scholarly journals Exploring New Redshift Indicators for Radio-Powerful AGN

Galaxies ◽  
2021 ◽  
Vol 9 (4) ◽  
pp. 86
Author(s):  
Rodrigo Carvajal ◽  
Israel Matute ◽  
José Afonso ◽  
Stergios Amarantidis ◽  
Davi Barbosa ◽  
...  
Keyword(s):  
Machine Learning ◽  
Active Galactic Nuclei ◽  
Prediction Error ◽  
Galactic Nuclei ◽  
Number Density ◽  
Massive Black Holes ◽  
Photometric Redshift ◽  
Large Samples ◽  
Large Numbers ◽  
The Universe

Active Galactic Nuclei (AGN) are relevant sources of radiation that might have helped reionising the Universe during its early epochs. The super-massive black holes (SMBHs) they host helped accreting material and emitting large amounts of energy into the medium. Recent studies have shown that, for epochs earlier than z∼5, the number density of SMBHs is on the order of few hundreds per square degree. Latest observations place this value below 300 SMBHs at z≳6 for the full sky. To overcome this gap, it is necessary to detect large numbers of sources at the earliest epochs. Given the large areas needed to detect such quantities, using traditional redshift determination techniques—spectroscopic and photometric redshift—is no longer an efficient task. Machine Learning (ML) might help obtaining precise redshift for large samples in a fraction of the time used by other methods. We have developed and implemented an ML model which can predict redshift values for WISE-detected AGN in the HETDEX Spring Field. We obtained a median prediction error of σzN=1.48×(zPredicted−zTrue)/(1+zTrue)=0.1162 and an outlier fraction of η=11.58% at (zPredicted−zTrue)/(1+zTrue)>0.15, in line with previous applications of ML to AGN. We also applied the model to data from the Stripe 82 area obtaining a prediction error of σzN=0.2501.

scholarly journals Symmetry and the Arrow of Time in Theoretical Black Hole Astrophysics

2015 ◽  
Vol 2015 ◽  
pp. 1-5
Author(s):  
David Garofalo
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Active Galactic Nuclei ◽  
Accretion Disks ◽  
Time Reversal ◽  
Large Scale ◽  
Galactic Nuclei ◽  
Arrow Of Time ◽  
Time Symmetry ◽  
The Universe

While the basic laws of physics seem time-reversal invariant, our understanding of the apparent irreversibility of the macroscopic world is well grounded in the notion of entropy. Because astrophysics deals with the largest structures in the Universe, one expects evidence there for the most pronounced entropic arrow of time. However, in recent theoretical astrophysics work it appears possible to identify constructs with time-reversal symmetry, which is puzzling in the large-scale realm especially because it involves the engines of powerful outflows in active galactic nuclei which deal with macroscopic constituents such as accretion disks, magnetic fields, and black holes. Nonetheless, the underlying theoretical structure from which this accreting black hole framework emerges displays a time-symmetric harmonic behavior, a feature reminiscent of basic and simple laws of physics. While we may expect such behavior for classical black holes due to their simplicity, manifestations of such symmetry on the scale of galaxies, instead, surprise. In fact, we identify a parallel between the astrophysical tug-of-war between accretion disks and jets in this model and the time symmetry-breaking of a simple overdamped harmonic oscillator. The validity of these theoretical ideas in combination with this unexpected parallel suggests that black holes are more influential in astrophysics than currently recognized and that black hole astrophysics is a more fundamental discipline.

scholarly journals Study of the Galactic Center with a High Resolution Gamma Ray Telescope

1989 ◽  
Vol 136 ◽  
pp. 639-643
Author(s):  
Ervin J. Fenyves ◽  
Stephen N. Balog ◽  
David B. Cline ◽  
M. Atac
Keyword(s):  
Black Holes ◽  
Active Galactic Nuclei ◽  
Gamma Ray ◽  
Galactic Center ◽  
Galactic Nuclei ◽  
Seyfert Galaxies ◽  
Hole Formation ◽  
Massive Black Holes ◽  
General Outcome ◽  
Enormous Amount

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.

scholarly journals Expanding Quasars and the Expansion of the Universe

1988 ◽  
Vol 129 ◽  
pp. 23-24
Author(s):  
M. H. Cohen ◽  
P. D. Barthel ◽  
T. J. Pearson ◽  
J. A. Zensus
Keyword(s):  
Active Galactic Nuclei ◽  
Upper Bound ◽  
Proper Motion ◽  
Galactic Nuclei ◽  
Radio Sources ◽  
Extragalactic Radio Sources ◽  
Expansion Of The Universe ◽  
The Universe

The μ–z diagram (Figure 1) plots the observed internal proper motion μ versus redshift z for 32 extragalactic radio sources associated with active galactic nuclei. The observed points fall below an upper bound which decreases with redshift; there is a statistically significant anticorrelation between redshift and internal proper motion.

scholarly journals Quasi-stellar object redshift estimates from optical, near-infrared, and ultraviolet colours

2019 ◽  
Vol 629 ◽  
pp. A56 ◽  
Author(s):  
S. J. Curran ◽  
J. P. Moss
Keyword(s):  
Active Galactic Nuclei ◽  
Rest Frame ◽  
Near Infrared ◽  
Galactic Nuclei ◽  
Additional Contribution ◽  
Stellar Objects ◽  
Simple Estimate ◽  
Photometric Redshift ◽  
Wide Range ◽  
Quasi Stellar Objects

A simple estimate of the photometric redshift would prove invaluable to forthcoming continuum surveys on the next generation of large radio telescopes, as well as mitigating the existing bias towards the most optically bright sources. While there is a well-known correlation between the near-infrared K-band magnitude and redshift for galaxies, we find the K − z relation to break down for samples dominated by quasi-stellar objects. We hypothesise that this is due to the additional contribution to the near-infrared flux by the active galactic nucleus, and, as such, the K-band magnitude can only provide a lower limit to the redshift in the case of active galactic nuclei, which will dominate the radio surveys. From a large optical dataset, we find a tight relationship between the rest-frame (U − K)/(W2 − FUV) colour ratio and spectroscopic redshift over a sample of 17 000 sources, spanning z ≈ 0.1−5. Using the observed-frame ratios of (U − K)/(W2 − FUV) for redshifts of z ≲ 1, (I − W2)/(W3 − U) for 1 ≲ z ≲ 3, and (I − W2.5)/(W4 − R) for z ≳ 3, where W2.5 is the λ = 8.0 μm magnitude and the appropriate redshift ranges are estimated from the W2 (4.5 μm) magnitude, we find this to be a robust photometric redshift estimator for quasars. We suggest that the rest-frame U − K colour traces the excess flux from the AGN over this wide range of redshifts, although the W2 − FUV colour is required to break the degeneracy.

Magnetic field and radius of the innermost stable circular orbit near super-massive black holes in active galactic nuclei

2015 ◽  
Vol 336 (10) ◽  
pp. 1013-1016 ◽  
Author(s):  
M. Yu. Piotrovich ◽  
Yu. N. Gnedin ◽  
N. A. Silant'ev ◽  
T. M. Natsvlishvili ◽  
S. D. Buliga
Keyword(s):  
Magnetic Field ◽  
Black Holes ◽  
Active Galactic Nuclei ◽  
Circular Orbit ◽  
Galactic Nuclei ◽  
Massive Black Holes ◽  
Stable Circular Orbit ◽  
Innermost Stable Circular Orbit

scholarly journals The Scaling of Solar Flare Hard X-ray Emission to Other Flaring Objects in the Universe

2000 ◽  
Vol 195 ◽  
pp. 133-134
Author(s):  
P. C. H. Martens
Keyword(s):  
Active Galactic Nuclei ◽  
Accretion Disks ◽  
Galactic Nuclei ◽  
Physical Parameters ◽  
X Ray ◽  
Transport Code ◽  
Type Particle ◽  
Fokker Planck Equations ◽  
The Universe ◽  
Fokker Planck

Fletcher & Martens have successfully modeled solar hard X-ray sources observed at the top and footpoints of flaring magnetic loops with a Fokker-Planck type particle transport code. I show here that there are invariances in the Fokker-Planck equations that make these results applicable to environments with vastly different physical parameters, such as hard X-ray flares in accretion disks in active galactic nuclei, and in RS CVn and ALGOL type binaries.

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