Related papers: Recurrent Activity in Active Galactic Nuclei
We present a brief overview of a very extensive studies of the group of active galactic nuclei (AGNs) that transitioned to radio-loud state over the past few decades. The sample consists of twelve sources, both quasars and galaxies, showing…
The physical origin of radio emission in Radio Quiet Active Galactic Nuclei (RQ AGN) remains unclear, whether it is a downscaled version of the relativistic jets typical of Radio Loud (RL) AGN, or whether it originates from the accretion…
The energy released by active galactic nuclei (AGNs) is considered to have a profound impact on the cold gas properties of their host galaxies, potentially heating or removing the gas and further suppressing star formation. To understand…
We have measured the angular sizes of radio cores of active galactic nuclei (AGN) and analyzed their sky distributions and frequency dependencies to study synchrotron opacity in AGN jets and the strength of angular broadening in the…
Using observations obtained with the LOw Fequency ARray (LOFAR), the Westerbork Synthesis Radio Telescope (WSRT) and archival Very Large Array (VLA) data, we have traced the radio emission to large scales in the complex source 4C 35.06…
Active Galactic Nuclei (AGN) are energetic astrophysical sources powered by accretion onto supermassive black holes in galaxies, and present unique observational signatures that cover the full electromagnetic spectrum over more than twenty…
The central nuclei of galaxies, where super-massive black holes (SMBHs) are thought to reside, can experience phases of activity when they become Active Galactic Nuclei (AGN). An AGN can eject winds, jets, and produce radiation across the…
Associated with one of the most important forms of active galactic nucleus (AGN) feedback, and showing a strong preference for giant elliptical host galaxies, radio AGN (L_1.4GHz > 10^24 W Hz^-1) are a key sub-class of the overall AGN…
We present near-infrared spectra of young radio quasars [P(1.4GHz) ~ 26-27 W/Hz] selected from the Wide-Field Infrared Survey Explorer. The detected objects have typical redshifts of z ~ 1.6-2.5 and bolometric luminosities ~ 10^47 erg/s.…
Observational searches for intermediate-mass black holes (IMBHs; $10^2 - 10^6$ $M_\odot$) include relatively isolated dwarf galaxies. For those that host active galactic nuclei (AGNs), the IMBH nature may be discerned through the accretion…
We consider the radiation pressure instability operating on short timescales 10^3 - 10^6 years in the accretion disk around a supermassive black hole as the origin of the intermittent activity of radio sources. We test whether this…
(Abridged) 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 QSOs that have been observed at low radio frequencies…
One of the striking examples of episodic activity in active galactic nuclei are the double-double radio galaxies (DDRGs) with two pairs of oppositely-directed radio lobes from two different cycles of activity. We illustrate, using the DDRG…
Radiation, winds and jets from the active nucleus of a massive galaxy can interact with its interstellar medium leading to ejection or heating of the gas. This can terminate star formation in the galaxy and stifle accretion onto the black…
We have studied the host galaxies of a sample of radio-loud AGN spanning more than four decades in the energy output of the nucleus. The core sample includes 40 low-power sources (BL Lac objects) and 22 high-power sources (radio-loud…
Powerful outflows with a broad range of properties (such as velocity, ionization, radial scale and mass loss rate) represent a key feature of active galactic nuclei (AGN), even more so since they have been simultaneously revealed also in…
Active Galactic Nuclei (AGN) are ideal sources for multi-wavelength studies as their emission can cover almost 20 orders of magnitude in frequency from the radio to the gamma-ray band. After reviewing their basic properties, I will assess…
Supermassive black holes at the centres of galaxies can cycle through periods of activity and quiescence. Characterising the duty cycle of active galactic nuclei is crucial for understanding the impact of the energy they release on the host…
I review some recent cosmological studies based on redshift surveys of radio sources selected at low frequencies. The accretion rate onto the central black hole is identified as the basis of a crude physical division of the low-frequency…
Accreting supermassive black holes at the centres of galaxies are the engine of active galactic nuclei (AGN). X-ray light curves of unabsorbed AGN show dramatic random variability on timescales ranging from seconds to years. The power…