Astronomy and Astrophysics, volume 560A, 23-23 (2013/12-1)
Exploring the bulk of the BL Lacertae object population. I. Parsec-scale radio structures.
LIUZZO E., GIROLETTI M., GIOVANNINI G., BOCCARDI B., TAMBURRI S., TAYLOR G.B., CASADIO C., KADLER M., TOSTI G. and MIGNANO A.
Abstract (from CDS):
The advent of Fermi is changing our understanding on the radio and γ-ray emission in active galactic nuclei. Unlike pre-Fermi ideas, BL Lac objects are found to be the most abundant emitters in the γ-ray band. However, since they are relatively weak radio sources, most of their parsec-scale structure and their multifrequency properties are poorly understood and/or have not been investigated in a systematic fashion. Our main goal is to analyze the radio and γ-ray emission properties of a sample of 42 BL Lacs selected, for the first time in the literature, with no constraint on their radio and γ-ray emission. Thanks to new Very Long Baseline Array observations at 8 and 15GHz for the whole sample, we present fundamental parameters here such as radio flux densities, spectral index information, and parsec-scale structure. Moreover, we search for γ-ray counterparts using data reported in the Second Catalog of Fermi Gamma-ray sources. Parsec-scale radio emission is observed in the majority of the sources at both frequencies. Gamma-ray counterparts are found for 14/42 sources. The comparison between our results in radio and gamma-ray bands points out the presence of a large number of faint BL Lacs showing ``non-classical'' properties such as low source compactness, core dominance, no gamma-ray emission, and steep radio spectral indexes. A deeper multiwavelength analysis will be needed.
radio continuum: galaxies - galaxies: active - galaxies: jets
VizieR on-line data:
<Available at CDS (J/A+A/560/A23): list.dat maps/*>
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