VLA Sky Survey Quick Look Images

Quick Look image products are 1x1 degree images of the 2-4GHz Stokes I continuum, and an associated image of the RMS.

Images are grouped by tiles, as described at Tile Definitions and Observing Status, and individual images are are named as follows:

• VLASS epoch (1.1=first half of first epoch; 1.2=second half of first epoch; 2.1=first half of second epoch, etc.)
• Product type (ql=Quick Look imaging)
• Tile name
• Image phase center
• Pixel size x10 (10=1.0arcsec)
• Bandwidth in MHz
• Version number
• Stokes type

Quick Look images do not fully sample the PSF, and are cleaned to a threshold of ~5 sigma (details can be found in the weblogs for individual images). They are used for Quality Assurance and for transient searches, but should not be used for any other purpose. In addition to imaging artifacts, source positions can be off by up to 1-arcsec, and the flux density uncertainties are ~10-20%.

UPDATE, Nov 2017: We have found a VLA system issue that is resulting in "ghost" images of bright sources separated by approximately 3 arcmin in RA. These can be either +RA or -RA, depending on the scan direction of the affected OTF row. We are investigating and will re-post corrected images as and when they are identified.