Deep sub-arcsecond widefield imaging of the Lockman Hole field at 144 MHz

Abstract

High quality low-frequency radio surveys have the promise of advancing our understanding of many important topics in astrophysics, including the life cycle of active galactic nuclei (AGN), particle acceleration processes in jets, the history of star formation, and exoplanet magnetospheres. Currently leading low-frequency surveys reach an angular resolution of a few arcseconds. However, this resolution is not yet sufficient to study the more compact and distant sources in detail. Sub-arcsecond resolution is therefore the next milestone in advancing these fields. The biggest challenge at low radio frequencies is the ionosphere. If not adequately corrected for, ionospheric seeing blurs the images to arcsecond or even arcminute scales. Additionally, the required image size to map the degree-scale field of view of low-frequency radio telescopes at this resolution is far greater than what typical soft- and hardware is currently capable of handling. Here we present for the first time (to the best of our knowledge) widefield sub-arcsecond imaging at low radio frequencies. We derive ionospheric corrections in a few dozen individual directions and apply those during imaging efficiently using a recently developed imaging algorithm (arXiv:1407.1943, arXiv:1909.07226). We demonstrate our method by applying it to an eight hour observation of the International LOw Frequency ARray (LOFAR) Telescope (ILT) (arXiv:1305.3550). Doing so we have made a sensitive $7.4{\mathrm{deg}}^2$ $144\mathrm{MHz}$ map at a resolution of $0.3^{\prime \prime }$ reaching $25\mu {\mathrm{Jy}\mathrm{beam}}^{-1}$ near the phase centre. The estimated $250,000$ core hours used to produce this image, fit comfortably in the budget of available computing facilities. This result will enable future mapping of the entire northern low-frequency sky at sub-arcsecond resolution.

19 pages, 4 figures; This preprint has not undergone peer review or any post-submission improvements or corrections. The Version of Record of this article is published in Nature Astronomy, and is available online at https://doi.org/10.1038/s41550-021-01573-z

References in corpus (10)

• WSClean: an implementation of a fast, generic wide-field imager for radio astronomy
• The LOFAR Two Meter Sky Survey: Deep Fields, I -- Direction-dependent calibration and imaging
• LOFAR observations of galaxy clusters in HETDEX
• The LOFAR Two Metre Sky Survey: Deep Fields Data Release 1 -- III. Host-galaxy identifications and value added catalogues
• Sub-arcsecond imaging with the International LOFAR Telescope I. Foundational calibration strategy and pipeline
• Deep, wide-field, global VLBI observations of the Hubble Deep Field North and Flanking Fields
• The e-MERLIN Galaxy Evolution Survey (e-MERGE): Overview and Survey Description
• A deep, high resolution survey of the low frequency radio sky
• Sub-arcsecond imaging with the International LOFAR Telescope: II. Completion of the LOFAR Long-Baseline Calibrator Survey
• VLBI imaging throughout the primary beam using accurate UV shifting

Cited by in corpus (23)

• The LOFAR Two-metre Sky Survey -- V. Second data release
• The LOFAR Two-metre Sky Survey Deep Fields Data Release 1: V. Survey description, source classifications and host galaxy properties
• The Faraday Rotation Measure Grid of the LOFAR Two-metre Sky Survey: Data Release 2
• Cosmic evolution of low-excitation radio galaxies in the LOFAR Two-meter Sky Survey Deep Fields
• The LOFAR LBA Sky Survey II. First data release
• Identifying active galactic nuclei via brightness temperature with sub-arcsecond International LOFAR Telescope observations
• The LOFAR Two-metre Sky Survey: the radio view of the cosmic star formation history
• The Second Radio Synchrotron Background Workshop: Conference Summary and Report
• Cosmic evolution of radio-AGN feedback: confronting models with data
• A machine learning based approach to gravitational lens identification with the International LOFAR Telescope
• A Quick Look at the 3GHz Radio Sky. II. Hunting for DRAGNs in the VLA Sky Survey
• The prototypical major cluster merger Abell 754. I. Calibration of MeerKAT data and radio/X-ray spectral mapping of the cluster
• Exploring diffuse radio emission in galaxy clusters and groups with the uGMRT and the SKA
• Noema formIng Cluster survEy (NICE): Discovery of a starbursting galaxy group with a radio-luminous core at z=3.95
• A super-linear "radio-AGN main sequence'' links mean radio-AGN power and galaxy stellar mass since z$\sim$3
• Kpc-scale Radio Structure in $z\sim 0.25$ Radio-Quiet QSOs
• 1-arcsecond imaging of ELAIS-N1 field at 144MHz using the LoTSS survey with international LOFAR telescope
• Monster radio jet (>66 kpc) observed in quasar at z$\sim$5
• The global energetics of radio AGN kinetic feedback in the local universe
• An extended and extremely thin gravitational arc from a lensed compact symmetric object at redshift 2.059
• The Jet Paths of Radio AGN and their Cluster Weather
• Revealing the intricacies of radio galaxies and filaments in the merging galaxy cluster Abell 2255. II. Properties of filaments using multi-frequency radio data
• Prospects for radio weak lensing: studies using LOFAR observations in the ELAIS-N1 field