Clues on Blazars Phenomenology from the FIRST Flat Spectrum Sample

Abstract

We highlight some results of our work on the FIRST Flat Spectrum Sample (FFSS) of blazars, in particular concerning the relationship between their luminosity and Spectral Energy Distribution (SED), including preliminary results on the power of the emission of their Broad Line Region (BLR). The current analysis shows that within the FFSS, which captures at once a broad range of blazar phenomenology, the SED-power correlation which constituted the observational basis of the blazar sequence hypothesis seems to be present. We also find that FFSS BL Lac and FSRQ sources, despite having been selected together, tend to stay separate with respect to several properties, such as SED type and luminosities (e.g. radio, γ-ray, BLR). The BLR analysis suggests that in BL Lac objects the BLR is indeed under-luminous compared with FSRQ. This in turn suggests that ratio between thermal and non-thermal emission in the two classes of objects is different. Finally, we discuss some clues emerging from the study of the sample of blazars detected at GeV γ-rays by Fermi/LAT, focusing again on the question of power of SED properties.