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1. Quantifying excess power from radio frequency interference in Epoch of Reionization measurements

   https://doi.org/10.1093/mnras/staa2442  

   Wilensky, Michael J ; Barry, Nichole ; Morales, Miguel F ; Hazelton, Bryna J ; Byrne, Ruby ( October 2020 , Monthly Notices of the Royal Astronomical Society)

   null (Ed.)

   ABSTRACT We quantify the effect of radio frequency interference (RFI) on measurements of the 21-cm power spectrum during the Epoch of Reionization (EoR). Specifically, we investigate how the frequency structure of RFI source emission generates contamination in higher order wave modes, which is much more problematic than smooth-spectrum foreground sources. Using a relatively optimistic EoR model, we find that even a single relatively dim RFI source can overwhelm the EoR power spectrum signal of $\sim 10\, {\rm mK}^2$ for modes $0.1 \ \lt k \lt 2 \, h\, {\rm Mpc}^{-1}$. If the total apparent RFI flux density in the final power spectrum integration is kept below 1 mJy, an EoR signal resembling this optimistic model should be detectable for modes $k \lt 0.9\, h\, {\rm Mpc}^{-1}$, given no other systematic contaminants and an error tolerance as high as 10 per cent. More pessimistic models will be more restrictive. These results emphasize the need for highly effective RFI mitigation strategies for telescopes used to search for the EoR. 

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2. Search for the Epoch of Reionization with HERA: upper limits on the closure phase delay power spectrum

   https://doi.org/10.1093/mnras/stad371  

   Keller, Pascal M. ; Nikolic, Bojan ; Thyagarajan, Nithyanandan ; Carilli, Chris L. ; Bernardi, Gianni ; Charles, Ntsikelelo ; Bester, Landman ; Smirnov, Oleg M. ; Kern, Nicholas S. ; Dillon, Joshua S. ; et al ( February 2023 , Monthly Notices of the Royal Astronomical Society)

   Radio interferometers aiming to measure the power spectrum of the redshifted 21 cm line during the Epoch of Reionization (EoR) need to achieve an unprecedented dynamic range to separate the weak signal from overwhelming foreground emissions. Calibration inaccuracies can compromise the sensitivity of these measurements to the effect that a detection of the EoR is precluded. An alternative to standard analysis techniques makes use of the closure phase, which allows one to bypass antenna-based direction-independent calibration. Similarly to standard approaches, we use a delay spectrum technique to search for the EoR signal. Using 94 nights of data observed with Phase I of the Hydrogen Epoch of Reionization Array (HERA), we place approximate constraints on the 21 cm power spectrum at z = 7.7. We find at 95 per cent confidence that the 21 cm EoR brightness temperature is ≤(372)2 ‘pseudo’ mK2 at 1.14 ‘pseudo’ h Mpc−1, where the ‘pseudo’ emphasizes that these limits are to be interpreted as approximations to the actual distance scales and brightness temperatures. Using a fiducial EoR model, we demonstrate the feasibility of detecting the EoR with the full array. Compared to standard methods, the closure phase processing is relatively simple, thereby providing an important independent check on results derived using visibility intensities, or related.

    

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3. Evidence of Ultrafaint Radio Frequency Interference in Deep 21 cm Epoch of Reionization Power Spectra with the Murchison Wide-field Array

   https://doi.org/10.3847/1538-4357/acffbd  

   Wilensky, Michael J. ; Morales, Miguel F. ; Hazelton, Bryna J. ; Star, Pyxie L. ; Barry, Nichole ; Byrne, Ruby ; Jordan, C. H. ; Jacobs, Daniel C. ; Pober, Jonathan C. ; Trott, C. M. ( November 2023 , The Astrophysical Journal)

   We present deep upper limits from the 2014 Murchison Widefield Array Phase I observing season, with a particular emphasis on identifying the spectral fingerprints of extremely faint radio frequency interference (RFI) contamination in the 21 cm power spectra (PS). After meticulous RFI excision involving a combination of theSSINSRFI flagger and a series of PS-based jackknife tests, our lowest upper limit on the Epoch of Reionization (EoR) 21 cm PS signal is Δ²≤ 1.61 × 10⁴mK²atk= 0.258h Mpc⁻¹at a redshift of 7.1 using 14.7 hr of data. By leveraging our understanding of how even fainter RFI is likely to contaminate the EoR PS, we are able to identify ultrafaint RFI signals in the cylindrical PS. Surprisingly this signature is most obvious in PS formed with less than 1 hr of data, but is potentially subdominant to other systematics in multiple-hour integrations. Since the total RFI budget in a PS detection is quite strict, this nontrivial integration behavior suggests a need to more realistically model coherently integrated ultrafaint RFI in PS measurements so that its potential contribution to a future detection can be diagnosed.

    

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4. Prospects for 21 cm Galaxy Cross-correlations with HERA and the Roman High-latitude Survey

   https://doi.org/10.3847/1538-4357/acaeb0  

   La Plante, Paul ; Mirocha, Jordan ; Gorce, Adélie ; Lidz, Adam ; Parsons, Aaron ( February 2023 , The Astrophysical Journal)

   The cross-correlation between the 21 cm field and the galaxy distribution is a potential probe of the Epoch of Reionization (EoR). The 21 cm signal traces neutral gas in the intergalactic medium and, on large spatial scales, this should be anticorrelated with the high-redshift galaxy distribution, which partly sources and tracks the ionized gas. In the near future, interferometers such as the Hydrogen Epoch of Reionization Array (HERA) are projected to provide extremely sensitive measurements of the 21 cm power spectrum. At the same time, the Nancy Grace Roman Space Telescope (Roman) will produce the most extensive catalog to date of bright galaxies from the EoR. Using seminumeric simulations of reionization, we explore the prospects for measuring the cross-power spectrum between the 21 cm and galaxy fields during the EoR. We forecast a 12σdetection between HERA and Roman, assuming an overlapping survey area of 500 deg², redshift uncertainties ofσ_z= 0.01 (as expected for the high-latitude spectroscopic survey of Lyα-emitting galaxies), and an effective Lyαemitter duty cycle off_LAE= 0.1. Thus the HERA–Roman cross-power spectrum may be used to help verify 21 cm detections from HERA. We find that the shot-noise in the galaxy distribution is a limiting factor for detection, and so supplemental observations using Roman should prioritize deeper observations, rather than covering a wider field of view. We have made a public GitHub repository containing key parts of the calculation, which accompanies this paper:https://github.com/plaplant/21cm_gal_cross_correlation.

    

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5. Investigating the contribution of extended radio sources to the Epoch of Reionization power spectrum

   https://doi.org/10.1093/mnras/stac1330  

   Cook, J. H. ; Trott, C. M. ; Line, J. L. B. ( May 2022 , Monthly Notices of the Royal Astronomical Society)

   We investigate the contribution of extended radio sources such as Centaurus A, and Galactic supernova remnants (SNRs) to our ability to detect the statistical 21-cm signal from the Epoch of Reionisation (EoR) with the Murchison Widefield Array (MWA). These sources are typically ignored because they are in highly attenuated parts of the MWA primary beam, however, in aggregate, these sources have apparent flux densities of $10\, \rm {Jy}$ on angular scales we expect to detect the 21-cm signal. We create bespoke multicomponent 2D Gaussian models for Galactic SNRs and for Centaurus A, and simulate the visibilities for two MWA snapshot observations. We grid those visibilities and then Fourier transform them with respect to frequency, averaging them both spherically and cylindrically to produce the 1D and 2D power spectra. We compare the simulated 1D power spectra to the expected 21-$\rm {cm}$ power spectrum. We find that although these extended sources are in highly attenuated parts of the MWA primary beam pattern, collectively they have enough power (∼104−105 $\rm {mK^2}\, {\it h^{-3}} \, \rm {Mpc^{3}}$) on EoR significant modes $(|{\boldsymbol k}| \lesssim 0.1\, h\, \rm {Mpc^{-1}})$ to prohibit detection of the 21-$\rm {cm}$ signal (∼104 $\rm {mK^2}\, {\it h^{-3}} \, \rm {Mpc^{3}}$). We find that $50{-}90{{\ \rm per\ cent}}$ of sources must be removed in order to reduce leakage to a level of $\sim 10{-}20{{\ \rm per\ cent}}$ of the 21-$\rm {cm}$ power spectrum on EoR significant modes. The effects of wide-field extended sources will have implications on the detectability of the 21-$\rm {cm}$ signal for the MWA and with the future Square Kilometre Array (SKA).

    

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