VLBI observations of weak extragalactic radio sources for the alignment of the future Gaia frame with the ICRF

G. Bourda (1, 2, 3, 4) , P. Charlot (1, 2, 3, 4) , R. Porcas (5) , S. Garrington (6)

1 LAB - Laboratoire d'Astrophysique de Bordeaux [Pessac]
2 OASU - Observatoire aquitain des sciences de l'univers
3 L3AB - Laboratoire d'astrodynamique, d'astrophysique et d'aéronomie de bordeaux
4 UB - Université Sciences et Technologies - Bordeaux 1
5 MPIfR
6 Jodrell Bank Observatory

The space astrometry mission Gaia will construct a dense optical QSO-based celestial reference frame. For consistency between the optical and radio positions, it will be important to align the Gaia frame and the International Celestial Reference Frame (ICRF) with the highest accuracy. Currently, it is found that only 10% of the ICRF sources are suitable to establish this link, either because they are not bright enough at optical wavelengths or because they have significant extended radio emission which precludes reaching the highest astrometric accuracy. In order to improve the situation, we have initiated a VLBI survey dedicated to finding additional high-quality radio sources for aligning the two frames. The sample consists of about 450 sources, typically 20 times weaker than the current ICRF sources, which have been selected by cross-correlating optical and radio catalogues. This paper presents the observing strategy and includes preliminary results of observation of 224 of these sources with the European VLBI Network in June 2007.

Mots clés: astrometry; reference systems; quasars

Domaines: Astrophysique [astro-ph]; Cosmologie et astrophysique extra-galactique [astro-ph.CO]; Cosmologie et astrophysique extra-galactique [astro-ph.CO]

G. Bourda, P. Charlot, R. Porcas, S. Garrington. VLBI observations of weak extragalactic radio sources for the alignment of the future Gaia frame with the ICRF. A Giant Step: from Milli- to Micro-arcsecond Astrometry, 2008, Shangai, China. p. 324-325. ⟨hal-00189628⟩