The BL-Lac gamma-ray blazar PKS 0447-439 as a probable member of a group of galaxies at z = 0.343

Context. The BL-Lac blazar PKS 0447-439 is one of the brightest HE gamma-ray sources that were first detected by Fermi-LAT. It was also detected by H.E.S.S. at VHE gamma-rays, which allowed constraining the redshift of PKS 0447-439 by considering the attenuation caused by gamma-ray interactions with...

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Detalles Bibliográficos
Publicado: 2015
Materias:
BL Lacertae objects
Distances and redshifts - galaxies
General
Groups
Individual
PKS 0447-439 - galaxies
Galaxies
Signal to noise ratio
Distances and redshifts
Gamma rays
Acceso en línea:https://bibliotecadigital.exactas.uba.ar/collection/paper/document/paper_00046361_v574_n_p_Muriel
http://hdl.handle.net/20.500.12110/paper_00046361_v574_n_p_Muriel
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Biblioteca Digital - Facultad de Ciencias Exactas y Naturales (UBA) de Universidad de Buenos Aires
id paper:paper_00046361_v574_n_p_Muriel
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spelling paper:paper_00046361_v574_n_p_Muriel2023-06-08T14:28:09Z The BL-Lac gamma-ray blazar PKS 0447-439 as a probable member of a group of galaxies at z = 0.343 BL Lacertae objects Distances and redshifts - galaxies General Groups Individual PKS 0447-439 - galaxies Galaxies Signal to noise ratio BL Lacertae objects Distances and redshifts General Groups Individual Gamma rays Context. The BL-Lac blazar PKS 0447-439 is one of the brightest HE gamma-ray sources that were first detected by Fermi-LAT. It was also detected by H.E.S.S. at VHE gamma-rays, which allowed constraining the redshift of PKS 0447-439 by considering the attenuation caused by gamma-ray interactions with ambient photons in the extragalactic background light (EBL). This constraint agreed with color-magnitude and spectroscopic redshift constraints (0.179 < z < 0.56). Recently, however, a much higher redshift was proposed for this blazar (z > 1.2). This value was debated because if true, it would imply either that the relevant absorption processes of gamma-rays are not well understood or that the EBL is dramatically different from what is believed today. This high redshift was not confirmed by three independent new spectroscopic observations at high signal-to-noise ratios. The scenario is clear evidence of the difficulties in estimating the redshift of BL-Lac objects, whose optical spectra are typically featureless. Neither of the estimated redshifts for PKS 0447-439 are confirmed as yet. Aims. Given that BL-Lac are typically hosted by elliptical galaxies, which in turn are associated with groups, we aim to find the host group of galaxies of PKS 0447-439. The ultimate goal is to estimate a redshift for this blazar. Methods. Spectra of twenty-one objects in the field of view of PKS 0447-439 were obtained with the Gemini Multi-Object Spectrograph. Based on the redshifts and coordinates of these galaxies, we searched for groups of galaxies. Using a deep catalog of groups, we studied the probability of finding by chance a group of galaxies in the line of sight of PKS 0447-439. Results. We identified a group of galaxies that was not previously cataloged at z = 0.343 with seven members, a virial radius of 0.42 Mpc, and a velocity dispersion of 622 km s-1.We found that the probability of the host galaxy of PKS 0447-439 to be a member of the new group is >∼97%. Therefore, we propose to adopt z = 0.343 ± 0.002 as the most likely redshift for PKS 0447-439. © ESO 2015. 2015 https://bibliotecadigital.exactas.uba.ar/collection/paper/document/paper_00046361_v574_n_p_Muriel http://hdl.handle.net/20.500.12110/paper_00046361_v574_n_p_Muriel
institution Universidad de Buenos Aires
institution_str I-28
repository_str R-134
collection Biblioteca Digital - Facultad de Ciencias Exactas y Naturales (UBA)
topic BL Lacertae objects
Distances and redshifts - galaxies
General
Groups
Individual
PKS 0447-439 - galaxies
Galaxies
Signal to noise ratio
BL Lacertae objects
Distances and redshifts
General
Groups
Individual
Gamma rays
spellingShingle BL Lacertae objects
Distances and redshifts - galaxies
General
Groups
Individual
PKS 0447-439 - galaxies
Galaxies
Signal to noise ratio
BL Lacertae objects
Distances and redshifts
General
Groups
Individual
Gamma rays
The BL-Lac gamma-ray blazar PKS 0447-439 as a probable member of a group of galaxies at z = 0.343
topic_facet BL Lacertae objects
Distances and redshifts - galaxies
General
Groups
Individual
PKS 0447-439 - galaxies
Galaxies
Signal to noise ratio
BL Lacertae objects
Distances and redshifts
General
Groups
Individual
Gamma rays
description Context. The BL-Lac blazar PKS 0447-439 is one of the brightest HE gamma-ray sources that were first detected by Fermi-LAT. It was also detected by H.E.S.S. at VHE gamma-rays, which allowed constraining the redshift of PKS 0447-439 by considering the attenuation caused by gamma-ray interactions with ambient photons in the extragalactic background light (EBL). This constraint agreed with color-magnitude and spectroscopic redshift constraints (0.179 < z < 0.56). Recently, however, a much higher redshift was proposed for this blazar (z > 1.2). This value was debated because if true, it would imply either that the relevant absorption processes of gamma-rays are not well understood or that the EBL is dramatically different from what is believed today. This high redshift was not confirmed by three independent new spectroscopic observations at high signal-to-noise ratios. The scenario is clear evidence of the difficulties in estimating the redshift of BL-Lac objects, whose optical spectra are typically featureless. Neither of the estimated redshifts for PKS 0447-439 are confirmed as yet. Aims. Given that BL-Lac are typically hosted by elliptical galaxies, which in turn are associated with groups, we aim to find the host group of galaxies of PKS 0447-439. The ultimate goal is to estimate a redshift for this blazar. Methods. Spectra of twenty-one objects in the field of view of PKS 0447-439 were obtained with the Gemini Multi-Object Spectrograph. Based on the redshifts and coordinates of these galaxies, we searched for groups of galaxies. Using a deep catalog of groups, we studied the probability of finding by chance a group of galaxies in the line of sight of PKS 0447-439. Results. We identified a group of galaxies that was not previously cataloged at z = 0.343 with seven members, a virial radius of 0.42 Mpc, and a velocity dispersion of 622 km s-1.We found that the probability of the host galaxy of PKS 0447-439 to be a member of the new group is >∼97%. Therefore, we propose to adopt z = 0.343 ± 0.002 as the most likely redshift for PKS 0447-439. © ESO 2015.
title The BL-Lac gamma-ray blazar PKS 0447-439 as a probable member of a group of galaxies at z = 0.343
title_short The BL-Lac gamma-ray blazar PKS 0447-439 as a probable member of a group of galaxies at z = 0.343
title_full The BL-Lac gamma-ray blazar PKS 0447-439 as a probable member of a group of galaxies at z = 0.343
title_fullStr The BL-Lac gamma-ray blazar PKS 0447-439 as a probable member of a group of galaxies at z = 0.343
title_full_unstemmed The BL-Lac gamma-ray blazar PKS 0447-439 as a probable member of a group of galaxies at z = 0.343
title_sort bl-lac gamma-ray blazar pks 0447-439 as a probable member of a group of galaxies at z = 0.343
publishDate 2015
url https://bibliotecadigital.exactas.uba.ar/collection/paper/document/paper_00046361_v574_n_p_Muriel
http://hdl.handle.net/20.500.12110/paper_00046361_v574_n_p_Muriel
_version_ 1768546048023724032

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