VLBA images of high frequency peakers

Orienti, M.; Dallacasa, D.; Tinti, S.; Stanghellini, C.

doi:10.1051/0004-6361:20054656

Cited by 66 publications

(109 citation statements)

References 30 publications

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“…This has been argued earlier by, among other, Snellen et al (1999) and Stanghellini et al (2001). Recent results by Stanghellini et al (2005) and Orienti et al (2006) support this view. Stanghellini et al (2005) studied extended emission around GPS sources and conclude that, if a GPS quasar exhibits a core-jet or a complex VLBI morphology, it is likely that it represents an intermediately beamed full-size radio source related to common flat-spectrum radio sources.…”

Section: Introductionsupporting

confidence: 64%

“…Thus, it would not be related to truly compact and young/recurrent/frustrated GPS galaxies at all. Orienti et al (2006) studied VLBI images of quasar and galaxy type HFPs, and they confirm that the convex shape of the spectrum originates from mini-lobes and/or hot-spots in galaxy-type sources and from the inner regions near the core and from the origins of the jets in quasar-type sources. Bolton et al (2006) studied the variability of a sample of 9C sources at 1.4 GHz, 4.8 GHz, and 15 GHz, including HFPs and GPS sources.…”

Section: Introductionmentioning

confidence: 80%

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Radio continuum spectra of gigahertz-peaked spectrum galaxies

Torniainen¹,

Tornikoski²,

Lähteenmäki³

et al. 2007

A&A

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Context. Recent studies have shown that a remarkable share of quasars classified in the literature as gigahertz-peaked spectrum (GPS) sources and high frequency peakers (HFPs) are actually flaring flat-spectrum sources or blazars. Thus, at least among the quasar-type samples, genuine GPS sources and HFPs seem to be rare. Aims. We have studied variability and the shape of the radio continuum spectra of a sample of 96 galaxy-type GPS sources and HFPs in order to find out whether there is a similar contamination in the galaxy-type samples. Methods. We collected radio data for the sample from the literature, our long-term monitoring campaigns, and recent observations, and then plotted the radio continuum spectra. We also calculated the peak frequencies, the spectral indices, and the variability indices, and finally classified the sources according to these parameters. Results. About 30% of the galaxies in our sample are clearly GPS sources, for another ∼30% there are not enough data for a solid classification, and the rest are flat-or steep-spectrum sources. Conclusions. The galaxy-type GPS samples seem to be cleaner than the quasar-type, but there is also a remarkable contamination of other source types among the galaxies. However, there may be a strong selection effect, originating from the different selection criteria of the original samples, which must be taken into consideration when comparing the results of this and our previous study. Both simultaneous spectra and long-term monitoring are essential when classifying convex-spectrum sources. However, even monitoring for several years may not reveal the variable nature of a source with a convex radio spectrum.

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Section: Introductionsupporting

confidence: 64%

Section: Introductionmentioning

confidence: 80%

Radio continuum spectra of gigahertz-peaked spectrum galaxies

Torniainen¹,

Tornikoski²,

Lähteenmäki³

et al. 2007

A&A

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“…For example, in the AT20G survey, Murphy et al (2010) found that 21% of sources peak between 5 and 20 GHz, and 14% have a spectrum rising up to 20 GHz (see also Hancock 2009). If we restrict ourselves to the almostcomplete subsample AT20G-d15S100, we find about 22% of sources with α with youth scenario (Dallacasa et al 2000;Stanghellini 2003;Torniainen et al 2005;Tinti et al 2005;Bolton et al 2006;Orienti et al 2006;Planck Collaboration 2011d), but indicative that they are most likely blazars caught in an active state, i.e. when a flaring, strongly self-absorbed synchrotron component dominates the emission spectrum.…”

Section: High-frequency Peaked Spectrum Sourcesmentioning

confidence: 87%

High-frequency predictions for number counts and spectral properties of extragalactic radio sources. New evidence of a break at mm wavelengths in spectra of bright blazar sources

Tucci

Toffolatti

Zotti

et al. 2011

A&A

103

201

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We present models to predict high-frequency counts of extragalactic radio sources using physically grounded recipes to describe the complex spectral behaviour of blazars that dominate the mm-wave counts at bright flux densities. We show that simple power-law spectra are ruled out by high-frequency (ν ≥ 100 GHz) data. These data also strongly constrain models featuring the spectral breaks predicted by classical physical models for the synchrotron emission produced in jets of blazars. A model dealing with blazars as a single population is, at best, only marginally consistent with data coming from current surveys at high radio frequencies. Our most successful model assumes different distributions of break frequencies, ν M , for BL Lacs and flat-spectrum radio quasars (FSRQs). The former objects have substantially higher values of ν M , implying that the synchrotron emission comes from more compact regions; therefore, a substantial increase of the BL Lac fraction at high radio frequencies and at bright flux densities is predicted. Remarkably, our best model is able to give a very good fit to all the observed data on number counts and on distributions of spectral indices of extragalactic radio sources at frequencies above 5 and up to 220 GHz. Predictions for the forthcoming sub-mm blazar counts from Planck, at the highest HFI frequencies, and from Herschel surveys are also presented.

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“…Torniainen et al 2005;Torniainen et al 2007). A clear division between high-frequency peaking (HFP) galaxies and quasars was found by Orienti et al (2006).…”

Section: Discussionmentioning

confidence: 99%

Multifrequency study of GHz-peaked spectrum sources and candidates with the RATAN-600 radio telescope

Мингалиев

Sotnikova

Torniainen

et al. 2012

A&A

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Context. Gigahertz peaked spectrum (GPS) radio sources are a class of extragalactic radio sources characterized by a spectral peak in the gigahertz domain. They are a mixed class of quasars and galaxies. A large proportion of the sources studied in the literature have only few data points in the radio domain, and the determination of variability and shape of the simultaneous spectra is inadequate. Sources currently included in the GPS source lists are very heterogeneous. Aims. We present the observational results from 12 observing campaigns (carried out between 2006 and 2010) at the RATAN-600 radio telescope to obtain the simultaneous radio spectra, which is valuable and necessary to derive genuine GPS sources from flatspectrum radio sources caught in a flaring state when their spectra are temporarily inverted. The sample contains both quasar-and galaxy-type GPS (122 sources) identified in the literature. Methods. The observations were carried out at six frequencies (1.1, 2.3, 4.8, 7.7, 11.2 and 21.7 GHz). The flux densities were measured at several epochs. A six-frequency broadband radio spectrum was obtained by observing simultaneously with an accuracy of up to a minute at 1.4, 2.7, 3.9, 6.25, 13, and 30 cm. Results. The original GPS source samples were highly contaminated. Finally, we selected 29% GPS source candidates within the sample. We found some difference in spectral properties between GPS galaxies and quasars within the sample. The GPS galaxies demonstrate a steeper spectral index in the optically thin part of the spectra. There are only relatively few (17) sources whose radio spectra strictly agree with the spectra of homogeneous self-absorbed synchrotron sources. The narrowest radio spectra are found in both ultra-high-z (z ≥ 1.8) and low-z (0.02 ≤ z ≤ 0.7, FWHM ∼ 0.9) convex spectrum radio sources. The majority of quasars within this sample should be considered as flat-spectrum radio sources with a temporarily inverted spectrum, and not as genuine GPS sources. The number of truly convex-spectrum sources remains low, and the lists of GPS sources should accordingly be revised.

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VLBA images of high frequency peakers

Cited by 66 publications

References 30 publications

Radio continuum spectra of gigahertz-peaked spectrum galaxies

Radio continuum spectra of gigahertz-peaked spectrum galaxies

High-frequency predictions for number counts and spectral properties of extragalactic radio sources. New evidence of a break at mm wavelengths in spectra of bright blazar sources

Multifrequency study of GHz-peaked spectrum sources and candidates with the RATAN-600 radio telescope

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