Science > Surveys > VLASS

VLA Sky Survey

by Davis Murphy last modified Oct 23, 2018 by Claire Chandler

VLASS logo (dark)


Click here for access to Quick Look images


News Update: September 14th 2018

There will be a VLASS special session at the AAS winter meeting in Seattle on Thursday 10th January 2019. We are actively seeking contributed talks and posters for this session. If you would like to give a VLASS-related talk or poster, please select the VLASS special session when submitting your abstract (due on the 3rd October).

The first VLASS papers have appeared on the preprint server: https://arxiv.org/abs/1808.07178 by Villarreal Hernández and Andernach discuss extended radio sources in VLASS, and how its high resolution allowed them to use morphologies to positively identify nine new >1Mpc radio sources. https://arxiv.org/abs/1808.08964 by Law et al. discusses a slowly fading transient discovered using FIRST and VLASS data.

Quicklook imaging of the first half of the first epoch of VLASS is now complete. The images cover 17,000 square degrees distributed over the sky. An interactive viewer based on Aladin Lite and HiPS showing the survey coverage (and zoomable to investigate individual sources) is available by following this link. The quicklook images (1" per pixel scale, Stokes I continuum) are posted to the VLA Sky Survey Resources web page. This link also provides the sky tile definitions and observing/processing status.

The quicklook images are adequate for many scientific uses, but are not designed to meet the  survey requirements for imaging. In particular, the flux density uncertainty for a typical high signal-to-noise detection is approximately 15% due to limitations of the imaging heuristics used. The position accuracy is also limited to approximately 0.2 arcsec. Better images in Stokes I,Q and U, spectral index maps, and spectral cubes around bright sources (also in Stokes I,Q,U) will be made available on a timescale of approximately 6 months.

All raw visibility data from the first half of the first epoch are available from the NRAO archive, under project code VLASS1.1.

In these early days of the survey, we especially encourage your feedback about the initial data products. Please contact us at vlass"at"nrao.edu with your comments, or provide feedback through the Science Working Group.


The VLA Sky Survey

The VLASS will consist of a survey of the entire sky visible to the VLA. The survey goals are listed below:

VLASS Summary
Frequency 2-4GHz
Resolution 2.5 arcsec
Sky coverage All Sky North of Dec. -40 deg. (33885 deg2)
Sensitivity per epoch 120 μJy RMS
Combined (3 epoch) sensitivity 69 μJy RMS
Polarization I,Q,U
Cadence 3 epochs separated by 32 months
Start Date September 15 2017
Expected number of sources ~5,000,000

Data Products

NRAO will make Basic Data Products (BDPs) for the survey available through the NRAO archive, including:

  • Raw visibility data (available immediately)
  • Calibration tables (within 1-2 weeks of observation)
  • "Quicklook" 2D Stokes I images (within 2 weeks of observation)
  • 2D images in Stokes I (per epoch and cumulative; available ~6-12 months after observations).
  • RMS images.
  • Coarse resolution cubes (128MHz channels, IQU polarization) around ~106 bright sources.
  • Fine resolution (16MHz channel, IQU polarization) cubes around the ~50000 brightest sources.
  • Catalogs of source components from both the 2D images and the cubes.

In addition, community groups will produce Enhanced Data Products to supplement the BDPs produced by NRAO, for example rotation measure maps and event brokers for transients. 

Pilot Survey. The VLASS Pilot Survey was completed in September 2016. 196 hours were observed in the fields listed in VLASS Memo #2, and raw data may be found in the archive under the TSKY0001 project code.

VLASS Memo Series. A series of VLASS memos has been written describing various aspects of the survey, ranging from the science case for the survey to technical details of the execution and calibration of the survey. The memo series may be found on the VLASS public wiki.

Reminder: A Google Group has been set up to facilitate communication and discussion on the Science Working Group, open to all.  Please sign up by visiting the above link!



Motivation

Very Large ArrayIn the 20 years since the initial observations were made for the NRAO VLA Sky Survey (NVSS) and the Faint Images of the Radio Sky at Twenty-Centimeters (FIRST), these pioneering programs have defined the state-of-the-art in centimeter radio sky surveys and produced a steady stream of excellent science. Given the enhanced capabilities of the Jansky Very Large Array (VLA), now is an appropriate time to exploit the scientific potential of new centimeter-wavelength sky surveys.

The astronomy community has already recognized that several of the high priority science goals of the 2010 decadal survey New Worlds, New Horizons in Astronomy and Astrophysics could be addressed by a new VLA sky survey. At the May 2013 Radio Astronomy in the LSST Era held at NRAO-Charlottesville many scientists expressed keen interest in employing the VLA to conduct new, wide-area centimeter wavelength sky surveys in support of multi-wavelength synoptic surveys using existing and future facilities, such as the Large Synoptic Survey Telescope (LSST). A community-led Science Survey Group (SSG) defined the science program and key components of VLASS, and NRAO supports its technical definition and implementation.