active Galactic Nuclei and Galactic Center assuming fluxes from current theoretical models.

Sign in / Sign up

Export Citation Format

Share Document