相关论文: The fraction of BL Lac objects in groups of galaxi…

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…

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…

The extragalactic $\gamma$-rays sky observed by Fermi-Large Area Telescope (LAT) is dominated by blazars. In the fourth release of the Fermi-LAT Point Source Catalog (4FGL), are sources showing a multifrequency behavior similar to that of…

The HST snapshot imaging survey of 110 BL Lac objects (Urry et al. 2000) has clearly shown that the host galaxies are massive and luminous ellipticals. The dispersion of the absolute magnitudes is sufficiently small, so that the measurement…

Observations of the gamma-ray sky with Fermi led to significant advances towards understanding blazars, the most extreme class of Active Galactic Nuclei. A large fraction of the population detected by Fermi is formed by BL Lacertae (BL Lac)…

Context: BL Lacertae objects have been the targets for numerous recent multiwavelength campaigns, continuum spectral variability studies, and theoretical spectral and variability modeling. A meaningful interpretation of the results of such…

The BL Lac object RGB 1745+398 lies in an environment that makes it possible to study the cluster around it more deeply than the environments of other BL Lac objects. The cluster centered on the BL Lac works as a strong gravitational lens,…

We have used the HST WFPC2 camera to survey 132 BL Lac objects comprising seven complete radio-, X-ray-, and optically-selected samples. We obtained useful images for 110 targets spanning the redshift range 0 < z < 1.3. In two thirds of the…

\textbf{Context.} Deep optical surveys open the avenue for find large numbers of BL Lac objects that are hard to identify because they lack the unique properties classifying them as such. While radio or X-ray surveys typically reveal dozens…

Direct redshift determination of BL Lac objects is highly challenging as the emission in the optical and near-infrared (NIR) bands is largely dominated by the non-thermal emission from the relativistic jet that points very close to our line…

We have optically identified a sample of 56 featureless continuum objects without significant proper motion from the 2dF QSO Redshift Survey (2QZ). The steep number--magnitude relation of the sample, $n(\bj) \propto 10^{0.7\bj}$, is similar…

We investigate the properties of the host galaxies of X-ray selected (high frequency peaked) BL Lac objects using a large and homogeneous data set of high spatial resolution R-band observations of 52 BL Lacs in the EMSS and Slew samples.…

In an optical monitoring program to characterize the variability properties of blazar, we observed 10 sources from the Roma-BZCAT catalogue for 26 nights in V and R bands during October 2014 to June 2015 with two telescopes located in…

We present optical images and spectroscopy for a dozen of BL Lac objects. Most of these objects were not previously studied and we give for the first time the properties of their host galaxies. The properties of the new host galaxies are…

Blazars, including BL Lacs and FSRQs, are the most luminous extragalactic {\gamma}-ray sources. They account for about 56% of the sources listed in the recent Fermi-LAT catalog (4FGL-DR4). The optical and UV spectra of BL Lacs are nearly…

Due to their almost featureless optical/UV spectra, it is challenging to measure the redshifts of BL Lacs. As a result, about 50% of gamma-ray BL Lacs lack a firm measurement of this property, which is fundamental for population studies,…

We present new spectroscopic data of the BL Lac RGB 2243+203, and its surroundings, obtained with the OSIRIS Multi Object Spectrograph (MOS) mounted in the Gran Telescopio Canarias (GTC). The spectra of neither the BL Lac nor its host…

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…

BL Lacertae (BL Lac) objects are a subclass of blazar, distinguished by their featureless optical spectrum. The featureless spectrum presents a challenge in measuring the redshift of the BL Lacs. In this paper, we measure the redshift of BL…

We present a new well defined sample of BL Lac objects selected from the ROSAT All-Sky Survey (RASS). The sample consists of 39 objects with 35 forming a flux limited sample down to f_X = 8 x 10^{-13} cgs, redshifts are known for 33 objects…