Galaxy-group-associated distances to Very High Energy gamma-ray emitting BL Lacs KUV 00311-1938 and S2 0109+22

TL;DR

This paper estimates the redshifts of two challenging BL Lac objects emitting very high energy gamma rays by combining spectroscopic and photometric methods, aiding understanding of their extragalactic nature.

Contribution

It provides tentative redshift measurements for two VHE gamma-ray emitting BL Lacs using combined spectroscopic and photometric techniques, addressing previous difficulties in redshift determination.

Findings

KUV 00311-1938 has a tentative redshift of z=0.634.

S2 0109+22 has a likely redshift of z=0.49.

Redshift estimates help in understanding VHE gamma-ray sources.

Abstract

Blazars constitute the most numerous source class in the known extragalactic population of very high energy (VHE) gamma-ray sources. However, determining their redshifts is often challenging due to weak or non-existent emission lines in their spectra. This study focuses on two BL Lacs, KUV 00311-1938 and S2 0109+22, where previous attempts at redshift determination have faced difficulties. By combining spectroscopic observations with photometric redshift estimates, we tentatively assign a redshift of z = 0.634 to KUV 00311-1938 and a likely redshift of z = 0.49 to S2 0109+22. Establishing redshift estimates for high-redshift blazars is crucial for understanding extragalactic VHE gamma-ray sources and their interactions with the surrounding universe.