NDLI: The BL-Lacertae gamma-ray blazar PKS 1424+240 associated with a group of galaxies at z = 0.6010

Content Provider	EDP Sciences
Author	A. C. Rovero H. Muriel C. Donzelli A. Pichel
Abstract	Context. PKS 1424+240 is a BL-Lac blazar with unknown redshift that was detected at high-energy gamma rays by Fermi-LAT with a hard spectrum. At very high energy (VHE), it was first detected by VERITAS and later confirmed by MAGIC. Its spectral energy distribution is highly attenuated at VHE gamma rays, which is coherent with distant sources. Several estimations enabled the redshift to be constrained to the range 0.6 <z< 1.3. These results place PKS 1424+240 in the very interesting condition of being probably the most distant blazar that has been detected at VHE. The ambiguity in the redshift is still large enough to prevent precise studies of the extragalatic background light and the intrinsic blazar spectrum.Aims. Given the difficulty of measuring spectroscopic redshifts for BL-Lac objects directly, we aim to establish a reliable redshift value for this blazar by finding its host group of galaxies.Methods. Elliptical galaxies are associated with groups, and BL-Lac objects are typically hosted by them, so we decided to search for the host group of the blazar. For this, we performed optical spectroscopic observations of thirty objects in the field of view of PKS 1424+240 using the Gemini Multi-Object Spectrograph. After analysing the data for groups, we evaluated the probability of finding groups of galaxies by chance around the position of PKS 1424+240, using a deep catalogue of groups. We also used photometric data from the SDSS catalogue to analyse the red sequence of the proposed blazar host groupResults. We found a new group of galaxies with eight members at z = 0.6010 ± 0.003, a virial radius of R_{vir_{= 1.53 Mpc, and a velocity dispersion of σ_{v_{= 813 ± 187 km s^{-1^{. The photometric study indicates that more members are probably populating this previously uncatalogued group of galaxies. The probability of PKS 1424+240 being a member of this group was found to be ≳98%.Conclusions. The new group of galaxies found at z = 0.6010 ± 0.003 is very likely hosting PKS 1424+240.}}}}}}
Page Count	6
File Format	HTM / HTML PDF
ISSN	00046361
Alternate Webpage(s)	https://www.aanda.org/articles/aa/abs/2016/05/aa27778-15/aa27778-15.html
e-ISSN	14320746
Journal	Astronomy & Astrophysics
Volume Number	589
DOI	10.1051/0004-6361/201527778
Language	English
Publisher	EDP Sciences
Publisher Date	2016-05-01
Access Restriction	Open
Rights Holder	© ESO, 2016
Subject Keyword	BL Lacertae objects: individual: PKS 1424+240 galaxies: distances and redshifts galaxies: groups: general BL Lacertae objects: individual: PKS 1424+240 / galaxies: distances and redshifts / galaxies: groups: general
Content Type	Text
Resource Type	Article
Subject	Astronomy and Astrophysics Space and Planetary Science

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