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VLA74MHZDP - VLA 74-MHz Deep High-Resolution Survey Source Catalog

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Overview

This table contains some of the results from a 74-MHz survey of a 165 deg2 region located near the North Galactic Pole (NGP). This survey has an unprecedented combination of both spatial resolution (25" FWHM) and sensitivity (1-sigma as low as 24mJy/beam). The authors detect 949 sources at the 5-sigma level in this region, enough to begin exploring the nature of the 74-MHz source population. In their paper, they present differential source counts, spectral index measurements, and the size distribution as determined from counterparts in the high-resolution FIRST 1.4-GHz survey. They find a trend of steeper spectral indices for the brighter sources. Further, there is a clear correlation between spectral index and median source size, with the flat-spectrum sources being much smaller on average. Ultra-steep spectrum objects (power-law index alpha <= -1.2, where S_nu ~ nualpha) are identified. These sources are excellent candidates for high-redshift radio galaxies.

The data used to produce this survey come from observations taken on 1998 March 7 intended to map two normal galaxies at 74 MHz (NGC 4565 and NGC 4631). These two pointings were separated by 6.4 degrees, roughly the radius of the primary beam at 74 MHz, allowing them to be ideally combined to produce a single deep image roughly 17 x 10 degrees in size. The combination of VLA A-configuration resolution (25 arcsec), favorable ionospheric conditions, and pointings in directions near the NGP, where the background temperature is low, produced the deepest observation ever obtained below 100 MHz. The same algorithm that was used in the 1.4-GHz NVSS was used to identify and characterize sources in this 74-MHz survey. The source detection algorithm had a threshold such that sources must have both a peak and integrated flux density level of at least 5 times the local rms noise level. Since the rms noise level varied from 24 mJy/beam to 80 mJy mJy/beam at the chosen field edge, the absolute level of the source-detection threshold of 5-sigma likewise varied over the image.


Catalog Bibcode

2004ApJS..150..417C

References

A deep, high-resolution survey at 74 MHz.
    Cohen A.S., Rottgering H.J.A., Jarvis M.J., Kassim N.E., Lazio T.J.W.
   <Astrophys. J. Suppl. Ser., 150, 417-430 (2004)>
   =2004ApJS..150..417C

Provenance

This table was created by the HEASARC in August 2010 based on CDS catalog J/ApJS/150/417/ file table2.dat.

Parameters

Name
The radio source designation, using the '[CRJ2004]' prefix (for Cohen, Rottgering, Jarvis 2004) and the J2000 position truncated to 0.1 minutes of time in RA and 1 arcminute in Dec, viz. '[CRJ2004] JHHMM.m+DDMM', as recommended by the Dictionary Of Nomenclature of Celestial Objects.

RA
The Right Ascension of the radio source in the selected equinox. This was given in J2000.0 equatorial coordinates to a precision of 0.01 seconds of time in the original table.

Dec
The Declination of the radio source in the selected equinox. This was given in J2000.0 equatorial coordinates to a precision of 0.1 arcseconds in the original table.

LII
The Galactic Longitude of the radio source.

BII
The Galactic Latitude of the radio source.

Flux_74_MHz
The integrated 74-MHz flux density of the radio source, in mJy (converted from the units of Jy used in the original reference table).

Spectral_Index
The radio source spectral index between 74 and 1400 MHz, with the latter measurement coming from the NVSS Catalog. 947 out of the 949 74-MHz sources have NVSS 1400-MHz matches within 60 arcsec: the 2 sources with no NVSS match ([CRJ2004] J1230.6+3247 and [CRJ2004] J1253.6+2509) have been assigned blank (null) values.


Contact Person

Questions regarding the VLA74MHZDP database table can be addressed to the HEASARC User Hotline.

Page Author: Browse Software Development Team
Last Modified: 26-Aug-2010