Title:	First Limits on the 21 cm Power Spectrum during the Epoch of X-ray heating
Authors:	Ewall-Wice, A. Dillon, Joshua S. Offringa, A.R. Saurabh, Paul Prabu, T. Udaya Shankar, N. Sethi, S.K. Srivani, K.S. Subrahmanyan, Ravi +55 Co-authors
Issue Date:	21-Aug-2016
Publisher:	Oxford University Press for The Royal Astronomical Society
Citation:	Monthly Notices of the Royal Astronomical Society, 2016, Vol. 460, p 4320-4347
Abstract:	We present first results from radio observations with the Murchison Widefield Array seeking to constrain the power spectrum of 21 cm brightness temperature fluctuations between the redshifts of 11.6 and 17.9 (113 and 75 MHz). 3 h of observations were conducted over two nights with significantly different levels of ionospheric activity. We use these data to assess the impact of systematic errors at low frequency, including the ionosphere and radio-frequency interference, on a power spectrum measurement. We find that after the 1–3 h of integration presented here, our measurements at the Murchison Radio Observatory are not limited by RFI, even within the FM band, and that the ionosphere does not appear to affect the level of power in the modes that we expect to be sensitive to cosmology. Power spectrum detections, inconsistent with noise, due to fine spectral structure imprinted on the foregrounds by reflections in the signal-chain, occupy the spatial Fourier modes where we would otherwise be most sensitive to the cosmological signal. We are able to reduce this contamination using calibration solutions derived from autocorrelations so that we achieve an sensitivity of 104 mK on comoving scales k ≲ 0.5 h Mpc−1. This represents the first upper limits on the 21 cm power spectrum fluctuations at redshifts 12 ≲ z ≲ 18 but is still limited by calibration systematics. While calibration improvements may allow us to further remove this contamination, our results emphasize that future experiments should consider carefully the existence of and their ability to calibrate out any spectral structure within the EoR window.
Description:	Open Access
URI:	http://hdl.handle.net/2289/6525
ISSN:	0035-8711 1365-2966 - (online)
Alternative Location:	http://adsabs.harvard.edu/abs/2016MNRAS.460.4320E http://arxiv.org/abs/1605.00016 http://dx.doi.org/10.1093/mnras/stw1022
Copyright:	2016 The authors & the Royal Astronomical Society
Appears in Collections:	Research Papers (A&A)

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