The Radio Sky at Meter Wavelengths: m-Mode Analysis Imaging with the Owens Valley Long Wavelength Array

Abstract

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 $20\gtrsim z\gtrsim 7$, 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 widefield 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 widefield 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 Long Wavelength Array (OVRO-LWA) by generating 8 new maps of the sky north of $\delta =-30^{\circ }$ with 15 arcmin angular resolution, at frequencies evenly spaced between 36.528 MHz and 73.152 MHz, and $\sim$800 mJy/beam thermal noise. These maps are a 10-fold improvement in angular resolution over existing full-sky maps at comparable frequencies, which have angular resolutions $\ge 2^{\circ }$. 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.

27 pages, 18 figures

References in corpus (43)

• HEALPix -- a Framework for High Resolution Discretization, and Fast Analysis of Data Distributed on the Sphere
• Cosmology at Low Frequencies: The 21 cm Transition and the High-Redshift Universe
• An absorption profile centred at 78 megahertz in the sky-averaged spectrum
• 21-cm cosmology
• WSClean: an implementation of a fast, generic wide-field imager for radio astronomy
• The GMRT 150 MHz All-sky Radio Survey: First Alternative Data Release TGSS ADR1
• A model of diffuse Galactic Radio Emission from 10 MHz to 100 GHz
• An Accurate Flux Density Scale from 50 MHz to 50 GHz
• Shapelets: I. A Method for Image Analysis
• A Per-Baseline, Delay-Spectrum Technique for Accessing the 21cm Cosmic Reionization Signature
• The non-coplanar baselines effect in radio interferometry: The W-Projection algorithm
• GLEAM: The GaLactic and Extragalactic All-sky MWA survey
• A broadband flux scale for low frequency radio telescopes
• Upper limits on the 21-cm Epoch of Reionization power spectrum from one night with LOFAR
• The Very Large Array Low-frequency Sky Survey Redux (VLSSr)
• PAPER-64 Constraints on Reionization: The 21cm Power Spectrum at z=8.4
• 21CMMC: an MCMC analysis tool enabling astrophysical parameter studies of the cosmic 21 cm signal
• Radio interferometric gain calibration as a complex optimization problem
• An Improved Model of Diffuse Galactic Radio Emission from 10 MHz to 5 THz
• All-Sky Interferometry with Spherical Harmonic Transit Telescopes
• Real-Time Calibration of the Murchison Widefield Array
• Coaxing Cosmic 21cm Fluctuations from the Polarized Sky using m-mode Analysis
• First Season MWA EoR Power Spectrum Results at Redshift 7
• Probing the Dark Ages at Z~20: The SCI-HI 21 cm All-Sky Spectrum Experiment
• Probing Ionospheric Structures using the LOFAR radio telescope
• BIGHORNS - Broadband Instrument for Global HydrOgen ReioNisation Signal
• All-sky Galactic radiation at 45 MHz and spectral index between 45 and 408 MHz
• The Scale of the Problem : Recovering Images of Reionization with GMCA
• Results from EDGES High-Band: I. Constraints on Phenomenological Models for the Global $21$ cm Signal
• The 74MHz System on the Very Large Array
• Wide-field wide-band interferometric imaging:The WB A-Projection and hybrid algorithms
• First Limits on the 21 cm Power Spectrum during the Epoch of X-ray heating
• The LOFAR Multifrequency Snapshot Sky Survey (MSSS) I. Survey description and first results
• The LWA1 Low Frequency Sky Survey
• Low frequency observations of linearly polarized structures in the interstellar medium near the south Galactic pole
• Improved Measurement of the Spectral Index of the Diffuse Radio Background Between 90 and 190 MHz
• Complete history of the observable 21-cm signal from the first stars during the pre-reionization era
• Fast gain calibration in radio astronomy using alternating direction implicit methods: Analysis and applications
• Scintillation noise in widefield radio interferometry
• A Technique for Primary Beam Calibration of Drift-Scanning, Wide-Field Antenna Elements
• The Evolution of Cas A at Low Radio Frequencies
• Brute-Force Mapmaking with Compact Interferometers: A MITEoR Northern Sky Map from 128 MHz to 175 MHz
• A practical theorem on using interferometry to measure the global 21-cm signal

Cited by in corpus (66)

• Data Analysis for Precision 21 cm Cosmology
• Deep multi-redshift limits on Epoch of Reionisation 21cm Power Spectra from Four Seasons of Murchison Widefield Array Observations
• The 21 cm Power Spectrum from the Cosmic Dawn: First Results from the OVRO-LWA
• Discovery of Magnetic Fields Along Stacked Cosmic Filaments as Revealed by Radio and X-Ray Emission
• BURSTT: Bustling Universe Radio Survey Telescope in Taiwan
• Spectral Index of the Diffuse Radio Background Between 50 and 100 MHz
• The Tianlai Dish Pathfinder Array: design, operation and performance of a prototype transit radio interferometer
• A 21-cm power spectrum at 48 MHz, using the Owens Valley Long Wavelength Array
• Absolute Calibration Strategies for the Hydrogen Epoch of Reionization Array and Their Impact on the 21 cm Power Spectrum
• DAYENU: A Simple Filter of Smooth Foregrounds for Intensity Mapping Power Spectra
• The Tianlai Cylinder Pathfinder Array: System Functions and Basic Performance Analysis
• Science with the Murchison Widefield Array: Phase I Results and Phase II Opportunities
• Patterns of primary beam non-redundancy in close-packed 21 cm array observations
• Calibration and 21-cm Power Spectrum Estimation in the Presence of Antenna Beam Variations
• Antenna beam characterisation for the global 21cm experiment LEDA and its impact on signal model parameter reconstruction
• Precision requirements for interferometric gridding in 21-cm power spectrum analysis
• A simultaneous search for prompt radio emission associated with the short GRB 170112A using the all-sky imaging capability of the OVRO-LWA
• Polarized accretion shocks from the cosmic web
• Spectral index of the Galactic foreground emission in the 50-87 MHz range
• Design and Initial Performance of the Prototype for the BEACON Instrument for Detection of Ultrahigh Energy Particles
• A Map of Diffuse Radio Emission at 182 MHz to Enhance Epoch of Reionization Observations in the Southern Hemisphere
• Modelling the Galactic Foreground and Beam Chromaticity for Global 21-cm Cosmology
• Self-triggered radio detection and identification of cosmic air showers with the OVRO-LWA
• A First Search for Prompt Radio Emission from a Gravitational-Wave Event
• Measuring HERA's primary beam in-situ: methodology and first results
• Extracting the 21 cm EoR signal using MWA drift scan data
• New Limits on the Low-frequency Radio Transient Sky Using 31 hr of All-sky Data with the OVRO-LWA
• Galactic synchrotron distribution derived from 152 HII region absorption features in the full GLEAM survey
• Murchison Widefield Array rapid-response observations of the short GRB 180805A
• The Tianlai dish array low-z surveys forecasts
• On the use of temporal filtering for mitigating galactic synchrotron calibration bias in 21 cm reionization observations
• A Semi-blind PCA-based Foreground Subtraction Method for 21 cm Intensity Mapping
• Filamentary structures of ionized gas in Cygnus X
• Imaging Spectroscopy of CME-Associated Solar Radio Bursts
• FIGARO Simulation: FIlaments & GAlactic RadiO Simulation
• AARTFAAC Flux Density Calibration and Northern Hemisphere Catalogue at 60 MHz
• Degree-Scale Galactic Radio Emission at 122 MHz around the North Celestial Pole with LOFAR-AARTFAAC
• Impact of $1/f$ noise on cosmological parameter constraints for SKA intensity mapping
• Direct Optimal Mapping for 21cm Cosmology: A Demonstration with the Hydrogen Epoch of Reionization Array
• Effects of model incompleteness on the drift-scan calibration of radio telescopes
• Synchrotron emission from virial shocks around stacked OVRO-LWA galaxy clusters
• Stacking the Synchrotron Cosmic Web with FIGARO
• Delay-Weighted Calibration: Precision Calibration for 21 cm Cosmology with Resilience to Sky Model Error
• Optimization and Commissioning of the EPIC Commensal Radio Transient Imager for the Long Wavelength Array
• A Differentiable, End-to-End Forward Model for 21 cm Cosmology: Estimating the Foreground, Instrument, and Signal Joint Posterior
• The Tracking Tapered Gridded Estimator (TTGE) for the power spectrum from drift scan observations
• The FHD Polarized Imaging Pipeline: A New Approach to Widefield Interferometric Polarimetry
• Statistical estimation of full-sky radio maps from 21cm array visibility data using Gaussian constrained realizations
• Global Sky Models can Improve Flux Estimates in Pulsar and FRB Studies
• Searching for the Synchrotron Cosmic Web Again: A replication attempt
• Bayesian evidence for flux scale errors in Galactic synchrotron maps
• Uncertainties of the 30-408 MHz Galactic emission as a calibration source for radio detectors in astroparticle physics
• Radio Observations as a Probe of Cosmic Web Magnetism
• Detecting 21 cm EoR Signal using Drift Scans: Correlation of Time-ordered Visibilities
• AlgoSCR: An algorithm for Solar Contamination Removal from radio interferometric data
• The Optical Depth of Foregrounds for the Highest Redshift 21 cm Signals
• A Matched Survey for the Enigmatic Low Radio Frequency Transient ILT J225347+862146
• Synthesis imaging with a lunar orbit array: I. global sky map and its systematics
• Bayesian recalibration of flux scale factors in diffuse radio maps using low-resolution absolute radiometers
• Forecasts on Interacting Dark Energy from 21-cm Angular Power Spectrum with BINGO and SKA observations
• Foreground Subtraction with a Tensor-Based Oriented Singular Value Decomposition Method for HI Experiments
• Measurements of the diffuse Galactic synchrotron spectral index and curvature from MeerKLASS pilot data
• Imaging the Southern Sky at 159MHz using Spherical Harmonics with the Engineering Development Array 2
• Constraints on the properties of warm ionized gas from low-frequency hydrogen radio recombination lines
• Tracking the Source of Solar Type II Bursts through Comparisons of Simulations and Radio Data
• All-Sky Imaging with Vector Sensor Interferometry