@article{74742f754e834bb3a3e0259ec38134d0,
title = "First limits on the 21 cm power spectrum during the Epoch of X-ray heating",
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 FMband, 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 cmpower 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.",
keywords = "Dark ages, reionization, first stars, Radio lines: general, Techniques: interferometric, X-rays: galaxies",
author = "A. Ewall-Wice and Dillon, {Joshua S.} and Hewitt, {J. N.} and A. Loeb and A. Mesinger and Neben, {A. R.} and Offringa, {A. R.} and M. Tegmark and N. Barry and Beardsley, {A. P.} and G. Bernardi and Judd Bowman and F. Briggs and Cappallo, {R. J.} and P. Carroll and Corey, {B. E.} and {de Oliveira-Costa}, A. and D. Emrich and L. Feng and Gaensler, {B. M.} and R. Goeke and Greenhill, {L. J.} and Hazelton, {B. J.} and N. Hurley-Walker and M. Johnston-Hollitt and Daniel Jacobs and Kaplan, {D. L.} and Kasper, {J. C.} and Kim, {H. S.} and E. Kratzenberg and E. Lenc and J. Line and Lonsdale, {C. J.} and Lynch, {M. J.} and B. McKinley and McWhirter, {S. R.} and Mitchell, {D. A.} and Morales, {M. F.} and E. Morgan and Nithyanandan Thyagarajan and D. Oberoi and Ord, {S. M.} and S. Paul and B. Pindor and Pober, {J. C.} and T. Prabu and P. Procopio and J. Riding and Rogers, {A. E E} and A. Roshi and {Udaya Shankar}, N. and Sethi, {Shiv K.} and Srivani, {K. S.} and R. Subrahmanyan and Sullivan, {I. S.} and Tingay, {S. J.} and Trott, {C. M.} and M. Waterson and Wayth, {R. B.} and Webster, {R. L.} and Whitney, {A. R.} and A. Williams and Williams, {C. L.} and C. Wu and Wyithe, {J. S B}",
note = "Funding Information: We would like to thank the referees for their helpful comments. We extend our gratitude to Jeff Zhang and Adrian Liu for useful discussions. This work was supported by NSF Grants AST-0457585, AST-0821321, AST-1105835, AST-1410719, AST-1410484, AST- 1411622, and AST-1440343, by the MIT School of Science, by the Marble Astrophysics Fund, and by generous donations from Jonathan Rothberg and an anonymous donor. AEW acknowledges support from the National Science Foundation Graduate Research Fellowship under Grant No. 1122374. AM acknowledges support from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (grant agreement No 638809 - AIDA). This scientific work makes use of the Murchison Radioastronomy Observatory, operated by CSIRO. We acknowledge the Wajarri Yamatji people as the traditional owners of the Observatory site. Support for the MWA comes from the U.S. National Science Foundation (grants AST-0457585, PHY-0835713, CAREER- 0847753, and AST-0908884), the Australian Research Council (LIEF grants LE0775621 and LE0882938), the U.S. Air Force Office of Scientific Research (grant FA9550-0510247), and the Centre for All-sky Astrophysics (an Australian Research Council Centre of Excellence funded by grant CE110001020). Support is also provided by the Smithsonian Astrophysical Observatory, the Raman Research Institute, the Australian National University, and the VictoriaUniversity ofWellington (via grantMED-E1799 from the New Zealand Ministry of Economic Development and an IBM Shared University Research Grant). The Australian Federal government provides additional support via the Commonwealth Scientific and Industrial Research Organisation (CSIRO), National Collaborative Research Infrastructure Strategy, Education Investment Fund, and the Australia India Strategic Research Fund, and Astronomy Australia Limited, under contract to Curtin University. We acknowledge the iVEC Petabyte Data Store, the Initiative in Innovative Computing and the CUDA Center for Excellence sponsored by NVIDIA at Harvard University, and the International Centre for Radio Astronomy Research (ICRAR), a Joint Venture of Curtin University and The University of Western Australia, funded by the Western Australian State government. Publisher Copyright: {\textcopyright} 2016 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.",
year = "2016",
month = aug,
day = "21",
doi = "10.1093/mnras/stw1022",
language = "English (US)",
volume = "460",
pages = "4320--4347",
journal = "Monthly Notices of the Royal Astronomical Society",
issn = "0035-8711",
publisher = "Oxford University Press",
number = "4",
}