Optical spectroscopy of BL Lacertae objects

et al. 2013

Self Cite

We present Very Large Telescope optical spectroscopy of nine BL Lac objects of unknown redshift belonging to the list of optically selected radio-loud BL Lac candidates. We explore their spectroscopic properties and possible link with gamma-ray emission. From the new observations we determine the redshifts of four objects from faint emission lines or from absorption features of their host galaxies. In three cases we find narrow intervening absorptions from which a lower limit to the redshift is inferred. For the remaining two featureless sources, lower limits to the redshift are deduced from the absence of spectral lines. A search for γ counterpart emission shows that six out of the nine candidates are Fermi γ -ray emitters and we find two new detections. Our analysis suggests that most of the BL Lac objects still lacking redshift information are most likely located at high redshifts.

Section: Introductionmentioning

confidence: 79%

SPECTROSCOPY OF OPTICALLY SELECTED BL LAC OBJECTS AND THEIR Γ-Ray EMISSION

Sandrinelli

Treves

et al. 2013

Self Cite

“…direct method is to use high quality images to detect the surrounding nebulosity, or to asses upper limits of the host brightness and then derive a redshift lower limit. Alternatively one can search for the host galaxy features that are heavily obscured by the dominant non thermal emission (Sbarufatti et al 2006a) . In the first case high resolution and deep images are required while in the second one very high SNR spectra of adequate resolution are needed.…”

Section: Discussionmentioning

confidence: 99%

“…Since the luminosity distribution of these host galaxies is relatively narrow (see e.g. Urry et al 2000) it is possible to use the host galaxy luminosity as a sort of standard candle to evaluate the distance of the objects or to set lower limits in the cases where no signature from the starlight is found (Sbarufatti et al (2006a) ).…”

Section: Discussionmentioning

confidence: 99%

On the Redshift of TeV BL Lac Objects

Paiano

Landoni

et al. 2017

ApJ

We report results of a spectroscopic campaign carried out at the 10 m Gran Telescopio Canarias for a sample of 22 BL Lac objects detected (or candidates) at TeV energies, aimed to determine or constrain their redshift. This is of fundamental importance for the interpretation of their emission models, for population studies and also mandatory to study the interaction of high energy photons with the extragalactic background light using TeV sources. High signal-to-noise optical spectra in the range 4250 -10000Å were obtained to search for faint emission and/or absorption lines from both the host galaxy or the nucleus. We determine a new redshift for PKS 1424+240 (z = 0.604) and a tentative one for 1ES 0033+595 (z = 0.467). We are able to set new spectroscopic redshift lower limits for other three sources on the basis of Mg II and Ca II intervening absorption features: BZB J1243+3627 (z > 0.483), BZB J1540+8155 (z > 0.672), and BZB 0J2323+4210 (z > 0.267). We confirm previous redshift estimates for four blazars: S3 0218+357 (z = 0.944), 1ES 1215+303 (z = 0.129), W Comae (z = 0.102), and MS 1221.8+2452 (z = 0.218). For the remaining targets, in seven cases (S2 0109+22, 3C 66A, VER J0521+211, S4 0954+65, BZB J1120+4214, S3 1227+25, BZB J2323+4210), we do not validate the proposed redshift. Finally for all sources of still unknown redshift, we set a lower limit based on the minimum equivalent width of absorption features expected from the host galaxy.

“…8 The flux calibrated (top panel) and continuum-normalized (bottom panel) optical spectra of H 1722+11. The only absorption features besides the telluric bands are due to the Galactic interstellar medium: Ca II λλ3934, 3968 and Na I λ5892 atomic lines and DIBs at 4428, 4726, 4882, and 5772Å (Sbarufatti et al, 2006b). See http://archive.oapd.inaf.it/zbllac/ for more examples.…”

Section: Broad Emission Linesmentioning

confidence: 99%

An optical view of BL Lacertae objects

Pian²,

Treves

2014

Astron Astrophys Rev

139

109

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 misaligned jet, that have been identified with low-power radiogalaxies. The spectrum of BL Lacs, dominated by non-thermal emission over the whole electromagnetic range, together with bright compact radio cores, high luminosities, rapid and large amplitude flux variability at all frequencies and strong polarization make these sources an optimal laboratory for high energy astrophysics. A most distinctive characteristic of the class is the weakness or absence of spectral lines, that historically hindered the identification of their nature and ever thereafter proved to be a hurdle in the determination of their distance. In this paper we review the main observational facts that contribute to the present basic interpretation of this class of active galaxies. We overview the history of the BL Lac objects research field and their population as it emerged from multi-wavelength surveys. The properties of the flux variability and polarization, compared with those at radio, X-ray and gamma-ray frequencies, are summarized together with the present knowledge of the host galaxies, their environments, and central black hole masses. We focus this review on the optical observations, that played a crucial role in the early phase of BL Lacs studies, and, in spite of extensive radio, X-ray, and recently gamma-ray observations, could represent the future major contribution to the unveiling of the origin of these sources. In particular they could provide a firm conclusion on the long debated issue of the cosmic evolution of this class of active galactic nuclei and on the connection between formation of supermassive black holes and relativistic jets.