Cosmological and kinematical criteria for the ICRF2 sources selection

TL;DR

This paper proposes new cosmological and kinematical criteria for selecting stable extragalactic radio sources to improve the inertial reference frame in astronomy, leading to the identification of 137 suitable sources for the ICRF2 catalogue.

Contribution

It introduces novel source selection criteria based on physical motion models and redshift analysis, enhancing the stability of the celestial reference frame.

Findings

Identified 137 stable sources for ICRF2

Determined optimal redshift range 0.8-3.0 for source stability

Proposed criteria improve inertial frame stability

Abstract

The most precise realization of inertial reference frame in astronomy is the catalogue of 212 defining extragalactic radiosources with coordinates obtained during VLBI observation runs in 1979-1995. IAU decided on the development of the second realization of the ICRF2 catalogue. The criteria of best sources selection (in terms of coordinates stability) must be defined as the first aim. The selected sources have to keep stable the coordinate axes of inertial astronomical frame. Here we propose new criteria of source selection for the new ICRF catalogue. The first one we call as "cosmological" and the second one as "kinematical". The physical basis of these criteria is based on the assumption that apparent motion of quasars (at angular scale of the order of hundred microarcseconds) is connected with real motion inside quasars. Therefore apparent angular motion corresponds to real physical motion of a "hot spot" inside a radio source. It is shown that interval of redshift $0.8 \div 3.0$ is the most favorable in terms that physical shift inside such sources corresponds to minimal apparent angular shift of a "hot spot". Among "cosmologically" selected sources we propose to select motionless sources and sources with linear motion which are predictable and stable over long time interval. To select sources which satisfies such conditions we analyzed known redshifts of sources and time series obtained by our code and by different centers of analysis of VLBI data. As a result of these analyses we select 137 sources as a basis for the ICRF2 catalogue.