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In this paper, we present a new compiled milliarcsecond compact radio dataset of 120 intermediate-luminosity quasars in the redshift range $0.46< z<2.76$. These quasars show negligible dependence on redshifts and intrinsicluminosity, and thus represents, in the standard model of cosmology, a fixedcomoving-length of standard ruler. We implement a new cosmology-independenttechnique to calibrate the linear size of of this standard ruler as $l_m=11.03\pm0.25$ pc, which is the typical radius at which AGN jets become opaqueat the observed frequency $\nu\sim 2$ GHz. In the framework of flat$\Lambda$CDM model, we find a high value of the matter density parameter,$\Omega_m=0.322^{+0.244}_{-0.141}$, and a low value of the Hubble constant,$H_0=67.6^{+7.8}_{-7.4}\; \rm{kms}^{-1}\rm{Mpc}^{-1}$, which is in excellentagreement with the CMB anisotropy measurements by \textit{Planck}. We obtain${\Omega_m}=0.309^{+0.215}_{-0.151}$, $w=-0.970^{+0.500}_{-1.730}$ at 68.3% CLfor the constant $w$ of a dynamical dark-energy model, which demonstrates nosignificant deviation from the concordance $\Lambda$CDM model. Consistentfitting results are also obtained for other cosmological models explaining thecosmic acceleration, like Ricci dark energy (RDE) or Dvali-Gabadadze-Porrati(DGP) brane-world scenario. While no significant change in $w$ with redshift isdetected, there is still considerable room for evolution in $w$ and thetransition redshift at which $w$ departing from -1 is located at $z\sim 2.0$.Our results demonstrate that the method extensively investigated in our work onobservational radio quasar data can be used to effectively derive cosmologicalinformation. Finally, we find the combination of high-redshift quasars andlow-redshift clusters may provide an important source of angular diameterdistances, considering the redshift coverage of these two astrophysical probes.

astronomy and astrophysics

Ultra-compact structure in intermediate-luminosity radio quasars:  building a sample of standard cosmological rulers and improving the dark  energy constraints up to $z\sim 3$