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Application of IVOA software tools for radio sources investigation

Zhelenkova O., Kopylov A., Chernenkov V.

The interrelationship between the objects of astronomical catalogs in the
different ranges of electromagnetic spectrum and their association into the
real astrophysical source has obvious scientific interest. Astronomical
community actively uses the Internet for the access to the scientific
information, but the heterogeneity of data and their constantly growing
volume is the certain difficulty. The gathering of information even about
one celestial object is time-taking work because of a large quantity of
resources, data access, formats of the obtained results and formats of
input data of the program applications, used for further analysis. The
community activity on the creation of the architecture of information
interaction, standards, format specifications, data models and services,
which increase the efficiency of work with the data, coordinates
International Virtual Observatory Alliance (IVOA). Within the framework of
this activity is created system Astrogrid (http://www.astrogrid.org) and
software tools Aladin (.http://aladin.u-strasbg.fr) and TOPCAT
(http://www.star.bris.ac.uk/~.mbt/topcat/), which make it possible to
realize the distributed computing and data access. AstroGrid developers
selected ten typical tasks, connected with physics of stars, galaxies,
interstellar medium and the Sun, whose solution is impossible without the
distributed computing and requests to the different information sources,
analysis and visualization of the large volumes of data. In the sense of
information technologies, we can represent the tasks are as a form of
scenarios. This is the certain type assignment of the actions, produced for
extraction and data analysis from www-resources. AstroGrid developers
decomposed scenarios on the component tasks, on the base that created the
functionality of the system.

We decided to analyze the usage of existing software tools for investigation
the radio sources list. The radio sources identification can be considered
as the sequence of the interconnected tasks, beginning from the extraction
of data, their analysis and visualizations of results. Optical identification
is not simple task for the automation because the radio sources are extensive,
has complex structure and, therefore, one source can be fetch in the catalog
as a few objects. As the radio sources list we used the RC sample, namely the
objects, which fell into the region of surveys FIRST and SDSS (8h11m-16h25m on
the right ascension and with the width on the declination, which includes all
sources RC, with the total area of ~120sq.deg.). The RC catalog has
insufficient coordinate accuracy for the optical identification; therefore
is necessary the refinement of coordinates by cross matching with the more
precise radio catalog. We used NVSS as the reference coordinate catalog.
For the program cross-identification of the RC sample, we tested the
different algorithms in the IVOA program applications, namely, the search
of the nearest neighbors with different radii of the separation between the
adjacent sources and the algorithm from the SPECFIND package, which considers
different angular resolution of compared radio catalogs. The algorithms gave
the low percentage of coincidences, and it is required the their modification,
i.e., the addition of constrains and conditions, which can be used for the
binding rows of different catalogs into one physical object not only coordinate
coincident, but also other conditions, caused by the radio source properties.
We are carrying out the detailed identification of the RC sample to study of
the properties of radio sources at the frequency of 3.9GHz and find possible
empirical constrains for changing the cross matching algorithm For the work
we use the catalogs and surveys in the optical and the radio-frequency band -
VLSS, TXS, NVSS, GB6, FIRST, SDSS, 2MASS, USNO-B1. We evaluated the fraction
of single-component and multicomponent radio sources in survey FIRST, on basis
of which (after the identification of the RC catalog objects with it) carried
out optical identification. Spectral data in the radio-frequency band from
74MHz to 4.85GHz are acquired for the sample. For 60% of radio sources
identified with the objects of the radio catalogs we discovered optical
candidates in SDSS survey.