Blazar candidates beyond redshift 4 observed by Swift

We have selected SDSS J222032.50+002537.5 and SDSS J142048.01+120545.9 as best blazar candidates out of a complete sample of extremely radio-loud quasars at z > 4, with highly massive black holes. We observed them and a third serendipitous candidate with similar features(PMNJ2134-0419) in theX-rays with the Swift/XRTtelescope, to confirm their blazar nature. We observed strong and hard X-ray fluxes (i.e. αX≲ 0.6, where F(v) ∝ v-αX in the 0.3-10 keV observed energy range, ~1-40 keV rest frame) in all three cases. This allowed us to classify our candidates as real blazars, being characterized by large Lorentz factors (~13) and very small viewing angles (~3°). All three sources have black hole masses exceeding 109M⊙ and their classification provides intriguing constraints on supermassive black hole formation and evolution models. We confirm our earlier suggestion that there are different formation epochs of extremely massive black holes hosted in jetted (z ~ 4) and non-jetted systems (z ~ 2.5).