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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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