Open AccessThe BeppoSAX High Energy Large Area Survey (HELLAS) – VI. The radio properties
Author(s) -
Ciliegi P.,
Vignali C.,
Comastri A.,
Fiore F.,
La Franca F.,
Perola G. C.
Publication year - 2003
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1046/j.1365-8711.2003.06573.x
Subject(s) - physics , astrophysics , active galactic nucleus , spectral index , radio galaxy , x shaped radio galaxy , galaxy , astronomy , radio spectrum , quiet , spectral line
We present results of a complete radio follow‐up obtained with the VLA and ATCA radio telescopes down to a 6‐cm flux limit of about 0.3 mJy (3σ) of all the 147 X‐ray sources detected in the BeppoSAX HELLAS survey. We found 53 X‐ray/radio likely associations, corresponding to about one‐third of the X‐ray sample. Using the two‐point spectral index α ro = 0.35 we divided all the HELLAS X‐ray sources into radio‐quiet and radio‐loud. We have 26 sources classified as radio‐loud objects, corresponding to ∼18 per cent of the HELLAS sample. In agreement with previous results, the identified radio‐loud sources are associated mainly with Type 1 active galactic nuclei (AGNs) with L 5–10 keV ≳ 10 44 erg s −1 , while all the identified Type 2 AGNs and emission‐line galaxies are radio‐quiet objects with L 5–10 keV ≲ 10 44 erg s −1 . The analysis of the radio spectral index suggests that Type 1 AGNs have a mean radio spectral index (〈α AGN1 〉= 0.25 ± 0.1) flatter than Type 2 AGNs and emission‐line galaxies (〈α AGN2 〉= 0.69 ± 0.11) . This result is in agreement with the idea that the core‐dominated radio emission from Type 1 AGNs is self‐absorbed, while in Type 2 AGNs and emission‐line galaxies the radio emission takes place on larger physical scale, without self‐absorption.