Study of radio spectra and variability of GPS sources

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The results of long-term monitoring of Gigahertz-Peaked Spectrum sources were found the statistically significant differences (0.05 significance level) in the high-frequency spectral index distribution between subgroups of galaxies and quasars. For galaxies the average spectral index of the optically thin part is equal to -0.93 (0.07), which is considerably less than for quasars -0.70 (0.04); the difference is about 0.23. This can mean that the electron energy distribution for GPS galaxies is steeper than for GPS quasars. In this distribution the mean value of γ index of electron energy spectrum dN(E)=kE^-γdE is 0.46 larger for galaxies (i.e. their energy spectra are steeper) than for quasars. Within the framework of a common model of GPS sources, this fact can be interpreted in the following ways: a) the observed sample of galaxies (their proper age) is older than the quasar sample (the proper age of quasars); the steepening of their energy spectra is related to additional (in comparison to quasars) age losses of energy for radiation [Kardashev 1962]; b) the proper ages of quasar and galaxy samples are approximately identical, but the observed difference in γ is related to the fact that the galaxies in the observed sample were born later than quasars at small red shift z, i.e. there is a cosmological difference in electron energy spectra.
It is precisely defined two areas with narrower spectra: z ≥ 1.7 (FWHM ≤ 1) and 0.02 ≤ z ≤ 0.7 (the narrowest spectra FWHM~0.9). The first area corresponds to GPS-quasars that have statistically larger value of redfhift, second area corresponds to GPS-galaxies. The result corresponds to the assumption by O'Dea (1990) found that about half of all ultra-high-z quasars are GPS sources and about half of all GPS quasars are at ultra-high-z. This may be an indication that a different physical mechanism may play an important role in forming spectral shape in GPS galaxies and quasars.
1. Mingaliev M.G., Sotnikova, Yu.V., Larionov M.G., Erkenov A.K., GPS Source Candidates in the Circumpolar Region of the Northern Sky, Astronomical Journal, Volume 88, no.1,. 1-7 (2011).
2. Mingaliev M.G., Sotnikova Yu.V., Torniainen I., Tornikoski M., Udovitsky R.Yu., Multifrequency study of GHz-peaked spectrum sources and candidates with RATAN-600, A&A in preparation.

Contact - Sotnikova Yu.V.

Fig.1. The relation "redshift-peak frequency-FWHM" for sources with FWHM≤1.3. The limit of value 1.3 corresponds to sources with inexact convex spectra shape (undetermined spectral shape due to uncertain flux densities or limited frequency range).