IMAGING THE EPOCH OF REIONIZATION: LIMITATIONS FROM FOREGROUND CONFUSION AND IMAGING ALGORITHMS

By H. Vedantham, N. Udaya Shankar, R. Subrahmanyan. 2011

156 citations recorded by the source corpus.

Tomography of redshifted 21 cm transition from neutral hydrogen using Fourier synthesis telescopes is a promising tool to study the Epoch of Reionization (EoR). Limiting the confusion from Galactic and extragalactic foregrounds is critical to the success of these telescopes. The instrumental response or the point-spread function (PSF) of such telescopes is inherently three dimensional with frequency mapping to the line-of-sight (LOS) distance. EoR signals will necessarily have to be detected in data where continuum confusion persists; therefore, it is important that the PSF has acceptable frequency structure so that the residual foreground does not confuse the EoR signature. This paper aims to understand the three-dimensional PSF and foreground contamination in the same framework. We develop a formalism to estimate the foreground contamination along frequency, or equivalently LOS dimension, and establish a relationship between foreground contamination in the image plane and visibility weights on the Fourier plane. We identify two dominant sources of LOS foreground contamination—“PSF contamination” and “gridding contamination.” We show that PSF contamination is localized in LOS wavenumber space, beyond which there potentially exists an “EoR window” with negligible foreground contamination where we may focus our efforts to detect EoR. PSF contamination in this window may be substantially reduced by judicious choice of a frequency window function. Gridding and imaging algorithms create additional gridding contamination and we propose a new imaging algorithm using the Chirp Z Transform that significantly reduces this contamination. Finally, we demonstrate the analytical relationships and the merit of the new imaging algorithm for the case of imaging with the Murchison Widefield Array.

Subfields: Astronomy and Astrophysics, Atomic and Molecular Physics, and Optics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/a4bc9e888416dfc9b47c4a3e895b4b978c168a90

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Citations in the corpus

FIRST SEASON MWA EOR POWER SPECTRUM RESULTS AT REDSHIFT 7 (2016, background): “…Fourier modes (Thyagarajan et al. 2015a,b; Trott et al. 2012; Liu et al. 2014a,b; Hazelton et al. 2013; Pober et al. 2013; Thyagarajan et al. 2013; Vedantham et al. 2012; Morales et al. 2012; Datta et al. 2010), while others are investigating the spectral structure of point sources themselves…”
21CMMC: an MCMC analysis tool enabling astrophysical parameter studies of the cosmic 21 cm signal (2015, background): “…across all frequencies, but instead localize the majority of the foreground noise into a foreground ‘wedge’ within cylindrical 2D k-space (Datta et al. 2010; Morales et al. 2012; Parsons et al. 2012b; Trott et al. 2012; Vedantham et al. 2012; Thyagarajan et al. 2013; Liu et al. 2014a,b).”
PAPER-64 CONSTRAINTS ON REIONIZATION: THE 21 cm POWER SPECTRUM AT z = 8.4 (2015, unknown): “This relationship, known colloquially as “the wedge,” was derived analytically (P12b; Vedantham et al. 2012; Thyagarajan et al. 2013; Liu et al. 2014a,b), and has been confirmed in simulations (Datta et al. 2010; Hazelton et al. 2013) and observationally (Pober et al. 2013; Dillon et al. 2014).”
THE IMPACT OF POINT-SOURCE SUBTRACTION RESIDUALS ON 21 cm EPOCH OF REIONIZATION ESTIMATION (2012, background): “…k‖ to large k⊥–large k‖ was first reported by Datta et al. (2010) (after initial indications from Bowman et al. 2009, and has been further discussed by Vedantham et al. 2012 and Morales et al. 2012), and is the power footprint of the instrument (A color version of this figure is available in…”
Hydrogen Epoch of Reionization Array (HERA) (2016, background): “For further discussion and an analytical derivation, see Vedantham et al. (2012), Thyagarajan et al. (2013), Liu et al. (2014a) and Liu et al. (2014b).”
Upper Limits on the 21 cm Epoch of Reionization Power Spectrum from One Night with LOFAR (2017, background): “Using the former one can assess remaining systematics due to e.g. foreground residuals, side-lobe noise and frequency-coherent effects (e.g. Bowman et al. 2009; Vedantham et al. 2012).”
Calibration requirements for detecting the 21 cm epoch of reionization power spectrum and implications for the SKA (2016, background): “…wedge” due to the mode-mixing of power from small k‖ values into larger k‖ values as demonstrated in Figure 1 (Datta et al. 2010; Morales et al. 2012; Vedantham et al. 2012; Parsons et al. 2012b; Trott et al. 2012; Hazelton et al. 2013; Thyagarajan et al. 2013; Pober et al. 2013; Liu et al.…”
WHAT NEXT-GENERATION 21 cm POWER SPECTRUM MEASUREMENTS CAN TEACH US ABOUT THE EPOCH OF REIONIZATION (2013, background): “…that has arisen in the last few years, i.e., the division of 2D cylindrical k-space into the foreground-contaminated “wedge” and the relatively clean “EoR window” (Datta et al. 2010; Vedantham et al. 2012; Morales et al. 2012; Parsons et al. 2012b; Trott et al. 2012; Thyagarajan et al. 2013).”
A PER-BASELINE, DELAY-SPECTRUM TECHNIQUE FOR ACCESSING THE 21 cm COSMIC REIONIZATION SIGNATURE (2012, methodology): “…the delay-spectrum technique differs substantially for other schemes that have been recently presented in the literature (e.g. Bowman et al. 2009; Vedantham et al. 2012) in that within an 8-MHz sub-band, every frequency channel has been formed from the same weighted sum of constituent baselines.”
OPENING THE 21 cm EPOCH OF REIONIZATION WINDOW: MEASUREMENTS OF FOREGROUND ISOLATION WITH PAPER (2013, methodology): “…this resolution is set by the 25 MHz bandwidth used in the analysis.15 The most prominent feature is the “wedge”-like shape of the foreground emissison as predicted in a number of studies, including Datta et al. (2010), Vedantham et al. (2012), Morales et al. (2012), Trott et al. (2012), and P12b.”