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arXiv · 2608.14412

Optical Spectroscopy of TeV-emitting BL Lac Candidates

Cassidy Metzger·Ryan C. Hickox·John R. Thorstensen
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Abstract

TeV-emitting BL Lacertae (BL Lac) blazars have important implications for the study of jet phenomenology, particle acceleration, and ultra high-energy cosmic ray production. They also allow for indirect studies of the extragalactic background light, cosmic magnetic fields, and axion-like particles. The upcoming Cherenkov Telescope Array (CTA), a ground-based gamma-ray observatory, will expand the observed TeV-emitting BL Lac population and enhance the aforementioned fields of study. However, reliable redshifts are crucial for planning and interpreting observations with CTA and only about 50% of gamma-ray BL Lacs have spectroscopic redshifts. We performed medium resolution optical spectroscopy of 16 TeV-emitting BL Lac candidates with the SALT and MDM telescopes. We measured spectroscopic redshifts for the full sample, ranging from 0.059 to 0.4, including 5 new spectroscopic redshift measurements.

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Cassidy Metzger, Ryan C. Hickox, John R. Thorstensen. 2026-08-14. Optical Spectroscopy of TeV-emitting BL Lac Candidates. https://arxiv.org/abs/2608.14412

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