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

Oct 5, 2020
16 pages
Published in:
  • Mon.Not.Roy.Astron.Soc. 499 (2020) 3, 4158-4173
  • Published: Nov 10, 2020
e-Print:
DOI:

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Abstract: (Oxford University Press)
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 |Δ212<(8139 mK)2\Delta _{21}^2 \lt (8139~\textrm {mK})^2| and |Δ212<(8549 mK)2\Delta _{21}^2 \lt (8549~\textrm {mK})^2| at |k=0.144 hcMpc1k = 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 |Δ212<(7388 mK)2\Delta _{21}^2 \lt (7388~\textrm {mK})^2| at |k=0.144 hcMpc1k = 0.144~h\, \textrm {cMpc}^{-1}|⁠. These are the deepest upper limits thus far at these redshifts.
Note:
  • 16 pages, 10 figures, accepted for publication in MNRAS
  • methods: data analysis
  • methods: statistical
  • techniques: interferometric
  • dark ages, reionization, first stars
  • diffuse radiation
  • radio lines: general