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