Related papers: Evolutionary behaviour of BL Lac objects
BL Lac objects (BLL) are defined by the presence of very weak (typically $<$ 5 {\AA}) or even absent spectral lines. This makes determining their distance particularly challenging, especially at high redshift, where the sources are fainter…
We present the radio detection of 18 BL Lac objects from our survey of over 575 square degrees of sky. These 18 objects are located within 20 arcsec of the X-ray position, of which 11 have a measured red-shift. All candidates are radio…
We evaluate with numerical simulations the hypothesis that BL Lacertae objects are the remnants of Quasi Stellar Objects. This hypothesis is based on their highly peculiar redshift evolution. They have a comoving space density that…
BL Lac objects are active nuclei, hosted in massive elliptical galaxies, the emission of which is dominated by a relativistic jet closely aligned with the line of sight. This implies the existence of a parent population of sources with a…
We carried out multi-color optical monitoring of a sample of ten blazars from 2005 to 2011. The sample contains 3 LBLs, 2 IBLs, 4 HBLs, and 1 FSRQ. Our monitoring focused on the long-term variability and the sample included nine BL Lac…
We present the X-ray luminosity function (XLF) of the ROSAT Brightest Cluster Sample (BCS), an X-ray selected, flux limited sample of 172 clusters of galaxies at $z\leq 0.3$ compiled from ROSAT All-Sky Survey data. While the bulk of the BCS…
We introduce a new method to determine the redshift of unknown-redshift BL Lac Objects. The method relies on simultaneous multi-wavelength (MWL) observations of BL Lac objects in optical, X-ray, HE (E>100 MeV) gamma-rays and VHE (E>100…
Combining newly identified and previously known BL Lacs from the RASS-Green Bank (RGB) catalog, we present a sample of 127 BL Lacs, the largest ever derived from a single uniform survey. A Complete sample of 33 objects brighter than O=18.0…
We present the results of near-infrared H band (1.65 microns) imaging of 11 BL Lac objects with redshifts ranging from z = 0.05 to 0.9. We are able to clearly detect the host galaxy in seven low redshift (z<=0.24) BL Lacs, while the four…
We present high S/N optical spectra of 10 BL Lac objects detected at GeV energies by Fermi satellite (3FGL catalog), for which previous observations suggested that they are at relatively high redshift. The new observations, obtained at the…
We have obtained WIYN and SOAR i' images of BL Lacertae objects (BL Lacs) and used these to detect or constrain the flux of the host galaxy. Under common standard candle assumptions these data provide estimates of, or lower bounds on, the…
We present the results of an extensive analysis of the optical, ultraviolet, X-ray and $\gamma$-ray data collected from the observations of the BL Lac objects prototype BL Lacertae carried out over a period of nearly 13 years, between…
AIMS. We are studying an unbiased sample of 42 nearby (z < 0.2) BL Lacertae objects with a multi-wavelength approach. The results of VLBI observations were presented in the first paper of this series. In this paper, we study the…
BL Lacertae (BL Lac) objects are the prominent members of the third {\it Fermi} Large Area Telescope catalog of $\gamma$-ray sources. Half of the BL Lac population ($\sim$ 300) lack redshift measurements, which is due to the absence of…
Context. The study of BL Lac objects (BLL) detected in gamma-rays gives insights on the acceleration mechanisms in play in such systems and is also a valuable tool to constrain the density of the extragalactic background light. As their…
The bright BL Lac object TXS 0506+056 is a most likely counterpart of the IceCube neutrino event EHE 170922A. The lack of this redshift prevents a comprehensive understanding of the modeling of the source. We present high signal-to-noise…
We present recent X-ray observations of intermediate BL Lac objects (IBLs), i.e. BL Lacs which are located between high-energy and low-energy peaked BL Lac objects with respect to alpha_rx. We briefly discuss the statistical properties of…
The very high energy (VHE) gamma-ray spectral indices of blazars show strong correlation with the source redshift. Absence of any such correlation in low energy gamma rays and X-rays indicate the presence of Extragalactic Background Light…
One of the major challenges in studying the cosmic evolution of relativistic jets is the identification of the high-redshift ($z>3$) BL Lacertae objects, a class of jetted active galactic nuclei characterized by their quasi-featureless…
(abridged) We present near-infrared Ks-band imaging of 13 high redshift (0.6 < z < 1.3) BL Lac objects. We clearly detect the host in eight objects, and marginally in three others. In all cases, the host galaxy is well represented by an…