Results 31 to 40 of about 719 (181)
Spectroscopic properties of radio-loud and radio-quiet quasars [PDF]
Proceedings of the International Astronomical Union, 2019 AbstractSurveys have shown radio-loud (RL) quasars constitute 10%-15% of the total quasar population and rest are radio-quiet (RQ). However, it is unknown if this radio-loud fraction (RLF) remains consistent among different parameter spaces. This study shows that RLF increases for increasing full width half maximum (FWHM) velocity of the Hβ broad ...
Chakraborty, Avinanda +1 more
openaire +4 more sources
Astrometric Apparent Motion of High-redshift Radio Sources
The Astronomical Journal, 2023 Radio-loud quasars at high redshift ( z ≥ 4) are rare objects in the universe and rarely observed with Very Long Baseline Interferometry (VLBI). But some of them have flux density sufficiently high for monitoring of their apparent position.
Oleg Titov +12 more
doaj +1 more source
Symmetry and the Arrow of Time in Theoretical Black Hole Astrophysics
Journal of Gravity, Volume 2015, Issue 1, 2015., 2015 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.
David Garofalo, Cosimo Bambi
wiley +1 more source
Retrograde versus Prograde Models of Accreting Black Holes
Advances in Astronomy, Volume 2013, Issue 1, 2013., 2013 There is a general consensus that magnetic fields, accretion disks, and rotating black holes are instrumental in the generation of the most powerful sources of energy in the known universe. Nonetheless, because magnetized accretion onto rotating black holes involves both the complications of nonlinear magnetohydrodynamics that currently cannot fully be
David Garofalo, Alberto J. Castro-Tirado
wiley +1 more source
The Cosmic History of Black Hole Growth from Deep Multiwavelength Surveys
Advances in Astronomy, Volume 2012, Issue 1, 2012., 2012 Significant progress has been made in the last few years on understanding how supermassive black holes form and grow. In this paper, we begin by reviewing the spectral signatures of active galactic nuclei (AGN) ranging from radio to hard X‐ray wavelengths.
Ezequiel Treister +2 more
wiley +1 more source
A Practical Guide to the Massive Black Hole Cosmic History
Advances in Astronomy, Volume 2012, Issue 1, 2012., 2012 I review our current understanding of massive black hole (MBH) formation and evolution along the cosmic history. After a brief introductory overview of the relevance of MBHs in the hierarchical structure formation paradigm, I discuss the main viable channels for seed BH formation at high redshift and for their subsequent mass growth and spin evolution.
A. Sesana, Francesco Shankar
wiley +1 more source
Evidence for AGN Feedback in Galaxy Clusters and Groups
Advances in Astronomy, Volume 2012, Issue 1, 2012., 2012 The current generation of flagship X‐ray missions, Chandra and XMM-Newton, has changed our understanding of the so‐called “cool‐core” galaxy clusters and groups. Instead of the initial idea that the thermal gas is cooling and flowing toward the center, the new picture envisages a complex dynamical evolution of the intracluster medium (ICM) regulated by
Myriam Gitti +3 more
wiley +1 more source
Gravitational Lensing as a Probe of Cold Dark Matter Subhalos
Advances in Astronomy, Volume 2010, Issue 1, 2010., 2010 In the cold dark matter scenario, dark matter halos are assembled hierarchically from smaller subunits. Some of these subunits are disrupted during the merging process, whereas others survive temporarily in the form of subhalos. A long‐standing problem with this picture is that the number of subhalos predicted by simulations exceeds the number of ...
Erik Zackrisson +2 more
wiley +1 more source
Radio Loud and Radio Quiet Quasars
, 2016 We discuss 6 GHz JVLA observations covering a volume-limited sample of 178 low redshift ($0.2 < z < 0.3$) optically selected QSOs. Our 176 radio detections fall into two clear categories: (1) About $20$\% are radio-loud QSOs (RLQs) having spectral luminosities $L_6 \gtrsim 10^{\,23.2} \mathrm{~W~Hz}^{-1}$ primarily generated in the active ...
Kellermann, K. I. +4 more
openaire +2 more sources
The Case for Two Quasar Populations
Open Astronomy, 2011 We present evidence for two populations of quasars showing distinctly different broad line structure and kinematics. The first evidence for quasar dichotomy involve differences between radio-quiet and radio-loud sources.
Sulentic Jack +2 more
doaj +1 more source