Epoch of Reionization Power Spectrum Limits from Murchison Widefield Array Data Targeted at EoR1 Field

Abstract

Current attempts to measure the 21cm Power Spectrum of neutral hydrogen during the Epoch of Reionization are limited by systematics which produce measured upper limits above both the thermal noise and the expected cosmological signal. These systematics arise from a combination of observational, instrumental, and analysis effects. In order to further understand and mitigate these effects, it is instructive to explore different aspects of existing datasets. One such aspect is the choice of observing field. To date, MWA EoR observations have largely focused on the EoR0 field. In this work, we present a new detailed analysis of the EoR1 field. The EoR1 field is one of the coldest regions of the Southern radio sky, but contains the very bright radio galaxy Fornax-A. The presence of this bright extended source in the primary beam of the interferometer makes the calibration and analysis of EoR1 particularly challenging. We demonstrate the effectiveness of a recently developed shapelet model of Fornax-A in improving the results from this field. We also describe and apply a series of data quality metrics which identify and remove systematically contaminated data. With substantially improved source models, upgraded analysis algorithms and enhanced data quality metrics, we determine EoR power spectrum upper limits based on analysis of the best ∼14-hours data observed during 2015 and 2014 at redshifts 6.5, 6.8 and 7.1, with the lowest 2𝜎 upper limit at z=6.5 of Δ 2 ≤ (73.78 mK) 2 at 𝑘 = 0.13 h Mpc −1 , improving on previous EoR1 measurement results.

Exploring the cosmic dawn and epoch of reionization with 21cm line

“…CHIPS; Trott et al (2016)). While the detection of the 21cm power spectrum has not been achieved, the upper limits on the power spectrum have been reported at various redshifts and scales: PAPER (Kolopanis et al 2019), GMRT (Paciga et al 2013), LWA (Eastwood et al 2019;Garsden et al 2021), MWA (Dillon et al 2015;Ewall-Wice et al 2016;Beardsley et al 2016;Li et al 2019a;Barry et al 2019b;Trott et al 2020;Patwa et al 2021;Yoshiura et al 2021b;Rahimi et al 2021), LOFAR (Patil et al 2017b;Gehlot et al 2019;Mertens et al 2020;Gehlot et al 2020) and HERA (The HERA Collaboration et al 2021a). Figure 19 compares the upper limits and theoretical models of power spectrum at a range of redshifts.…”

“…The radio catalogue with deep integration toward the targeted field has also been made so far (Procopio et al 2017;Lynch et al 2021). Furthermore, the modelling of extended sources is important as the residuals of extremely bright sources has to be minimized (Line et al 2020;Rahimi et al 2021). The radio catalogues are used for either the removal of foreground and instrumental calibration.…”

The large-scale 21-cm power spectrum from reionization

“…However, at present it is difficult to know the lowest 𝑘 which can be reliable extracted. For example Rahimi et al (2021) arrive at a minimal value of approximately 0.1 Mpc −1 for data from the MWA whereas Mertens et al (2020) manage to subtract the foreground signals down to 𝑘 = 0.0525 Mpc −1 . While it remains true that the shape of Δ 2 21cm for 𝑘 0.3 Mpc −1 is the shape of the neutral fraction power spectrum for most of reionization, the transition to a scaleindependent bias may or may not be detectable, depending on the effectiveness of the foreground mitigation techniques and of course the scale at which this transition occurs.…”