DOI

https://doi.org/10.48717/25bj-c523

Project

EG102

Title

e-EVN: eg102a, es088a, rsd04

Abstract

Volonteri et al. (2011) found that the number of radio-loud quasars above redshift 4 calculated from the luminosity function (based upon Swift/BAT observations) is much smaller than the number derived from the known high-redshift beamed sources, blazars. To explain the missing misaligned (non-beamed) population of high-redshift sources they proposed three explanations: (i) heavy optical obscuration of host galaxies, (ii) a lower value of the jet bulk Lorentz factor at early cosmological epochs, and (iii) substantial dimming of radio lobes. Our previous EVN observations of different samples of high-redshift radio sources also indicate the overabudance of blazar sources, however among the claimed blazars several showed steep spectra and double morphology on ~arcsec scale. The proposed observations will increase the number of VLBI-imaged high-redshift radio-loud sources by approx. 30%, thus extending the experimental data set for disentangling potential evolutionary and observational selection effects in radio-loud quasars. The proposed observations will allow us to strengthen arguments for one or another possible explanation of the apparent inconsistency in the abundance of high-redshift blazars and obtain the first epoch images for potential future studies of proper motion at the milliarcsecond scale for cosmological purposes.