Extragalactic source structure

Details Extragalactic source structure Extragalactic source structure

Jan 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005hia....13..604c&link_type=abstract

In: Highlights of Astronomy, Vol. 13, as presented at the XXVth General Assembly of the IAU - 2003 [Sydney, Australia, 13 - 26 J

Astronomy and Astrophysics

Astronomy

International Celestial Reference System

Scientific paper

The compact extragalactic radio-emitting objects used to define the celestial reference frame are only imperfect fiducial points in the sky on milliarcsecond scales. Astrophysical imaging shows that many sources have frequency-dependent extended emission structures which evolve with time in impredictable ways. Such internal structures can induce extra ""noise"" and temporal variations in the astrometric source positions which shall limit the accuracy of the celestial frame if not corrected. Various imaging surveys are now available to evaluate the impact of unmodeled source structure on a statistical basis. A specific item is the study of source compactness as a function of the observing radio frequency. Exploratory work is also being conducted to correct for the effect of source structure in actual astrometric analyses by using hundreds of source maps as available from ongoing structure monitoring. Recent progress in these areas will be reviewed in the framework of future possible ICRF realizations. Ultimately the achievable accuracy of a celestial reference frame based on extragalactic radio objects may be limited by an irreducible uncertainty inherent in locating truly kinematically-stable emission features within the source brightness distributions.

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