%0 Journal Article
%A Paliya, Vaidehi S.
%A Domínguez, A.
%A Cabello González, Cristina
%A Cardiel López, Nicolás
%A Gallego Maestro, Jesús
%A Siana, Brian
%A Ajello, M.
%A Hartmann, D.
%A Gil De Paz, Armando
%A Stalin, C.S.
%T The first gamma-ray emitting BL lacertae object at the cosmic dawn
%D 2020
%@ 2041-8205
%U https://hdl.handle.net/20.500.14352/7567
%X One of the major challenges in studying the cosmic evolution of relativistic jets is the identification of the high-redshift (z > 3) BL Lacertae objects, a class of jetted active galactic nuclei characterized by their quasi-featureless optical spectra. Here we report the identification of the first γ-ray emitting BL Lac object, 4FGL J1219.0+3653 (J1219), beyond z = 3, i.e., within the first two billion years of the age of the Universe. The optical and near-infrared spectra of J1219 taken from 10.4 m Gran Telescopio Canarias exhibit no emission lines down to an equivalent width of ∼3.5 Å supporting its BL Lac nature. The detection of a strong Lyman- α break at ∼5570 Å, on the other hand, confirms that J2119 is indeed a high-redshift ( z ∼ 3.59) quasar. Based on the prediction of a recent BL Lac evolution model, J1219 is one of the only two such objects expected to be present within the comoving volume at z = 3.5. Future identifications of more z > 3 γ-ray emitting BL Lac sources, therefore, will be crucial to verify the theories of their cosmic evolution.
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