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Published July 2018 | Published + Submitted
Journal Article Open

The Radio Sky at Meter Wavelengths: m-mode Analysis Imaging with the OVRO-LWA


A host of new low-frequency radio telescopes seek to measure the 21 cm transition of neutral hydrogen from the early universe. These telescopes have the potential to directly probe star and galaxy formation at redshifts 20 ≳ z ≳ 7 but are limited by the dynamic range they can achieve against foreground sources of low-frequency radio emission. Consequently, there is a growing demand for modern, high-fidelity maps of the sky at frequencies below 200 MHz for use in foreground modeling and removal. We describe a new wide-field imaging technique for drift-scanning interferometers: Tikhonov-regularized m-mode analysis imaging. This technique constructs images of the entire sky in a single synthesis imaging step with exact treatment of wide-field effects. We describe how the CLEAN algorithm can be adapted to deconvolve maps generated by m-mode analysis imaging. We demonstrate Tikhonov-regularized m-mode analysis imaging using the Owens Valley Radio Observatory Long Wavelength Array (OVRO-LWA) by generating eight new maps of the sky north of δ = −30° with 15' angular resolution at frequencies evenly spaced between 36.528 and 73.152 MHz and ~800 mJy beam^(−1) thermal noise. These maps are a 10-fold improvement in angular resolution over existing full-sky maps at comparable frequencies, which have angular resolutions ≥2°. Each map is constructed exclusively from interferometric observations and does not represent the globally averaged sky brightness. Future improvements will incorporate total power radiometry, improved thermal noise, and improved angular resolution due to the planned expansion of the OVRO-LWA to 2.6 km baselines. These maps serve as a first step on the path to the use of more sophisticated foreground filters in 21 cm cosmology incorporating the measured angular and frequency structure of all foreground contaminants.

Additional Information

© 2018 The American Astronomical Society. Received 2017 October 25; revised 2018 May 9; accepted 2018 May 20; published 2018 June 29. This work is dedicated to the memory of Professor Marjorie Corcoran, who was an influential mentor to MWE. This material is based in part upon work supported by the National Science Foundation under grants AST-1654815 and AST-1212226. The OVRO-LWA project was initiated through the kind donation of Deborah Castleman and Harold Rosen. Part of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration, including partial funding through the President's and Director's Fund Program. This work has benefited from open-source technology shared by the Collaboration for Astronomy Signal Processing and Electronics Research (CASPER). We thank the Xilinx University Program for donations; NVIDIA for proprietary tools, discounts, and donations; and Digicom for collaboration on the manufacture and testing of DSP processors. We thank the Smithsonian Astrophysical Observatory Submillimeter Receiver Lab for the collaboration of its members. Development, adaptation, and operation of the LEDA real-time digital signal-processing systems at OVRO-LWA have been supported in part by NSF grants AST/1106059, PHY/0835713, and OIA/1125087. G.B.T., J.D., and F.K.S. acknowledge support from the National Science Foundation under grant AST-1139974.

Attached Files

Published - Eastwood_2018_AJ_156_32.pdf

Submitted - 1711.00466.pdf


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August 22, 2023
October 18, 2023