The LOFAR Multifrequency Snapshot Sky Survey (MSSS) I. Survey description and first results

TL;DR

The MSSS is a pioneering northern-sky radio survey with multifrequency coverage from 30 to 160 MHz, providing valuable spectral data and demonstrating LOFAR's fast survey capabilities, serving as a precursor to SKA surveys.

Contribution

This paper introduces the first northern-sky LOFAR imaging survey with multifrequency data, detailed methodology, and initial results, setting the stage for future large-scale radio surveys.

Findings

Achieved 90% completeness at 100 mJy (135 MHz) and 550 mJy (50 MHz).

Compared MSSS results with previous surveys, assessing uncertainties.

Produced images and catalogs for a 100 sq. degree field, with plans for full survey release.

Abstract

We present the Multifrequency Snapshot Sky Survey (MSSS), the first northern-sky LOFAR imaging survey. In this introductory paper, we first describe in detail the motivation and design of the survey. Compared to previous radio surveys, MSSS is exceptional due to its intrinsic multifrequency nature providing information about the spectral properties of the detected sources over more than two octaves (from 30 to 160 MHz). The broadband frequency coverage, together with the fast survey speed generated by LOFAR's multibeaming capabilities, make MSSS the first survey of the sort anticipated to be carried out with the forthcoming Square Kilometre Array (SKA). Two of the sixteen frequency bands included in the survey were chosen to exactly overlap the frequency coverage of large-area Very Large Array (VLA) and Giant Metrewave Radio Telescope (GMRT) surveys at 74 MHz and 151 MHz respectively. The survey performance is illustrated within the "MSSS Verification Field" (MVF), a region of 100 square degrees centered at J2000 (RA,Dec)=(15h,69deg). The MSSS results from the MVF are compared with previous radio survey catalogs. We assess the flux and astrometric uncertainties in the catalog, as well as the completeness and reliability considering our source finding strategy. We determine the 90% completeness levels within the MVF to be 100 mJy at 135 MHz with 108" resolution, and 550 mJy at 50 MHz with 166" resolution. Images and catalogs for the full survey, expected to contain 150,000-200,000 sources, will be released to a public web server. We outline the plans for the ongoing production of the final survey products, and the ultimate public release of images and source catalogs.