Exploring the properties of milliarcsecond radio sources
Abstract
Cosmological applications of the "redshift - angular size" test require knowledge of the linear size of the "standard rod" used. In this paper, we study the properties of a large sample of 140 milliarcsecond compact radio sources with flux densities measured at 6 cm and 20 cm, compiled by Gurvits et al.(1999). Using the best-fitted cosmological parameters given by Planck/WMAP9 observations, we investigate the characteristic length lm as well as its dependence on the source luminosity L and redshift lm=l Lβ (1+z)n. For the full sample, measurements of the angular size θ provide a tight constraint on the linear size parameters. We find that cosmological evolution of the linear size is small (|n| 10-2) and consistent with previous analysis. However, a substantial evolution of linear sizes with luminosity is still required (β 0.17). Furthermore, similar analysis done on sub-samples defined by different source optical counterparts and different redshift ranges, seems to support the scheme of treating radio galaxies and quasars with distinct strategies. Finally, a cosmological-model-independent method is discussed to probe the properties of angular size of milliarcsecond radio quasars. Using the corrected redshift - angular size relation for quasar sample, we obtained a value of the matter density parameter, m=0.292+0.065-0.090, in the spatially flat cosmology.