Exploring the bulk of the BL Lacertae object population: I. Parsec-scale radio structures

DOI: 
10.1051/0004-6361/201322144
Publication date: 
01/12/2013
Main author: 
Liuzzo E.
IAA authors: 
Casadio C.
Authors: 
Liuzzo E., Giroletti M., Giovannini G., Boccardi B., Tamburri S., Taylor G.B., Casadio C., Kadler M., Tosti G., Mignano A.
Journal: 
Astronomy and Astrophysics
Publication type: 
Article
Volume: 
560
Pages: 
Number: 
A23
Abstract: 
Context. 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. Aims. 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. Methods. Thanks to new Very Long Baseline Array observations at 8 and 15 GHz 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. Results. Parsec-scale radio emission is observed in the majority of the sources at both frequencies. Gamma-ray counterparts are found for 14/42 sources. Conclusions. 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. © ESO, 2013.
Database: 
WOK
SCOPUS
ADS
URL: 
https://ui.adsabs.harvard.edu/#abs/2013A&A...560A..23L/abstract
ADS Bibcode: 
2013A&A...560A..23L
Keywords: 
Galaxies: active; Galaxies: jets; Radio continuum: galaxies