On the Redshift of TeV BL Lac Objects

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, aiming to determine or constrain their redshift. This is of fundamental importance for the interpretation of their emission model...

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Bibliographic Details
Published in:The Astrophysical journal 2017-03, Vol.837 (2), p.144
Main Authors: Paiano, Simona, Landoni, Marco, Falomo, Renato, Treves, Aldo, Scarpa, Riccardo, Righi, Chiara
Format: Article
Language:English
Subjects:
ABSORPTION
Astrophysics
ASTROPHYSICS, COSMOLOGY AND ASTRONOMY
Background noise
BL LACERTAE OBJECTS
BL Lacertae objects: general
EMISSION
Emission analysis
GALAXIES
galaxies: distances and redshifts
GAMMA RADIATION
gamma rays: galaxies
INTERACTIONS
Object recognition
Optical communication
PHOTONS
Population studies
QUASARS
quasars: absorption lines
quasars: emission lines
RED SHIFT
SIGNAL-TO-NOISE RATIO
SPECTRA
Spectroscopy
TEV RANGE
VISIBLE RADIATION
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Summary: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, aiming to determine or constrain their redshift. This is of fundamental importance for the interpretation of their emission models and for population studies and is also mandatory for studying the interaction of high-energy photons with the extragalactic background light using TeV sources. Optical spectra with high signal-to-noise ratios in the range 4250-10000 Å were obtained to search for faint emission or absorption lines from both the host galaxy and 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 three other 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.
ISSN:0004-637X
1538-4357
DOI:10.3847/1538-4357/837/2/144