Astronomy & Astrophysics
Context.Observations of the γ -ray sky with Fermi led to signiﬁcant advances towards understanding blazars, the most extreme classof Active Galactic Nuclei. A large fraction of the population detected by Fermi is formed by BL Lacertae (BL Lac) objects, whosesample has always suﬀ ered from a severe redshift incompleteness due to the quasi-featureless optical spectra.Aims.Our goal is to provide a signiﬁcant increase of the number of conﬁrmed high-redshift BL Lac objects contained in the 2 LACFermi/LAT cataloge.Methods.For 103 Fermi/LAT blazars, photometric redshifts using spectral energy distribution ﬁtting have been obtained. The pho-tometry includes 13 broad-band ﬁlters from the far ultraviolet to the near-IR observed with Swift/UVOT and the multi-channel imagerGROND at the MPG/ESO 2.2m telescope. Data have been taken quasi-simultaneously and the remaining source-intrinsic variabilityhas been corrected for. Results.We release the UV-to-near-IR 13-band photometry for all 103 sources and provide redshift constraints for 75 sources withoutpreviously known redshift. Out of those, eight have reliable photometric redshifts at z >1. 3, while for the other 67 sources we pro-vide upper limits. Six of the former eight are BL Lac objects, which quadruples the sample of conﬁrmed high-redshift BL Lac. Thisincludes three sources with redshifts higher than the previous record for BL Lac, including CRATES J0402-2615, with the best-ﬁtsolution at z ≈ 1. 9.
Please use publisher's recommended citation.