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1995BuSAO.39..150Trushkin & Verkhodanov

On the cross-identification of the IRAS-Point Source and Texas catalogs

S. A. Trushkin & O.V. Verkhodanov

Abstract

We present results of cross-identifications of the objects from two large catalogs, IRAS-Point Source and Texas, in the database CATS. The list consists of 1208 pairs of sources. More than half of the IRAS sources have been identified for the first time. The resulting catalog has been cross-identified with the Green Bank 1.4 GHz catalog. Histograms of distributions of spectral indices and flux densities are presented. Spectra of some unusual radio sources are shown. Some statistical and physical selection criteria are considered.

Cross-identification

The main problems in identification and classification of IRAS point sources have been described by Preite-Marinez (1993). For each source from IRAS catalog the CATS database (Verkhodanov and Trushkin, 1995a, 1995b) searched for coordinates association within a radius of 120 arcsec. The resulting list we have identified through the Green Bank 1.4 GHz (GB1.4) catalog (White and Becker, 1992) to estimate spectral indices distribution.

But we have excluded 40 duplications of the Texas sources, occuring in the preliminary version of the Texas catalog because of merging of nine declination strips of the survey into joint table.

Procedure of cross-identification consisted in matching the IRAS sources to the Texas sources by seaching for their coincident positions. The position uncertainties of each object have not been taken into account because of they vary from 40 to 80" for the IRAS coordinates. The Texas sources have high coordinate accuracy about 1", but position shifts of interferometrical sidelobes are possible up to 52" in these measurements (Douglas at al., 1980). Here it is more preferable to retain any small portion of false identifications than they lost true ones. Thus we have concluded that the search radius of 120" is acceptable for initial statistical consideration. The simple estimation of occasional coordinate coincidence probability (P) within the circle radius of 120" for 133000 IRAS sources in the region |b| >10^o is equal to 0.012, while for the rest 113000 IRAS sources in the region |b|<10^o P = 0.063. However for identification of extended sources of the Galactic plane we have to take a radius of search larger than 1-2'. Probably a small portion of cross-identifications is occasional.

As a result we have obtained a list of 1208 sources (IRAS-Texas association or ITA catalog) after the cross-identification of the IRAS and Texas catalogs. One Texas source is associated with two different IRAS sources in the extended (6'x 8') Crab nebula. 697 of these 1208 IRAS-sources have been identified for the first time with objects from any other catalog.

In the 511 ITA sources, already identified with different sources in the initial IRAS catalog, galaxies and Milky Way radio sources dominated. There are 596 and 458 sources in the region of the Galactic plane (|b| >10^o and |b| <5.5^o, respectively).

Conclusion

The potentialities of the database of the astronomical catalogs have made it possible to work out a techtechnique of cross-identification of different kinds of objects which can be regularly used in sky surcey investigation. This is the first paper demonstating one of potentialities -- selection using large Texas and IRAS-PS catalogs. The following steps of data base processing will include the estimations of probability on base of boxes of errors for positional association.

But the most important element of counterpart search is to assess the identity of the physical nature of cosmic sources of different range radiation. Now it is possible to say something about nature of many Texas catalog sources. Large portions of them are spiral or normal galaxies. Cross-identification of radio sources (as tracers of active energy release processes) with other cosmic objects, especially in complex Galactic regions, is a powerful method of investigation. However radio catalogs at the higher frequencies than those of the Texas catalog, which are more sensitive to extended objects radiation, are needed for cross-identification with the IRAS catalog.

References


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