VLASS2.1.se.T28t01.J001924+723000 (0:13:00.8, 72:31:18.7 - Planetary Nebula/Tycho Brahe SN Remnant) (Left) & VLASS2.1.se.T27t08.J122846+673000 (12:33:14.1, 67:07:43.8 - Radio Galaxy) (Right). Credit: NSF/AUI/NSF NRAO/VLASS - Hi-Res File
The U.S. National Science Foundation National Radio Astronomy Observatory (NSF NRAO) has completed observations for the Very Large Array Sky Survey (VLASS), the most detailed radio survey of the sky ever conducted, providing an unprecedented view of the dynamic radio universe.
Scope and Scale of VLASS
Conducted with the U.S. National Science Foundation Very Large Array (NSF VLA), VLASS spans nearly a decade of observations, from September 2017 through February 2026, and represents one of the most ambitious radio surveys ever undertaken. Covering approximately 34,000 square degrees, essentially the entire sky visible to the VLA down to -40 degrees declination, the survey delivers a powerful new resource for astronomers worldwide. The survey produced approximately 0.5 petabytes of raw data, and the total volume of processed data products is expected to reach about 2 petabytes, making it the largest survey the VLA has undertaken in terms of data volume.
“With VLASS, we now have a radio map of the sky that matches the resolution of modern optical and infrared surveys,” said Amy Kimball, VLASS Head of Operations. “This opens the door to truly multiwavelength discoveries at a level of detail that was not previously possible.”
VLASS achieves an angular resolution of about 2.5 arcseconds, making it the highest-resolution full-sky radio survey to date. Observations were carried out across the 2–4 GHz frequency range, enabling astronomers to measure in-band spectral indices, which are key to understanding the physical processes powering radio emission from cosmic sources.
“With VLASS, we now have a radio map of the sky that matches the resolution of modern optical and infrared surveys,” said Amy Kimball, VLASS Head of Operations. “This opens the door to truly multiwavelength discoveries at a level of detail that was not previously possible.”
VLASS achieves an angular resolution of about 2.5 arcseconds, making it the highest-resolution full-sky radio survey to date. Observations were carried out across the 2–4 GHz frequency range, enabling astronomers to measure in-band spectral indices, which are key to understanding the physical processes powering radio emission from cosmic sources.
Observing Strategy and Coverage
Over the course of roughly 6,500 observing hours, the NSF VLA repeatedly scanned the sky using an innovative “on-the-fly mosaicking” technique. In this mode, antennas continuously sweep across the sky in a raster pattern while collecting data, maximizing efficiency and uniform coverage. The survey observed the sky three and a half times in total, with half the sky imaged four times and the other half three times, enabling both deep imaging and the detection of variable and transient sources.
VLASS was conducted in full polarization, allowing astronomers to probe cosmic magnetic fields through measurements such as Faraday rotation. These data provide new insights into the structure and evolution of magnetism across the universe. The survey is a cornerstone of NSF NRAO’s Science Ready Data Products initiative, which provides fully calibrated data and high-quality images directly to the scientific community and the public. By lowering technical barriers, VLASS makes cutting-edge radio astronomy accessible to both experts and non-specialists.
VLASS is designed to address four major science themes:
– Hidden Explosions and Transient Events, including supernovae, gamma-ray bursts, and other short-lived phenomena.
– Faraday Tomography of the Magnetic Sky, using polarization data to map magnetic fields across cosmic environments.
– Imaging Galaxies through Time and Space, tracing the evolution of galaxies and active galactic nuclei.
– The New Milky Way, revealing previously unseen structures and sources within our own galaxy.
These themes are described in detail in the survey’s foundational paper (Lacy et al. 2020, PASP, 132, 035001), which outlines the scientific goals and design of VLASS.
VLASS was conducted in full polarization, allowing astronomers to probe cosmic magnetic fields through measurements such as Faraday rotation. These data provide new insights into the structure and evolution of magnetism across the universe. The survey is a cornerstone of NSF NRAO’s Science Ready Data Products initiative, which provides fully calibrated data and high-quality images directly to the scientific community and the public. By lowering technical barriers, VLASS makes cutting-edge radio astronomy accessible to both experts and non-specialists.
VLASS is designed to address four major science themes:
– Hidden Explosions and Transient Events, including supernovae, gamma-ray bursts, and other short-lived phenomena.
– Faraday Tomography of the Magnetic Sky, using polarization data to map magnetic fields across cosmic environments.
– Imaging Galaxies through Time and Space, tracing the evolution of galaxies and active galactic nuclei.
– The New Milky Way, revealing previously unseen structures and sources within our own galaxy.
These themes are described in detail in the survey’s foundational paper (Lacy et al. 2020, PASP, 132, 035001), which outlines the scientific goals and design of VLASS.
A Legacy Dataset for the Future
By combining high resolution, wide sky coverage, spectral information, and time-domain sensitivity, VLASS establishes a new benchmark for radio surveys and provides a legacy dataset that will support discovery for years to come. Processing and imaging of the full dataset will continue over the next several years as these science-ready products are completed and released.
“VLASS is not just a survey, it is a long-term investment in the future of astrophysics,” said Mark Lacy, VLASS Project Director. “Its combination of depth, coverage, and accessibility ensures that it will remain a foundational resource for the community.”
“VLASS is not just a survey, it is a long-term investment in the future of astrophysics,” said Mark Lacy, VLASS Project Director. “Its combination of depth, coverage, and accessibility ensures that it will remain a foundational resource for the community.”
Additional information and access to VLASS data products are available through NRAO here.
About NRAO
The National Radio Astronomy Observatory is a major facility of the U.S. National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.
