The AARTFAAC Cosmic Explorer: Observations of the 21-cm power spectrum in the EDGES absorption trough

B. K. Gehlot, F. G. Mertens, L. V. E. Koopmans, A. R. Offringa, A. Shulevski, M. Mevius, M. A. Brentjens, M. Kuiack, V. N. Pandey, A. Rowlinson, A. M. Sardarabadi, H. K. Vedantham, R. A. M. J. Wijers, S. Yatawatta, S. Zaroubi

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Abstract

The 21-cm absorption feature reported by the EDGES collaboration is several times stronger than that predicted by traditional astrophysical models. If genuine, a deeper absorption may lead to stronger fluctuations on the 21-cm signal on degree scales (up to 1 K in rms), allowing these fluctuations to be detectable in nearly 50 times shorter integration times compared to previous predictions. We commenced the 'AARTFAAC Cosmic Explorer' (ACE) program, which employs the AARTFAAC wide-field image, to measure or set limits on the power spectrum of the 21-cm fluctuations in the redshift range z = 17.9-18.6 (Δν = 72.36-75.09 MHz) corresponding to the deep part of the EDGES absorption feature. Here, we present first results from two LST bins: 23.5-23.75 and 23.75-24.00 h, each with 2 h of data, recorded in 'semi drift-scan' mode. We demonstrate the application of the new ACE data-processing pipeline (adapted from the LOFAR-EoR pipeline) on the AARTFAAC data. We observe that noise estimates from the channel and time-differenced Stokes V visibilities agree with each other. After 2 h of integration and subtraction of bright foregrounds, we obtain 2σ upper limits on the 21-cm power spectrum of $\Delta _{21}^2 \lt (8139~\textrm {mK})^2$ and $\Delta _{21}^2 \lt (8549~\textrm {mK})^2$ at $k = 0.144~h\, \textrm {cMpc}^{-1}$ for the two LST bins. Incoherently averaging the noise bias-corrected power spectra for the two LST bins yields an upper limit of $\Delta _{21}^2 \lt (7388~\textrm {mK})^2$ at $k = 0.144~h\, \textrm {cMpc}^{-1}$ . These are the deepest upper limits thus far at these redshifts.
Original languageEnglish
Pages (from-to)4158-4173
Number of pages16
JournalMonthly Notices of the Royal Astronomical Society
Volume499
Issue number3
DOIs
Publication statusPublished - 1-Dec-2020

Keywords

  • methods: data analysis
  • methods: statistical
  • techniques: interferometric
  • dark ages
  • reionization
  • first stars
  • diffuse radiation
  • radio lines: general

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