Foregrounds in Wide-Field Redshifted 21 cm Power Spectra
Abstract
Detection of 21~cm emission of HI from the epoch of reionization, at redshifts z>6, is limited primarily by foreground emission. We investigate the signatures of wide-field measurements and an all-sky foreground model using the delay spectrum technique that maps the measurements to foreground object locations through signal delays between antenna pairs. We demonstrate interferometric measurements are inherently sensitive to all scales, including the largest angular scales, owing to the nature of wide-field measurements. These wide-field effects are generic to all observations but antenna shapes impact their amplitudes substantially. A dish-shaped antenna yields the most desirable features from a foreground contamination viewpoint, relative to a dipole or a phased array. Comparing data from recent Murchison Widefield Array observations, we demonstrate that the foreground signatures that have the largest impact on the HI signal arise from power received far away from the primary field of view. We identify diffuse emission near the horizon as a significant contributing factor, even on wide antenna spacings that usually represent structures on small scales. For signals entering through the primary field of view, compact emission dominates the foreground contamination. These two mechanisms imprint a characteristic "pitchfork" signature on the "foreground wedge" in Fourier delay space. Based on these results, we propose that selective down-weighting of data based on antenna spacing and time can mitigate foreground contamination substantially by a factor ~100 with negligible loss of sensitivity.
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@article{arxiv.1502.07596,
title = {Foregrounds in Wide-Field Redshifted 21 cm Power Spectra},
author = {Nithyanandan Thyagarajan and Daniel C. Jacobs and Judd D. Bowman and N. Barry and A. P. Beardsley and G. Bernardi and F. Briggs and R. J. Cappallo and P. Carroll and B. E. Corey and A. de Oliveira-Costa and Joshua S. Dillon and D. Emrich and A. Ewall-Wice and L. Feng and R. Goeke and L. J. Greenhill and B. J. Hazelton and J. N. Hewitt and N. Hurley-Walker and M. Johnston-Hollitt and D. L. Kaplan and J. C. Kasper and Han-Seek Kim and P. Kittiwisit and E. Kratzenberg and E. Lenc and J. Line and A. Loeb and C. J. Lonsdale and M. J. Lynch and B. McKinley and S. R. McWhirter and D. A. Mitchell and M. F. Morales and E. Morgan and A. R. Neben and D. Oberoi and A. R. Offringa and S. M. Ord and Sourabh Paul and B. Pindor and J. C. Pober and T. Prabu and P. Procopio and J. Riding and A. E. E. Rogers and A. Roshi and N. Udaya Shankar and Shiv K. Sethi and K. S. Srivani and R. Subrahmanyan and I. S. Sullivan and M. Tegmark and S. J. Tingay and C. M. Trott and M. Waterson and R. B. Wayth and R. L. Webster and A. R. Whitney and A. Williams and C. L. Williams and C. Wu and J. S. B. Wyithe},
journal= {arXiv preprint arXiv:1502.07596},
year = {2016}
}
Comments
Published in ApJ