https://doi.org/10.1140/epjc/s10052-018-6197-y
Regular Article - Theoretical Physics
Cosmological investigation of multi-frequency VLBI observations of ultra-compact structure in 
radio quasars
1
Department of Astronomy, Beijing Normal University, Beijing, 100875, China
2
Department of Astrophysics and Cosmology, Institute of Physics, University of Silesia, Uniwersytecka 4, 40-007, Katowice, Poland
3
Department of Physics, College of Sciences, Northeastern University, Shenyang, 110004, China
4
College of Science, Chongqing University of Posts and Telecommunications, Chongqing, 400065, China
5
School of Physics and Technology, Wuhan University, Wuhan, 430072, China
* e-mail: zhuzh@bnu.edu.cn
Received:
20
May
2018
Accepted:
28
August
2018
Published online:
18
September
2018
In this paper, we use multi-frequency angular size measurements of 58 intermediate-luminosity quasars reaching the redshifts and demonstrate that they can be used as standard rulers for cosmological inference. Our results indicate that, for the majority of radio-sources in our sample their angular sizes are inversely proportional to the observing frequency. From the physical point of view it means that opacity of the jet is governed by pure synchrotron self-absorption, i.e. external absorption does not play any significant role in the observed angular sizes at least up to 43 GHz. Therefore, we use the value of the intrinsic metric size of compact milliarcsecond radio quasars derived in a cosmology independent manner from survey conducted at 2 GHz and rescale it properly according to predictions of the conical jet model. This approach turns out to work well and produce quite stringent constraints on the matter density parameter 
in the flat 
CDM model and Dvali–Gabadadze–Porrati braneworld model. The results presented in this paper pave the way for the follow up engaging multi-frequency VLBI observations of more compact radio quasars with higher sensitivity and angular resolution.
© The Author(s), 2018
