Tables aux_iers_gdr2_cross_id and aux_allwise_agn_gdr2_cross_id list sources whose positions in Gaia DR2 define the celestial reference frame of Gaia DR2 (GaiaCRF2).
aux_iers_gdr2_cross_id lists 2820 sources in Gaia DR2 identified as the optical counterparts of VLBI sources with accurate VLBI positions in the ICRF. The first column is the IERS name of the VLBI source, the second column is the source identifier in Gaia DR2 of the optical counterpart.
aux_allwise_agn_gdr2_cross_id lists 555934 sources in Gaia DR2 cross-matched to sources in the AllWISE AGN catalogue (Secrest et al.2015). The first column is the AllWISE identifier, the second column is the source identifier in Gaia DR2.
1885 of the Gaia DR2 source identifiers in table aux_iers_gdr2_cross_id appear also in table aux_allwise_agn_gdr2_cross_id
The selection of sources is described in Lindegren et al. (2018). Based on these sources, the quality of the GaiaCRF2 is discussed in Mignard et al. (2018).
allwise_name : Identifier in the ALLWISE AGN catalogue (string)
WISE All-Sky Release Catalog name, based on J2000 position.
source_id : Gaia source identifier (long)
A unique single numerical identifier of the source obtained from gaia_source (for a detailed description see gaia_source.source_id).