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TGSS-NVSS spectral index maps and catalog
Science team: Francesco de Gasperin (Leiden), Huib T. Intema (Leiden) & Dale A. Frail (NRAO)
We produced a spectral index catalog matching specially re-processed images from two radio surveys at different frequencies: NVSS and TGSS. These surveys were chosen because they are the most sensitive metre and centimetre wavelength surveys currently available, they both cover a large fraction of the sky, and their separation in frequency provides a large lever arm for spectral index calculation. The resulting catalogue includes >1.4 million entries, making it the largest collection of spectral index information to date. Furthermore, we provide the community a spectral index map of 80% of the sky that can be used to classify radio sources.
Sources in the catalog are classified into categories:
single (S): a matched (detection in both NVSS and TGSS) source with no other detections in the same island – these sources are simple, usually point-like or slightly extended in both surveys;
multiple (M): a matched source with other matched sources (but no unmatched sources) in the same island – these sources are most of the time double-lobe radio galaxies or collections of nearby point sources;
complex (C): a matched source with unmatched detections in one of the two surveys in the same island – these sources might be part of a more complex object, e.g. a lobe of a radio galaxy where the other lobe is too faint to be detected in one of the surveys;
upper limit (L): a detection in NVSS with no TGSS detection in the same island – multiple NVSS detections in the island create multiple entries in the catalogue;
lower limit (U): a detection in TGSS with no NVSS detection in the same island – multiple TGSS detections in the island create multiple entries in the catalogue;
island (I): if an island is not only made by matched sources (S, M) or unmatched source of the same survey (L, U), the global values of that island are saved as a separate entry – these sources have naturally a poor positional constrain, complex sources (C) are always also part of an island source (I).