Identifying the 3FHL catalog: V. Results of the CTIO-COSMOS optical spectroscopy campaign 2019

TL;DR

This paper reports optical spectroscopic observations of 28 blazars from the 3FHL catalog, classifying most as BL Lacs or FSRQs and measuring redshifts, aiding in understanding blazar emission and the extragalactic background light.

Contribution

It provides new classifications and redshift measurements for 28 blazars, advancing the completeness of the 3FHL blazar sample.

Findings

25 BL Lacs and 3 FSRQs identified

Redshifts or limits measured for 16 blazars

Enhanced understanding of blazar population above 10 GeV

Abstract

As a follow-up of the optical spectroscopic campaign aimed at achieving completeness in the Third Catalog of Hard Fermi-LAT Sources (3FHL), we present here the results of a sample of 28 blazars of uncertain type observed using the 4m telescope at Cerro Tololo Inter-American Observatory (CTIO) in Chile. Out of these 28 sources, we find that 25 are BL Lacertae objects (BL Lacs) and 3 are Flat Spectrum Radio Quasars (FSRQs). We measure redshifts or lower limits for 16 of these blazars, whereas it is observed that the 12 remaining blazars have featureless optical spectra. These results are part of a more extended campaign of optical spectroscopy follow-up of 3FHL blazars, where until now 51 blazars of uncertain type have been classified into BL Lac and FSRQ categories. Further, this campaign has resulted in redshift measurements and lower limits for 15 of these sources. Our results contribute towards attaining a complete sample of blazars above 10 GeV, which then will be crucial in extending our knowledge on blazar emission mechanisms and the extragalactic background light.