First Results from HERA Phase I: Upper Limits on the Epoch of Reionization 21 cm Power Spectrum
Zara Abdurashidova, James Aguirre, Paul Alexander, Zaki S. Ali, Yanga Balfour, Adam P. Beardsley, G. Bernardi, Tashalee S. Billings, Judd D. Bowman, Richard F. Bradley, Philip Bull, Jacob Burba, Steve Carey, C. L. Carilli, Carina Cheng, David R. DeBoer, Matt Dexter, Eloy de Lera Acedo, Taylor Dibblee-Barkman, Joshua S. Dillon, John Ely, Aaron Ewall‐Wice, Nicolas Fagnoni, Randall Fritz, Steven R. Furlanetto, Kingsley Gale‐Sides, Brian Glendenning, Deepthi Gorthi, Bradley Greig, Jasper Grobbelaar, Ziyaad Halday, B. J. Hazelton, Jacqueline N. Hewitt, J. Hickish, Daniel Jacobs, Austin Julius, Nicholas S. Kern, Joshua Kerrigan, Piyanat Kittiwisit, Saul A. Kohn, Matthew Kolopanis, Adam Lanman, Paul La Plante, Telalo Lekalake, David Lewis, Adrian Liu, David H. E. MacMahon, Lourence Malan, Cresshim Malgas, Matthys Maree, Zachary E. Martinot, Eunice Matsetela, Andrei Mesinger, Mathakane Molewa, M. F. Morales, Tshegofalang Mosiane, Steven Murray, Abraham R. Neben, Bojan Nikolic, Chuneeta D. Nunhokee, Aaron R. Parsons, Nipanjana Patra, Robert Pascua, Samantha Pieterse, Jonathan C. Pober, N. Razavi‐Ghods, Jon Ringuette, James Robnett, Kathryn Rosie, Peter Sims, Saurabh Singh, Craig Smith, Angelo Syce, Nithyanandan Thyagarajan, Peter K. G. Williams, Haoxuan Zheng
Abstract
Abstract We report upper limits on the Epoch of Reionization 21 cm power spectrum at redshifts 7.9 and 10.4 with 18 nights of data (∼36 hr of integration) from Phase I of the Hydrogen Epoch of Reionization Array (HERA). The Phase I data show evidence for systematics that can be largely suppressed with systematic models down to a dynamic range of ∼10 9 with respect to the peak foreground power. This yields a 95% confidence upper limit on the 21 cm power spectrum of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi mathvariant="normal">Δ</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>21</mml:mn> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msubsup> <mml:mo>≤</mml:mo> <mml:msup> <mml:mrow> <mml:mo stretchy="false">(</mml:mo> <mml:mn>30.76</mml:mn> <mml:mo stretchy="false">)</mml:mo> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> <mml:mspace width="0.33em"/> <mml:msup> <mml:mrow> <mml:mi>mK</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> </mml:math> at k = 0.192 h Mpc −1 at z = 7.9, and also <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi mathvariant="normal">Δ</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>21</mml:mn> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msubsup> <mml:mo>≤</mml:mo> <mml:msup> <mml:mrow> <mml:mo stretchy="false">(</mml:mo> <mml:mn>95.74</mml:mn> <mml:mo stretchy="false">)</mml:mo> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> <mml:mspace width="0.33em"/> <mml:msup> <mml:mrow> <mml:mi>mK</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> </mml:math> at k = 0.256 h Mpc −1 at z = 10.4. At z = 7.9, these limits are the most sensitive to date by over an order of magnitude. While we find evidence for residual systematics at low line-of-sight Fourier k ∥ modes, at high k ∥ modes we find our data to be largely consistent with thermal noise, an indicator that the system could benefit from deeper integrations. The observed systematics could be due to radio frequency interference, cable subreflections, or residual instrumental cross-coupling, and warrant further study. This analysis emphasizes algorithms that have minimal inherent signal loss, although we do perform a careful accounting in a companion paper of the small forms of loss or bias associated with the pipeline. Overall, these results are a promising first step in the development of a tuned, instrument-specific analysis pipeline for HERA, particularly as Phase II construction is completed en route to reaching the full sensitivity of the experiment.