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VLSSR - VLA Low-Frequency Sky Survey Redux Source Catalog

 HEASARC
Archive

Overview

The Very Large Array (VLA) Low-Frequency Sky Survey (VLSS) covers 95% of the 3 pi sr of sky area above -30 degrees Declination at most RAs (complete above -10 degrees Declination, while in some areas data are available down to Declinations of -36 degrees) at a frequency of 74 MHz, a resolution of approximately 75", an rms sensitivity of ~ 0.1 Jy/beam, and a limiting peak source brightness of about 500 mJy/beam. The main survey products consist of a publicly available catalog and a set of maps (available at http://www.cv.nrao.edu/vlss/MAPS/). The survey was intended to serve as a low-frequency counterpart to the National Radio Astronomy Observatory (NRAO)-VLA Sky Survey (NVSS) at 1400 MHz, allowing spectral information to be compiled for statistical samples of sources. It also provides a low-frequency sky model. In their 2012 reference paper, the authors present the details of improvements to data processing and analysis which were recently used for a re-reduction of the VLSS data, which they dub the VLSS redux or VLSSr. The algorithms described are implemented in the data-reduction package Obit, and include smart-windowing to reduce clean bias, improved automatic radio frequency interference removal, improved bright-source peeling, and higher-order Zernike fits to model the ionospheric phase contributions. An additional, but less technical improvement was using the original VLSS catalog as a same-frequency/same-resolution reference for calculating ionospheric corrections, allowing more accuracy and a higher percentage of data for which solutions are found. The authors also discuss new algorithms for extracting a source catalog and analyzing ionospheric fluctuations present in the data. The improved reduction techniques led to substantial improvements including images of six previously unpublished fields (1% of the survey area) and reducing the clean bias by 50%. The largest angular size imaged has been roughly doubled to 36 arcminutes, and the number of cataloged sources is increased by 35% to 95,000 compared to the original VLSS. (In the VLSS catalog, multiple-component sources were summed to create one entry; the authors have chosen to leave the individual component entries uncombined for the VLSSr).The VLSSr maps and catalog use the Roger, Costain and Bridle (1973, AJ, 78, 130) flux scale, based on the source models presented in Scaife and Heald (2012, MNRAS, 423, 30).

The final VLSSr Catalog includes approximately 95,000 source components, of which 74,000 are unresolved. Sources were fitted with Gaussians which could have maximum sizes of 120"; larger sources were fitted with multiple Gaussians.

Catalog Bibcode

2012RaSc...47.....L

References

VLSS redux: Software improvements applied to the Very Large Array Low-Frequency
            Sky Survey
    Lane W.M., Cotton W.D., Helmboldt J.F., Kassim N.E.
   <Radio Science, Volume 47, CiteID RS0K04>
   =2012RaSc...47.....L

The VLA Low-frequency Sky Survey
     Cohen A.S., Lane W.M., Cotton W.D., Kassim N.E., Lazio T.J.W.,
     Perley R.A., Condon J.J., Erickson W.C.
    <Astron. J., 134, 1245-1262 (2007)>
    =2007AJ....134.1245C

Provenance

This table was created by the HEASARC in December 2012, based on the FITS file CATALOG.DAT which was obtained from the NRAO web site at http://www.cv.nrao.edu/vlss/CATALOG/.

HEASARC Implementation

The HEASARC converted the flux densities from Jy/beam to mJy/beam and the size units of the major and minor axes from degrees to arcseconds. The HEASARC did not include 4 parameters from the CATALOG.FIT file which had all of their entries set to null values, the parameter 'JD PROCESSED' for which all 95,491 entries had the same value of 2456127 JD (2012-Jul-18), and 2 other parameters from the CATALOG.FIT file (RES PEAK and RES FLUX) which did not seem of general interest. The HEASARC also added a unique sequential identification number (source_number) for each source in the VLSSr Catalog in order of increasing J2000.0 Right Ascension.

Parameters

Source_Number
A unique sequential identification number NNNNN for each source in the VLSSr Catalog in order of increasing J2000.0 Right Ascension. This parameter, essentially the row number of the entry in the original input file CATALOG.FIT, was added by the HEASARC. This parameter could be used to create a (unique) alternate name for the source using the standard Dictionary of Nomenclature of Celestial Objects style, viz., '[LCH2012] NNNNN', where the prefix stands for Lane, Cotton, Helmboldt 2012.

Name
The designation for the VLSSr source based on the schema recommended by the authors of the original VLSS catalog, but using the 'VLSSr' prefix, and the J2000.0 coordinates truncated to 0.1 minutes of time in RA and 1 arcminute in Declination. Notice that there are 95,491 entries in this catalog, but only 95,476 unique names, so this is not in all cases a unique identifier.

RA
The Right Ascension of the VLSSr source in the selected equinox. This was given in J2000.0 decimal degrees in the original table. The average error in RA is ~ 3".

Dec
The Declination of the VLSSr source in the selected equinox. This was given in J2000.0 decimal degrees in the original table. The average error in Dec is ~ 3.4".

LII
The Galactic Longitude of the VLSSr source.

BII
The Galactic Latitude of the VLSSr source.

Flux_74_MHz
The peak flux density of the VLSSr source at 74 MHz, in mJy/beam.

Flux_74_MHz_Error
The rms noise level at 74 MHz, in mJy/beam.

RMS_74_MHz
The residual rms noise level at 74 MHz, in mJy/beam.

Major_Axis
The measured (undeconvolved) major axis of the source, in arcseconds.

Minor_Axis
The measured (undeconvolved) minor axis of the source, in arcseconds.

Position_Angle
The measured position angle of the source, i.e., the orientation of its major axis, in degrees, from north through east.

Field_Name
The name of the original survey field in which the source was found.

X_Pixel
The X-axis (RA) pixel number of the source in the original survey image field (specified by the field_name parameter) in which the source was present.

Y_Pixel
The Y-axis (Dec) pixel number of the source in the original survey image field (specified by the field_name parameter) in which the source was present.

Contact Person

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

A service of the Astrophysics Science Division at NASA/GSFC and the High Energy Astrophysics Division of the Smithsonian Astrophysics Observatory (SAO)

Page Author: Browse Software Development Team
Last Modified: 18-Dec-2012