Deconvolving the Wedge: Maximum-Likelihood Power Spectra via Spherical-Wave Visibility Modeling
arXiv:1709.06752 · doi:10.1093/mnras/stx2959
Abstract
Direct detection of the Epoch of Reionization (EoR) via the red-shifted 21-cm line will have unprecedented implications on the study of structure formation in the infant Universe. To fulfill this promise, current and future 21-cm experiments need to detect this weak EoR signal in the presence of foregrounds that are several orders of magnitude larger. This requires extreme noise control and improved wide-field high dynamic-range imaging techniques. We propose a new imaging method based on a maximum likelihood framework which solves for the interferometric equation directly on the sphere, or equivalently in the -domain. The method uses the one-to-one relation between spherical waves and spherical harmonics (SpH). It consistently handles signals from the entire sky, and does not require a -term correction. The spherical-harmonics coefficients represent the sky-brightness distribution and the visibilities in the -domain, and provide a direct estimate of the spatial power spectrum. Using these spectrally-smooth SpH coefficients, bright foregrounds can be removed from the signal, including their side-lobe noise, which is one of the limiting factors in high dynamics range wide-field imaging. Chromatic effects causing the so-called "wedge" are effectively eliminated (i.e. deconvolved) in the cylindrical () power spectrum, compared to a power spectrum computed directly from the images of the foreground visibilities where the wedge is clearly present. We illustrate our method using simulated LOFAR observations, finding an excellent reconstruction of the input EoR signal with minimal bias.
13 pages, 8 figures. Replaced to match accepted MNRAS version; few typos corrected & textual clarification added (no changes to results)
References in corpus (27)
- Cosmology at Low Frequencies: The 21 cm Transition and the High-Redshift Universe
- Cosmic Reionization and Early Star-Forming Galaxies: A Joint Analysis of New Constraints from Planck and Hubble Space Telescope
- Observational constraints on Cosmic Reionization
- Efficient Simulations of Early Structure Formation and Reionization
- Measurement of 21 cm brightness fluctuations at z ~ 0.8 in cross-correlation
- Foreground simulations for the LOFAR - Epoch of Reionization Experiment
- Evolution of the 21 cm signal throughout cosmic history
- On using visibility correlations to probe the HI distribution from the dark ages to the present epoch I: Formalism and the expected signal
- Blind foreground subtraction for intensity mapping experiments
- The Scale of the Problem : Recovering Images of Reionization with GMCA
- An Improved Method for 21cm Foreground Removal
- Foregrounds for redshifted 21 cm studies of reionization: GMRT 153 MHz observations
- 21 cm signal from cosmic dawn: Imprints of spin temperature fluctuations and peculiar velocities
- The multi-frequency angular power spectrum of the epoch of reionization 21 cm signal
- Characterizing Foreground for redshifted 21-cm radiation: 150 MHz GMRT observations
- Non-parametric foreground subtraction for 21cm epoch of reionization experiments
- SZ and CMB reconstruction using Generalized Morphological Component Analysis
- A generalised Measurement Equation and van Cittert-Zernike theorem for wide-field radio astronomical interferometry
- Visibility based angular power spectrum estimation in low frequency radio interferometric observations
- Towards simulating and quantifying the light-cone EoR 21-cm signal
- Spherical Harmonic Analyses of Intensity Mapping Power Spectra
- Re-examining the case for neutral gas near the redshift 7 quasar ULAS J1120+0641
- Studying 21cm power spectrum with one-point statistics
- Simulating full-sky interferometric observations
- Imaging on a Sphere with Interferometers: the Spherical Wave Harmonic Transform
- Simulated foreground predictions for HI at z = 3.35 with the Ooty Wide Field Array: I. Instrument and the foregrounds
- Direct reconstruction of spherical harmonics from interferometer observations of the CMB polarization