Astronomy and Astrophysics – Astrophysics
Scientific paper
2001-10-15
Astronomy and Astrophysics
Astrophysics
Accepted for publication in Part 1 of The Astrophysical Journal
Scientific paper
10.1086/338073
We study the cosmological evolution of BL Lac objects by applying the Ve/Va analysis to a new sample of 55 objects presented for the first time in this paper. This sample has been selected from the 239 sources with the brightest X-ray flux (>4X10^-13 erg s^-1 cm^-2) and relatively bright optical counterpart (B<20.5) among the ~1600 objects included in the REX survey. The uniform distribution of the Ve/Va values found in the sample suggests that BL Lac objects are not affected by a strong cosmological evolution in contrast with the behavior observed in the emission line AGNs. The Ve/Va analysis applied to the subsample of the High energy peaked BL Lacs (HBL) does not reveal a significant departure from a uniform distribution. This result suggests either that the cosmological evolution is less extreme than that previously found in other samples or that it is carried out only by a minority of objects, namely by the most extreme HBLs.
Caccianiga Alessandro
Ceca Roberto Della
Gioia Isabella Maria
Maccacaro Tomasso
Wolter Anna
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