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First Results from HERA Phase I: Upper Limits on the Epoch of Reionization 21 cm Power Spectrum
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Abdurashidova_2022_ApJ_925_221.pdf
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Published version
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4.52 MB
Format
Adobe PDF
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Author(s)
Abdurashidova, Zara
Aguirre, James E.
Alexander, Paul
Ali, Zaki S.
Balfour, Yanga
Beardsley, Adam P.
Bernardi, Gianni
Billings, Tashalee S.
Bowman, Judd D.
Bradley, Richard F.
Date Issued
February 1, 2022
Journal
The Astrophysical Journal
Publisher
American Astronomical Society
Citation
Abdurashidova, Zara, Aguirre, James E., Alexander, Paul, Ali, Zaki S., Balfour, Yanga et al. 2022. "First Results from HERA Phase I: Upper Limits on the Epoch of Reionization 21 cm Power Spectrum." The Astrophysical Journal, 925 (2).
Version
Final published version
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 ∼109 with respect to the peak foreground power. This yields a 95% confidence upper limit on the 21 cm power spectrum of ${{\rm{\Delta }}}_{21}^{2}\leqslant {(30.76)}^{2}\ {\mathrm{mK}}^{2}$ at k = 0.192 h Mpc−1 at z = 7.9, and also ${{\rm{\Delta }}}_{21}^{2}\leqslant {(95.74)}^{2}\ {\mathrm{mK}}^{2}$ 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.
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Creative Commons Attribution 4.0 International license
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DOI of Published Version
10.3847/1538-4357/ac1c78
