VLA74MHZDP ivo://nasa.heasarc/vla74mhzdp NASA/GSFC HEASARC Cohen et al. 2026-10-09 NASA/GSFC HEASARC help desk heasarc-vo at athena.gsfc.nasa.gov Survey Source 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 <a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/ApJS/150/417/">CDS catalog J/ApJS/150/417/</a> file table2.dat. This is a service provided by NASA HEASARC . 2004ApJS..150..417C https://heasarc.gsfc.nasa.gov/W3Browse/all/vla74mhzdp.html Catalog Research served-by HEASARC TAP https://heasarc.gsfc.nasa.gov/xamin/vo/cone?showoffsets&table=vla74mhzdp& GET text/xml 180 99999 true 189.23475 21.06130556 0.0333333333333333 https://heasarc.gsfc.nasa.gov/xamin/vo/tap https://heasarc.gsfc.nasa.gov/cgi-bin/W3Browse/getvotable.pl?name=vla74mhzdp GET text/xml https://heasarc.gsfc.nasa.gov/cgi-bin/W3Browse/w3query.pl?tablehead=name=heasarc_vla74mhzdp&Action=More+Options&Action=Parameter+Search&ConeAdd=1 RADIO CATALOG 0.0333333333333333 Radio public vla74mhzdp VLA 74-MHz Deep High-Resolution Survey Source Catalog name Source Designation meta.id;meta.main char nullable ra Right Ascension degree pos.eq.ra;meta.main double nullable dec Declination degree pos.eq.dec;meta.main double nullable flux_74_mhz Integrated 74MHz Flux Density (mJy) mJy phot.flux.density;em.radio.20-100MHz double nullable spectral_index Spectral Index Between 74 and 1400MHz spect.index;em.radio.20-100MHz;em.radio.750-1500MHz double nullable lii Galactic Longitude degree pos.galactic.lon double nullable bii Galactic Latitude degree pos.galactic.lat double nullable "__x_ra_dec" System unit vector column double nullable "__y_ra_dec" System unit vector column double nullable "__z_ra_dec" System unit vector column double nullable "__row" System index column char nullable