Showing 1–50 of 61 results for author: Murray, S G

Inferring Cosmology and Astrophysics from the High-redshift 21cm Signal with SKA-Low

Authors: Anshuman Acharya, Satadru Bag, Sabrina Berger, Michele Bianco, Daniela Breitman, Lilian Crascall-Kennedy, Saswata Dasgupta, Abhirup Datta, Marian Douspis, Ivelin Georgiev, Sambit K. Giri, Adélie Gorce, Caroline Heneka, Julien Hiegel, Ian Hothi, Akanksha Kapahtia, Nicholas Kern, Yashrajsinh Mahida, Barun Maity, Suman Majumdar, Romain Mériot, Rajesh Mondal, Steven G. Murray, Leon Noble, Samit Kumar Pal , et al. (7 additional authors not shown)

Abstract: The Square Kilometre Array's low frequency telescope (SKA-Low) will enable inference of astrophysical and cosmological parameters from the redshifted 21 cm signal, probing the Cosmic Dawn and Epoch of Reionisation. While the power spectrum is the primary target for initial detection, the inherently non-Gaussian nature of the 21 cm signal, driven by the patchy evolution of ionised regions and spin… ▽ More The Square Kilometre Array's low frequency telescope (SKA-Low) will enable inference of astrophysical and cosmological parameters from the redshifted 21 cm signal, probing the Cosmic Dawn and Epoch of Reionisation. While the power spectrum is the primary target for initial detection, the inherently non-Gaussian nature of the 21 cm signal, driven by the patchy evolution of ionised regions and spin temperature fluctuations, encodes rich information accessible through higher-order statistics and morphological measurements. Extracting these constraints requires diverse inference tools, encompassing both sophisticated modelling frameworks (analytical, semi-numerical, numerical, and emulators) used to predict the 21 cm signal, and advanced inference techniques (Bayesian, simulation-based, field-level) to connect statistics to the underlying physics. This chapter reviews these tools and explores the constraining power of different statistical probes accessible with SKA-Low, including the power spectrum, statistics beyond order two, moments of the signal distribution, and morphological measures. Combining these complementary statistics is crucial for breaking parameter degeneracies and unveiling the properties of the early Universe. We specifically assess the potential of the initial SKA-Low configuration (AA*) to measure galaxy and IGM properties, demonstrating its capability for early science results. This chapter forms part of a comprehensive set detailing the Epoch of Reionisation and Cosmic Dawn science case for the SKA-Low telescope. △ Less

Submitted 26 June, 2026; originally announced June 2026.

Comments: Published in Advancing Astrophysics with the SKA II (AASKAII), 2026 (arXiv:2606.20366). Report-no:AASKAII/Acharya01

Report number: AASKAII/Acharya01

21cmEMUv3: a hybrid diffusion-LSTM emulator of 21cmFAST summary observables

Authors: Daniela Breitman, Andrei Mesinger, Steven G. Murray, Ivan Nikolic, Roberto Trotta

Abstract: We are witnessing a surge in observations of the cosmic dawn (CD) and epoch of reionisation (EoR), driving an increasing demand for fast and robust theoretical interpretation frameworks. In response, machine learning (ML), and emulation in particular, has emerged as a powerful approach to accelerate and enhance inference pipelines. In this work, we present 21cmEMUv3, an emulator trained on 21cmFAS… ▽ More We are witnessing a surge in observations of the cosmic dawn (CD) and epoch of reionisation (EoR), driving an increasing demand for fast and robust theoretical interpretation frameworks. In response, machine learning (ML), and emulation in particular, has emerged as a powerful approach to accelerate and enhance inference pipelines. In this work, we present 21cmEMUv3, an emulator trained on 21cmFASTv3 simulations that model both atomically and molecularly cooling galaxies. 21cmEMUv3 is conditioned on $σ_8$ and ten astrophysical parameters to produce seven summary observables: (i) the cylindrical 21cm power spectrum (PS), emulated for the first time at such high resolution and accuracy across a wide redshift range of $z \sim$ 6--30; (ii) the spherically-averaged 21cm PS; (iii) the mean neutral fraction of the intergalactic medium (IGM); (iv) the mean 21cm spin temperature; (v) the global 21cm signal; (vi) the ultraviolet (UV) luminosity functions (LFs); and (vii) the Thomson scattering optical depth. Notably, the cylindrical 21cm PS is emulated via score-based diffusion, while the remaining six summaries are emulated via long-short term memory (LSTM) networks, all achieving sub-percent median accuracy. We use the emulator to reinterpret current 21cm PS upper limits from HERA, for the first time using state-of-the-art hydrodynamical simulations to inform priors on star formation inside molecularly cooling galaxies. We find that our inferred soft-band X-ray luminosity per unit star formation rate is consistent with extrapolations of high-mass X-ray binaries to the low-metallicity regimes expected in the first galaxies, excluding values below $10^{39.2}$ erg s$^{-1}M^{-1}_\odot \rm{yr}$ at $95\%$ confidence. Finally, we produce forecasts for the detection of the cosmic 21cm PS with the Square Kilometre Array for different array configurations. The 21cmEMU package is publicly available. △ Less

Submitted 29 May, 2026; originally announced June 2026.

Comments: 12 pages, 6 figures

The EDGES Analysis Pipeline: Description and Validation

Authors: Steven G. Murray, Nivedita Mahesh, Akshatha K. Vydula, Peter Sims, Judd Bowman, Raul A. Monsalve, Alan E. E. Rogers, Rigel C. Capallo, John P. Barrett, Colin J. Lonsdale

Abstract: The sky-averaged redshifted 21-cm signal from Cosmic Dawn is expected to provide a unique view of the first compact objects. However, its measurement remains daunting. Difficulties are driven by the large dynamic contrast between the intervening foregrounds and the signal-of-interest, which places extremely high demands on instrumental calibration and data quality measures. The ongoing debate with… ▽ More The sky-averaged redshifted 21-cm signal from Cosmic Dawn is expected to provide a unique view of the first compact objects. However, its measurement remains daunting. Difficulties are driven by the large dynamic contrast between the intervening foregrounds and the signal-of-interest, which places extremely high demands on instrumental calibration and data quality measures. The ongoing debate within the field concerning the evidence of a potential first detection by the EDGES experiment highlights the need for a more robust set of analysis methods and tools that are reliable and accessible. In this paper, we detail for the first time the precise calibration and analysis methodology adopted in previous EDGES data releases. These methods are presented in the context of a new open-source end-to-end analysis and simulation package for 21-cm global signal experiments that both formalizes these methods and provides general tools for the broader community. Finally, we describe the raw data used in previous EDGES papers and release these data publicly for extended scrutiny. △ Less

Submitted 15 May, 2026; originally announced May 2026.

Comments: 35 pages, 16 figures, submitted to ApJ. Comments welcome!

Patient Safety Risks from AI Scribes: Signals from End-User Feedback

Authors: Jessica Dai, Anwen Huang, Catherine Nasrallah, Rhiannon Croci, Hossein Soleimani, Sarah J. Pollet, Julia Adler-Milstein, Sara G. Murray, Jinoos Yazdany, Irene Y. Chen

Abstract: AI scribes are transforming clinical documentation at scale. However, their real-world performance remains understudied, especially regarding their impacts on patient safety. To this end, we initiate a mixed-methods study of patient safety issues raised in feedback submitted by AI scribe users (healthcare providers) in a large U.S. hospital system. Both quantitative and qualitative analysis sugges… ▽ More AI scribes are transforming clinical documentation at scale. However, their real-world performance remains understudied, especially regarding their impacts on patient safety. To this end, we initiate a mixed-methods study of patient safety issues raised in feedback submitted by AI scribe users (healthcare providers) in a large U.S. hospital system. Both quantitative and qualitative analysis suggest that AI scribes may induce various patient safety risks due to errors in transcription, most significantly regarding medication and treatment; however, further study is needed to contextualize the absolute degree of risk. △ Less

Submitted 1 December, 2025; originally announced December 2025.

Comments: ML4H Findings 2025

First Results from HERA Phase II

Authors: The HERA Collaboration, Zuhra Abdurashidova, Tyrone Adams, James E. Aguirre, Rushelle Baartman, Rennan Barkana, Lindsay M. Berkhout, Gianni Bernardi, Tashalee S. Billings, Bruno B. Bizarria, Judd D. Bowman, Daniela Breitman, Philip Bull, Jacob Burba, Ruby Byrne, Steven Carey, Rajorshi Sushovan Chandra, Kai-Feng Chen, Samir Choudhuri, Tyler Cox, David R. DeBoer, Eloy de Lera Acedo, Matt Dexter, Jiten Dhandha, Joshua S. Dillon , et al. (61 additional authors not shown)

Abstract: We report the first upper limits on the power spectrum of 21-cm fluctuations during the Epoch of Reionization and Cosmic Dawn from Phase II of the Hydrogen Epoch of Reionization Array (HERA) experiment. HERA Phase II constitutes several significant improvements in the signal chain compared to Phase I, most notably resulting in expanded frequency bandwidth, from 50-250 MHz. In these first upper lim… ▽ More We report the first upper limits on the power spectrum of 21-cm fluctuations during the Epoch of Reionization and Cosmic Dawn from Phase II of the Hydrogen Epoch of Reionization Array (HERA) experiment. HERA Phase II constitutes several significant improvements in the signal chain compared to Phase I, most notably resulting in expanded frequency bandwidth, from 50-250 MHz. In these first upper limits, we investigate a small two-week subset of the available Phase II observations, with a focus on identifying new systematic characteristics of the instrument, and establishing an analysis pipeline to account for them. We report 2$σ$ upper limits in eight spectral bands, spanning $5.6 \leq z \leq 24.4$ that are consistent with thermal noise at the $2σ$ level for $k \gtrsim 0.6-0.9 h{\rm Mpc}^{-1}$ (band dependent). Our tightest limit during Cosmic Dawn ($z>12$) is $1.13\times 10^6 {\rm mK}^2$ at ($k=0.55 h{\rm Mpc}^{-1}, z=16.78$), and during the EoR ($5.5<z<12$) it is $1.78\times 10^3 {\rm mK}^2$ at ($k=0.70 h{\rm Mpc}^{-1}, z=7.05$). We find that mutual coupling has become our dominant systematic, leaking foreground power that strongly contaminates the low-$k$ modes, resulting in the loss of modes from $k=0.35-0.55$ compared to Phase I data. △ Less

Submitted 26 November, 2025; originally announced November 2025.

Comments: 61 pages, 18 figures, submitted to ApJ

Exploring One-point Statistics in HERA Phase I Data: Effects of Foregrounds and Systematics on Measuring One-Point Statistics

Authors: Honggeun Kim, Jacqueline N. Hewitt, Nicholas S. Kern, Joshua S. Dillon, Kai-Feng Chen, Zhilei Xu, Eleanor Rath, Vincent MacKay, Tyrone Adams, James E. Aguirre, Rushelle Baartman, Adam P. Beardsley, Gianni Bernardi, Tashalee S. Billings, Judd D. Bowman, Richard F. Bradley, Philip Bull, Jacob Burba, Steven Carey, Chris L. Carilli, David R. DeBoer, Eloy de Lera Acedo, Matt Dexter, Nico Eksteen, John Ely , et al. (39 additional authors not shown)

Abstract: Measuring one-point statistics in redshifted 21 cm intensity maps offers an opportunity to explore non-Gaussian features of the early universe. We assess the impact of instrumental effects on measurements made with the Hydrogen Epoch of Reionization Array (HERA) by forward modeling observational and simulation data. Using HERA Phase I observations over 94 nights, we examine the second (m2, varianc… ▽ More Measuring one-point statistics in redshifted 21 cm intensity maps offers an opportunity to explore non-Gaussian features of the early universe. We assess the impact of instrumental effects on measurements made with the Hydrogen Epoch of Reionization Array (HERA) by forward modeling observational and simulation data. Using HERA Phase I observations over 94 nights, we examine the second (m2, variance) and third (m3) moments of images. We employ the DAYENU-filtering method for foreground removal and reduce simulated foreground residuals to 10% of the 21 cm signal residuals. In noiseless cosmological simulations, the amplitudes of one-point statistics measurements are significantly reduced by the instrument response and further reduced by wedge-filtering. Analyses with wedge-filtered observational data, along with expected noise simulations, show that systematics alter the probability distribution of the map pixels. Likelihood analysis based on the observational data shows m2 measurements disfavor the cold reionization model characterized by inefficient X-ray heating, in line with other power spectra measurements. Small signals in m3 due to the instrument response of the Phase I observation and wedge-filtering make it challenging to use these non-Gaussian statistics to explore model parameters. Forecasts with the full HERA array predict high signal-to-noise ratios for m2, m3, and S3 assuming no foregrounds, but wedge-filtering drastically reduces these ratios. This work demonstrates conclusively that a comprehensive understanding of instrumental effects on m2 and m3 is essential for their use as a cosmological probe, given their dependence on the underlying model. △ Less

Submitted 3 November, 2025; originally announced November 2025.

Comments: 29 pages, 18 figures

Journal ref: ApJ, 993, 189 (2025)

EDGES-3: Instrument Design and Commissioning

Authors: Rigel C. Cappallo, Alan E. E. Rogers, Colin J. Lonsdale, Judd D. Bowman, John P. Barrett, Steven G. Murray, Nivedita Mahesh, Peter Sims, Akshatha K. Vydula, Raul A. Monsalve, Christopher J. Eckert, Parker Steen, Kenneth M. Wilson

Abstract: EDGES-3 is the third iteration of the EDGES experiment, designed to measure the predicted global absorption feature in the radio spectrum produced by neutral hydrogen gas at cosmic dawn, a critical observation determining when and how the first stars populated the universe. The EDGES-3 instrument has been redesigned to include both the analog and digital electronics within the antenna, allowing fo… ▽ More EDGES-3 is the third iteration of the EDGES experiment, designed to measure the predicted global absorption feature in the radio spectrum produced by neutral hydrogen gas at cosmic dawn, a critical observation determining when and how the first stars populated the universe. The EDGES-3 instrument has been redesigned to include both the analog and digital electronics within the antenna, allowing for in-situ calibration and removal of the lossy balun found in EDGES-2. EDGES-3 has been on multiple deployments in the past 4 years; to Oregon, Devon Island, Adak Island, and is currently installed and taking data in the outback of Western Australia. This paper provides an accounting of the challenges inherent in the detection of the global, cosmological 21-cm signal, the strategies EDGES employs to mitigate each of these challenges, a description of the instrument, and a report on the Western Australia deployment along with observational data. △ Less

Submitted 4 August, 2025; originally announced August 2025.

Comments: 22 pages, 20 figures

Sample Variance Denoising in Cylindrical 21-cm Power Spectra

Authors: Daniela Breitman, Andrei Mesinger, Steven G. Murray, Anshuman Acharya

Abstract: State-of-the-art simulations of reionisation-era 21-cm signal have limited volumes, generally orders of magnitude smaller than observations. Consequently, the Fourier modes in common between simulation and observation have limited overlap, especially in cylindrical (2D) k-space that is natural for 21-cm interferometry. This makes sample variance (i.e. the deviation of the simulated sample from the… ▽ More State-of-the-art simulations of reionisation-era 21-cm signal have limited volumes, generally orders of magnitude smaller than observations. Consequently, the Fourier modes in common between simulation and observation have limited overlap, especially in cylindrical (2D) k-space that is natural for 21-cm interferometry. This makes sample variance (i.e. the deviation of the simulated sample from the population mean due to finite box size) a potential issue when interpreting upcoming 21-cm observations. We introduce \texttt{21cmPSDenoiser}, a score-based diffusion model that can be applied to a single, forward-modelled realisation of the 21-cm 2D power spectrum (PS), predicting the corresponding \textit{population mean} on-the-fly during Bayesian inference. Individual samples of 2D Fourier amplitudes of wave modes relevant to current 21-cm observations can deviate from the mean by over 50\% for 300 cMpc simulations, even when only considering stochasticity due to sampling of Gaussian initial conditions. \texttt{21cmPSDenoiser} reduces this deviation by an order of magnitude, outperforming current state-of-the-art sample variance mitigation techniques like Fixing \& Pairing by a factor of few at almost no additional computational cost ($\sim6$s per PS). Unlike emulators, the denoiser is not tied to a particular model or simulator since its input is a (model-agnostic) realisation of the 2D 21-cm PS. Indeed, we confirm that it generalises to PS produced with a different 21-cm simulator than those on which it was trained. To quantify the improvement in parameter recovery, we simulate a 21-cm PS detection by the Hydrogen Epoch of Reionization Arrays (HERA) and run different inference pipelines corresponding to commonly-used approximations. We find that using \texttt{21cmPSDenoiser} in the inference pipeline outperforms other approaches, yielding an unbiased posterior that is 50\% narrower. △ Less

Submitted 16 July, 2025; originally announced July 2025.

Comments: 12 pages, 10 figures, submitted to A&A

Journal ref: A&A 703, A130 (2025)

A Bayesian approach to modelling spectrometer data chromaticity corrected using beam factors -- II. Model priors and posterior odds

Authors: Peter H. Sims, Judd D. Bowman, Steven G. Murray, John P. Barrett, Rigel C. Cappallo, Colin J. Lonsdale, Nivedita Mahesh, Raul A. Monsalve, Alan E. E. Rogers, Titu Samson, Akshatha K. Vydula

Abstract: The reliable detection of the global 21-cm signal, a key tracer of Cosmic Dawn and the Epoch of Reionization, requires meticulous data modelling and robust statistical frameworks for model validation and comparison. In Paper I of this series, we presented the Beam-Factor-based Chromaticity Correction (BFCC) model for spectrometer data processed using BFCC to suppress instrumentally induced spectra… ▽ More The reliable detection of the global 21-cm signal, a key tracer of Cosmic Dawn and the Epoch of Reionization, requires meticulous data modelling and robust statistical frameworks for model validation and comparison. In Paper I of this series, we presented the Beam-Factor-based Chromaticity Correction (BFCC) model for spectrometer data processed using BFCC to suppress instrumentally induced spectral structure. We demonstrated that the BFCC model, with complexity calibrated by Bayes factor-based model comparison (BFBMC), enables unbiased recovery of a 21-cm signal consistent with the one reported by EDGES from simulated data. Here, we extend the evaluation of the BFCC model to lower amplitude 21-cm signal scenarios where deriving reliable conclusions about a model's capacity to recover unbiased 21-cm signal estimates using BFBMC is more challenging. Using realistic simulations of chromaticity-corrected EDGES-low spectrometer data, we evaluate three signal amplitude regimes -- null, moderate, and high. We then conduct a Bayesian comparison between the BFCC model and three alternative models previously applied to 21-cm signal estimation from EDGES data. To mitigate biases introduced by systematics in the 21-cm signal model fit, we incorporate the Bayesian Null-Test-Evidence-Ratio (BaNTER) validation framework and implement a Bayesian inference workflow based on posterior odds of the validated models. We demonstrate that, unlike BFBMC alone, this approach consistently recovers 21-cm signal estimates that align with the true signal across all amplitude regimes, advancing robust global 21-cm signal detection methodologies. △ Less

Submitted 24 June, 2025; originally announced June 2025.

Comments: 25 pages, 6 figures; submitted for publication in MNRAS

Journal ref: Mon Not R Astron Soc (2025) 2340-2364

fftvis: A Non-Uniform Fast Fourier Transform Based Interferometric Visibility Simulator

Authors: Tyler A. Cox, Steven G. Murray, Aaron R. Parsons, Joshua S. Dillon, Kartik Mandar, Zachary E. Martinot, Robert Pascua, Piyanat Kittiwisit, James E. Aguirre

Abstract: The detection and characterization of the 21cm signal from the Epoch of Reionization (EoR) demands extraordinary precision in radio interferometric observations and analysis. For modern low-frequency arrays, achieving the dynamic range necessary to detect this signal requires simulation frameworks to validate analysis techniques and characterize systematic effects. However, the computational expen… ▽ More The detection and characterization of the 21cm signal from the Epoch of Reionization (EoR) demands extraordinary precision in radio interferometric observations and analysis. For modern low-frequency arrays, achieving the dynamic range necessary to detect this signal requires simulation frameworks to validate analysis techniques and characterize systematic effects. However, the computational expense of direct visibility calculations grows rapidly with sky model complexity and array size, posing a potential bottleneck for scalable forward modeling. In this paper, we present fftvis, a high-performance visibility simulator built on the Flatiron Non-Uniform Fast-Fourier Transform (finufft) algorithm. We show that fftvis matches the well-validated matvis simulator to near numerical precision while delivering substantial runtime reductions, up to two orders of magnitude for dense, many-element arrays. We provide a detailed description of the fftvis algorithm and benchmark its computational performance, memory footprint, and numerical accuracy against matvis, including a validation study against analytic solutions for diffuse sky models. We further assess the utility of fftvis in validating 21cm analysis pipelines through a study of the dynamic range in simulated delay and fringe-rate spectra. Our results establish fftvis as a fast, precise, and scalable simulation tool for 21cm cosmology experiments, enabling end-to-end validation of analysis pipelines. △ Less

Submitted 10 December, 2025; v1 submitted 2 June, 2025; originally announced June 2025.

Comments: 20 pages, 8 figures, Published to RASTI

A general Bayesian model-validation framework based on null-test evidence ratios, with an example application to global 21-cm cosmology

Authors: Peter H. Sims, Steven G. Murray, Judd D. Bowman, John P. Barrett, Rigel C. Cappallo, Colin J. Lonsdale, Nivedita Mahesh, Raul A. Monsalve, Alan E. E. Rogers, Titu Samson, Akshatha K. Vydula

Abstract: Comparing composite models for multi-component observational data is a prevalent scientific challenge. When fitting composite models, there exists the potential for systematics from a poor fit of one model component to be absorbed by another, resulting in the composite model providing an accurate fit to the data in aggregate but yielding biased a posteriori estimates for individual components. We… ▽ More Comparing composite models for multi-component observational data is a prevalent scientific challenge. When fitting composite models, there exists the potential for systematics from a poor fit of one model component to be absorbed by another, resulting in the composite model providing an accurate fit to the data in aggregate but yielding biased a posteriori estimates for individual components. We begin by defining a classification scheme for composite model comparison scenarios, identifying two categories: category I, where models with accurate and predictive components are separable through Bayesian comparison of the unvalidated composite models, and category II, where models with accurate and predictive components may not be separable due to interactions between components, leading to spurious detections or biased signal estimation. To address the limitations of category II model comparisons, we introduce the Bayesian Null Test Evidence Ratio-based (BaNTER) validation framework. Applying this classification scheme and BaNTER to a composite model comparison problem in 21-cm cosmology, where minor systematics from imperfect foreground modelling can bias global 21-cm signal recovery, we validate six composite models using mock data. We show that incorporating BaNTER alongside Bayes-factor-based comparison reliably ensures unbiased inferences of the signal of interest across both categories, positioning BaNTER as a valuable addition to Bayesian inference workflows with potential applications across diverse fields. △ Less

Submitted 19 February, 2025; originally announced February 2025.

Comments: 20 pages, 5 figures; accepted for publication in MNRAS

Journal ref: Mon Not R Astron Soc (2025) 2262-2281

Impacts and Statistical Mitigation of Missing Data on the 21cm Power Spectrum: A Case Study with the Hydrogen Epoch of Reionization Array

Authors: Kai-Feng Chen, Michael J. Wilensky, Adrian Liu, Joshua S. Dillon, Jacqueline N. Hewitt, Tyrone Adams, James E. Aguirre, Rushelle Baartman, Adam P. Beardsley, Lindsay M. Berkhout, Gianni Bernardi, Tashalee S. Billings, Judd D. Bowman, Philip Bull, Jacob Burba, Ruby Byrne, Steven Carey, Samir Choudhuri, Tyler Cox, David R. DeBoer, Matt Dexter, Nico Eksteen, John Ely, Aaron Ewall-Wice, Steven R. Furlanetto , et al. (44 additional authors not shown)

Abstract: The precise characterization and mitigation of systematic effects is one of the biggest roadblocks impeding the detection of the fluctuations of cosmological 21cm signals. Missing data in radio cosmological experiments, often due to radio frequency interference (RFI), poses a particular challenge to power spectrum analysis as it could lead to the ringing of bright foreground modes in Fourier space… ▽ More The precise characterization and mitigation of systematic effects is one of the biggest roadblocks impeding the detection of the fluctuations of cosmological 21cm signals. Missing data in radio cosmological experiments, often due to radio frequency interference (RFI), poses a particular challenge to power spectrum analysis as it could lead to the ringing of bright foreground modes in Fourier space, heavily contaminating the cosmological signals. Here we show that the problem of missing data becomes even more arduous in the presence of systematic effects. Using a realistic numerical simulation, we demonstrate that partially flagged data combined with systematic effects can introduce significant foreground ringing. We show that such an effect can be mitigated through inpainting the missing data. We present a rigorous statistical framework that incorporates the process of inpainting missing data into a quadratic estimator of the 21cm power spectrum. Under this framework, the uncertainties associated with our inpainting method and its impact on power spectrum statistics can be understood. These results are applied to the latest Phase II observations taken by the Hydrogen Epoch of Reionization Array, forming a crucial component in power spectrum analyses as we move toward detecting 21cm signals in the ever more noisy RFI environment. △ Less

Submitted 6 December, 2024; v1 submitted 15 November, 2024; originally announced November 2024.

Comments: 25 pages, 11 figures; Replaced to match accepted ApJ version. New version contains small editorial changes throughout in response to referee comments, no changes to results

The EDGES measurement disfavors an excess radio background during the cosmic dawn

Authors: Junsong Cang, Andrei Mesinger, Steven G. Murray, Daniela Breitman, Yuxiang Qin, Roberto Trotta

Abstract: In 2018 the EDGES experiment claimed the first detection of the global cosmic 21cm signal, which featured an absorption trough centered around $z \sim 17$ with a depth of approximately -500mK. This amplitude is deeper than the standard prediction (in which the radio background is determined by the cosmic microwave background) by a factor of two and potentially hints at the existence of a radio bac… ▽ More In 2018 the EDGES experiment claimed the first detection of the global cosmic 21cm signal, which featured an absorption trough centered around $z \sim 17$ with a depth of approximately -500mK. This amplitude is deeper than the standard prediction (in which the radio background is determined by the cosmic microwave background) by a factor of two and potentially hints at the existence of a radio background excess. While this result was obtained by fitting the data with a phenomenological flattened-Gaussian shape for the cosmological signal, here we develop a physical model for the inhomogeneous radio background sourced by the first galaxies hosting population III stars. Star formation in these galaxies is quenched at lower redshifts due to various feedback mechanisms, so they serve as a natural candidate for the excess radio background hinted by EDGES, without violating present day measurements by ARCADE2. We forward-model the EDGES sky temperature data, jointly sampling our physical model for the cosmic signal, a foreground model, and residual calibration errors. We compare the Bayesian evidences obtained by varying the complexity and prior ranges for the systematics. We find that the data is best explained by a model with seven log-polynomial foreground terms, and that it requires calibration residuals. Interestingly, the presence of a cosmic 21cm signal with a non-standard depth is decisively disfavored. This is contrary to previous EDGES analysis in the context of extra radio background models, serving as a caution against using a ''pseudo-likelihood'' built on a model (flattened Gaussian) that is different from the one being used for inference. We make our simulation code and associated emulator publicly-available. △ Less

Submitted 12 November, 2024; originally announced November 2024.

Comments: 17 pages, 9 figures, 1 table, version submitted to A&A

Journal ref: A&A 698, A152 (2025)

Investigating Mutual Coupling in the Hydrogen Epoch of Reionization Array and Mitigating its Effects on the 21-cm Power Spectrum

Authors: E. Rath, R. Pascua, A. T. Josaitis, A. Ewall-Wice, N. Fagnoni, E. de Lera Acedo, Z. E. Martinot, Z. Abdurashidova, T. Adams, J. E. Aguirre, R. Baartman, A. P. Beardsley, L. M. Berkhout, G. Bernardi, T. S. Billings, J. D. Bowman, P. Bull, J. Burba, R. Byrne, S. Carey, K. -F. Chen, S. Choudhuri, T. Cox, D. R. DeBoer, M. Dexter , et al. (56 additional authors not shown)

Abstract: Interferometric experiments designed to detect the highly redshifted 21-cm signal from neutral hydrogen are producing increasingly stringent constraints on the 21-cm power spectrum, but some k-modes remain systematics-dominated. Mutual coupling is a major systematic that must be overcome in order to detect the 21-cm signal, and simulations that reproduce effects seen in the data can guide strategi… ▽ More Interferometric experiments designed to detect the highly redshifted 21-cm signal from neutral hydrogen are producing increasingly stringent constraints on the 21-cm power spectrum, but some k-modes remain systematics-dominated. Mutual coupling is a major systematic that must be overcome in order to detect the 21-cm signal, and simulations that reproduce effects seen in the data can guide strategies for mitigating mutual coupling. In this paper, we analyse 12 nights of data from the Hydrogen Epoch of Reionization Array and compare the data against simulations that include a computationally efficient and physically motivated semi-analytic treatment of mutual coupling. We find that simulated coupling features qualitatively agree with coupling features in the data; however, coupling features in the data are brighter than the simulated features, indicating the presence of additional coupling mechanisms not captured by our model. We explore the use of fringe-rate filters as mutual coupling mitigation tools and use our simulations to investigate the effects of mutual coupling on a simulated cosmological 21-cm power spectrum in a "worst case" scenario where the foregrounds are particularly bright. We find that mutual coupling contaminates a large portion of the "EoR Window", and the contamination is several orders-of-magnitude larger than our simulated cosmic signal across a wide range of cosmological Fourier modes. While our fiducial fringe-rate filtering strategy reduces mutual coupling by roughly a factor of 100 in power, a non-negligible amount of coupling cannot be excised with fringe-rate filters, so more sophisticated mitigation strategies are required. △ Less

Submitted 12 June, 2024; originally announced June 2024.

Comments: 19 pages, 12 figures, submitted to MNRAS

21cmSense v2: A modular, open-source 21cm sensitivity calculator

Authors: Steven G. Murray, Jonathan Pober, Matthew Kolopanis

Abstract: The 21cm line of neutral hydrogen is a powerful probe of the high-redshift universe (Cosmic Dawn and the Epoch of Reionization), with an unprecedented potential to inform us about key processes of early galaxy formation, the first stars and even cosmology and structure formation, via intensity mapping. It is the subject of a number of current and upcoming low-frequency radio experiments. This pape… ▽ More The 21cm line of neutral hydrogen is a powerful probe of the high-redshift universe (Cosmic Dawn and the Epoch of Reionization), with an unprecedented potential to inform us about key processes of early galaxy formation, the first stars and even cosmology and structure formation, via intensity mapping. It is the subject of a number of current and upcoming low-frequency radio experiments. This paper presents 21cmSense v2.0, which is a Python package that provides a modular framework for calculating the sensitivity of these experiments, in order to enhance the process of their design and forecasting their power for parameter inference. Version 2.0 of 21cmSense has been re-written from the ground up to be more modular and extensible than its venerable predecessor (Pober et al., 2013, 2014), and to provide a more user-friendly interface. The package is freely available both to use and contribute towards at https://github.com/rasg-affiliates/21cmSense. △ Less

Submitted 4 June, 2024; originally announced June 2024.

Comments: 2 figures. Published in JOSS. Comments and contributions very welcome!

Journal ref: Journal of Open Source Software, 9(97), 6501 (2024)

A demonstration of the effect of fringe-rate filtering in the Hydrogen Epoch of Reionization Array delay power spectrum pipeline

Authors: Hugh Garsden, Philip Bull, Mike Wilensky, Zuhra Abdurashidova, Tyrone Adams, James E. Aguirre, Paul Alexander, Zaki S. Ali, Rushelle Baartman, Yanga Balfour, Adam P. Beardsley, Lindsay M. Berkhout, Gianni Bernardi, Tashalee S. Billings, Judd D. Bowman, Richard F. Bradley, Jacob Burba, Steven Carey, Chris L. Carilli, Kai-Feng Chen, Carina Cheng, Samir Choudhuri, David R. DeBoer, Eloy de Lera Acedo, Matt Dexter , et al. (72 additional authors not shown)

Abstract: Radio interferometers targeting the 21cm brightness temperature fluctuations at high redshift are subject to systematic effects that operate over a range of different timescales. These can be isolated by designing appropriate Fourier filters that operate in fringe-rate (FR) space, the Fourier pair of local sidereal time (LST). Applications of FR filtering include separating effects that are correl… ▽ More Radio interferometers targeting the 21cm brightness temperature fluctuations at high redshift are subject to systematic effects that operate over a range of different timescales. These can be isolated by designing appropriate Fourier filters that operate in fringe-rate (FR) space, the Fourier pair of local sidereal time (LST). Applications of FR filtering include separating effects that are correlated with the rotating sky vs. those relative to the ground, down-weighting emission in the primary beam sidelobes, and suppressing noise. FR filtering causes the noise contributions to the visibility data to become correlated in time however, making interpretation of subsequent averaging and error estimation steps more subtle. In this paper, we describe fringe rate filters that are implemented using discrete prolate spheroidal sequences, and designed for two different purposes -- beam sidelobe/horizon suppression (the `mainlobe' filter), and ground-locked systematics removal (the `notch' filter). We apply these to simulated data, and study how their properties affect visibilities and power spectra generated from the simulations. Included is an introduction to fringe-rate filtering and a demonstration of fringe-rate filters applied to simple situations to aid understanding. △ Less

Submitted 7 July, 2025; v1 submitted 13 February, 2024; originally announced February 2024.

Comments: Updated to published version. 21 pages, 20 figures, 3 tables, 2 appendices. Published in Monthly Notices of the Royal Astronomical Society

Hydrogen Epoch of Reionization Array (HERA) Phase II Deployment and Commissioning

Authors: Lindsay M. Berkhout, Daniel C. Jacobs, Zuhra Abdurashidova, Tyrone Adams, James E. Aguirre, Paul Alexander, Zaki S. Ali, Rushelle Baartman, Yanga Balfour, Adam P. Beardsley, Gianni Bernardi, Tashalee S. Billings, Judd D. Bowman, Richard F. Bradley, Philip Bull, Jacob Burba, Steven Carey, Chris L. Carilli, Kai-Feng Chen, Carina Cheng, Samir Choudhuri, David R. DeBoer, Eloy de Lera Acedo, Matt Dexter, Joshua S. Dillon , et al. (71 additional authors not shown)

Abstract: This paper presents the design and deployment of the Hydrogen Epoch of Reionization Array (HERA) phase II system. HERA is designed as a staged experiment targeting 21 cm emission measurements of the Epoch of Reionization. First results from the phase I array are published as of early 2022, and deployment of the phase II system is nearing completion. We describe the design of the phase II system an… ▽ More This paper presents the design and deployment of the Hydrogen Epoch of Reionization Array (HERA) phase II system. HERA is designed as a staged experiment targeting 21 cm emission measurements of the Epoch of Reionization. First results from the phase I array are published as of early 2022, and deployment of the phase II system is nearing completion. We describe the design of the phase II system and discuss progress on commissioning and future upgrades. As HERA is a designated Square Kilometer Array (SKA) pathfinder instrument, we also show a number of "case studies" that investigate systematics seen while commissioning the phase II system, which may be of use in the design and operation of future arrays. Common pathologies are likely to manifest in similar ways across instruments, and many of these sources of contamination can be mitigated once the source is identified. △ Less

Submitted 8 January, 2024; originally announced January 2024.

Journal ref: PASP 2024 136 045002

matvis: A matrix-based visibility simulator for fast forward modelling of many-element 21 cm arrays

Authors: Piyanat Kittiwisit, Steven G. Murray, Hugh Garsden, Philip Bull, Christopher Cain, Aaron R. Parsons, Jackson Sipple, Zara Abdurashidova, Tyrone Adams, James E. Aguirre, Paul Alexander, Zaki S. Ali, Rushelle Baartman, Yanga Balfour, Adam P. Beardsley, Lindsay M. Berkhout, Gianni Bernardi, Tashalee S. Billings, Judd D. Bowman, Richard F. Bradley, Jacob Burba, Steven Carey, Chris L. Carilli, Kai-Feng Chen, Carina Cheng , et al. (73 additional authors not shown)

Abstract: Detection of the faint 21 cm line emission from the Cosmic Dawn and Epoch of Reionisation will require not only exquisite control over instrumental calibration and systematics to achieve the necessary dynamic range of observations but also validation of analysis techniques to demonstrate their statistical properties and signal loss characteristics. A key ingredient in achieving this is the ability… ▽ More Detection of the faint 21 cm line emission from the Cosmic Dawn and Epoch of Reionisation will require not only exquisite control over instrumental calibration and systematics to achieve the necessary dynamic range of observations but also validation of analysis techniques to demonstrate their statistical properties and signal loss characteristics. A key ingredient in achieving this is the ability to perform high-fidelity simulations of the kinds of data that are produced by the large, many-element, radio interferometric arrays that have been purpose-built for these studies. The large scale of these arrays presents a computational challenge, as one must simulate a detailed sky and instrumental model across many hundreds of frequency channels, thousands of time samples, and tens of thousands of baselines for arrays with hundreds of antennas. In this paper, we present a fast matrix-based method for simulating radio interferometric measurements (visibilities) at the necessary scale. We achieve this through judicious use of primary beam interpolation, fast approximations for coordinate transforms, and a vectorised outer product to expand per-antenna quantities to per-baseline visibilities, coupled with standard parallelisation techniques. We validate the results of this method, implemented in the publicly-available matvis code, against a high-precision reference simulator, and explore its computational scaling on a variety of problems. △ Less

Submitted 8 January, 2025; v1 submitted 15 December, 2023; originally announced December 2023.

Comments: 24 pages, 10 figures, accepted to RAS Techniques and Instruments, matvis is publicly available at https://github.com/HERA-Team/matvis

Bayesian estimation of cross-coupling and reflection systematics in 21cm array visibility data

Authors: Geoff G. Murphy, Philip Bull, Mario G. Santos, Zara Abdurashidova, Tyrone Adams, James E. Aguirre, Paul Alexander, Zaki S. Ali, Rushelle Baartman, Yanga Balfour, Adam P. Beardsley, Gianni Bernardi, Tashalee Billings, Judd D. Bowman, Richard F. Bradley, Jacob Burba, Christopher Cain, Steven Carey, Chris L. Carilli, Carina Cheng, David R. DeBoer, Eloy de Lera Acedo, Matt Dexter, Joshua S. Dillon, Nico Eksteen , et al. (54 additional authors not shown)

Abstract: Observations with radio arrays that target the 21-cm signal originating from the early Universe suffer from a variety of systematic effects. An important class of these are reflections and spurious couplings between antennas. We apply a Hamiltonian Monte Carlo sampler to the modelling and mitigation of these systematics in simulated Hydrogen Epoch of Reionisation Array (HERA) data. This method all… ▽ More Observations with radio arrays that target the 21-cm signal originating from the early Universe suffer from a variety of systematic effects. An important class of these are reflections and spurious couplings between antennas. We apply a Hamiltonian Monte Carlo sampler to the modelling and mitigation of these systematics in simulated Hydrogen Epoch of Reionisation Array (HERA) data. This method allows us to form statistical uncertainty estimates for both our models and the recovered visibilities, which is an important ingredient in establishing robust upper limits on the Epoch of Reionisation (EoR) power spectrum. In cases where the noise is large compared to the EoR signal, this approach can constrain the systematics well enough to mitigate them down to the noise level for both systematics studied. Incoherently averaging the recovered power spectra can further reduce the noise and improve recovery. Where the noise level is lower than the EoR, our modelling can mitigate the majority of the reflections and coupling with there being only a minor level of residual systematics. Our approach performs similarly to existing filtering/fitting techniques used in the HERA pipeline, but with the added benefit of rigorously propagating uncertainties. In all cases it does not significantly attenuate the underlying signal. △ Less

Submitted 5 March, 2025; v1 submitted 6 December, 2023; originally announced December 2023.

Comments: 22 pages, 15 figures, published in MNRAS

Direct Optimal Mapping Image Power Spectrum and its Window Functions

Authors: Zhilei Xu, Honggeun Kim, Jacqueline N. Hewitt, Kai-Feng Chen, Nicholas S. Kern, Eleanor Rath, Ruby Byrne, Adélie Gorce, Robert Pascua, Zachary E. Martinot, Joshua S. Dillon, Bryna J. Hazelton, Adrian Liu, Miguel F. Morales, Zara Abdurashidova, Tyrone Adams, James E. Aguirre, Paul Alexander, Zaki S. Ali, Rushelle Baartman, Yanga Balfour, Adam P. Beardsley, Gianni Bernardi, Tashalee S. Billings, Judd D. Bowman , et al. (57 additional authors not shown)

Abstract: The key to detecting neutral hydrogen during the epoch of reionization (EoR) is to separate the cosmological signal from the dominating foreground radiation. We developed direct optimal mapping (DOM) to map interferometric visibilities; it contains only linear operations, with full knowledge of point spread functions from visibilities to images. Here, we demonstrate a fast Fourier transform-based… ▽ More The key to detecting neutral hydrogen during the epoch of reionization (EoR) is to separate the cosmological signal from the dominating foreground radiation. We developed direct optimal mapping (DOM) to map interferometric visibilities; it contains only linear operations, with full knowledge of point spread functions from visibilities to images. Here, we demonstrate a fast Fourier transform-based image power spectrum and its window functions computed from the DOM images. We use noiseless simulation, based on the Hydrogen Epoch of Reionization Array Phase I configuration, to study the image power spectrum properties. The window functions show $<10^{-11}$ of the integrated power leaks from the foreground-dominated region into the EoR window; the 2D and 1D power spectra also verify the separation between the foregrounds and the EoR. △ Less

Submitted 5 July, 2024; v1 submitted 17 November, 2023; originally announced November 2023.

Comments: Published in ApJ

Low-Frequency Radio Recombination Lines Away From the Inner Galactic Plane

Authors: Akshatha K. Vydula, Judd D. Bowman, David Lewis, Kelsie Crawford, Matthew Kolopanis, Alan E. E. Rogers, Steven G. Murray, Nivedita Mahesh, Raul A. Monsalve, Peter Sims, Titu Samson

Abstract: Diffuse radio recombination lines (RRLs) in the Galaxy are possible foregrounds for redshifted 21~cm experiments. We use EDGES drift scans centered at $-26.7^o$~declination to characterize diffuse RRLs across the southern sky. We find RRLs averaged over the large antenna beam ($ 72^o \times 110^o $) reach minimum amplitudes between right ascensions~2-6~h. In this region, the C$α$ absorption amplit… ▽ More Diffuse radio recombination lines (RRLs) in the Galaxy are possible foregrounds for redshifted 21~cm experiments. We use EDGES drift scans centered at $-26.7^o$~declination to characterize diffuse RRLs across the southern sky. We find RRLs averaged over the large antenna beam ($ 72^o \times 110^o $) reach minimum amplitudes between right ascensions~2-6~h. In this region, the C$α$ absorption amplitude is $33\pm11$~mK (1$σ$) averaged over 50-87~MHz ($27\gtrsim z \gtrsim15$ for the 21~cm line) and increases strongly as frequency decreases. C$β$ and H$α$ lines are consistent with no detection with amplitudes of $13\pm14$ and $12\pm10$~mK (1$σ$), respectively. At 108-124.5~MHz ($z\approx11$) in the same region, we find no evidence for carbon or hydrogen lines at the noise level of 3.4~mK (1$σ$). Conservatively assuming observed lines come broadly from the diffuse interstellar medium, as opposed to a few compact regions, these amplitudes provide upper limits on the intrinsic diffuse lines. The observations support expectations that Galactic RRLs can be neglected as significant foregrounds for a large region of sky until redshifted 21~cm experiments, particularly those targeting Cosmic Dawn, move beyond the detection phase. We fit models of the spectral dependence of the lines averaged over the large beam of EDGES, which may contain multiple line sources with possible line blending, and find that including degrees of freedom for expected smooth, frequency-dependent deviations from local thermodynamic equilibrium (LTE) is preferred over simple LTE assumptions for C$α$ and H$α$ lines. For C$α$ we estimate departure coefficients $0.79<b_nβ_n<4.5$ along the inner Galactic Plane and $0<b_nβ_n<2.3$ away from the inner Galactic Plane. △ Less

Submitted 1 November, 2023; v1 submitted 27 February, 2023; originally announced February 2023.

Comments: 25 pages, 14 figures, 3 tables, Accepted in Astronomical Journal

Search for the Epoch of Reionisation with HERA: Upper Limits on the Closure Phase Delay Power Spectrum

Authors: Pascal M. Keller, Bojan Nikolic, Nithyanandan Thyagarajan, Chris L. Carilli, Gianni Bernardi, Ntsikelelo Charles, Landman Bester, Oleg M. Smirnov, Nicholas S. Kern, Joshua S. Dillon, Bryna J. Hazelton, Miguel F. Morales, Daniel C. Jacobs, Aaron R. Parsons, Zara Abdurashidova, Tyrone Adams, James E. Aguirre, Paul Alexander, Zaki S. Ali, Rushelle Baartman, Yanga Balfour, Adam P. Beardsley, Tashalee S. Billings, Judd D. Bowman, Richard F. Bradley , et al. (58 additional authors not shown)

Abstract: Radio interferometers aiming to measure the power spectrum of the redshifted 21 cm line during the Epoch of Reionisation (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 standa… ▽ More Radio interferometers aiming to measure the power spectrum of the redshifted 21 cm line during the Epoch of Reionisation (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% confidence that the 21 cm EoR brightness temperature is $\le$(372)$^2$ "pseudo" mK$^2$ at 1.14 "pseudo" $h$ Mpc$^{-1}$, where the "pseudo" emphasises 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. △ Less

Submitted 15 February, 2023; originally announced February 2023.

Comments: 16 pages, 14 figures, accepted for publication by MNRAS

Analytic approximations of scattering effects on beam chromaticity in 21-cm global experiments

Authors: Alan E. E. Rogers, John P. Barrett, Judd D. Bowman, Rigel Cappallo, Colin J. Lonsdale, Nivedita Mahesh, Raul A. Monsalve, Steven G. Murray, Peter H. Sims

Abstract: Scattering from objects near an antenna produce correlated signals from strong compact radio sources in a manner similar to those used by the Sea Interferometer to measure the radio source positions using the fine frequency structure in the total power spectrum of a single antenna. These fringes or ripples due to correlated signal interference are present at a low level in the spectrum of any sing… ▽ More Scattering from objects near an antenna produce correlated signals from strong compact radio sources in a manner similar to those used by the Sea Interferometer to measure the radio source positions using the fine frequency structure in the total power spectrum of a single antenna. These fringes or ripples due to correlated signal interference are present at a low level in the spectrum of any single antenna and are a major source of systematics in systems used to measure the global redshifted 21-cm signal from the early universe. In the Sea Interferometer a single antenna on a cliff above the sea is used to add the signal from the direct path to the signal from the path reflected from the sea thereby forming an interferometer. This was used for mapping radio sources with a single antenna by Bolton and Slee in the 1950s. In this paper we derive analytic expressions to determine the level of these ripples and compare these results in a few simple cases with electromagnetic modeling software to verify that the analytic calculations are sufficient to obtain the magnitude of the scattering effects on the measurements of the global 21-cm signal. These analytic calculations are needed to evaluate the magnitude of the effects in cases that are either too complex or take too much time to be modeled using software. △ Less

Submitted 8 December, 2022; originally announced December 2022.

A Bayesian approach to modelling spectrometer data chromaticity corrected using beam factors -- I. Mathematical formalism

Authors: Peter H. Sims, Judd D. Bowman, Nivedita Mahesh, Steven G. Murray, John P. Barrett, Rigel Cappallo, Raul A. Monsalve, Alan E. E. Rogers, Titu Samson, Akshatha K. Vydula

Abstract: Accurately accounting for spectral structure in spectrometer data induced by instrumental chromaticity on scales relevant for detection of the 21-cm signal is among the most significant challenges in global 21-cm signal analysis. In the publicly available EDGES low-band data set, this complicating structure is suppressed using beam-factor based chromaticity correction (BFCC), which works by dividi… ▽ More Accurately accounting for spectral structure in spectrometer data induced by instrumental chromaticity on scales relevant for detection of the 21-cm signal is among the most significant challenges in global 21-cm signal analysis. In the publicly available EDGES low-band data set, this complicating structure is suppressed using beam-factor based chromaticity correction (BFCC), which works by dividing the data by a sky-map-weighted model of the spectral structure of the instrument beam. Several analyses of this data have employed models that start with the assumption that this correction is complete. However, while BFCC mitigates the impact of instrumental chromaticity on the data, given realistic assumptions regarding the spectral structure of the foregrounds, the correction is only partial. This complicates the interpretation of fits to the data with intrinsic sky models (models that assume no instrumental contribution to the spectral structure of the data). In this paper, we derive a BFCC data model from an analytic treatment of BFCC and demonstrate using simulated observations that, in contrast to using an intrinsic sky model for the data, the BFCC data model enables unbiased recovery of a simulated global 21-cm signal from beam-factor chromaticity corrected data in the limit that the data is corrected with an error-free beam-factor model. △ Less

Submitted 28 March, 2023; v1 submitted 7 December, 2022; originally announced December 2022.

Comments: 26 pages, 8 figures; accepted for publication in MNRAS

Improved Constraints on the 21 cm EoR Power Spectrum and the X-Ray Heating of the IGM with HERA Phase I Observations

Authors: The HERA Collaboration, Zara Abdurashidova, Tyrone Adams, James E. Aguirre, Paul Alexander, Zaki S. Ali, Rushelle Baartman, Yanga Balfour, Rennan Barkana, Adam P. Beardsley, Gianni Bernardi, Tashalee S. Billings, Judd D. Bowman, Richard F. Bradley, Daniela Breitman, Philip Bull, Jacob Burba, Steve Carey, Chris L. Carilli, Carina Cheng, Samir Choudhuri, David R. DeBoer, Eloy de Lera Acedo, Matt Dexter, Joshua S. Dillon , et al. (70 additional authors not shown)

Abstract: We report the most sensitive upper limits to date on the 21 cm epoch of reionization power spectrum using 94 nights of observing with Phase I of the Hydrogen Epoch of Reionization Array (HERA). Using similar analysis techniques as in previously reported limits (HERA Collaboration 2022a), we find at 95% confidence that $Δ^2(k = 0.34$ $h$ Mpc$^{-1}$) $\leq 457$ mK$^2$ at $z = 7.9$ and that… ▽ More We report the most sensitive upper limits to date on the 21 cm epoch of reionization power spectrum using 94 nights of observing with Phase I of the Hydrogen Epoch of Reionization Array (HERA). Using similar analysis techniques as in previously reported limits (HERA Collaboration 2022a), we find at 95% confidence that $Δ^2(k = 0.34$ $h$ Mpc$^{-1}$) $\leq 457$ mK$^2$ at $z = 7.9$ and that $Δ^2 (k = 0.36$ $h$ Mpc$^{-1}) \leq 3,496$ mK$^2$ at $z = 10.4$, an improvement by a factor of 2.1 and 2.6 respectively. These limits are mostly consistent with thermal noise over a wide range of $k$ after our data quality cuts, despite performing a relatively conservative analysis designed to minimize signal loss. Our results are validated with both statistical tests on the data and end-to-end pipeline simulations. We also report updated constraints on the astrophysics of reionization and the cosmic dawn. Using multiple independent modeling and inference techniques previously employed by HERA Collaboration (2022b), we find that the intergalactic medium must have been heated above the adiabatic cooling limit at least as early as $z = 10.4$, ruling out a broad set of so-called "cold reionization" scenarios. If this heating is due to high-mass X-ray binaries during the cosmic dawn, as is generally believed, our result's 99% credible interval excludes the local relationship between soft X-ray luminosity and star formation and thus requires heating driven by evolved low-metallicity stars. △ Less

Submitted 19 January, 2023; v1 submitted 10 October, 2022; originally announced October 2022.

Comments: 57 pages, 37 figures. Updated to match the accepted ApJ version. Corresponding author: Joshua S. Dillon

Journal ref: 2023 ApJ 945 124

Impact of instrument and data characteristics in the interferometric reconstruction of the 21 cm power spectrum

Authors: Adélie Gorce, Samskruthi Ganjam, Adrian Liu, Steven G. Murray, Zara Abdurashidova, Tyrone Adams, James E. Aguirre, Paul Alexander, Zaki S. Ali, Rushelle Baartman, Yanga Balfour, Adam P. Beardsley, Gianni Bernardi, Tashalee S. Billings, Judd D. Bowman, Richard F. Bradley, Philip Bull, Jacob Burba, Steven Carey, Chris L. Carilli, Carina Cheng, David R. DeBoer, Eloy de Lera Acedo, Matt Dexter, Joshua S. Dillon , et al. (53 additional authors not shown)

Abstract: Combining the visibilities measured by an interferometer to form a cosmological power spectrum is a complicated process. In a delay-based analysis, the mapping between instrumental and cosmological space is not a one-to-one relation. Instead, neighbouring modes contribute to the power measured at one point, with their respective contributions encoded in the window functions. To better understand t… ▽ More Combining the visibilities measured by an interferometer to form a cosmological power spectrum is a complicated process. In a delay-based analysis, the mapping between instrumental and cosmological space is not a one-to-one relation. Instead, neighbouring modes contribute to the power measured at one point, with their respective contributions encoded in the window functions. To better understand the power measured by an interferometer, we assess the impact of instrument characteristics and analysis choices on these window functions. Focusing on the Hydrogen Epoch of Reionization Array (HERA) as a case study, we find that long-baseline observations correspond to enhanced low-k tails of the window functions, which facilitate foreground leakage, whilst an informed choice of bandwidth and frequency taper can reduce said tails. With simple test cases and realistic simulations, we show that, apart from tracing mode mixing, the window functions help accurately reconstruct the power spectrum estimator of simulated visibilities. The window functions depend strongly on the beam chromaticity, and less on its spatial structure - a Gaussian approximation, ignoring side lobes, is sufficient. Finally, we investigate the potential of asymmetric window functions, down-weighting the contribution of low-k power to avoid foreground leakage. The window functions presented here correspond to the latest HERA upper limits for the full Phase I data. They allow an accurate reconstruction of the power spectrum measured by the instrument and will be used in future analyses to confront theoretical models and data directly in cylindrical space. △ Less

Submitted 11 January, 2023; v1 submitted 7 October, 2022; originally announced October 2022.

Comments: 18 pages, 19 figures, accepted for publication in MNRAS

A Bayesian Calibration Framework for EDGES

Authors: Steven G. Murray, Judd D. Bowman, Peter H. Sims, Nivedita Mahesh, Alan E. E. Rogers, Raul A. Monsalve, Titu Samson, Akshatha Konakondula Vydula

Abstract: We develop a Bayesian model that jointly constrains receiver calibration, foregrounds and cosmic 21cm signal for the EDGES global 21\,cm experiment. This model simultaneously describes calibration data taken in the lab along with sky-data taken with the EDGES low-band antenna. We apply our model to the same data (both sky and calibration) used to report evidence for the first star formation in 201… ▽ More We develop a Bayesian model that jointly constrains receiver calibration, foregrounds and cosmic 21cm signal for the EDGES global 21\,cm experiment. This model simultaneously describes calibration data taken in the lab along with sky-data taken with the EDGES low-band antenna. We apply our model to the same data (both sky and calibration) used to report evidence for the first star formation in 2018. We find that receiver calibration does not contribute a significant uncertainty to the inferred cosmic signal (<1%), though our joint model is able to more robustly estimate the cosmic signal for foreground models that are otherwise too inflexible to describe the sky data. We identify the presence of a significant systematic in the calibration data, which is largely avoided in our analysis, but must be examined more closely in future work. Our likelihood provides a foundation for future analyses in which other instrumental systematics, such as beam corrections and reflection parameters, may be added in a modular manner. △ Less

Submitted 7 September, 2022; originally announced September 2022.

Comments: 18 pages + 3 for appendices. 13 figures. Accepted to MNRAS

Multi-frequency angular power spectrum of the 21~cm signal from the Epoch of Reionisation using the Murchison Widefield Array

Authors: Cathryn M. Trott, Rajesh Mondal, Garrelt Mellema, Steven G. Murray, Bradley Greig, Jack L. B. Line, Nichole Barry, Miguel F. Morales

Abstract: The Multi-frequency Angular Power Spectrum (MAPS) is an alternative to spherically-averaged power spectra, and computes local fluctuations in the angular power spectrum without need for line-of-sight spectral transform. To test different approaches to MAPS and treatment of the foreground contamination, and compare with the spherically-averaged power spectrum, and the single-frequency angular power… ▽ More The Multi-frequency Angular Power Spectrum (MAPS) is an alternative to spherically-averaged power spectra, and computes local fluctuations in the angular power spectrum without need for line-of-sight spectral transform. To test different approaches to MAPS and treatment of the foreground contamination, and compare with the spherically-averaged power spectrum, and the single-frequency angular power spectrum. We apply the MAPS to 110~hours of data in $z=6.2-7.5$ obtained for the Murchison Widefield Array Epoch of Reionisation experiment to compute the statistical power of 21~cm brightness temperature fluctuations. In the presence of bright foregrounds, a filter is applied to remove large-scale modes prior to MAPS application, significantly reducing MAPS power due to systematics. The MAPS shows a contrast of 10$^2$--10$^3$ to a simulated 21~cm cosmological signal for spectral separations of 0--4~MHz after application of the filter, reflecting results for the spherically-averaged power spectrum. The single-frequency angular power spectrum is also computed. At $z=7.5$ and $l=200$, we find an angular power of 53~mK$^2$, exceeding a simulated cosmological signal power by a factor of one thousand. Residual spectral structure, inherent to the calibrated data, and not spectral leakage from large-scale modes, is the dominant source of systematic power bias. The single-frequency angular power spectrum yields slightly poorer results compared with the spherically-averaged power spectrum, having applied a spectral filter to reduce foregrounds. Exploration of other filters may improve this result, along with consideration of wider bandwidths. △ Less

Submitted 11 August, 2022; originally announced August 2022.

Comments: 9 pages, 9 figures; accepted for publication in Astronomy & Astrophysics

Journal ref: A&A 666, A106 (2022)

Generating extremely large-volume reionisation simulations

Authors: Bradley Greig, J. Stuart B. Wyithe, Steven G. Murray, Simon J. Mutch, Cathryn M. Trott

Abstract: Preparing for the first detection of the cosmic 21-cm signal from large-scale interferometer experiments requires rigorous testing of the data analysis and reduction pipelines. To validate that these pipelines do not erroneously remove or add features that can mimic the cosmic signal (e.g. from side-lobes or large-scale power leakage), we require reionisation simulations larger than the experiment… ▽ More Preparing for the first detection of the cosmic 21-cm signal from large-scale interferometer experiments requires rigorous testing of the data analysis and reduction pipelines. To validate that these pipelines do not erroneously remove or add features that can mimic the cosmic signal (e.g. from side-lobes or large-scale power leakage), we require reionisation simulations larger than the experiments primary field of view. For an experiment such as the MWA, with a field of view of $\sim25^{2}$ deg.$^{2}$, this would require a simulation of several Gpcs, which is currently infeasible. To overcome this, we developed a simplified version of the semi-numerical reionisation simulation code 21CMFAST preferencing large volumes over some physical accuracy by assuming linear theory for structure formation. With this, we constructed a 7.5 Gpc comoving volume with voxel resolution of $\sim1.17$ cMpc tailored specifically to the binned spectral resolution of the MWA. This simulation was used for validating the pipelines for the 2020 MWA 21-cm power spectrum (PS) upper limits (Trott et al.). We then use this large-volume simulation to explore: (i) whether smaller volume simulations are biased by the missing large-scale modes, (ii) non-Gaussianity in estimates of the cosmic variance, (iii) biases in the recovered 21-cm PS following foreground wedge removal and (iv) the impact of tiling smaller volume simulations to achieve extremely large volumes. In summary, we find: (i) no biases from missing large-scale power, (ii) significant contribution from non-Gaussianity in the cosmic variance as expected following Mondal et al. (iii) an over-estimate of the 21-cm PS of 10-20 per cent following wedge mode excision for our particular model and (iv) tiling smaller volume simulations under-estimates the large-scale power and also the estimated cosmic variance. △ Less

Submitted 20 May, 2022; originally announced May 2022.

Comments: 13 pages, 9 figures and 1 table. Submitted to MNRAS, comments welcome

Direct Optimal Mapping for 21cm Cosmology: A Demonstration with the Hydrogen Epoch of Reionization Array

Authors: Zhilei Xu, Jacqueline N. Hewitt, Kai-Feng Chen, Honggeun Kim, Joshua S. Dillon, Nicholas S. Kern, Miguel F. Morales, Bryna J. Hazelton, Ruby Byrne, Nicolas Fagnoni, Eloy de Lera Acedo, Zara Abdurashidova, Tyrone Adams, James E. Aguirre, Paul Alexander, Zaki S. Ali, Rushelle Baartman, Yanga Balfour, Adam P. Beardsley, Gianni Bernardi, Tashalee S. Billings, Judd D. Bowman, Richard F. Bradley, Philip Bull, Jacob Burba , et al. (56 additional authors not shown)

Abstract: Motivated by the desire for wide-field images with well-defined statistical properties for 21cm cosmology, we implement an optimal mapping pipeline that computes a maximum likelihood estimator for the sky using the interferometric measurement equation. We demonstrate this direct optimal mapping with data from the Hydrogen Epoch of Reionization (HERA) Phase I observations. After validating the pipe… ▽ More Motivated by the desire for wide-field images with well-defined statistical properties for 21cm cosmology, we implement an optimal mapping pipeline that computes a maximum likelihood estimator for the sky using the interferometric measurement equation. We demonstrate this direct optimal mapping with data from the Hydrogen Epoch of Reionization (HERA) Phase I observations. After validating the pipeline with simulated data, we develop a maximum likelihood figure-of-merit for comparing four sky models at 166MHz with a bandwidth of 100kHz. The HERA data agree with the GLEAM catalogs to <10%. After subtracting the GLEAM point sources, the HERA data discriminate between the different continuum sky models, providing most support for the model of Byrne et al. 2021. We report the computation cost for mapping the HERA Phase I data and project the computation for the HERA 320-antenna data; both are feasible with a modern server. The algorithm is broadly applicable to other interferometers and is valid for wide-field and non-coplanar arrays. △ Less

Submitted 26 October, 2022; v1 submitted 12 April, 2022; originally announced April 2022.

Comments: 16 pages, 10 figures, 2 tables, published on ApJ

Measurements of one-point statistics in 21 cm intensity maps via foreground avoidance strategy

Authors: Piyanat Kittiwisit, Judd D. Bowman, Steven G. Murray, Bharat K. Gehlot, Daniel C. Jacobs, Adam P. Beardsley

Abstract: Measurements of the one-point probability distribution function and higher-order moments (variance, skewness, and kurtosis) of the high-redshift 21 cm fluctuations are among the most direct statistical probes of the non-Gaussian nature of structure formation and evolution during reionization. However, contamination from astrophysical foregrounds and instrument systematics pose significant challeng… ▽ More Measurements of the one-point probability distribution function and higher-order moments (variance, skewness, and kurtosis) of the high-redshift 21 cm fluctuations are among the most direct statistical probes of the non-Gaussian nature of structure formation and evolution during reionization. However, contamination from astrophysical foregrounds and instrument systematics pose significant challenges in measuring these statistics in real observations. In this work, we use forward modelling to investigate the feasibility of measuring 21 cm one-point statistics through a foreground avoidance strategy. Leveraging the characteristic wedge-shape of the foregrounds in k-space, we apply a wedge-cut filter that removes the foreground contaminated modes from a mock data set based on the Hydrogen Epoch of Reionization Array (HERA) instrument, and measure the one-point statistics from the image-space representation of the remaining non-contaminated modes. We experiment with varying degrees of wedge-cutting over different frequency bandwidths and find that the centre of the band is the least susceptible to bias from wedge-cutting. Based on this finding, we introduce a rolling filter method that allows reconstruction of an optimal wedge-cut 21~cm intensity map over the full bandwidth using outputs from wedge-cutting over multiple sub-bands. We perform Monte Carlo simulations to show that HERA should be able to measure the rise in skewness and kurtosis near the end of reionization with the rolling wedge-cut method if foreground leakage from the Fourier transform window function can be controlled. △ Less

Submitted 29 September, 2022; v1 submitted 3 April, 2022; originally announced April 2022.

Comments: 13 pages, 10 figures, Accepted to MNRAS

The multi-frequency angular power spectrum in parameter studies of the cosmic 21-cm signal

Authors: Rajesh Mondal, Garrelt Mellema, Steven G. Murray, Bradley Greig

Abstract: The light-cone effect breaks the periodicity and statistical homogeneity (ergodicity) along the line-of-sight direction of cosmological emission/absorption line surveys. The spherically averaged power spectrum (SAPS), which by definition assumes ergodicity and periodicity in all directions, can only quantify some of the second-order statistical information in the 3D light-cone signals and therefor… ▽ More The light-cone effect breaks the periodicity and statistical homogeneity (ergodicity) along the line-of-sight direction of cosmological emission/absorption line surveys. The spherically averaged power spectrum (SAPS), which by definition assumes ergodicity and periodicity in all directions, can only quantify some of the second-order statistical information in the 3D light-cone signals and therefore gives a biased estimate of the true statistics. The multi-frequency angular power spectrum (MAPS), by extracting more information from the data, does not rely on these assumptions. It is therefore better aligned with the properties of the signal. We have compared the performance of the MAPS and SAPS metrics for parameter estimation for a mock 3D light-cone observation of the 21-cm signal from the Epoch of Reionization. Our investigation is based on a simplified 3-parameter 21cmFAST model. We find that the MAPS produces parameter constraints which are a factor of $\sim 2$ more stringent than when the SAPS is used. The significance of this result does not change much even in the presence of instrumental noise expected for 128 hours of SKA-Low observations. Our results therefore suggest that a parameter estimation framework based on the MAPS metric would yield superior results over one using the SAPS metric. △ Less

Submitted 12 May, 2022; v1 submitted 21 March, 2022; originally announced March 2022.

Comments: Published in MNRAS Letters

Journal ref: MNRAS: Letters, Volume 514, Issue 1, July 2022, Pages L31-L35

Estimating the Feasibility of 21cm-Ly$α$ Synergies using the Hydrogen Epoch of Reionization Array

Authors: Tyler A. Cox, Daniel C. Jacobs, Steven G. Murray

Abstract: Cross-correlating 21cm and Ly$α$ intensity maps of the Epoch of Reionization (EoR) promises to be a powerful tool for exploring the properties of the first galaxies. Next-generation intensity mapping experiments such as the Hydrogen Epoch of Reionization Array (HERA) and SPHEREx will individually probe reionization through the power spectra of the 21cm and Ly$α$ lines respectively, but will be lim… ▽ More Cross-correlating 21cm and Ly$α$ intensity maps of the Epoch of Reionization (EoR) promises to be a powerful tool for exploring the properties of the first galaxies. Next-generation intensity mapping experiments such as the Hydrogen Epoch of Reionization Array (HERA) and SPHEREx will individually probe reionization through the power spectra of the 21cm and Ly$α$ lines respectively, but will be limited by bright foregrounds and instrumental systematics. Cross-correlating these measurements could reduce systematics, potentially tightening constraints on the inferred astrophysical parameters. In this study, we present forecasts of cross-correlation taking into account the effects of exact uv-sampling and foreground filtering to estimate the feasibility of HERAxSPHEREx making a detection of the 21cm-Ly$α$ cross-power spectrum. We also project the sensitivity of a cross-power spectrum between HERA and the proposed next-generation Cosmic Dawn Intensity Mapper. By isolating the sources of uncertainty, we explore the impacts of experimental limitations such as foreground filtering and Ly$α$ thermal noise uncertainty have on making a detection of the cross-power spectrum. We then implement this strategy in a simulation of the cross-power spectrum and observational error to identify redshifts where fiducial 21cmFAST models predict the highest signal-to-noise detection ($z \sim 8$). We conclude that detection of the SPHEREx-HERA cross-correlation will require an optimistic level of 21cm foreground filtering, as well as deeper thermal noise integrations due to a lack of overlapping sensitive modes but for CDIM with its larger range of scales and lower noise forecast detection levels, may be possible even with stricter 21cm foreground filtering. △ Less

Submitted 17 February, 2022; originally announced February 2022.

Comments: 11 pages, 6 figures, Accepted by MNRAS

Characterizing Beam Errors for Radio Interferometric Observations of Reionization

Authors: Ainulnabilah Nasirudin, David Prelogovic, Steven G. Murray, Andrei Mesinger, Gianni Bernardi

Abstract: A limiting systematic effect in 21-cm interferometric experiments is the chromaticity due to the coupling between the sky and the instrument. This coupling is sourced by the instrument primary beam; therefore it is important to know the beam to extremely high precision. Here we demonstrate how known beam uncertainties can be characterized using databases of beam models. In this introductory work,… ▽ More A limiting systematic effect in 21-cm interferometric experiments is the chromaticity due to the coupling between the sky and the instrument. This coupling is sourced by the instrument primary beam; therefore it is important to know the beam to extremely high precision. Here we demonstrate how known beam uncertainties can be characterized using databases of beam models. In this introductory work, we focus on beam errors arising from physically offset and/or broken antennas within a station. We use the public code OSKAR to generate an "ideal" SKA beam formed from 256 antennas regularly-spaced in a 35-m circle, as well as a large database of "perturbed" beams sampling distributions of broken/offset antennas. We decompose the beam errors ("ideal" minus "perturbed") using Principal Component Analysis (PCA) and Kernel PCA (KPCA). Using 20 components, we find that PCA/KPCA can reduce the residual of the beam in our datasets by 60-90% compared with the assumption of an ideal beam. Using a simulated observation of the cosmic signal plus foregrounds, we find that assuming the ideal beam can result in 1% error in the EoR window and 10% in the wedge of the 2D power spectrum. When PCA/KPCA is used to characterize the beam uncertainties, the error in the power spectrum shrinks to below 0.01% in the EoR window and <1% in the wedge. Our framework can be used to characterize and then marginalize over uncertainties in the beam for robust next-generation 21-cm parameter estimation. △ Less

Submitted 26 January, 2022; originally announced January 2022.

Comments: 12 pages, 9 main figures

Validation Solutions to the Full-Sky Radio Interferometry Measurement Equation for Diffuse Emission

Authors: Adam E. Lanman, Steven G. Murray, Daniel C. Jacobs

Abstract: Low-frequency radio observatories are reaching unprecedented levels of sensitivity in an effort to detect the 21 cm signal from the Cosmic Dawn. High precision is needed because the expected signal is overwhelmed by foreground contamination, largely from so-called diffuse emission -- a non-localized glow comprising Galactic synchrotron emission and radio galaxies. The impact of this diffuse emissi… ▽ More Low-frequency radio observatories are reaching unprecedented levels of sensitivity in an effort to detect the 21 cm signal from the Cosmic Dawn. High precision is needed because the expected signal is overwhelmed by foreground contamination, largely from so-called diffuse emission -- a non-localized glow comprising Galactic synchrotron emission and radio galaxies. The impact of this diffuse emission on observations may be better understood through detailed simulations, which evaluate the Radio Interferometry Measurement Equation (RIME) for a given instrument and sky model. Evaluating the RIME involves carrying out an integral over the full sky, which is naturally discretized for point sources but must be approximated for diffuse emission. The choice of integration scheme can introduce errors that must be understood and isolated from the instrumental effects under study. In this paper, we present several analytically-defined patterns of unpolarized diffuse sky emission for which the RIME integral is manageable, yielding closed-form or series visibility functions. We demonstrate the usefulness of these RIME solutions for validation by comparing them to simulated data, and show that the remaining differences behave as expected with varied sky resolution and baseline orientation and length. △ Less

Submitted 21 December, 2021; originally announced December 2021.

Comments: 28 pages, 13 figures

The Impact of the First Galaxies on Cosmic Dawn and Reionization

Authors: Julian B. Muñoz, Yuxiang Qin, Andrei Mesinger, Steven G. Murray, Bradley Greig, Charlotte Mason

Abstract: The formation of the first galaxies during cosmic dawn and reionization (at redshifts $z=5-30$), triggered the last major phase transition of our universe, as hydrogen evolved from cold and neutral to hot and ionized. The 21-cm line of neutral hydrogen will soon allow us to map these cosmic milestones and study the galaxies that drove them. To aid in interpreting these observations, we upgrade the… ▽ More The formation of the first galaxies during cosmic dawn and reionization (at redshifts $z=5-30$), triggered the last major phase transition of our universe, as hydrogen evolved from cold and neutral to hot and ionized. The 21-cm line of neutral hydrogen will soon allow us to map these cosmic milestones and study the galaxies that drove them. To aid in interpreting these observations, we upgrade the publicly available code {\tt 21cmFAST}. We introduce a new, flexible parametrization of the additive feedback from: an inhomogeneous, $H_2$-dissociating (Lyman-Werner; LW) background; and dark matter -- baryon relative velocities; which recovers results from recent, small-scale hydrodynamical simulations with both effects. We perform a large, "best-guess" simulation as the 2021 installment of the Evolution of 21-cm Structure (EOS) project. This improves the previous release with a galaxy model that reproduces the observed UV luminosity functions (UVLFs), and by including a population of molecular-cooling galaxies. The resulting 21-cm global signal and power spectrum are significantly weaker, primarily due to a more rapid evolution of the star-formation rate density required to match the UVLFs. Nevertheless, we forecast high signal-to-noise detections for both HERA and the SKA. We demonstrate how the stellar-to-halo mass relation of the unseen, first galaxies can be inferred from the 21-cm evolution. Finally, we show that the spatial modulation of X-ray heating due to relative velocities provides a unique acoustic signature that is detectable at $z \approx 10-15$ in our fiducial model. Ours are the first public simulations with joint inhomogeneous LW and relative-velocity feedback across the entire cosmic dawn and reionization. △ Less

Submitted 10 March, 2022; v1 submitted 26 October, 2021; originally announced October 2021.

Comments: 23+3 pages, 23+3 figures. Matches accepted version. Simulation output available at https://www.dropbox.com/sh/dqh9r6wb0s68jfo/AACc9ZCqsN0SQ_JJN7GRVuqDa?dl=0

Automated Detection of Antenna Malfunctions in Large-N Interferometers: A Case Study with the Hydrogen Epoch of Reionization Array

Authors: Dara Storer, Joshua S. Dillon, Daniel C. Jacobs, Miguel F. Morales, Bryna J. Hazelton, Aaron Ewall-Wice, Zara Abdurashidova, James E. Aguirre, Paul Alexander, Zaki S. Ali, Yanga Balfour, Adam P. Beardsley, Gianni Bernardi, Tashalee S. Billings, Judd D. Bowman, Richard F. Bradley, Philip Bull, Jacob Burba, Steven Carey, Chris L. Carilli, Carina Cheng, David R. DeBoer, Eloy de Lera Acedo, Matt Dexter, Scott Dynes , et al. (53 additional authors not shown)

Abstract: We present a framework for identifying and flagging malfunctioning antennas in large radio interferometers. We outline two distinct categories of metrics designed to detect outliers along known failure modes of large arrays: cross-correlation metrics, based on all antenna pairs, and auto-correlation metrics, based solely on individual antennas. We define and motivate the statistical framework for… ▽ More We present a framework for identifying and flagging malfunctioning antennas in large radio interferometers. We outline two distinct categories of metrics designed to detect outliers along known failure modes of large arrays: cross-correlation metrics, based on all antenna pairs, and auto-correlation metrics, based solely on individual antennas. We define and motivate the statistical framework for all metrics used, and present tailored visualizations that aid us in clearly identifying new and existing systematics. We implement these techniques using data from 105 antennas in the Hydrogen Epoch of Reionization Array (HERA) as a case study. Finally, we provide a detailed algorithm for implementing these metrics as flagging tools on real data sets. △ Less

Submitted 4 May, 2022; v1 submitted 26 September, 2021; originally announced September 2021.

Comments: 31 pages, 17 figures

Journal ref: Radio Science, vol. 57, no. 1, 2022

First Results from HERA Phase I: Upper Limits on the Epoch of Reionization 21 cm Power Spectrum

Authors: The HERA Collaboration, Zara Abdurashidova, James E. Aguirre, Paul Alexander, Zaki S. Ali, Yanga Balfour, Adam P. Beardsley, Gianni Bernardi, Tashalee S. Billings, Judd D. Bowman, Richard F. Bradley, Philip Bull, Jacob Burba, Steve Carey, Chris L. Carilli, Carina Cheng, David R. DeBoer, Matt Dexter, Eloy de Lera Acedo, Taylor Dibblee-Barkman, Joshua S. Dillon, John Ely, Aaron Ewall-Wice, Nicolas Fagnoni, Randall Fritz , et al. (52 additional authors not shown)

Abstract: We report upper-limits on the Epoch of Reionization (EoR) 21 cm power spectrum at redshifts 7.9 and 10.4 with 18 nights of data ($\sim36$ hours of integration) from Phase I of the Hydrogen Epoch of Reionization Array (HERA). The Phase I data show evidence for systematics that can be largely suppressed with systematic models down to a dynamic range of $\sim10^9$ with respect to the peak foreground… ▽ More We report upper-limits on the Epoch of Reionization (EoR) 21 cm power spectrum at redshifts 7.9 and 10.4 with 18 nights of data ($\sim36$ hours of integration) from Phase I of the Hydrogen Epoch of Reionization Array (HERA). The Phase I data show evidence for systematics that can be largely suppressed with systematic models down to a dynamic range of $\sim10^9$ with respect to the peak foreground power. This yields a 95% confidence upper limit on the 21 cm power spectrum of $Δ^2_{21} \le (30.76)^2\ {\rm mK}^2$ at $k=0.192\ h\ {\rm Mpc}^{-1}$ at $z=7.9$, and also $Δ^2_{21} \le (95.74)^2\ {\rm mK}^2$ at $k=0.256\ h\ {\rm Mpc}^{-1}$ at $z=10.4$. At $z=7.9$, these limits are the most sensitive to-date by over an order of magnitude. While we find evidence for residual systematics at low line-of-sight Fourier $k_\parallel$ modes, at high $k_\parallel$ modes we find our data to be largely consistent with thermal noise, an indicator that the system could benefit from deeper integrations. The observed systematics could be due to radio frequency interference, cable sub-reflections, or residual instrumental cross-coupling, and warrant further study. This analysis emphasizes algorithms that have minimal inherent signal loss, although we do perform a careful accounting in a companion paper of the small forms of loss or bias associated with the pipeline. Overall, these results are a promising first step in the development of a tuned, instrument-specific analysis pipeline for HERA, particularly as Phase II construction is completed en route to reaching the full sensitivity of the experiment. △ Less

Submitted 4 August, 2021; originally announced August 2021.

Comments: Accepted to ApJ. https://reionization.org/science/public-data-release-1/

A new MWA limit on the 21 cm Power Spectrum at Redshifts $\sim$ 13 $-$ 17

Authors: S. Yoshiura, B. Pindor, J. L. B. Line, N. Barry, C. M. Trott, A. Beardsley, J. Bowman, R. Byrne, A. Chokshi, B. J. Hazelton, K. Hasegawa, E. Howard, B. Greig, D. Jacobs, C. H. Jordan, R. Joseph, M. Kolopanis, C. Lynch, B. McKinley, D. A. Mitchell, M. F. Morales, S. G. Murray, J. C. Pober, M. Rahimi, K. Takahashi , et al. (7 additional authors not shown)

Abstract: Observations in the lowest MWA band between $75-100$ MHz have the potential to constrain the distribution of neutral hydrogen in the intergalactic medium at redshift $\sim 13-17$. Using 15 hours of MWA data, we analyse systematics in this band such as radio-frequency interference (RFI), ionospheric and wide field effects. By updating the position of point sources, we mitigate the direction indepen… ▽ More Observations in the lowest MWA band between $75-100$ MHz have the potential to constrain the distribution of neutral hydrogen in the intergalactic medium at redshift $\sim 13-17$. Using 15 hours of MWA data, we analyse systematics in this band such as radio-frequency interference (RFI), ionospheric and wide field effects. By updating the position of point sources, we mitigate the direction independent calibration error due to ionospheric offsets. Our calibration strategy is optimized for the lowest frequency bands by reducing the number of direction dependent calibrators and taking into account radio sources within a wider field of view. We remove data polluted by systematics based on the RFI occupancy and ionospheric conditions, finally selecting 5.5 hours of the cleanest data. Using these data, we obtain two sigma upper limits on the 21 cm power spectrum in the range of $0.1\lessapprox k \lessapprox 1 ~\rm ~h~Mpc^{-1}$ and at $z$=14.2, 15.2 and 16.5, with the lowest limit being $6.3\times 10^6 ~\rm mK^2$ at $\rm k=0.14 \rm ~h~Mpc^{-1}$ and at $z=15.2$ with a possibility of a few \% of signal loss due to direction independent calibration. △ Less

Submitted 26 May, 2021; originally announced May 2021.

Comments: 17 pages, 18 figures, accepted to MNRAS

Effects of model incompleteness on the drift-scan calibration of radio telescopes

Authors: Bharat K. Gehlot, Daniel C. Jacobs, Judd D. Bowman, Nivedita Mahesh, Steven G. Murray, Matthew Kolopanis, Adam P. Beardsley, Zara Abdurashidova, James E. Aguirre, Paul Alexander, Zaki S. Ali, Yanga Balfour, Gianni Bernardi, Tashalee S. Billings, Richard F. Bradley, Phil Bull, Jacob Burba, Steve Carey, Chris L. Carilli, Carina Cheng, David R. DeBoer, Matt Dexter, Eloy de Lera Acedo, Joshua S. Dillon, John Ely , et al. (54 additional authors not shown)

Abstract: Precision calibration poses challenges to experiments probing the redshifted 21-cm signal of neutral hydrogen from the Cosmic Dawn and Epoch of Reionization (z~30-6). In both interferometric and global signal experiments, systematic calibration is the leading source of error. Though many aspects of calibration have been studied, the overlap between the two types of instruments has received less at… ▽ More Precision calibration poses challenges to experiments probing the redshifted 21-cm signal of neutral hydrogen from the Cosmic Dawn and Epoch of Reionization (z~30-6). In both interferometric and global signal experiments, systematic calibration is the leading source of error. Though many aspects of calibration have been studied, the overlap between the two types of instruments has received less attention. We investigate the sky based calibration of total power measurements with a HERA dish and an EDGES style antenna to understand the role of auto-correlations in the calibration of an interferometer and the role of sky in calibrating a total power instrument. Using simulations we study various scenarios such as time variable gain, incomplete sky calibration model, and primary beam model. We find that temporal gain drifts, sky model incompleteness, and beam inaccuracies cause biases in the receiver gain amplitude and the receiver temperature estimates. In some cases, these biases mix spectral structure between beam and sky resulting in spectrally variable gain errors. Applying the calibration method to the HERA and EDGES data, we find good agreement with calibration via the more standard methods. Although instrumental gains are consistent with beam and sky errors similar in scale to those simulated, the receiver temperatures show significant deviations from expected values. While we show that it is possible to partially mitigate biases due to model inaccuracies by incorporating a time-dependent gain model in calibration, the resulting errors on calibration products are larger and more correlated. Completely addressing these biases will require more accurate sky and primary beam models. △ Less

Submitted 15 July, 2021; v1 submitted 25 April, 2021; originally announced April 2021.

Comments: 16 pages, 13 figures, 1 table; accepted for publication in MNRAS main journal

Validation of the HERA Phase I Epoch of Reionization 21 cm Power Spectrum Software Pipeline

Authors: James E. Aguirre, Steven G. Murray, Robert Pascua, Zachary E. Martinot, Jacob Burba, Joshua S. Dillon, Daniel C. Jacobs, Nicholas S. Kern, Piyanat Kittiwisit, Matthew Kolopanis, Adam Lanman, Adrian Liu, Lily Whitler, Zara Abdurashidova, Paul Alexander, Zaki S. Ali, Yanga Balfour, Adam P. Beardsley, Gianni Bernardi, Tashalee S. Billings, Judd D. Bowman, Richard F. Bradley, Philip Bull, Steve Carey, Chris L. Carilli , et al. (51 additional authors not shown)

Abstract: We describe the validation of the HERA Phase I software pipeline by a series of modular tests, building up to an end-to-end simulation. The philosophy of this approach is to validate the software and algorithms used in the Phase I upper limit analysis on wholly synthetic data satisfying the assumptions of that analysis, not addressing whether the actual data meet these assumptions. We discuss the… ▽ More We describe the validation of the HERA Phase I software pipeline by a series of modular tests, building up to an end-to-end simulation. The philosophy of this approach is to validate the software and algorithms used in the Phase I upper limit analysis on wholly synthetic data satisfying the assumptions of that analysis, not addressing whether the actual data meet these assumptions. We discuss the organization of this validation approach, the specific modular tests performed, and the construction of the end-to-end simulations. We explicitly discuss the limitations in scope of the current simulation effort. With mock visibility data generated from a known analytic power spectrum and a wide range of realistic instrumental effects and foregrounds, we demonstrate that the current pipeline produces power spectrum estimates that are consistent with known analytic inputs to within thermal noise levels (at the 2 sigma level) for k > 0.2 h/Mpc for both bands and fields considered. Our input spectrum is intentionally amplified to enable a strong `detection' at k ~0.2 h/Mpc -- at the level of ~25 sigma -- with foregrounds dominating on larger scales, and thermal noise dominating at smaller scales. Our pipeline is able to detect this amplified input signal after suppressing foregrounds with a dynamic range (foreground to noise ratio) of > 10^7. Our validation test suite uncovered several sources of scale-independent signal loss throughout the pipeline, whose amplitude is well-characterized and accounted for in the final estimates. We conclude with a discussion of the steps required for the next round of data analysis. △ Less

Submitted 19 April, 2021; originally announced April 2021.

Comments: 32 pages, 20 figures. Submitted to the Astrophysical Journal

Methods of Error Estimation for Delay Power Spectra in $21\,\textrm{cm}$ Cosmology

Authors: Jianrong Tan, Adrian Liu, Nicholas S. Kern, Zara Abdurashidova, James E. Aguirre, Paul Alexander, Zaki S. Ali, Yanga Balfour, Adam P. Beardsley, Gianni Bernardi, Tashalee S. Billings, Judd D. Bowman, Richard F. Bradley, Philip Bull, Jacob Burba, Steven Carey, Christopher L. Carilli, Carina Cheng, David R. DeBoer, Matt Dexter, Eloy de Lera Acedo, Joshua S. Dillon, John Ely, Aaron Ewall-Wice, Nicolas Fagnoni , et al. (49 additional authors not shown)

Abstract: Precise measurements of the 21 cm power spectrum are crucial for understanding the physical processes of hydrogen reionization. Currently, this probe is being pursued by low-frequency radio interferometer arrays. As these experiments come closer to making a first detection of the signal, error estimation will play an increasingly important role in setting robust measurements. Using the delay power… ▽ More Precise measurements of the 21 cm power spectrum are crucial for understanding the physical processes of hydrogen reionization. Currently, this probe is being pursued by low-frequency radio interferometer arrays. As these experiments come closer to making a first detection of the signal, error estimation will play an increasingly important role in setting robust measurements. Using the delay power spectrum approach, we have produced a critical examination of different ways that one can estimate error bars on the power spectrum. We do this through a synthesis of analytic work, simulations of toy models, and tests on small amounts of real data. We find that, although computed independently, the different error bar methodologies are in good agreement with each other in the noise-dominated regime of the power spectrum. For our preferred methodology, the predicted probability distribution function is consistent with the empirical noise power distributions from both simulated and real data. This diagnosis is mainly in support of the forthcoming HERA upper limit, and also is expected to be more generally applicable. △ Less

Submitted 25 May, 2021; v1 submitted 17 March, 2021; originally announced March 2021.

Comments: 35 Pages, 9 Figures, 4 Tables. Replaced with accepted ApJ version; some clarifying text added in response to referee comments with no changes to results

Validation of EDGES Low-Band Antenna Beam Model

Authors: Nivedita Mahesh, Judd D. Bowman, Thomas J. Mozdzen, Alan E. E. Rogers, Raul A. Monsalve, Steven G. Murray, David Lewis

Abstract: The response of the antenna is a source of uncertainty in measurements with the Experiment to Detect the Global EoR Signature (EDGES). We aim to validate the beam model of the low-band (50-100 MHz) dipole antenna with comparisons between models and against data. We find that simulations of a simplified model of the antenna over an infinite perfectly conducting ground plane are, with one exception,… ▽ More The response of the antenna is a source of uncertainty in measurements with the Experiment to Detect the Global EoR Signature (EDGES). We aim to validate the beam model of the low-band (50-100 MHz) dipole antenna with comparisons between models and against data. We find that simulations of a simplified model of the antenna over an infinite perfectly conducting ground plane are, with one exception, robust to changes of numerical electromagnetic solver code or algorithm. For simulations of the antenna with the actual finite ground plane and realistic soil properties, we find that two out of three numerical solvers agree well. Applying our analysis pipeline to a simulated driftscan observation from an early EDGES low-band instrument that had a 10 m $\times$ 10 m ground plane, we find residual levels after fitting and removing a five-term foreground model to data binned in Local Sidereal Time (LST) average about 250 mK with $\pm$40 mK variation between numerical solvers. A similar analysis of the primary 30 m $\times$ 30 m sawtooth ground plane reduced the LST-averaged residuals to about 90 mK with $\pm$10 mK between the two viable solvers. More broadly we show that larger ground planes generally perform better than smaller ground planes. Simulated data have a power which is within 4$\%$ of real observations, a limitation of net accuracy of the sky and beam models. We observe that residual spectral structures after foreground model fits match qualitatively between simulated data and observations, suggesting that the frequency dependence of the beam is reasonably represented by the models. We find that soil conductivity of 0.02 Sm$^{-1}$ and relative permittivity of 3.5 yield good agreement between simulated spectra and observations. This is consistent with the soil properties reported by Sutinjo et al. (2015) for the Murchison Radio-astronomy Observatory, where EDGES is located. △ Less

Submitted 2 March, 2021; v1 submitted 28 February, 2021; originally announced March 2021.

Comments: 19 pages, 17 figures

Absolute Calibration of Diffuse Radio Surveys at 45 and 150 MHz

Authors: Raul A. Monsalve, Alan E. E. Rogers, Judd D. Bowman, Nivedita Mahesh, Steven G. Murray, Thomas J. Mozdzen, Leroy Johnson, John Barrett, Titu Samson, David Lewis

Abstract: We use EDGES measurements to determine scale and zero-level corrections to the diffuse radio surveys by Guzmán et al. at $45$ MHz and Landecker & Wielebinski at $150$ MHz. We find that the Guzmán et al. map requires a scale correction of $1.076 \pm 0.034$ ($2σ$) and a zero-level correction of $-160 \pm 78$ K ($2σ$) to best-fit the EDGES data. For the Landecker & Wielebinski map, the scale correcti… ▽ More We use EDGES measurements to determine scale and zero-level corrections to the diffuse radio surveys by Guzmán et al. at $45$ MHz and Landecker & Wielebinski at $150$ MHz. We find that the Guzmán et al. map requires a scale correction of $1.076 \pm 0.034$ ($2σ$) and a zero-level correction of $-160 \pm 78$ K ($2σ$) to best-fit the EDGES data. For the Landecker & Wielebinski map, the scale correction is $1.112 \pm 0.023$ ($2σ$) and the zero-level correction is $0.7 \pm 6.0$ K ($2σ$). The correction uncertainties are dominated by systematic effects, of which the most significant are uncertainty in the calibration of the EDGES receivers, antenna pointing, and tropospheric and ionospheric effects. We propagate the correction uncertainties to estimate the uncertainties in the corrected maps themselves and find that the $2σ$ uncertainty in the map brightness temperature is in the range $3.2-7.5\%$ for the Guzmán et al. map and $2.1-9.0\%$ for the Landecker & Wielebinski map, with the largest percent uncertainties occurring at high Galactic latitudes. The corrected maps could be used to improve existing diffuse low-frequency radio sky models, which are essential tools in analyses of cosmological $21$ cm observations, as well as to investigate the existence of a radio monopole excess above the cosmic microwave background and known Galactic and extragalactic contributions. △ Less

Submitted 20 December, 2020; originally announced December 2020.

Comments: Accepted for publication in ApJ

21cmFAST v3: A Python-integrated C code forgenerating 3D realizations of the cosmic 21cm signal

Authors: Steven G. Murray, Bradley Greig, Andrei Mesinger, Julian B. Muñoz, Yuxiang Qin, Jaehong Park, Catherine A. Watkinson

Abstract: This brief code paper presents a new Python-wrapped version of the popular 21cm cosmology simulator, 21cmFAST. The new version, v3+, maintains the same core functionality of previous versions of 21cmFAST, but features a simple and intuitive interface, and a great deal more flexibility. This evolution represents the work of a formalized collaboration, and the new version, available publicly on GitH… ▽ More This brief code paper presents a new Python-wrapped version of the popular 21cm cosmology simulator, 21cmFAST. The new version, v3+, maintains the same core functionality of previous versions of 21cmFAST, but features a simple and intuitive interface, and a great deal more flexibility. This evolution represents the work of a formalized collaboration, and the new version, available publicly on GitHub, provides a single point-of-reference for all future upgrades and community-added features. In this paper, we describe simple usage of 21cmFAST, some of its new features, and provide a simple performance benchmark. △ Less

Submitted 28 October, 2020; originally announced October 2020.

Comments: 6 pages, 3 figures, published in JOSS

Extracting HI Astrophysics from Interferometric Intensity Mapping

Authors: Zhaoting Chen, Laura Wolz, Marta Spinelli, Steven G. Murray

Abstract: We present a new halo model of neutral hydrogen (HI) calibrated to galaxy formation simulations at redshifts $z\sim0.1$ and $z\sim1.0$ that we employ to investigate the constraining power of interferometric HI intensity mapping on HI astrophysics. We demonstrate that constraints on the small-scale HI power spectrum can break the degeneracy between the HI density $Ω_{\rm HI}$ and the HI bias… ▽ More We present a new halo model of neutral hydrogen (HI) calibrated to galaxy formation simulations at redshifts $z\sim0.1$ and $z\sim1.0$ that we employ to investigate the constraining power of interferometric HI intensity mapping on HI astrophysics. We demonstrate that constraints on the small-scale HI power spectrum can break the degeneracy between the HI density $Ω_{\rm HI}$ and the HI bias $b_{\rm HI}$. For $z\sim0.1$, we forecast that an accurate measurement of $Ω_{\rm HI}$ up to 6% level precision and the large-scale HI bias $b_{\rm HI}^0$ up to 1% level precision can be achieved using Square Kilometre Array (SKA) pathfinder data from MeerKAT and Australian SKA Pathfinder (ASKAP). We also propose a new description of the HI shot noise in the halo model framework in which a scatter of the relation between the HI mass of galaxies and their host halo mass is taken into account. Furthermore, given the number density of HI galaxies above a certain HI mass threshold, future surveys will also be able to constrain the HI mass function using only the HI shot noise. This will lead to constraints at the 10% level using the standard Schechter function. This technique will potentially provide a new way of measuring the HI Mass Function, independent from existing methods. We predict that the SKA will be able to further improve the low-redshift constraints by a factor of 3, as well as pioneering measurements of HI astrophysics at higher redshifts. △ Less

Submitted 20 March, 2021; v1 submitted 15 October, 2020; originally announced October 2020.

Comments: 19 pages, 11 figures and 6 tables. Updated to match the published version in MNRAS. For the computational tool used in this paper see arXiv:2009.14066 and https://halomod.readthedocs.io/en/latest/examples/extension.html

Journal ref: Monthly Notices of the Royal Astronomical Society, Volume 502, Issue 4, April 2021, Pages 5259-5276

TheHaloMod: An online calculator for the halo model

Authors: Steven G. Murray, Benedikt Diemer, Zhaoting Chen, Anton Glenn Neuhold Jr., M. A. Schnapp, Tia Peruzzi, Daniel Blevins, Trent Engelman

Abstract: The halo model is a successful framework for describing the distribution of matter in the Universe -- from weak lensing observables to galaxy 2-point correlation functions. We review the basic formulation of the halo model and several of its components in the context of galaxy two-point statistics, developing a coherent framework for its application. We use this framework to motivate the presentat… ▽ More The halo model is a successful framework for describing the distribution of matter in the Universe -- from weak lensing observables to galaxy 2-point correlation functions. We review the basic formulation of the halo model and several of its components in the context of galaxy two-point statistics, developing a coherent framework for its application. We use this framework to motivate the presentation of a new Python tool for simple and efficient calculation of halo model quantities, and their extension to galaxy statistics via a \textit{halo occupation distribution}, called \halomod. This tool is efficient, simple to use, comprehensive and importantly provides a great deal of flexibility in terms of custom extensions. This Python tool is complemented by a new web-application at https://thehalomod.app that supports the generation of many halo model quantities directly from the browser -- useful for educators, students, theorists and observers. △ Less

Submitted 9 August, 2021; v1 submitted 29 September, 2020; originally announced September 2020.

Comments: 39 pages (32 w/o refs and appendices), 13 figures, accepted to Astronomy and Computing (v2 is the accepted version)

Journal ref: Astronomy and Computing, Volume 36 (2021) pg. 100487

Absolute Calibration Strategies for the Hydrogen Epoch of Reionization Array and Their Impact on the 21 cm Power Spectrum

Authors: Nicholas S. Kern, Joshua S. Dillon, Aaron R. Parsons, Christopher L. Carilli, Gianni Bernardi, Zara Abdurashidova, James E. Aguirre, Paul Alexander, Zaki S. Ali, Yanga Balfour, Adam P. Beardsley, Tashalee S. Billings, Judd D. Bowman, Richard F. Bradley, Philip Bull, Jacob Burba, Steven Carey, Carina Cheng, David R. DeBoer, Matt Dexter, Eloy de Lera Acedo, John Ely, Aaron Ewall-Wice, Nicolas Fagnoni, Randall Fritz , et al. (47 additional authors not shown)

Abstract: We discuss absolute calibration strategies for Phase I of the Hydrogen Epoch of Reionization Array (HERA), which aims to measure the cosmological 21 cm signal from the Epoch of Reionization (EoR). HERA is a drift-scan array with a 10 degree wide field of view, meaning bright, well-characterized point source transits are scarce. This, combined with HERA's redundant sampling of the uv plane and the… ▽ More We discuss absolute calibration strategies for Phase I of the Hydrogen Epoch of Reionization Array (HERA), which aims to measure the cosmological 21 cm signal from the Epoch of Reionization (EoR). HERA is a drift-scan array with a 10 degree wide field of view, meaning bright, well-characterized point source transits are scarce. This, combined with HERA's redundant sampling of the uv plane and the modest angular resolution of the Phase I instrument, make traditional sky-based and self-calibration techniques difficult to implement with high dynamic range. Nonetheless, in this work we demonstrate calibration for HERA using point source catalogues and electromagnetic simulations of its primary beam. We show that unmodeled diffuse flux and instrumental contaminants can corrupt the gain solutions, and present a gain smoothing approach for mitigating their impact on the 21 cm power spectrum. We also demonstrate a hybrid sky and redundant calibration scheme and compare it to pure sky-based calibration, showing only a marginal improvement to the gain solutions at intermediate delay scales. Our work suggests that the HERA Phase I system can be well-calibrated for a foreground-avoidance power spectrum estimator by applying direction-independent gains with a small set of degrees of freedom across the frequency and time axes. △ Less

Submitted 4 January, 2020; v1 submitted 28 October, 2019; originally announced October 2019.

Comments: Accepted to ApJ

Mitigating Internal Instrument Coupling II: A Method Demonstration with the Hydrogen Epoch of Reionization Array

Authors: Nicholas S. Kern, Aaron R. Parsons, Joshua S. Dillon, Adam E. Lanman, Adrian Liu, Philip Bull, Aaron Ewall-Wice, Zara Abdurashidova, James E. Aguirre, Paul Alexander, Zaki S. Ali, Yanga Balfour, Adam P. Beardsley, Gianni Bernardi, Judd D. Bowman, Richard F. Bradley, Jacob Burba, Chris L. Carilli, Carina Cheng, David R. DeBoer, Matt Dexter, Eloy de Lera Acedo, Nicolas Fagnoni, Randall Fritz, Steve R. Furlanetto , et al. (42 additional authors not shown)

Abstract: We present a study of internal reflection and cross coupling systematics in Phase I of the Hydrogen Epoch of Reionization Array (HERA). In a companion paper, we outlined the mathematical formalism for such systematics and presented algorithms for modeling and removing them from the data. In this work, we apply these techniques to data from HERA's first observing season as a method demonstration. T… ▽ More We present a study of internal reflection and cross coupling systematics in Phase I of the Hydrogen Epoch of Reionization Array (HERA). In a companion paper, we outlined the mathematical formalism for such systematics and presented algorithms for modeling and removing them from the data. In this work, we apply these techniques to data from HERA's first observing season as a method demonstration. The data show evidence for systematics that, without removal, would hinder a detection of the 21 cm power spectrum for the targeted EoR line-of-sight modes in the range 0.2 < k_parallel < 0.5\ h^-1 Mpc. After systematic removal, we find we can recover these modes in the power spectrum down to the integrated noise-floor of a nightly observation, achieving a dynamic range in the EoR window of 10^-6 in power (mK^2 units) with respect to the bright galactic foreground signal. In the absence of other systematics and assuming the systematic suppression demonstrated here continues to lower noise levels, our results suggest that fully-integrated HERA Phase I may have the capacity to set competitive upper limits on the 21 cm power spectrum. For future observing seasons, HERA will have upgraded analog and digital hardware to better control these systematics in the field. △ Less

Submitted 29 October, 2019; v1 submitted 25 September, 2019; originally announced September 2019.

Comments: Submitted to ApJ

A Roadmap for Astrophysics and Cosmology with High-Redshift 21 cm Intensity Mapping

Authors: The Hydrogen Epoch of Reionization Array, Collaboration, James E. Aguirre, Adam P. Beardsley, Gianni Bernardi, Judd D. Bowman, Philip Bull, Chris L. Carilli, Wei-Ming Dai, David R. DeBoer, Joshua S. Dillon, Aaron Ewall-Wice, Steve R. Furlanetto, Bharat K. Gehlot, Deepthi Gorthi, Bradley Greig, Bryna J. Hazelton, Jacqueline N. Hewitt, Daniel C. Jacobs, Nicholas S. Kern, Piyanat Kittiwisit, Matthew Kolopanis, Paul La Plante, Adrian Liu, Yin-Zhe Ma , et al. (7 additional authors not shown)

Abstract: In this white paper, we lay out a US roadmap for high-redshift 21 cm cosmology (30 < z < 6) in the 2020s. Beginning with the currently-funded HERA and MWA Phase II projects and advancing through the decade with a coordinated program of small-scale instrumentation, software, and analysis projects targeting technology development, this roadmap incorporates our current best understanding of the syste… ▽ More In this white paper, we lay out a US roadmap for high-redshift 21 cm cosmology (30 < z < 6) in the 2020s. Beginning with the currently-funded HERA and MWA Phase II projects and advancing through the decade with a coordinated program of small-scale instrumentation, software, and analysis projects targeting technology development, this roadmap incorporates our current best understanding of the systematics confronting 21 cm cosmology into a plan for overcoming them, enabling next-generation, mid-scale 21 cm arrays to be proposed late in the decade. Submitted for consideration by the Astro2020 Decadal Survey Program Panel for Radio, Millimeter, and Submillimeter Observations from the Ground as a Medium-Sized Project. △ Less

Submitted 15 July, 2019; originally announced July 2019.

Comments: 10 pages (plus a cover page and references), 6 figures. Submitted as a APC White Paper for Astro2020