Radio continuum spectra of gigahertz-peaked spectrum galaxies

Abstract

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.

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

“…Thus, as a result of monitoring, we have formed a list of 36 (29%) GPS candidates. This agrees well with previous results (Torniainen et al 2005(Torniainen et al , 2007Tornikoski et al 2009). Obviously the original samples are highly contaminated.…”

“…Variability studies of GPS sources and candidates also indicate that GPS galaxies are less variable than quasar-type GPS sources (e.g. 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).…”

NH‐NHI correlation in gigahertz‐peaked‐spectrum galaxies

“…This sample is composed of 21 sources, belonging to at least one of the following GPS samples: Stanghellini et al (1998), Snellen et al (1998), Torniainen et al (2007), and Vermeulen et al (2003). All of these sources were also classified as CSOs.…”

Radio and spectroscopic properties of miniature radio galaxies: revealing the bulk of the radio-loud AGN population

“…We selected the sources with the highest values of P c from Giovannini et al (1988) setting an arbitrary threshold at P c > ∼ 0.1, 2 yielding 11 objects. B2 0648+27 was later resolved into a compact (∼1 ) steep spectrum (CSS) double (Morganti et al 2003), while B2 1144+35B is a Gigahertz Peaked Source (GPS, Torniainen et al 2007) with a peculiar radio-morphology (Giovannini et al 2007); these objects will not be further considered here. One of them (B2 1217+29) is instead already included in our CoreG sample (as UGC 7386).…”