Optical spectroscopic observations of gamma-ray blazar candidates, X: results from the 2018–2019 SOAR and OAN-SPM observations of blazar candidates of uncertain type

The fourth Fermi Large Area Telescope Source Catalog (4FGL) lists over 5000 γ-ray sources with statistical significance above 4 σ. About 23% of the sources listed in this catalog are unidentified/unassociated γ-ray sources while ∼26% of the sources are classified as blazar candidates of uncertain type (BCUs), lacking optical spectroscopic information. To probe the blazar nature of candidate counterparts of UGSs and BCUs, we started our optical spectroscopic follow up campaign in 2012, which up to date account for more than 350 observed sources. In this paper, the tenth of our campaign, we report on the spectroscopic observations of 37 sources, mostly BCUs, whose observations were carried out predominantly at the Observatorio Astronómico Nacional San Pedro Mártir and the Southern Astrophysical Research Observatory between August 2018 and September 2019. We confirm the BL Lac nature of 27 sources and the flat spectrum radio quasar nature of three sources. The remaining ones are classified as six BL Lacs galaxy-dominated and one normal galaxy. We were also able to measure the redshifts for 20 sources, including 10 BL Lacs. As in previous analyses, the largest fraction of BCUs revealed to be BL Lac objects.Fil: de Menezes, Raniere. Universidade de Sao Paulo; Brasil. Università di Torino; ItaliaFil: Amaya Almazán, R. A.. Instituto Nacional de Astrofisica Optica y Electronica; MéxicoFil: Marchesini, Ezequiel Joaquín. Università di Torino; Italia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; ArgentinaFil: Peña Herazo, H. A.. Istituto Nazionale di Astrofisica; Italia. Università di Torino; ItaliaFil: Massaro, F.. Istituto Nazionale di Astrofisica; Italia. Università di Torino; ItaliaFil: Chavushyan, V.. Instituto Nacional de Astrofisica Optica y Electronica; MéxicoFil: Paggi, A.. Istituto Nazionale di Astrofisica; ItaliaFil: Landoni, M.. Osservatorio Astronomico Di Brera; ItaliaFil: Masetti, N.. Inaf Istituto Di Astrofisica Spaziale E Fisica Cosmica, Bologna; Italia. Universidad Andrés Bello; ChileFil: Ricci, F.. Universidad Católica de Chile; ChileFil: D'Abrusco, R.. Harvard-Smithsonian Center for Astrophysics; Estados UnidosFil: La Franca, F.. Università Degli Studi Roma Tre; ItaliaFil: Smith, Howard A.. Harvard-Smithsonian Center for Astrophysics; Estados UnidosFil: Milisavljevic, D.. College Of Science; ItaliaFil: Tosti, G.. Università di Perugia; ItaliaFil: Jiménez Bailón, E.. Universidad Nacional Autónoma de México; MéxicoFil: Cheung, C. C.. Spece Sciences División. Naval Research Laboratory; Estados Unido