Abstract
AbstractAre the FRI and FRII radio galaxies representative of the radio‐loud (RL) AGN population in the local Universe? Recent studies on the local low‐luminosity radio sources cast lights on an emerging population of compact radio galaxies which lack extended radio emission. In a pilot JVLA project, we study the high‐resolution images of a small but representative sample of this population. The radio maps reveal compact unresolved or slightly resolved radio structures on a scale of 1–3 kpc. We find that these RL AGN live in red massive early‐type galaxies, with large black hole masses (≳108 M⊙), and spectroscopically classified as Low Excitation Galaxies, all characteristics typical of FRI radio galaxies which they also share the same nuclear luminosity with. However, they are more core dominated (by a factor of ∼30) than FRIs and show a clear deficit of extended radio emission. We call these sources “FR0” to emphasize their lack of prominent extended radio emission. A posteriori, other compact radio sources found in the literature fulfill the requirements for a FR0 classification. Hence, the emerging FR0 population appears to be the dominant radio class of the local Universe. Considering their properties we speculate on their possible origins and the possible cosmological scenarios they imply. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Highlights
Classical radio catalogs (e.g. 3C, 2Jy...) are set at low radio frequencies and limited by high flux density
A high core dominance is generally interpreted as evidence of Doppler boosting in a radio source oriented at a small angle with respect to the line of sight
The correlation found with the core radio power and emission line luminosity indicates that this is a genuine deficit of extended radio emission and that no geometric effect is present
Summary
Classical radio catalogs (e.g. 3C, 2Jy...) are set at low radio frequencies and limited by high flux density These selection criteria favor the inclusions of extended steep spectrum sources, Fanaroff-Riley classes (FR I and FR II), where the core emission contributes ∼1% of their total emission and their sizes are of tens or hundreds of kpc (e.g Morganti et al 1997). We investigate the properties of the local RL AGN population, selected by Best et al (2005) (hereafter B05), a sample of RGs by cross-correlating the SDSS (DR2), NVSS, and FIRST datasets. This sample is highly (95%) complete down to the flux threshold of 5 mJy and provides a very good representation of RGs in the local Universe, up to a redshift of 0.3, covering the range 1038−42 erg s−1 in
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