Arne Rau, P. Schady, J. Greiner, M. Salvato, M. Ajello, E. Bottacini, N. Gehrels, P. M. J. Afonso, J. Elliott, R. Filgas, D. A. Kann, S. Klose, Thomas Kruehler, M. Nardini, A. Nicuesa Guelbenzu, F. Olivares E., A. Rossi, V. Sudilovsky, A. C. Updike, D. H. Hartmann
Observations of the gamma-ray sky with Fermi led to significant advances
towards understanding blazars, the most extreme class of Active Galactic
Nuclei. A large fraction of the population detected by Fermi is formed by BL
Lacertae (BL Lac) objects, whose sample has always suffered from a severe
redshift incompleteness due to the quasi-featureless optical spectra. Our goal
is to provide a significant increase of the number of confirmed high-redshift
BL Lac objects contained in the 2 LAC Fermi/LAT catalog. For 103 Fermi/LAT
blazars, photometric redshifts using spectral energy distribution fitting have
been obtained. The photometry includes 13 broad-band filters from the far
ultraviolet to the near-IR observed with Swift/UVOT and the multi-channel
imager GROND at the MPG/ESO 2.2m telescope. Data have been taken
quasi-simultaneously and the remaining source-intrinsic variability has been
corrected for. We release the UV-to-near-IR 13-band photometry for all 103
sources and provide redshift constraints for 75 sources without previously
known redshift. Out of those, eight have reliable photometric redshifts at
z>1.3, while for the other 67 sources we provide upper limits. Six of the
former eight are BL Lac objects, which quadruples the sample of confirmed
high-redshift BL Lac. This includes three sources with redshifts higher than
the previous record for BL Lac, including CRATES J0402-2615 with the best-fit
solution at z~1.9.
View original:
http://arxiv.org/abs/1112.0025
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