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gaia early data release 3 documentation

9.3 External catalogues matched with Gaia EDR3

9.3.7 2MASS PSC XSC

2MASS PSC Catalogue

Reference paper:
—Skrutskie et al. 2006

The 2MASS All-Sky Data Release contains Image and Catalogue data covering 99.998% of the sky, derived from all northern and southern survey observations. The all-sky release products include a Point Source Catalog (PSC), containing positions and photometry for 470 992 970 objects, an Extended Source Catalog (XSC), containing positions, photometry and basic shape information for 1 647 599 resolved sources, most of which are galaxies, and the Image Atlas, containing over 41̇21 439 J, H, and Ks FITS images covering the sky.

2MASS XSC Catalog

Reference paper:
—Skrutskie et al. 2006

The 2MASS Extended Source Catalog (XSC) is comprised of near-infrared sources that are clearly resolved and extended beyond the beam/PSF. Sources range in angular size from 10′′to 2∘: from faint little galaxies to the largest local group galaxies. By their very nature, galaxies are complex and therefore demand characterisation measurements that are much more detailed than that of point sources. Although galaxies dominate the total numbers, the XSC is also comprised of Milky Way entities, such as globular and open clusters, planetary nebulae, HII regions, ISM emission and nebulosity, young stellar objects and compact star-formation regions, and even Solar System comets.

Data curation and catalogue preparation

For cross-match purposes, 2MASS PSC was merged with 2MASS XSC using the ext_key available in PSC, which is the unique identification number of the record in the XSC catalogue that corresponds to a given point source. The XSC sources with no corresponding PSC source were then added. When a source is present in both PSC and XSC, the coordinates and reference epoch used in the cross-match are the PSC coordinates and reference epoch. For the sources present only in XSC which do not have a reference epoch, a value of 2000.0 was used.

Catalogue cleaning and Join table

In the case of the binaries/triplets present in the PSC catalogue, only one of them is used for cross-match purposes, giving priority to the component with an XSC counterpart first and with smaller position errors as a second criteria. Binaries/triplets are flagged as multiples in the cross-match results tables.

A convenience table is available that can be used to join 2MASS PSC and XSC catalogues with the cross-match results. The table links the external catalogues (PSC and XSC) original sourceIds ( original_psc_source_id and (original_xsc_source_id) to the corresponding additional numerical identifier ( clean_tmass_psc_xsc_oid). In the cross-match output tables ( tmass_psc_xsc_best_neighbour and tmass_psc_xsc_neighbourhood) are present a merged original_ext_source_id and clean_tmass_psc_xsc_oid. The sourceIds listed in the column original_ext_source_id are either PSC or XSC depending on the catalogue they come from. In case of binaries/triplets, different original_ext_source_id will correspond to the same clean_tmass_psc_xsc_oid. In practice, users should use the clean_tmass_psc_xsc_oid to find the matching source(s) in the Join table and then the corresponding sourceIds to find the sources in 2MASS PSC or 2MASS XSC.

Cross-match algorithm

According to the definition used in this work, 2MASSPscXsc is a dense survey, in the cross-match algorithm Gaia is the leading catalogue, this means that Gaia objects matches are searched for in 2MASSPscXsc. For this catalogue special treatment was done for a) the sources which are resolved in Gaia, and b) small issues in Gaia astrometry, especially for bright stars.