Identifying the 3FHL catalog: VI. Results of the 2019 Gemini optical spectroscopy campaign

TL;DR

This paper reports optical spectroscopic observations of five blazars from the 3FHL catalog using Gemini-S, classifying them and providing redshift information to improve the catalog's completeness for understanding blazar physics.

Contribution

It presents new optical spectroscopic data for five blazars, increasing the classification and redshift data for the 3FHL catalog, aiding in blazar studies.

Findings

All five sources are classified as BL Lacs.

Redshift lower limits established for two sources.

Featureless spectra obtained for three sources.

Abstract

Active galactic Nuclei (AGNs) with their relativistic jets pointed toward the observer, are a class of luminous gamma-ray sources commonly known as blazars. The study of this source class is essential to unveil the physical processes powering these extreme jets, to understand their cosmic evolution, as well as to indirectly probe the extragalactic background light. To do so, however, one needs to correctly classify and measure a redshift for a large sample of these sources. The Third Fermi-LAT Catalog of High-Energy Sources (3FHL) contains $1212$ blazars detected at energies greater than 10 GeV. However, $\sim$25% of these sources are unclassified and $\sim$56% lack redshift information. To increase the optical completeness of blazars in the 3FHL catalog, we devised an optical spectroscopic follow-up campaign using 4 $m$ and 8 $m$ telescopes. In this paper, we present the results of the last part of this campaign, where we observed 5 blazars using the 8 $m$ Gemini-S telescope in Chile. We report all 5 sources to be classified as BL Lacs, a redshift lower limit for 2 sources, and featureless spectra for the remaining 3 sources. We also performed a one-zone leptonic fit to the two sources with the redshift lower limits.