Empirical covariance modeling for 21 cm power spectrum estimation: A method demonstration and new limits from early Murchison Widefield Array 128-tile data

Abstract

The separation of the faint cosmological background signal from bright astrophysical foregrounds remains one of the most daunting challenges of mapping the high-redshift intergalactic medium with the redshifted 21 cm line of neutral hydrogen. Advances in mapping and modeling of diffuse and point source foregrounds have improved subtraction accuracy, but no subtraction scheme is perfect. Precisely quantifying the errors and error correlations due to missubtracted foregrounds allows for both the rigorous analysis of the 21 cm power spectrum and for the maximal isolation of the "EoR window" from foreground contamination. We present a method to infer the covariance of foreground residuals from the data itself in contrast to previous attempts at a priori modeling. We demonstrate our method by setting limits on the power spectrum using a three hour integration from the 128-tile Murchison Widefield Array. Observing between 167-198 MHz, we find at 95% confidence a best limit of ∆ 2 (k) < 3.7 × 10 4 mK 2 at comoving scale k = 0.18 h Mpc −1 and at z = 6.8, consistent with existing limits.PACS numbers: 95.75.Kk, 98.80.Es

First Season Mwa Eor Power Spectrum Results at Redshift 7

“…We found that a small buffer beyond the horizon was necessary to completely mask out the wedge, consistent with Dillon et al (2015a). We implement the buffer by increasing the slope of the horizon line by 14%.…”

“…The best result from this analysis is an upper limit on the power spectrum of  D2.7 10 2 4 mK 2 at = k h 0.27 Mpc −1 and z = 7.1. This is a modest improvement over the previous best MWA results (Dillon et al 2015a), which is not surprising-given that this integration contains about 10times more data, but is systematics limited. Our results are also consistent with the 40 hr GMRT limit of  D6.15 10 2 4 mK 2 at = k h 0.5 Mpc −1 and z = 8.6 (Paciga et al 2013), though they probe significantly different periods of the EoR.…”

“…First we use a set of 94 two-minute high-band observations of the EoR0 field from 2013 August 23, which were taken early in telescope operations and found to be particularly well behaved. The MWA EoR collaboration has designated this set as a "golden data set," which is used to build analysis tools and compare early results (e.g., Dillon et al 2015a;Jacobs et al 2016;Pober et al 2016;Trott et al 2016). All techniques demonstrated here will use this golden data set.…”

DELAY SPECTRUM WITH PHASE-TRACKING ARRAYS: EXTRACTING THE H i POWER SPECTRUM FROM THE EPOCH OF REIONIZATION

“…In this paper we present 3 hr of tracking analysis of the EoR1 field centered at R.A.=4 h , decl.=−27°. Many research groups are currently developing pipelines to extract statistical information from radio interferometric data, with an aim to detect the H I signal from EoR (Dillon et al 2015;Jacobs et al 2016;Trott et al 2016; B. J. Hazelton et al 2016, in prepration).…”

“…The image based pipelines (Dillon et al 2015; B. J. Hazelton et al 2016, in prepration) use a source catalog created through the deconvolution of the data which are subtracted to obtain a residual image cube.…”