VLSSR - VLA Low-Frequency Sky Survey Redux Source Catalog

Overview

The Very Large Array (VLA) Low-Frequency Sky Survey (VLSS: see Cohen et al. 2007, AJ, 134, 1245) 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 80", and an average rms map sensitivity of sigma ~ 0.130 Jy/beam. 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 and 2014 reference papers, the authors present the details of improvements to data processing and analysis which were used for a re-reduction of the VLSS data, which they dub the VLSS redux or VLSSr. They used the VLSS catalogue as a sky model to correct the ionospheric distortions in the data and create a new set of sky maps and corresponding catalog at 73.8 MHz. The VLSS Redux (VLSSr) has a resolution of 75", and an average map rms noise level of sigma ~ 0.1 Jy beam^-1. The clean bias is 0.66 x sigma and the theoretical largest angular size is 36 arcminutes. Six previously unimaged fields are included in the VLSSr, which has an unbroken sky coverage over 9.3 steradian above an irregular southern boundary. The final catalog includes 92,965 sources (in the abstract of Lane et al. (2014) it states 92.964 sources). The VLSSr improves upon the original VLSS in a number of areas including imaging of large sources, image sensitivity, and clean bias; however the most critical improvement is the replacement of an inaccurate primary beam correction which caused source flux errors which vary as a function of radius to the nearest pointing center in the VLSS.

Catalog Bibcodes

2014MNRAS.440..327L
2012RaSc...47.....L

References

The Very Large Array Low-frequency Sky Survey Redux (VLSSr)
    Lane W.M., Cotton W.D., van Velzen S., Clarke T.E., Kassim N.E.,
    Helmboldt J.F., Lazio T.J.W., Cohen A.S.
   <Mon, Not. RAS, Volume 440, 327>
   =2014MNRAS.440..327L

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

Provenance

This table was initially created by the HEASARC in December 2012, based on the FITS file CATALOG.FIT obtained from the NRAO website at http://www.cv.nrao.edu/vlss/CATALOG/. It was updated in July 2014 with the the table data from the latest file on the NRAO website (which was marked as last modified on 26 August 2013). Some of the values for the name parameter in the HEASARC's implementation of this table were corrected in April 2018.

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 92,965 entries had the same value of 2456435 JD (2013-May-22), 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., '[LCV2014] NNNNN', where the prefix stands for Lane, Cotton, van Velzen 2014.

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.

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 Help Desk.

Page Author: Browse Software Development Team
Last Modified: Monday, 16-Sep-2024 17:36:32 EDT