GMRTLBDSLY - Giant Metrewave Radio Telescope LBDS-Lynx Region 150-MHz Radio Source Catalog
The 150-MHz image made with the GMRT has an rms noise of ~ 0.7 mJy beam-1 and a resolution of ~ 19 x 15 arcsec2. It is the deepest low-frequency image of the LBDS-Lynx field. The source catalog of this field at 150 MHz has 765 sources down to ~ 20% of the primary beam response, covering an area of about 15 deg2. The spectral index was estimated by cross-correlating each source detected at 150 MHz with the available observations at 327, 610, 1400 and 4860 MHz and also using available radio surveys such as the Westerbork Northern Sky Survey (WENSS) at 327 MHz and the NRAO VLA Sky Survey (NVSS) and the Faint Images of the Radio Sky at Twenty-cm (FIRST) survey at 1400 MHz. A total of 639 sources out of 765 (83%) have spectral indices determined. The remaining 17% of the sources are mostly weak radio sources with a median flux density of ~ 9 mJy, or fall in the regions where deep observations at higher frequencies do not exist. The median spectral index of the sample is 0.78. The authors find about 150 radio sources with spectra steeper than 1. About two-thirds of these are not detected in the Sloan Digital Sky Survey (SDSS), hence are strong candidate high-redshift radio galaxies, which need to be further explored with deep infrared imaging and spectroscopy to estimate the redshift. The list of the 98 such steep-spectrum sources lacking SDSS counterparts is given in Table 4 of the published paper.
Deep GMRT 150-MHz observations of the LBDS-Lynx region: ultrasteep spectrum radio sources. Ishwara-Chandra C.H., Sirothia S.K., Wadadekar Y., Pal S., Windhorst R. <Mon. Not. R. Astron. Soc., 405, 436-446 (2010)> =2010MNRAS.405..436I
The name of the 150-MHz radio source using the IAU-style designation for the source based on its truncated J2000.0 equatorial coordinates, viz., '[ISW2010] GMRT JHHMMSS+DDMMSS' as recommended by the CDS Dictionary of Nomenclature of Celestial Objects, where the prefix stands for 'Ishwara-Chandra, Sirothia, Wadadekar 2010, Giant Metrewave Radio Telescope'.
The Right Ascension of the 150-MHz source in the selected equinox. This was given in J2000.0 coordinates to a precision of 0.1 seconds of time in the original table.
The Declination of the 150-MHz source in the selected equinox. This was given in J2000.0 coordinates to a precision of 0.1 arcseconds in the original table.
The Galactic Longitude of the 150-MHz source.
The Galactic Latitude of the 150-MHz source.
The flux density of the radio source at 150 MHz as measured by the GMRT, in mJy.
The flux density of the radio source at 327 MHz as measured by the WSRT, from Oort et al. (1988, A&AS, 73, 103; CDS Catalog J/A+AS/73/103), in mJy.
The flux density of the radio source at 327 MHz as given in the Westerbork Northern Sky Survey (WENSS), in mJy.
The flux density of the radio source at 610 MHz as measured by the WSRT, from Windhorst (private communication), in mJy.
The flux density of the radio source at 1412 MHz, as measured by the WSRT, from Windhorst et al. (1984, A&AS, 58, 1; CDS Catalog J/A+AS/58/1), in mJy.
The flux density of the radio source at 1412 MHz as measured by the WSRT, from Oort (1987, A&AS, 71, 221; CDS Catalog J/A+AS/71/221), in mJy.
The flux density of the radio source at 1400 MHz as given in the NRAO VLA Sky Survey (NVSS) Catalog, in mJy.
The flux density of the radio source at 1400 MHz as given in the FIRST Catalog, in mJy.
The flux density of the radio source at 1462 MHz as measured by the VLA, from Windhorst et al. (1985, ApJ, 289, 494), in mJy.
The flux density of the radio source at 4860 MHz as measured by the VLA, from Donnelly (1987, ApJ, 321, 94), in mJy.
Since the aim of the project is to search for steep spectrum sources, the spectral indices were computed using the GMRT 150-MHz catalog as the primary catalog. The spectral index was computed if a counterpart was found at 610 MHz or at any of the higher frequencies. If the counterpart was seen only at 327 MHz, the spectral index was not computed, since the two frequencies are quite close by and the error in the spectral index would be large. Nonetheless, if the source was detected at 327 MHz either in WENSS or at the deep observation of this field at 327 MHz, this value of flux was also used to fit the spectrum along with other available measurements. The typical error on the spectral index estimate was about 0.1, or better.