Statistical redshift of the very-high-energy blazar S5 0716+714

¹ Instituto de Astronomía y Física del Espacio (IAFE (CONICET-UBA)), Av. Int. Guiraldes 2620, C1428BNB CABA, Argentina
e-mail: anapichel@iafe.uba.ar
² Instituto de Investigaciones en Astronomía Teórica y Experimental (IATE (CONICET-UNC)), Laprida 854, X5000BGR Córdoba, Argentina
³ Observatorio Astronómico de Córdoba, Universidad Nacional de Córdoba, Córdoba, Argentina
⁴ Instituto Nacional de Astrofísica, Optica y Electrónica, Tonantzintla, 72840 Puebla, Mexico
⁵ Instituto de Astrofísica de Canarias, C/ Vía Láctea s/n, 38205 La Laguna, Spain
⁶ Departamento de Astrofísica, Universidad de La Laguna, 38206 La Laguna, Spain
⁷ Institute of Astronomy, University of Cambridge, Cambridge CB3 0HA, UK

Received: 29 November 2022
Accepted: 25 September 2023

Abstract

Context. Blazars are the most numerous class of very-high-energy (VHE; E > 100 GeV) gamma-ray emitters. At present, measured redshifts are available only for about 80% of the VHE gamma-ray sources; this is mainly due to the difficulty in measuring reliable redshifts from their nearly featureless continuum optical spectra.

Aims. As the VHE sky is still vastly unexplored, VHE blazars are unique objects. High-energy spectra from blazars are used for extragalactic background light studies, to investigate topics related to cosmology or fundamental physics, and to find the source luminosity. This allows one to study the properties of the host galaxy, its black hole, and the gamma-ray emission mechanisms. All of these studies require suitable estimations of the blazar distance, which has motivated the use of novel approaches when measuring the redshift of faint optical lines in their spectra is very uncertain.

Methods. We present the new optical spectroscopic observations of S5 0716+714 and its environment taken on December 20, 2019, with the Gemini GMOS North telescope.

Results. We do not find any absorption lines in the blazar spectrum; however, we were able to get the redshifts of 21 other galaxies in the field, 15 of which form a group at z = 0.2304 ± 0.0013. Performing a population study of galaxies, we found that S5 0716+714 belongs to this group with a probability > 99%.