The VLA Low-frequency Sky Survey

The Very Large Array (VLA) Low-frequency Sky Survey (VLSS) has imaged 95% of the 3π sr of sky north of δ = −30◦ at a frequency of 74 MHz (4 meter wavelength). The resolution is 80 (FWHM) throughout, and the typical RMS noise level is 〈σ〉 ≈ 0.1 Jy/beam. The typical point-source detection limit is 0.7 Jy/beam and so far nearly 70,000 sources have been catalogued. This survey used the 74 MHz system added to the VLA in 1998. It required new imaging algorithms to remove the large ionospheric distortions at this very low frequency throughout the entire ∼ 11.9 field of view. This paper describes the observation and data reduction methods used for the VLSS and presents the survey images and source catalog. All of the calibrated images and the source catalog are available online (URL=http://lwa.nrl.navy.mil/VLSS) for use by the astronomical community. Subject headings: surveys — catalogs — atmospheric effects — radio continuum: general