# Identifying the 3FHL catalog: CTIO results

## TL;DR

This paper reports optical spectroscopic observations of 23 blazars from the 3FHL catalog using CTIO telescopes, classifying them as BL Lacs and providing redshift measurements to improve catalog completeness.

## Contribution

It presents new spectroscopic data for 23 blazars, enhancing the classification and redshift information for the 3FHL catalog, which was previously incomplete.

## Key findings

- All 23 sources classified as BL Lacs.
- Redshift measured for 3 sources.
- Redshift lower limits for 2 sources.

## Abstract

Active galactic Nuclei (AGNs) with their relativistic jets pointed towards the observer, form a subclass of luminous gamma-ray sources commonly known as blazars. The study of blazars is essential to improve our understanding on the AGNs emission mechanisms and evolution, as well as to map 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 {\it Fermi}--LAT Catalog of High-Energy Sources (3FHL) contains $\approx1160$ blazars reported at energies greater than $10$\,GeV. However $\sim$25\% of these sources are unclassified and $\sim$50\% lack of redshift information. To increase the spectral completeness of the 3FHL catalog, we are working on an optical spectroscopic follow up campaign using 4--m and 8--m telescopes. In this paper, we present the results of the second part of this campaign, where we observed 23 blazars using the 4\,$m$ telescope at CTIO in Chile. We report all the 23 sources to be classified as BL Lacs, a confirmed redshift measurement for 3 sources, a redshift lower limit for 2 sources and a tentative redshift measurement for 3 sources.