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The planck-ATCA co-eval observations project: The spectrally selected sample

AuthorsBonaldi, A.; Bonavera, Laura ; Massardi, Marcella; Zotti, G. de
KeywordsRadio continuum: galaxies
Radio continuum: general
Galaxies: active
Issue Date2013
PublisherBlackwell Publishing
CitationMonthly Notices of the Royal Astronomical Society 428(2): 1845-1854 (2013)
AbstractThe Planck AustraliaTelescope Compact Array (Planck-ATCA)Co-evalObservations (PACO) have provided multi-frequency (5-40 GHz) flux density measurements of complete samples of Australia Telescope 20 GHz (AT20G) radio sources at frequencies below and overlapping with Planck frequency bands, almost simultaneously with Planck observations. In this work we analyse the data in total intensity for the spectrally selected PACO sample, a complete sample of 69 sources brighter than S20 GHz = 200 mJy selected from the AT20G survey catalogue to be inverted or upturning between 5 and 20 GHz. We study the spectral behaviour and variability of the sample. We use the variability between AT20G (2004-2007) and PACO (2009-2010) epochs to discriminate between candidate High-Frequency Peakers (HFPs) and candidate blazars. The HFPs picked up by our selection criteria have spectral peaks >10 GHz in the observer frame and turn out to be rare (<0.5 per cent of the S20 GHz ≥ 200 mJy sources), consistent with the short duration of this phase implied by the 'youth' scenario. Most (~ 89 per cent) of blazar candidates have remarkably smooth spectra, well described by a double power law, suggesting that the emission in the PACO frequency range is dominated by a single emitting region. Sources with peaked PACO spectra show a decrease of the peak frequency with time at a mean rate of -3 ± 2 GHz yr-1 on an average time-scale of median τ median = 2.1 ± 0.5 yr (median: τ median = 1.3 yr). The 5-20 GHz spectral indices show a systematic decrease from AT20G to PACO. At higher frequencies spectral indices steepen: the median α40 30 is steeper than the median α20 5 by δα = 0.6. Taking further into account the Wide-field Infrared Survey Explorer data we find that the Spectral Energy Distributions (SEDs), νS(ν), of most of our blazars peak at νSED p < 105 GHz; the median peak wavelength is λSED p ~ 93 μm. Only six have νSED p > 105 GHz.
Publisher version (URL)http://dx.doi.org/10.1093/mnras/sts166
Identifiersdoi: 10.1093/mnras/sts166
issn: 0035-8711
e-issn: 1365-2966
Appears in Collections:(IFCA) Artículos
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