VLA 74-MHz Deep High-Resolution Survey Source Catalog

This table contains some of the results from a 74-MHz survey of a 165 deg<sup>2</sup> 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 ~ nu<sup>alpha</sup>) 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. This table was created by the HEASARC in August 2010 based on CDS catalog J/ApJS/150/417/ file table2.dat. This is a service provided by NASA HEASARC .

Identifier
Source https://dc.g-vo.org/rr/q/lp/custom/nasa.heasarc/vla74mhzdp
Related Identifier https://heasarc.gsfc.nasa.gov/W3Browse/all/vla74mhzdp.html
Related Identifier https://heasarc.gsfc.nasa.gov/cgi-bin/W3Browse/w3query.pl?tablehead=name=heasarc_vla74mhzdp&Action=More+Options&Action=Parameter+Search&ConeAdd=1
Metadata Access http://dc.g-vo.org/rr/q/pmh/pubreg.xml?verb=GetRecord&metadataPrefix=oai_b2find&identifier=ivo://nasa.heasarc/vla74mhzdp
Provenance
Creator Cohen et al.
Publisher NASA/GSFC HEASARC
Publication Year 2024
OpenAccess true
Contact NASA/GSFC HEASARC help desk <heasarc-vo at athena.gsfc.nasa.gov>
Representation
Resource Type Dataset; AstroObjects
Discipline Astrophysics and Astronomy; Natural Sciences; Observational Astronomy; Physics