First limits on the 21 cm power spectrum during the Epoch of X-ray heating

Abstract

We present first results from radio observations with the Murchison Widefield Array seeking to constrain the power spectrum of 21 cm brightness temperature fluctuations between the redshifts of 11.6 and 17.9 (113 and 75 MHz). Three hours of observations were conducted over two nights with significantly different levels of ionospheric activity. We use these data to assess the impact of systematic errors at low frequency, including the ionosphere and radio-frequency interference, on a power spectrum measurement. We find that after the 1-3 hours of integration presented here, our measurements at the Murchison Radio Observatory are not limited by RFI, even within the FM band, and that the ionosphere does not appear to affect the level of power in the modes that we expect to be sensitive to cosmology. Power spectrum detections, inconsistent with noise, due to fine spectral structure imprinted on the foregrounds by reflections in the signal-chain, occupy the spatial Fourier modes where we would otherwise be most sensitive to the cosmological signal. We are able to reduce this contamination using calibration solutions derived from autocorrelations so that we achieve an sensitivity of 10 4 mK on comoving scales k 0.5 hMpc −1 . This represents the first upper limits on the 21 cm power spectrum fluctuations at redshifts 12 z 18 but is still limited by calibration systematics. While calibration improvements may allow us to further remove this contamination, our results emphasize that future experiments should consider carefully the existence of and their ability to calibrate out any spectral structure within the EoR window.

Emulating Simulations of Cosmic Dawn for 21 cm Power Spectrum Constraints on Cosmology, Reionization, and X-Ray Heating

“…Furlanetto et al (2006); Morales & Wyithe (2010); Pritchard & Loeb (2012) ;Loeb & Furlanetto (2013); Mesinger (2016). While 21 cm cosmology faces formidable observational challenges, recent years have seen significant advances toward resolving issues of optimal array design Parsons et al 2012b;Dillon & Parsons 2016), internal systematics (Ewall-Wice et al 2016c;Barry et al 2016;Patil et al 2016;Ewall-Wice et al 2016a), and astrophysical foreground mitigation (Datta et al 2010;Morales et al 2012;Vedantham et al 2012;Parsons et al 2012b;Trott et al 2012;Chapman et al 2012Chapman et al , 2013Thyagarajan et al 2013;Pober et al 2013a;Liu et al 2014a,b;Switzer & Liu 2014;Wolz et al 2013;Moore et al 2015;Thyagarajan et al 2015a,b;Asad et al 2015;Chapman et al 2016;Pober et al 2016;Kohn et al 2016;. Increasingly competitive upper limits have been placed on the red-shifted 21 cm signal, using instruments such as the Donald C. Backer Precision Array for Probing the Epoch of Reionization (PAPER; Parsons et al 2014;Jacobs et al 2015;Ali et al 2015), the Giant Metrewave Radio Telescope (GMRT; Paciga et al 2013), the Murchison Widefield Array (MWA; Dillon et al 2014Dillon et al , 2015…”

Mitigating Internal Instrument Coupling for 21 cm Cosmology. I. Temporal and Spectral Modeling in Simulations

“…The prospect of robustly characterizing the 21 cm signal from these epochs is daunting, as galactic and extragalactic foreground emission outshine the fiducial cosmological signal by many orders of magnitude. Nevertheless, the path towards detecting the 21 cm signal from the Cosmic Dawn and EoR has seen tremendous progress over the past decade, as first generation radio interferometric experiments such as the Donald C. Backer Precision Array for Probing the Epoch of Reionization (PAPER; Parsons et al 2014;Jacobs et al 2015;Ali et al 2015), the Murchison Widefield Array (MWA; Dillon et al 2014;Beardsley et al 2016;Ewall-Wice et al 2016), the Low Frequency Array (LOFAR; Patil et al 2017), and the Giant Metre Wave Radio Telescope (GMRT; Paciga et al 2013) have placed increasingly competitive limits on the 21 cm power spectrum, while single-dish experiments may have made a first detection of the global signal (Bowman et al 2018). Going forward, second generation interferometric experiments like the Hydrogen Epoch of Reionization Array (HERA; DeBoer et al 2017) and the Square Kilometer Array (SKA; Koopmans et al 2015) are expected to have the raw sensitivity needed to not only detect the 21 cm signal but provide a power spectrum characterization across a wide range of redshifts, leading to drastic improvements in our understanding of astrophysical and cosmological parameters that govern large scale structure and star formation at these epochs (Pober et al 2014;Ewall-Wice et al 2016;Kern et al 2017).…”

“…Cross coupling produces a spurious phase-stable term in the data across time that can occupy a wide range of k modes depending on its origin. These systematics are of critical concern for low-frequency radio surveys (Parsons et al 2012;Zheng et al 2014;Chaudhari et al 2017), and have proven to be a partially limiting factor in previous 21 cm interferometric analyses (Beardsley et al 2016;Ewall-Wice et al 2016). We use HERA sky and systematic simulations to study the temporal and spectral behavior of internal coupling systematics in the context of HERA data, and proposes techniques for modeling and removing them from the interferometric data products.…”

Analysing the 21 cm signal from the epoch of reionization with artificial neural networks

“…During the Cosmic Dawn, X-ray heating of the IGM plays an important role. Thus, it is important to incorporate X-ray heating models and study their impact on the 21 cm (Baek et al 2010;Mesinger et al 2013;Ewall-Wice et al 2016;Fialkov et al 2017). Recently, (Cohen et al 2016) explored the behaviour of the 21cm global signal in a large parameter space from z = 40 to z = 6.…”