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 (>=4×10-13 ergs s-1 cm-2) and relatively bright optical counterparts (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 active galactic nuclei. The Ve/Va analysis applied to the subsample of the high-energy-peaked BL Lac objects (HBLs) 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 not selected in our sample.
Cosmological Evolution of BL Lac Objects
2002
Abstract
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 (>=4×10-13 ergs s-1 cm-2) and relatively bright optical counterparts (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 active galactic nuclei. The Ve/Va analysis applied to the subsample of the high-energy-peaked BL Lac objects (HBLs) 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 not selected in our sample.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
