Journal Article

Multifrequency spectral analysis of extragalactic radio sources in the 33-GHz VSA catalogue: sources with flattening and upturn spectrum

M. Tucci, J. A. Rubiño-Martin, R. Rebolo, R. Genova-Santos, R. A. Watson, R. A. Battye, K. A. Cleary, R. D. Davies, R. J. Davis, K. Grainge, M. Hobson, R. D. E. Saunders, A. Scaife and P. F. Scott

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 386, issue 3, pages 1729-1738
Published in print May 2008 | ISSN: 0035-8711
Published online April 2008 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2008.13161.x
Multifrequency spectral analysis of extragalactic radio sources in the 33-GHz VSA catalogue: sources with flattening and upturn spectrum

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We present an analysis of the spectral properties of the extragalactic radio sources in the nearly complete Very Small Array (VSA) sample at 33 GHz. Data from different surveys are used to study source spectra between 1.4 and 33 GHz. We find that, in general, spectra cannot be well described by a single power law in the range of frequencies considered. In particular, most of the VSA sources that are steep between 1.4 and 5 GHz, show a spectral flattening at ν > 5 GHz. We identify 20 objects (19 per cent of the sample) clearly characterized by an upturn spectrum, i.e. a spectrum falling at low frequencies (ν≲ 5 GHz) and inverted at higher frequencies. Spectra with high-frequency flattening or upturn shape are supposed to occur when the emission from the active galactic nucleus (AGN) compact core begins to dominate over the component from extended lobes. This picture fits well with the AGN unified scheme, for objects observed at intermediate viewing angles of the AGN jet. Finally, we discuss implications that this class of sources can have on future cosmic microwave background observations at high resolution.

Keywords: galaxies: active; quasars: general; cosmic microwave background; radio continuum: galaxies

Journal Article.  8403 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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