Related papers: BL Lac evolution revisited
It has been speculated that low luminosity radio-loud AGN have the potential to serve as an important source of AGN feedback, and may be responsible for suppressing star-formation activity in massive elliptical galaxies at late times. As…
We explore the cosmic evolution of radio AGN with low radio powers (L_1.4GHz < 5\times10^25 W/Hz) out to z=1.3 using to-date the largest sample of ~600 low luminosity radio AGN at intermediate redshift drawn from the VLA-COSMOS survey. We…
We report on spectroscopic observations covering most of the 475 BL Lacs in the 2nd Fermi LAT catalog of AGN. Including archival measurements (correcting several erroneous literature values) we now have spectroscopic redshifts for 44% of…
We discuss alternative interpretations of the differences in the Spectral Energy Distributions (SEDs) of BL Lacs found in complete Radio or X-ray surveys. A large body of observations in different bands suggests that the SEDs of BL Lac…
While BL Lacertae objects are widely believed to be highly beamed, low-luminosity radio galaxies, many radio-selected BL Lacs have extended radio power levels and optical emission lines that are too luminous to be low-luminosity radio…
Active Galactic Nuclei (AGN) are now known to be strong gamma-ray emitters. After briefly describing AGN classification and the main ideas behind unified schemes, I summarize the main properties of blazars (that is BL Lacs and flat-spectrum…
A fraction of active galactic nuclei do not show the classical Seyfert-type signatures in their optical spectra, i.e. they are optically "elusive". X-ray observations are an optimal tool to identify this class of objects. We combine new…
We present an analysis of the 2-10 keV X-ray emission associated with the active galactic nuclei (AGNs) in brightest cluster galaxies (BCGs). Our sample consists of 32 BCGs that lie in highly X-ray luminous cluster of galaxies (L_X-ray…
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 a polarization variability analysis of a sample of 26 $\gamma$-ray blazars monitored by the Steward Observatory between 2008 and 2018 in the optical band. We investigate the properties and long-term variability of their optical…
Active Galactic Nuclei (AGN) are now known to be strong gamma-ray emitters. After briefly describing the different classes of AGN and the basic tenets of unified schemes, I discuss the role of blazars (that is BL Lacs and flat-spectrum…
X-ray data from the blazar BL Lac are used to investigate the nature of its variability, and more precisely the flux dependency of the variability and the distribution of fluxes. The variations in the flux are found to have a lognormal…
Fermi has provided the largest sample of gamma-ray selected blazars to date. In this work we use a uniformly selected set of 211 BL Lacertae (BL Lac) objects detected by it Fermi during its first year of operation. We have obtained redshift…
This article discusses the our changing knowledge of the evolution of AGN from an optical perspective. It focusses on optically-unobscured (type-1) AGN as it is much trickier to investigate the evolution type-2 objects from an optical point…
We present the results of a systematic observational campaign designed to search for microvariability in the optical polarization of BL Lac objects. We have observed a sample formed by 8 X-ray-selected and 10 radio-selected sources, looking…
The incidence and properties of Active Galactic Nuclei (AGN) in the field, groups, and clusters can provide new information about how these objects are triggered and fueled, similar to how these environments have been employed to study…
From an optical spectroscopic survey of 3CR radiogalaxies (RGs) with z<0.3, we discovered three objects characterized by an extremely low level of gas excitation and a large deficit of line emission with respect to RGs of similar radio…
The nature of the so-called ``changing-look'' (CL) active galactic nucleus (AGN), which is characterized by spectral-type transitions within $\sim10$~yr, remains an open question. As the first in our series of studies, we here attempt to…
We present radio and X-ray observations, as well as optical light curves, for a subset of 26 BL Lac candidates from the Sloan Digital Sky Survey (SDSS) lacking strong radio emission and with z<2.2. Half of these 26 objects are shown to be…
We have obtained high dynamic range, good natural seeing i' images of BL Lacertae objects (BL Lacs) to search for the AGN host and thus constrain the source redshift. These objects are drawn from a sample of bright flat-spectrum radio…