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GMRTLBDSLY - Giant Metrewave Radio Telescope LBDS-Lynx Region 150-MHz Radio Source Catalog

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Overview

It has been known for nearly three decades that high-redshift radio galaxies exhibit steep radio spectra, and hence ultrasteep spectrum radio sources provide candidates for high-redshift radio galaxies. Nearly all radio galaxies with z > 3 have been found using this redshift-spectral index correlation. The authors have started a program with the Giant Metrewave Radio Telescope (GMRT) to exploit this correlation at flux density levels about 10 to 100 times deeper than the known high-redshift radio galaxies which were identified primarily using the already available radio catalogs. In their program, they have obtained deep, high-resolution radio observations at 150 MHz with the GMRT for several "deep" fields which are well studied at higher radio frequencies and in other bands of the electromagnetic spectrum, with the aim to detect candidate high-redshift radio galaxies. In their paper, they present results from the deep 150-MHz observations of the LBDS (Leiden-Berkeley Deep Survey) Lynx field, which has been already imaged at 327, 610 and 1412 MHz with the Westerbork Synthesis Radio Telescope (WSRT) and at 1400 and 4860 MHz with the Very Large Array (VLA). The counterparts for the 150-MHz sources at higher radio frequencies were searched within a 20-arcsec radius from the 150-MHz position.

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.


Catalog Bibcode

2010MNRAS.405..436I

References

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

Provenance

This table was created by the HEASARC in February 2012 based on CDS Catalog J/MNRAS/405/436 file table3.dat.

Parameters

Name
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'.

RA
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.

Dec
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.

LII
The Galactic Longitude of the 150-MHz source.

BII
The Galactic Latitude of the 150-MHz source.

Flux_150_MHz
The flux density of the radio source at 150 MHz as measured by the GMRT, in mJy.

WSRT_Flux_327_MHz
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.

WENSS_Flux_327_MHz
The flux density of the radio source at 327 MHz as given in the Westerbork Northern Sky Survey (WENSS), in mJy.

WSRT_Flux_610_MHz
The flux density of the radio source at 610 MHz as measured by the WSRT, from Windhorst (private communication), in mJy.

WSRT_Flux_A_1412_MHz
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.

WSRT_Flux_B_1412_MHz
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.

NVSS_Flux_1400_MHz
The flux density of the radio source at 1400 MHz as given in the NRAO VLA Sky Survey (NVSS) Catalog, in mJy.

FIRST_Flux_1400_MHz
The flux density of the radio source at 1400 MHz as given in the FIRST Catalog, in mJy.

VLA_Flux_1462_MHz
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.

VLA_Flux_4860_MHz
The flux density of the radio source at 4860 MHz as measured by the VLA, from Donnelly (1987, ApJ, 321, 94), in mJy.

Spectral_Index
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.


Contact Person

Questions regarding the GMRTLBDSLY database table can be addressed to the HEASARC User Hotline.

Page Author: Browse Software Development Team
Last Modified: 23-Feb-2012