Applications of statistical techniques to the angular size - Flux density relation for extragalactic radio sources

Abstract

The data on the angular sizes and flux densities of extragalactic radio sources from the 3CR and the Ooty surveys is subjected to two independent statistical tests. The purpose of these tests is to investigate whether the data necessitates the conclusion that the properties of the radio sources evolve with the epoch of the Universe. The first test uses a minimum χ² technique to compare the observed (θ,S) plot with a theroretical one. In the second, the so-called median test, the two distributions are compared in a narrow range of flux densities. It is shown that the present scatter in this data is such that within the usual confidence limits it is not possible to distinguish between a number of evolutionary and non-evolutionary models. In fact, a non-evolutionary model in which there is a reasonable correlation between the linear size and power of radio sources passes both the tests. It is shown how future improved data on (θ,S) may be able to distinguish between the evolutionary and non-evolutionary models.