The Karl G. Jansky Very Large Array Sky Survey (VLASS). Science case and survey design (1907.01981v3)

Abstract: The Very Large Array Sky Survey (VLASS) is a synoptic, all-sky radio sky survey with a unique combination of high angular resolution ($\approx$2.5"), sensitivity (a 1$\sigma$ goal of 70 $\mu$Jy/beam in the coadded data), full linear Stokes polarimetry, time domain coverage, and wide bandwidth (2-4 GHz). The first observations began in September 2017, and observing for the survey will finish in 2024. VLASS will use approximately 5500 hours of time on the Karl G. Jansky Very Large Array (VLA) to cover the whole sky visible to the VLA (Declination $>-40^{\circ}$), a total of 33,885 deg$^2$. The data will be taken in three epochs to allow the discovery of variable and transient radio sources. The survey is designed to engage radio astronomy experts, multi-wavelength astronomers, and citizen scientists alike. By utilizing an "on the fly" interferometry mode, the observing overheads are much reduced compared to a conventional pointed survey. In this paper, we present the science case and observational strategy for the survey, and also results from early survey observations.

• The paper presents a new survey design using rapid 'on the fly' imaging to cover 33,885 sq deg with 2.5 arcsec resolution.
• The paper details a three-epoch strategy repeating every 32 months to enhance time-domain and transient studies in radio astronomy.
• The paper provides robust polarization data that facilitate detailed investigations of magnetic fields and AGN feedback across cosmic environments.

Overview of the Karl G. Jansky Very Large Array Sky Survey (VLASS)

The Karl G. Jansky Very Large Array Sky Survey (VLASS) represents a significant undertaking by the National Radio Astronomy Observatory (NRAO) to survey the radio sky using cutting-edge techniques and technology. This extensive survey is conducted using the powerful capabilities of the Very Large Array (VLA), leveraging its increased sensitivity following recent upgrades. The design and execution of VLASS have been carefully orchestrated to produce a wealth of data across several dimensions, including temporal, spectral, and polarimetric domains.

VLASS Design and Observational Methodology

VLASS is orchestrated over three epochs, covering a vast expanse of the sky to capture transient phenomena, thereby enriching the time-domain astrophysics landscape. Each epoch of observations spans several months, with observation cycles repeating approximately every 32 months, facilitating the paper of the dynamic sky and allowing for the detection of variable sources. The survey targets all sky areas visible to the VLA above a declination of -40 degrees, providing coverage for a staggering 33,885 square degrees.

The survey uses "on the fly" interferometry methods, significantly reducing observational overheads compared to traditional pointed observations. This technique allows for swift, comprehensive imaging, capturing a resolution of approximately 2.5 arcseconds across the entire survey to offer high-fidelity imaging akin to those at optical wavelengths, vital for reliable source identification and classification.

Scientific Objectives and Implications

VLASS is guided by succinct scientific aims which underpin the survey's design and execution. It approaches various thematic research domains including:

1. Transient and Time-Domain Astronomy: The survey is poised to investigate the transient radio sky meticulously, unveiling phenomena such as supernovae, gamma-ray bursts, and tidal disruption events. By executing three separate epochs, VLASS is able to discern variables and transients unfolding over an array of timescales, adding rich layers of context to known explosive events and possibly uncovering new classes of transient phenomena.
2. Polarization and Magnetic Fields: With robust polarization capabilities, VLASS enables in-depth studies of Faraday rotation measures across a spectrum of astronomical radio sources, casting light on the intervening magneto-ionic media and thereby shedding light on magnetic structures in galaxies and AGNs.
3. AGN Evolution and Feedback Mechanisms: High-resolution imaging allows detailed inspection of radio galaxy morphologies, helping to decipher accretion mechanisms and feedback processes in various AGN classes. The survey aims to provide statistical clarity on the developmental trajectories of AGN outflows and their interactions with constituent environments.
4. Stellar Activity and Galactic Studies: VLASS retains strong implications for Galactic physics, particularly in probing compact sources and stellar magnetic activity. The deployment over significant sections of the Galactic plane enhances the capacity to probe stars, compact objects, and diffuse emission associated with Galactic structure.

Technological Implementation and Data Products

The VLASS makes extensive use of the infrastructure provided by the VLA, leveraging its wideband frequency capabilities and its ability to observe in full polarization. The survey generates a suite of data products, ranging from calibrated raw visibility data to advanced image cubes in Stokes parameters, providing robust inputs for research into spectral energy distributions, polarization, and transient events.

As a collaborative effort, the VLASS opens avenues for enhanced data services and products to be developed within the community, allowing integration with multi-wavelength data to provide insightful interpretations and applications of the collected data. Moreover, the VLASS’s comprehensive archiving and data distribution system ensures public access to the wealth of data being collected, thus democratizing scientific tools and outcomes across the astronomical community.

Conclusion and Prospect

VLASS stands as an exemplary initiative in radio astronomy, promising to broaden our knowledge base across different cosmological epochs and environments. Its synergy with other large-scale surveys facilitates cross-correlation studies and amplifies its scientific utility. As it reaches completion, VLASS is set to redefine our understanding of the radio universe, laying foundations for future radio surveys and the exciting science they promise to deliver.