results.json

{"documents": ["2025arXiv250101417C", "2024arXiv241214023K", "2024arXiv241202552S", "2024MNRAS.534.1317M", "2024MNRAS.531.4734C", "2024MNRAS.531.1113P", "2024PhRvD.109l3541G", "2024MNRAS.529.1642S", "2024arXiv240410908B", "2024arXiv240410502B", "2024RASTI...3..724S", "2024MNRAS.527.8305K", "2024RASTI...3..372A", "2024MNRAS.527.2413P", "2024MNRAS.527.5649P", "2023PhRvD.108f2006L", "2023MNRAS.522.1022S", "2023arXiv230700099R", "2023PASA...40...16S", "2023MNRAS.520..850A", "2022PASA...39...52S", "2022MNRAS.515.4565S", "2022NatAs...6..984D", "2022MNRAS.509.4679A", "2022JAI....1150001C", "2021MNRAS.508.2923B", "2021MNRAS.506.2041A", "2021MNRAS.505.2638R", "2021MNRAS.503..344S", "2021MNRAS.502.4405B"], "solr": {"responseHeader": {"status": 0, "QTime": 40, "params": {"q": "*:*", "fl": "bibcode,alternate_bibcode,title,author,abstract,date,pub,pubdate,first_author,issue,keyword,doi", "start": "0", "internal_logging_params": "X-Amzn-Trace-Id=Root=1-677d18a3-6598b3185447caa41104f791", "fq": "{!bitset}", "sort": "date desc", "rows": "2000", "wt": "json"}}, "response": {"numFound": 30, "start": 0, "numFoundExact": true, "docs": [{"bibcode": "2025arXiv250101417C", "abstract": "We introduce the Bayesian Global Sky Model (B-GSM), a novel data-driven Bayesian approach to modelling radio foregrounds at frequencies &lt;400~MHz. B-GSM aims to address the limitations of previous models by incorporating robust error quantification and calibration. Using nested sampling, we compute Bayesian evidence and posterior distributions for the spectral behaviour and spatial amplitudes of diffuse emission components. Bayesian model comparison is used to determine the optimal number of emission components and their spectral parametrisation. Posterior sky predictions are conditioned on both diffuse emission and absolute temperature datasets, enabling simultaneous component separation and calibration. B-GSM is validated against a synthetic dataset designed to mimic the partial sky coverage, thermal noise, and calibration uncertainties present in real observations of the diffuse sky at low frequencies. B-GSM correctly identifies a model parametrisation with two emission components featuring curved power-law spectra. The posterior sky predictions agree with the true synthetic sky within statistical uncertainty. We find that the root-mean-square (RMS) residuals between the true and posterior predictions for the sky temperature as a function of LST are significantly reduced, when compared to the uncalibrated dataset. This indicates that B-GSM is able to correctly calibrate its posterior sky prediction to the independent absolute temperature dataset. We find that while the spectral parameters and component amplitudes exhibit some sensitivity to prior assumptions, the posterior sky predictions remain robust across a selection of different priors. This is the first of two papers, and is focused on validation of B-GSMs Bayesian framework, the second paper will present results of deployment on real data and introduce the low-frequency sky model which will be available for public download.", "author": ["Carter, George", "Handley, Will", "Ashdown, Mark", "Razavi-Ghods, Nima"], "date": "2025-01-01T00:00:00Z", "doi": ["10.48550/arXiv.2501.01417"], "first_author": "Carter, George", "keyword": ["Astrophysics - Instrumentation and Methods for Astrophysics", "Astrophysics - Cosmology and Nongalactic Astrophysics"], "pub": "arXiv e-prints", "pubdate": "2025-01-00", "title": ["The Bayesian Global Sky Model (B-GSM): Validation of a Data Driven Bayesian Simultaneous Component Separation and Calibration Algorithm for EoR Foreground Modelling"]}, {"bibcode": "2024arXiv241214023K", "abstract": "Due to the large dynamic ranges involved with separating the cosmological 21-cm signal from the Cosmic Dawn from galactic foregrounds, a well-calibrated instrument is essential to avoid biases from instrumental systematics. In this paper we present three methods for calibrating a global 21-cm cosmology experiment using the noise wave parameter formalisation to characterise a low noise amplifier including a careful consideration of how calibrator temperature noise and singularities will bias the result. The first method presented in this paper builds upon the existing conjugate priors method by weighting the calibrators by a physically motivated factor, thereby avoiding singularities and normalising the noise. The second method fits polynomials to the noise wave parameters by marginalising over the polynomial coefficients and sampling the polynomial orders as parameters. The third method introduces a physically motivated noise model to the marginalised polynomial method. Running these methods on a suite of simulated datasets based on the REACH receiver design and a lab dataset, we found that our methods produced a calibration solution which is equally as or more accurate than the existing conjugate priors method when compared with an analytic estimate of the calibrator's noise. We find in the case of the measured lab dataset the conjugate priors method is biased heavily by the large noise on the shorted load calibrator, resulting in incorrect noise wave parameter fits. This is mitigated by the methods introduced in this paper which calibrate the validation source spectra to within 5% of the noise floor.", "author": ["Kirkham, Christian J.", "Handley, William J.", "Zhu, Jiacong", "Artuc, Kaan", "Leeney, Samuel A. K.", "Bevins, Harry T. J.", "Anstey, Dominic J.", "de Lera Acedo, Eloy"], "date": "2024-12-01T00:00:00Z", "doi": ["10.48550/arXiv.2412.14023"], "first_author": "Kirkham, Christian J.", "keyword": ["Astrophysics - Instrumentation and Methods for Astrophysics", "Astrophysics - Cosmology and Nongalactic Astrophysics"], "pub": "arXiv e-prints", "pubdate": "2024-12-00", "title": ["Accounting for Noise and Singularities in Bayesian Calibration Methods for Global 21-cm Cosmology Experiments"]}, {"bibcode": "2024arXiv241202552S", "abstract": "The precise measurement of the sky-averaged HI absorption signal between 50 and 200 MHz is the primary goal of global 21-cm cosmology. This measurement has the potential to unravel the underlying physics of cosmic structure formation and evolution during the Cosmic Dawn. It is, however, hindered by various non-smooth, frequency-dependent effects, whose structures resemble those of the signal. One such effect is the leakage of polarised foregrounds into the measured intensity signal: polarised foreground emission undergoes Faraday rotation as it passes through the magnetic fields of the interstellar medium, imprinting a chromatic structure in the relevant frequency range which complicates the extraction of the cosmological HI absorption feature. We investigate the effect of polarised Galactic foregrounds on extracting the global 21-cm signal from simulated data using REACH's data analysis pipeline; the Radio Experiment for the Analysis of Cosmic Hydrogen (REACH) is an experiment designed to detect the sky-averaged 21-cm HI signal from the early Universe using physically informed models. Using the REACH pipeline, we successfully recover an injected global 21-cm signal with an amplitude of approximately 0.16 K, centred between 80 and 120 MHz, achieving a low root-mean-square error (less than 30\\% of the injected signal strength) in all the tested cases. This includes scenarios with simulated polarised Galactic diffuse emissions and polarised point source emissions, provided the overall polarisation fraction is below $\\sim 3\\%$. The linear mixing of contamination, caused by the superposition of multiple patches with varying strengths of Faraday rotation, produces patterns that are more distinct from the global signal. This distinction makes global signal recovery easier compared to contamination resulting from a single, slow oscillation pattern.", "author": ["Shen, Emma", "Anstey, Dominic", "Spinelli, Marta", "de Lera Acedo, Eloy", "Fialkov, Anastasia"], "date": "2024-12-01T00:00:00Z", "doi": ["10.48550/arXiv.2412.02552"], "first_author": "Shen, Emma", "keyword": ["Astrophysics - Cosmology and Nongalactic Astrophysics", "Astrophysics - Instrumentation and Methods for Astrophysics"], "pub": "arXiv e-prints", "pubdate": "2024-12-00", "title": ["Bayesian data analysis for sky-averaged 21-cm experiments with contamination from linearly polarised foreground"]}, {"bibcode": "2024MNRAS.534.1317M", "abstract": "The contribution of resolved and unresolved extragalactic point sources to the low-frequency sky spectrum is a potentially non-negligible part of the astrophysical foregrounds for cosmic dawn 21-cm experiments. The clustering of such point sources on the sky, combined with the frequency dependence of the antenna beam, can also make this contribution chromatic. By combining low-frequency measurements of the luminosity function and the angular correlation function of extragalactic point sources, we develop a model for the contribution of these sources to the low-frequency sky spectrum. Using this model, we find that the contribution of sources with flux density <inline-formula><tex-math id=\"TM0001\" notation=\"LaTeX\">${\\gt} 10^{-6}$</tex-math></inline-formula> Jy to the sky-averaged spectrum is smooth and of the order of a few kelvins at 50-200 MHz. We combine this model with measurements of the galactic foreground spectrum and weigh the resultant sky by the beam directivity of the conical log-spiral antenna planned as part of the Radio Experiment for the Analysis of Cosmic Hydrogen (REACH) project. We find that the contribution of point sources to the resultant spectrum is <inline-formula><tex-math id=\"TM0002\" notation=\"LaTeX\">${\\sim}\\, 0.4 {{\\, \\rm per\\, cent}}$</tex-math></inline-formula> of the total foregrounds, but still larger by at least an order of magnitude than the standard predictions for the cosmological 21-cm signal. As a result, not accounting for the point-source contribution leads to a systematic bias in 21-cm signal recovery. We show, however, that in the REACH case, this reconstruction bias can be removed by modelling the point-source contribution as a power law with a running spectral index. We make our code publicly available as a python package labelled epspy.", "alternate_bibcode": ["2024MNRAS.tmp.2063M", "2024arXiv240617031M"], "author": ["Mittal, Shikhar", "Kulkarni, Girish", "Anstey, Dominic", "de Lera Acedo, Eloy"], "date": "2024-10-01T00:00:00Z", "doi": ["10.1093/mnras/stae2111", "10.48550/arXiv.2406.17031"], "first_author": "Mittal, Shikhar", "issue": "2", "keyword": ["Astrophysics - Cosmology and Nongalactic Astrophysics", "Astrophysics - Astrophysics of Galaxies", "Astrophysics - Instrumentation and Methods for Astrophysics"], "pub": "Monthly Notices of the Royal Astronomical Society", "pubdate": "2024-10-00", "title": ["Impact of extragalactic point sources on the low-frequency sky spectrum and cosmic dawn global 21-cm measurements"]}, {"bibcode": "2024MNRAS.531.4734C", "abstract": "Measuring the redshifted sky-averaged neutral hydrogen 21 cm signal with a wide-band antenna operating at metre wavelengths can probe the thermal history of the Universe and the first star and galaxy formation during the Cosmic Dawn. Measurement of this 'global 21 cm' signal is extremely challenging due to foreground signals that are orders of magnitude brighter than the cosmological signal, which must be modelled and removed first. The Radio Experiment for the Analysis of Cosmic Hydrogen (REACH) aims to improve this process by simultaneously fitting the full posterior distribution of both the cosmological and foreground signals with Bayesian inference. The method, however, relies on an informed prior; partially derived from a simulated antenna power pattern. This simulated antenna power pattern will differ from the true antenna power pattern of the deployed instrument, and the impact of this uncertainty is unknown. We investigate this problem by forward modelling mock data with different levels of power pattern uncertainty through the REACH pipeline. We construct perturbed antenna power patterns through truncation of a singular-value-decomposed simulated power pattern; using one to generate mock observation data and the others to inform the prior. The power pattern uncertainty is quantified as \u0394D, the absolute mean of the difference between the original and perturbed power patterns. Comparing the evidence and root-mean-square error we find that \u0394D better than -35 dB, equivalent to millimetre accuracy in the antennas dimensions, is necessary for confident detection of the global signal. We discuss potential solutions to achieve this high level of accuracy.", "alternate_bibcode": ["2024MNRAS.tmp.1433C", "2023arXiv231107392C"], "author": ["Cumner, John", "Pieterse, Carla", "de Villiers, Dirk", "de Lera Acedo, Eloy"], "date": "2024-07-01T00:00:00Z", "doi": ["10.1093/mnras/stae1475", "10.48550/arXiv.2311.07392"], "first_author": "Cumner, John", "issue": "4", "keyword": ["Astrophysics - Instrumentation and Methods for Astrophysics"], "pub": "Monthly Notices of the Royal Astronomical Society", "pubdate": "2024-07-00", "title": ["The effects of the antenna power pattern uncertainty within a global 21 cm experiment"]}, {"bibcode": "2024MNRAS.531.1113P", "abstract": "The early Universe, spanning 400 000 to 400 million years after the big bang (z \u2248 1100-11), has been left largely unexplored as the light from luminous objects is too faint to be observed directly. While new experiments are pushing the redshift limit of direct observations, measurements in the low-frequency radio band promise to probe early star and black hole formation via observations of the hydrogen 21-cm line. In this work, we explore synergies between 21-cm data from the HERA and SARAS 3 experiments and observations of the unresolved radio and X-ray backgrounds using multiwavelength Bayesian analysis. We use the combined data set to constrain properties of Population II and Population III stars as well as early X-ray and radio sources. The joint fit reveals a 68 percentile disfavouring of Population III star formation efficiencies $\\gtrsim 5.7~{{\\ \\rm per\\ cent}}$. We also show how the 21-cm and the X-ray background data synergistically constrain opposite ends of the X-ray efficiency prior distribution to produce a peak in the 1D posterior of the X-ray luminosity per star formation rate. We find (at 68 per cent confidence) that early galaxies were likely 0.3-318 times as X-ray efficient as present-day starburst galaxies. We also show that the functional posteriors from our joint fit rule out global 21-cm signals deeper than \u2272-203 mK and power spectrum amplitudes at k = 0.34 h Mpc<SUP>-1</SUP> greater than $\\Delta _{21}^2 \\gtrsim 946\\ \\mathrm{mK}^2$ with 3\u03c3 confidence.", "alternate_bibcode": ["2024MNRAS.tmp.1177P", "2023arXiv231208095P"], "author": ["Pochinda, S.", "Gessey-Jones, T.", "Bevins, H. T. J.", "Fialkov, A.", "Heimersheim, S.", "Abril-Cabezas, I.", "de Lera Acedo, E.", "Singh, S.", "Sikder, S.", "Barkana, R."], "date": "2024-06-01T00:00:00Z", "doi": ["10.1093/mnras/stae1185", "10.48550/arXiv.2312.08095"], "first_author": "Pochinda, S.", "issue": "1", "keyword": ["Astrophysics - Cosmology and Nongalactic Astrophysics", "Astrophysics - Astrophysics of Galaxies"], "pub": "Monthly Notices of the Royal Astronomical Society", "pubdate": "2024-06-00", "title": ["Constraining the properties of Population III galaxies with multiwavelength observations"]}, {"bibcode": "2024PhRvD.109l3541G", "abstract": "Sensitivity forecasts inform the design of experiments and the direction of theoretical efforts. To arrive at representative results, Bayesian forecasts should marginalize their conclusions over uncertain parameters and noise realizations rather than picking fiducial values. However, this is typically computationally infeasible with current methods for forecasts of an experiment's ability to distinguish between competing models. We thus propose a novel simulation-based methodology capable of providing expedient and rigorous Bayesian model comparison forecasts without relying on restrictive assumptions.", "alternate_bibcode": ["2023arXiv230906942G"], "author": ["Gessey-Jones, T.", "Handley, W. J."], "date": "2024-06-01T00:00:00Z", "doi": ["10.1103/PhysRevD.109.123541", "10.48550/arXiv.2309.06942"], "first_author": "Gessey-Jones, T.", "issue": "12", "keyword": ["Astrophysics - Instrumentation and Methods for Astrophysics", "Astrophysics - Cosmology and Nongalactic Astrophysics", "General Relativity and Quantum Cosmology"], "pub": "Physical Review D", "pubdate": "2024-06-00", "title": ["Fully Bayesian forecasts with evidence networks"]}, {"bibcode": "2024MNRAS.529.1642S", "abstract": "Global 21-cm experiments are built to study the evolution of the Universe between the cosmic dawn and the epoch of reionization. FlexKnot is a function parametrized by freely moving knots stringed together by splines. Adopting the FlexKnot function as the signal model has the potential to separate the global 21-cm signal from the foregrounds and systematics while being capable of recovering the crucial features given by theoretical predictions. In this paper, we implement the FlexKnot method by integrating twice over a function of freely moving knots interpolated linearly. The function is also constrained at the lower frequencies corresponding to the dark ages by theoretical values. The FlexKnot model is tested in the framework of the realistic data analysis pipeline of the REACH global signal experiment using simulated antenna temperature data. We demonstrate that the FlexKnot model performs better than existing signal models, e.g. the Gaussian signal model, at reconstructing the shape of the true signals present in the simulated REACH data, especially for injected signals with complex structures. The capabilities of the FlexKnot signal model is also tested by introducing various systematics and simulated global signals of different types. These tests show that four to five knots are sufficient to recover the general shape of most realistic injected signals, with or without sinusoidal systematics. We show that true signals whose absorption trough is of amplitude between 120 and 450 mK can be well recovered with systematics up to about 50 mK.", "alternate_bibcode": ["2024MNRAS.tmp..655S", "2023arXiv231114537S"], "author": ["Shen, Emma", "Anstey, Dominic", "de Lera Acedo, Eloy", "Fialkov, Anastasia"], "date": "2024-04-01T00:00:00Z", "doi": ["10.1093/mnras/stae614", "10.48550/arXiv.2311.14537"], "first_author": "Shen, Emma", "issue": "2", "keyword": ["methods: data analysis", "dark ages", "reionization", "first stars", "Astrophysics - Instrumentation and Methods for Astrophysics"], "pub": "Monthly Notices of the Royal Astronomical Society", "pubdate": "2024-04-00", "title": ["FlexKnot as a generalized model of the sky-averaged 21-cm signal at z   6-30 in the presence of systematics"]}, {"bibcode": "2024arXiv240410908B", "abstract": "We analyse a lossy transmission line and the Johnson-Nyquist noise generated therein. A representation as a noisy two-port with a voltage and a current noise sources on one end of a noiseless two-port is given. An expression for the noise properties is given for an arbitrary temperature profile along the transmission line. Agreement is demonstrated between the general expression found here and special cases calculable using thermodynamics. This work is motivated by the REACH experiment to observe the global 21 cm signal for which modelling noise with exquisite precision is essential for a reliable calibration.", "author": ["Bucher, Martin", "Molnar, Daniel"], "date": "2024-04-01T00:00:00Z", "doi": ["10.48550/arXiv.2404.10908"], "first_author": "Bucher, Martin", "keyword": ["Astrophysics - Instrumentation and Methods for Astrophysics"], "pub": "arXiv e-prints", "pubdate": "2024-04-00", "title": ["Representation of a Noisy Transmission Line"]}, {"bibcode": "2024arXiv240410502B", "abstract": "Much has been written about the representation of noisy linear 2-ports. Here we present a theory of noisy $N$-ports. We show how in the general case there are $(2N)!/(N!)^2$ equivalent representations and give the transformations relating them. We also discuss singular cases in which some of the transformations are not possible as well as how to measure the noise properties of an $N$-port. This work is motivated by the REACH experiment to observe the global 21 cm signal for which modelling noise with exquisite precision is essential for a reliable calibration.", "author": ["Bucher, Martin", "Molnar, Daniel"], "date": "2024-04-01T00:00:00Z", "doi": ["10.48550/arXiv.2404.10502"], "first_author": "Bucher, Martin", "keyword": ["Astrophysics - Instrumentation and Methods for Astrophysics"], "pub": "arXiv e-prints", "pubdate": "2024-04-00", "title": ["Representations of Noisy $N$-Ports"]}, {"bibcode": "2024RASTI...3..724S", "abstract": "The redshifted 21-cm signal from the cosmic dawn and epoch of reionization carries invaluable information about the cosmology and astrophysics of the early Universe. Analysing data from a sky-averaged 21-cm signal experiment requires navigating through an intricate parameter space addressing various factors such as foregrounds, beam uncertainties, ionospheric distortions, and receiver noise for the search of the 21-cm signal. The traditional likelihood-based sampling methods for modelling these effects could become computationally demanding for such complex models, which makes it infeasible to include physically motivated 21-cm signal models in the analysis. Moreover, the inference is driven by the assumed functional form of the likelihood. We demonstrate how simulation-based inference through truncated marginal neural ratio estimation (TMNRE) can naturally handle these issues at a reduced computational cost. We estimate the posterior distribution on our model parameters with TMNRE for simulated mock observations, incorporating beam-weighted foregrounds, physically motivated 21-cm signal, and radiometric noise. We find that maximizing information content by analysing data from multiple time slices and antennas significantly improves the parameter constraints and enhances the exploration of the cosmological signal. We discuss the application of TMNRE for the current configuration of the REACH experiment and demonstrate its potential for exploring new avenues.", "alternate_bibcode": ["2024arXiv240314618S"], "author": ["Saxena, Anchal", "Meerburg, P. Daniel", "Weniger, Christoph", "Acedo, Eloy de Lera", "Handley, Will"], "date": "2024-01-01T00:00:00Z", "doi": ["10.1093/rasti/rzae047", "10.48550/arXiv.2403.14618"], "first_author": "Saxena, Anchal", "issue": "1", "keyword": ["Astrophysics - Cosmology and Nongalactic Astrophysics", "Astrophysics - Instrumentation and Methods for Astrophysics"], "pub": "RAS Techniques and Instruments", "pubdate": "2024-01-00", "title": ["Simulation-based inference of the sky-averaged 21-cm signal from CD-EoR with REACH"]}, {"bibcode": "2024MNRAS.527.8305K", "abstract": "Radio observations of the neutral hydrogen signal from the Cosmic Dawn and Epoch of Reionization have helped to provide constraints on the properties of the first stars and galaxies. Since this global 21-cm cosmological signal from the Cosmic Dawn is effectively constant on observing time-scales and since effects resulting from systematics will vary with time, the effects of these systematics can be mitigated without the need for a model of the systematic. We present a method to account for unmodelled time-varying systematics in 21-cm radio cosmology experiments using a squared exponential Gaussian process kernel to account for correlations between time bins in a fully Bayesian way. We find by varying the model parameters of a simulated systematic that the Gaussian process method improves our ability to recover the signal parameters by widening the posterior in the presence of a systematic and reducing the bias in the mean fit parameters. When varying the amplitude of a model sinusoidal systematic between 0.25 and 2.00 times the 21-cm signal amplitude and the period between 0.5 and 4.0 times the signal width, we find on average a 5 per cent improvement in the root mean squared error of the fitted signal. We can use the fitted Gaussian process hyperparameters to identify the presence of a systematic in the data, demonstrating the method's utility as a diagnostic tool. Furthermore, we can use Gaussian process regression to calculate a mean fit to the residuals over time, providing a basis for producing a model of the time-varying systematic.", "alternate_bibcode": ["2023MNRAS.tmp.3561K", "2023arXiv231017975K"], "author": ["Kirkham, Christian J.", "Anstey, Dominic J.", "de Lera Acedo, Eloy"], "date": "2024-01-01T00:00:00Z", "doi": ["10.1093/mnras/stad3725", "10.48550/arXiv.2310.17975"], "first_author": "Kirkham, Christian J.", "issue": "3", "keyword": ["methods: data analysis", "cosmology: dark ages", "reionization", "first stars", "cosmology: early Universe", "Astrophysics - Cosmology and Nongalactic Astrophysics", "Astrophysics - Instrumentation and Methods for Astrophysics"], "pub": "Monthly Notices of the Royal Astronomical Society", "pubdate": "2024-01-00", "title": ["A Bayesian method to mitigate the effects of unmodelled time-varying systematics for 21-cm cosmology experiments"]}, {"bibcode": "2024RASTI...3..372A", "abstract": "Contamination by radio frequency interference (RFI) is a ubiquitous challenge for radio astronomy. In particular, transient RFI is difficult to detect and avoid, especially in large data sets with many time bins. In this work, we present a Bayesian methodology for time-dependent, transient anomaly mitigation performed jointly with model fitting. The computation time for correcting transient anomalies in this manner in time-separated data sets grows proportionally with the number of time bins. We demonstrate that utilizing likelihood reweighting can allow our Bayesian anomaly mitigation method to be performed with a computation time close to independent of the number of time bins. In particular, we identify a factor of 44 improvement in computation time for a test case with 2000 time bins. We also demonstrate how this method enables the flagging threshold to be fit as a free parameter, fully automating the mitigation process. We find that this threshold fitting also prevents overcorrecting of the data in the case of wide priors. Finally, we investigate the potential of the methodology as a transient detector. We demonstrate that the method is able to reliably flag an individual anomalous data point out of 302 000 provided the Signal to Noise Ratio is <inline-formula><tex-math id=\"TM0001\" notation=\"LaTeX\">$\\ge\\!{10}$</tex-math></inline-formula>.", "alternate_bibcode": ["2023arXiv231002146A"], "author": ["Anstey, Dominic", "Leeney, Samuel A. K."], "date": "2024-01-01T00:00:00Z", "doi": ["10.1093/rasti/rzae025", "10.48550/arXiv.2310.02146"], "first_author": "Anstey, Dominic", "issue": "1", "keyword": ["Astrophysics - Instrumentation and Methods for Astrophysics"], "pub": "RAS Techniques and Instruments", "pubdate": "2024-01-00", "title": ["Enhanced Bayesian RFI mitigation and transient flagging using likelihood reweighting"]}, {"bibcode": "2024MNRAS.527.2413P", "abstract": "The 21-cm signal from cosmic hydrogen is one of the most propitious probes of the early Universe. The detection of this signal would reveal key information about the first stars, dark matter, and early structure formation. We explore the impact of an emissive and reflective, or 'hot', horizon on the recovery of this signal for global 21-cm experiments. It is demonstrated that when using physically motivated foreground models to recover the sky-averaged 21-cm signal one must accurately describe the horizon around the radiometer. Not accounting for the horizon will lead to a signal recovery with residuals an order of magnitude larger than the injected signal, with a log Bayesian evidence of 1600 lower than when one does account for it. Signal recovery is sensitive to incorrect values of soil temperature and reflection coefficient in describing the horizon, with a 10 per cent error in reflectance causing twofold increases in the root mean square error (RMSE) of a given fit. These parameters may be fitted using Bayesian inference to mitigate these issues without overfitting and mischaracterizing a non-detection. Signal recovery is sensitive to errors in measurements of the horizon projection onto the sky, but fitting for soil temperature and reflection coefficients with priors that extend beyond physical expectation can resolve these problems. We show that using an expanded prior range can reliably recover the signal even when the height of the horizon is mismeasured by up to 20 per cent, decreasing the RMSE from the model that does not perform this fitting by a factor of 9.", "alternate_bibcode": ["2023arXiv230702908P", "2023MNRAS.tmp.3260P"], "author": ["Pattison, Joe H. N.", "Anstey, Dominic J.", "de Lera Acedo, Eloy"], "date": "2024-01-01T00:00:00Z", "doi": ["10.1093/mnras/stad3378", "10.48550/arXiv.2307.02908"], "first_author": "Pattison, Joe H. N.", "issue": "2", "keyword": ["methods: data analysis", "dark ages", "reionization", "first stars", "early Universe", "Astrophysics - Cosmology and Nongalactic Astrophysics", "Astrophysics - Instrumentation and Methods for Astrophysics"], "pub": "Monthly Notices of the Royal Astronomical Society", "pubdate": "2024-01-00", "title": ["Modelling a hot horizon in global 21-cm experimental foregrounds"]}, {"bibcode": "2024MNRAS.527.5649P", "abstract": "Measurement of the global 21-cm signal during Cosmic Dawn and the Epoch of Reionization is made difficult by bright foreground emission which is 2-5 orders of magnitude larger than the expected signal. Fitting for a physics-motivated parametric forward model of the data within a Bayesian framework provides a robust means to separate the signal from the foregrounds, given sufficient information about the instrument and sky. It has previously been demonstrated that, within such a modelling framework, a foreground model of sufficient fidelity can be generated by dividing the sky into N regions and scaling a base map assuming a distinct uniform spectral index in each region. Using the Radio Experiment for the Analysis of Cosmic Hydrogen as our fiducial instrument, we show that, if unaccounted-for, amplitude errors in low-frequency radio maps used for our base map model will prevent recovery of the 21-cm signal within this framework, and that the level of bias in the recovered 21-cm signal is proportional to the amplitude and the correlation length of the base-map errors in the region. We introduce an updated foreground model that is capable of accounting for these measurement errors by fitting for a monopole offset and a set of spatially dependent scale factors describing the ratio of the true and model sky temperatures, with the size of the set determined by Bayesian evidence-based model comparison. We show that our model is flexible enough to account for multiple foreground error scenarios allowing the 21-cm sky-averaged signal to be detected without bias from simulated observations with a smooth conical log spiral antenna.", "alternate_bibcode": ["2023MNRAS.tmp.3244P", "2022arXiv221110448P"], "author": ["Pagano, Michael", "Sims, Peter", "Liu, Adrian", "Anstey, Dominic", "Handley, Will", "de Lera Acedo, Eloy"], "date": "2024-01-01T00:00:00Z", "doi": ["10.1093/mnras/stad3392", "10.48550/arXiv.2211.10448"], "first_author": "Pagano, Michael", "issue": "3", "keyword": ["methods: observational", "methods: statistical", "dark ages", "reionization", "first stars", "large-scale structure of Universe", "Astrophysics - Cosmology and Nongalactic Astrophysics", "Astrophysics - Instrumentation and Methods for Astrophysics"], "pub": "Monthly Notices of the Royal Astronomical Society", "pubdate": "2024-01-00", "title": ["A general Bayesian framework to account for foreground map errors in global 21-cm experiments"]}, {"bibcode": "2023PhRvD.108f2006L", "abstract": "Interfering signals such as radio frequency interference from ubiquitous satellite constellations are becoming an endemic problem in fields involving physical observations of the electromagnetic spectrum. To address this we propose a novel data cleaning methodology. Contamination is simultaneously flagged and managed at the likelihood level. It is modeled in a Bayesian fashion through a piecewise likelihood that is constrained by a Bernoulli prior distribution. The techniques described in this paper can be implemented with just a few lines of code.", "alternate_bibcode": ["2022arXiv221115448L"], "author": ["Leeney, S. A. K.", "Handley, W. J.", "Acedo, E. de Lera"], "date": "2023-09-01T00:00:00Z", "doi": ["10.1103/PhysRevD.108.062006", "10.48550/arXiv.2211.15448"], "first_author": "Leeney, S. A. K.", "issue": "6", "keyword": ["Astrophysics - Instrumentation and Methods for Astrophysics", "Astrophysics - Cosmology and Nongalactic Astrophysics"], "pub": "Physical Review D", "pubdate": "2023-09-00", "title": ["Bayesian approach to radio frequency interference mitigation"]}, {"bibcode": "2023MNRAS.522.1022S", "abstract": "In a sky-averaged 21-cm signal experiment, the uncertainty of the extracted signal depends mainly on the covariance between the foreground and 21-cm signal models. In this paper, we construct these models using the modes of variation obtained from the singular value decomposition of a set of simulated foreground and 21-cm signals. We present a strategy to reduce this overlap between the 21-cm and foreground modes by simultaneously fitting the spectra from multiple different antennas, which can be used in combination with the method of utilizing the time dependence of foregrounds while fitting multiple drift scan spectra. To demonstrate this idea, we consider two different foreground models (i) a simple foreground model, where we assume a constant spectral index over the sky, and (ii) a more realistic foreground model, with a spatial variation of the spectral index. For the simple foreground model, with just a single antenna design, we are able to extract the signal with good accuracy if we simultaneously fit the data from multiple time slices. The 21-cm signal extraction is further improved when we simultaneously fit the data from different antennas as well. This improvement becomes more pronounced while using the more realistic mock observations generated from the detailed foreground model. We find that even if we fit multiple time slices, the recovered signal is biased and inaccurate for a single antenna. However, simultaneously fitting the data from different antennas reduces the bias and the uncertainty by a factor of 2-3 on the extracted 21-cm signal.", "alternate_bibcode": ["2023MNRAS.tmp..995S", "2022arXiv221207415S"], "author": ["Saxena, Anchal", "Meerburg, P. Daniel", "de Lera Acedo, Eloy", "Handley, Will", "Koopmans, L\u00e9on V. E."], "date": "2023-06-01T00:00:00Z", "doi": ["10.1093/mnras/stad1047", "10.48550/arXiv.2212.07415"], "first_author": "Saxena, Anchal", "issue": "1", "keyword": ["methods: data analysis", "dark ages", "reionization", "first stars", "Astrophysics - Cosmology and Nongalactic Astrophysics"], "pub": "Monthly Notices of the Royal Astronomical Society", "pubdate": "2023-06-00", "title": ["Sky-averaged 21-cm signal extraction using multiple antennas with an SVD framework: the REACH case"]}, {"bibcode": "2023arXiv230700099R", "abstract": "We detail the the REACH radiometric system designed to enable measurements of the 21-cm neutral hydrogen line. Included is the radiometer architecture and end-to-end system simulations as well as a discussion of the challenges intrinsic to highly-calibratable system development. Following this, we share laboratory results based on the calculation of noise wave parameters utilising an over-constrained least squares approach demonstrating a calibration RMSE of 80 mK for five hours of integration on a custom-made source with comparable impedance to that of the antenna used in the field. This paper therefore documents the state of the calibrator and data analysis in December 2022 in Cambridge before shipping to South Africa.", "author": ["Razavi-Ghods, Nima", "Roque, Ian L. V.", "Carey, Steven H.", "Ely, John A.", "Handley, Will", "Magro, Alessio", "Chiello, Riccardo", "Huang, Tian", "Alexander, P.", "Anstey, D.", "Bernardi, G.", "Bevins, H. T. J.", "Cavillot, J.", "Croukamp, W.", "Cumner, J.", "de Lera Acedo, E.", "de Villiers, D. I. L.", "Fialkov, A.", "Gessey-Jones, T.", "Gueuning, Q.", "Josaitis, A. T.", "Kulkarni, G.", "Leeney, S. A. K.", "Maiolino, R.", "Meerburg, P. D.", "Mittal, S.", "Pagano, M.", "Pegwal, S.", "Pieterse, C.", "Pritchard, J. R.", "Saxena, A.", "Scheutwinkel, K. H.", "Scott, P.", "Shen, E.", "Sims, P. H.", "Smirnov, O.", "Spinelli, M.", "Zarb-Adami, K."], "date": "2023-06-01T00:00:00Z", "doi": ["10.48550/arXiv.2307.00099"], "first_author": "Razavi-Ghods, Nima", "keyword": ["Astrophysics - Instrumentation and Methods for Astrophysics"], "pub": "arXiv e-prints", "pubdate": "2023-06-00", "title": ["Receiver design for the REACH global 21-cm signal experiment"]}, {"bibcode": "2023PASA...40...16S", "abstract": "We demonstrate that the Bayesian evidence can be used to find a good approximation of the ground truth likelihood function of a dataset, a goal of the likelihood-free inference (LFI) paradigm. As a concrete example, we use forward modelled sky-averaged 21-cm signal antenna temperature datasets where we artificially inject noise structures of various physically motivated forms. We find that the Gaussian likelihood performs poorly when the noise distribution deviates from the Gaussian case, for example, heteroscedastic radiometric or heavy-tailed noise. For these non-Gaussian noise structures, we show that the generalised normal likelihood is on a similar Bayesian evidence scale with comparable sky-averaged 21-cm signal recovery as the ground truth likelihood function of our injected noise. We therefore propose the generalised normal likelihood function as a good approximation of the true likelihood function if the noise structure is a priori unknown.", "alternate_bibcode": ["2022arXiv220404491S"], "author": ["Scheutwinkel, K. H.", "Handley, W.", "de Lera Acedo, E."], "date": "2023-04-01T00:00:00Z", "doi": ["10.1017/pasa.2023.16", "10.48550/arXiv.2204.04491"], "first_author": "Scheutwinkel, K. H.", "keyword": ["dark ages", "reionisation", "first stars", "methods: statistical", "methods: data analysis", "Astrophysics - Cosmology and Nongalactic Astrophysics"], "pub": "Publications of the Astronomical Society of Australia", "pubdate": "2023-04-00", "title": ["Bayesian evidence-driven likelihood selection for sky-averaged 21-cm signal extraction"]}, {"bibcode": "2023MNRAS.520..850A", "abstract": "Global 21-cm cosmology aims to investigate the cosmic dawn and epoch of reionization by measuring the sky averaged H I absorption signal, which requires, accurate modelling of, or correction for, the bright radio foregrounds and distortions arising from chromaticity of the antenna beam. We investigate the effect of improving foreground modelling by fitting data sets from many observation times simultaneously in a single Bayesian analysis, fitting for the same parameter set by performing these fits on simulated data. We find that for a hexagonal dipole antenna, this simultaneous fitting produces a significant improvement in the accuracy of the recovered 21-cm signal, relative to fitting a time average of the data. Furthermore, the recovered models of the foreground are also seen to become more accurate by up to a factor of ~2-3 relative to time averaged fitting. For a less chromatic log spiral antenna, no significant improvement in signal recovery was found by this process. However, the modelling of the foregrounds was still significantly improved. We also investigate extending this technique to fit multiple data sets from different antennas simultaneously for the same parameters. This is also found to improve both 21-cm signal and foreground modelling, to a higher degree than fitting data set from multiple times from the same antenna.", "alternate_bibcode": ["2022arXiv221004707A", "2023MNRAS.tmp..164A"], "author": ["Anstey, Dominic", "de Lera Acedo, Eloy", "Handley, Will"], "date": "2023-03-01T00:00:00Z", "doi": ["10.1093/mnras/stad156", "10.48550/arXiv.2210.04707"], "first_author": "Anstey, Dominic", "issue": "1", "keyword": ["methods: data analysis", "dark ages", "reionization", "first stars", "Astrophysics - Cosmology and Nongalactic Astrophysics", "Astrophysics - Instrumentation and Methods for Astrophysics"], "pub": "Monthly Notices of the Royal Astronomical Society", "pubdate": "2023-03-00", "title": ["Use of time dependent data in Bayesian global 21-cm foreground and signal modelling"]}, {"bibcode": "2022PASA...39...52S", "abstract": "We demonstrate the effectiveness of a Bayesian evidence -based analysis for diagnosing and disentangling the sky-averaged 21-cm signal from instrumental systematic effects. As a case study, we consider a simulated REACH pipeline with an injected systematic. We demonstrate that very poor performance or erroneous signal recovery is achieved if the systematic remains unmodelled. These effects include sky-averaged 21-cm posterior estimates resembling a very deep or wide signal. However, when including parameterised models of the systematic, the signal recovery is dramatically improved in performance. Most importantly, a Bayesian evidence-based model comparison is capable of determining whether or not such a systematic model is needed as the true underlying generative model of an experimental dataset is in principle unknown. We, therefore, advocate a pipeline capable of testing a variety of potential systematic errors with the Bayesian evidence acting as the mechanism for detecting their presence.", "alternate_bibcode": ["2022arXiv220404445S"], "author": ["Scheutwinkel, K. H.", "de Lera Acedo, E.", "Handley, W."], "date": "2022-10-01T00:00:00Z", "doi": ["10.1017/pasa.2022.49", "10.48550/arXiv.2204.04445"], "first_author": "Scheutwinkel, K. H.", "keyword": ["Astrophysics - Cosmology and Nongalactic Astrophysics"], "pub": "Publications of the Astronomical Society of Australia", "pubdate": "2022-10-00", "title": ["Bayesian evidence-driven diagnosis of instrumental systematics for sky-averaged 21-cm cosmology experiments"]}, {"bibcode": "2022MNRAS.515.4565S", "abstract": "The ionosphere introduces chromatic distortions on low frequency radio waves, and thus poses a hurdle for 21-cm cosmology. In this paper, we introduce time-varying chromatic ionospheric effects on simulated antenna temperature data of a global 21-cm data analysis pipeline, and try to detect the injected global signal. We demonstrate that given turbulent ionospheric conditions, more than 5 per cent error in our knowledge of the ionospheric parameters could lead to comparatively low evidence and high root-mean-square error (RMSE), suggesting a false or null detection. When using a constant antenna beam for cases that include data at different times, the significance of the detection lowers as the number of time samples increases. It is also shown that for observations that include data at different times, readjusting beam configurations according to the time-varying ionospheric conditions should greatly improve the significance of a detection, yielding higher evidences and lower RMSE, and that it is a necessary procedure for a successful detection when the ionospheric conditions are not ideal.", "alternate_bibcode": ["2022MNRAS.tmp.1854S", "2022arXiv220410859S"], "author": ["Shen, Emma", "Anstey, Dominic", "de Lera Acedo, Eloy", "Fialkov, Anastasia"], "date": "2022-09-01T00:00:00Z", "doi": ["10.1093/mnras/stac1900", "10.48550/arXiv.2204.10859"], "first_author": "Shen, Emma", "issue": "3", "keyword": ["atmospheric effects", "methods: data analysis", "dark ages", "reionization", "first stars", "Astrophysics - Instrumentation and Methods for Astrophysics", "Astrophysics - Cosmology and Nongalactic Astrophysics"], "pub": "Monthly Notices of the Royal Astronomical Society", "pubdate": "2022-09-00", "title": ["Bayesian data analysis for sky-averaged 21-cm experiments in the presence of ionospheric effects"]}, {"bibcode": "2022NatAs...6..984D", "abstract": "Observations of the 21-cm line from primordial hydrogen promise to be one of the best tools to study the early epochs of the Universe: the dark ages, the cosmic dawn and the subsequent epoch of reionization. In 2018, the Experiment to Detect the Global Epoch of Reionization Signature (EDGES) caught the attention of the cosmology community with a potential detection of an absorption feature in the sky-averaged radio spectrum centred at 78 MHz. The feature is deeper than expected, and, if confirmed, would call for new physics. However, different groups have re-analysed the EDGES data and questioned the reliability of the signal. The Radio Experiment for the Analysis of Cosmic Hydrogen (REACH) is a sky-averaged 21-cm experiment aiming at improving the current observations by tackling the issues faced by current instruments related to residual systematic signals in the data. The novel experimental approach focuses on detecting and jointly explaining these systematics together with the foregrounds and the cosmological signal using Bayesian statistics. To achieve this, REACH features simultaneous observations with two different antennas, an ultra-wideband system (redshift range about 7.5 to 28) and a receiver calibrator based on in-field measurements. Simulated observations forecast percent-level constraints on astrophysical parameters, potentially opening up a new window to the infant Universe.", "alternate_bibcode": ["2022arXiv221007409D", "2022NatAs.tmp..167D"], "author": ["de Lera Acedo, E.", "de Villiers, D. I. L.", "Razavi-Ghods, N.", "Handley, W.", "Fialkov, A.", "Magro, A.", "Anstey, D.", "Bevins, H. T. J.", "Chiello, R.", "Cumner, J.", "Josaitis, A. T.", "Roque, I. L. V.", "Sims, P. H.", "Scheutwinkel, K. H.", "Alexander, P.", "Bernardi, G.", "Carey, S.", "Cavillot, J.", "Croukamp, W.", "Ely, J. A.", "Gessey-Jones, T.", "Gueuning, Q.", "Hills, R.", "Kulkarni, G.", "Maiolino, R.", "Meerburg, P. D.", "Mittal, S.", "Pritchard, J. R.", "Puchwein, E.", "Saxena, A.", "Shen, E.", "Smirnov, O.", "Spinelli, M.", "Zarb-Adami, K."], "date": "2022-07-01T00:00:00Z", "doi": ["10.1038/s41550-022-01709-9", "10.48550/arXiv.2210.07409"], "first_author": "de Lera Acedo, E.", "keyword": ["Astrophysics - Cosmology and Nongalactic Astrophysics", "Astrophysics - Astrophysics of Galaxies", "Astrophysics - Instrumentation and Methods for Astrophysics"], "pub": "Nature Astronomy", "pubdate": "2022-07-00", "title": ["The REACH radiometer for detecting the 21-cm hydrogen signal from redshift z \u2248 7.5-28"]}, {"bibcode": "2022MNRAS.509.4679A", "abstract": "Global 21-cm experiments aim to measure the sky-averaged H I absorption signal from cosmic dawn and the epoch of reionization. However, antenna chromaticity coupling to bright foregrounds can introduce distortions into the observational data of such experiments. We demonstrate a method for guiding the antenna design of a global experiment through data analysis simulations. This is done by performing simulated observations for a range of inserted 21-cm signals and then attempting to identify the signals with a data analysis pipeline. We demonstrate this method on five antennas that were considered as potential designs for the Radio Experiment for the Analysis of Cosmic Hydrogen: a conical log spiral antenna, an inverted conical sinuous antenna, and polygonal-, rectangular-, and elliptical-bladed dipoles. We find that the log spiral performs significantly better than the other antennas tested, able to correctly and confidently identify every inserted 21-cm signal. In second place is the polygonal dipole antenna, which was only unable to detect signals with both very low amplitudes of 0.05 K and low centre frequency of 80 MHz. The conical sinuous antenna was found to perform least accurately, only able to detect the highest amplitude 21-cm signals, and even then with biases. We also demonstrate that, due to the non-trivial nature of chromatic distortion and the processes of correcting for it, these are not the results that could have been expected superficially from the extent of chromatic variation in each antenna.", "alternate_bibcode": ["2021MNRAS.tmp.2933A", "2021arXiv210610193A"], "author": ["Anstey, Dominic", "Cumner, John", "de Lera Acedo, Eloy", "Handley, Will"], "date": "2022-02-01T00:00:00Z", "doi": ["10.1093/mnras/stab3211", "10.48550/arXiv.2106.10193"], "first_author": "Anstey, Dominic", "issue": "4", "keyword": ["instrumentation: miscellaneous", "methods: data analysis", "dark ages", "reionization", "first stars", "Astrophysics - Instrumentation and Methods for Astrophysics", "Astrophysics - Cosmology and Nongalactic Astrophysics"], "pub": "Monthly Notices of the Royal Astronomical Society", "pubdate": "2022-02-00", "title": ["Informing antenna design for sky-averaged 21-cm experiments using a simulated Bayesian data analysis pipeline"]}, {"bibcode": "2022JAI....1150001C", "abstract": "Following the reported detection of an absorption profile associated with the 21cm sky-averaged signal from the Cosmic Dawn by the EDGES experiment in 2018, a number of experiments have been set up to verify this result. This paper discusses the design process used for global 21cm experiments, focusing specifically on the Radio Experiment for the Analysis of Cosmic Hydrogen (REACH). This experiment will seek to understand and compensate for systematic errors present using detailed modeling and characterization of the instrumentation. Detailed quantitative figures of merit and numerical modeling are used to assist the design process of the REACH dipole antenna (one of the two antenna designs for REACH Phase I). This design process produced a 2.5:1 frequency bandwidth dipole. The aim of this design was to balance spectral smoothness and low impedance reflections with the ability to describe and understand the antenna response to the sky signal to inform the critically important calibration during observation and data analysis.", "alternate_bibcode": ["2021arXiv210910098C"], "author": ["Cumner, J.", "de Lera Acedo, E.", "de Villiers, D. I. L.", "Anstey, D.", "Kolitsidas, C. I.", "Gurdon, B.", "Fagnoni, N.", "Alexander, P.", "Bernardi, G.", "Bevins, H. T. J.", "Carey, S.", "Cavillot, J.", "Chiello, R.", "Craeye, C.", "Croukamp, W.", "Ely, J. A.", "Fialkov, A.", "Gessey-Jones, T.", "Gueuning, Q.", "Handley, W.", "Hills, R.", "Josaitis, A. T.", "Kulkarni, G.", "Magro, A.", "Maiolino, R.", "Meerburg, P. D.", "Mittal, S.", "Pritchard, J. R.", "Puchwein, E.", "Razavi-Ghods, N.", "Roque, I. L. V.", "Saxena, A.", "Scheutwinkel, K. H.", "Shen, E.", "Sims, P. H.", "Smirnov, O.", "Spinelli, M.", "Zarb-Adami, K."], "date": "2022-01-01T00:00:00Z", "doi": ["10.1142/S2251171722500015", "10.48550/arXiv.2109.10098"], "first_author": "Cumner, J.", "issue": "1", "keyword": ["21cm cosmology", "radio antenna", "global experiment", "Astrophysics - Instrumentation and Methods for Astrophysics", "Astrophysics - Cosmology and Nongalactic Astrophysics"], "pub": "Journal of Astronomical Instrumentation", "pubdate": "2022-00-00", "title": ["Radio Antenna Design for Sky-Averaged 21cm Cosmology Experiments: The REACH Case"]}, {"bibcode": "2021MNRAS.508.2923B", "abstract": "Emulation of the Global (sky-averaged) 21-cm signal with neural networks has been shown to be an essential tool for physical signal modelling. In this paper, we present GLOBALEMU, a Global 21-cm signal emulator that uses redshift as a character-defining variable alongside a set of astrophysical parameters to estimate the signal brightness temperature. Combined with physically motivated data pre-processing, this makes for a reliable and fast emulator that is relatively insensitive to the network design. GLOBALEMU can emulate a high-resolution signal in 1.3 ms in comparison to 133 ms, a factor of 102 improvement, when using the existing public state-of-the-art 21CMGEM. We illustrate, with the standard astrophysical models used to train 21CMGEM, that GLOBALEMU is almost twice as accurate and for a test set of \u22481700 signals we achieve a mean root mean squared error of 2.52 mK across the band z = 7-28 [\u224810 per cent the expected noise of the Radio Experiment for the Analysis of Cosmic Hydrogen (REACH)]. The models are parametrized by the star formation efficiency, f<SUB>*</SUB>, minimum virial circular velocity, V<SUB>c</SUB>, X-ray efficiency, f<SUB>X</SUB>, cosmic microwave background optical depth, \u03c4, the slope and low energy cut-off of the X-ray spectral energy density, \u03b1 and \u03bd<SUB>min</SUB>, respectively, and the mean free path of ionizing photons, R<SUB>mfp</SUB>. GLOBALEMU provides a flexible framework for easily emulating updated simulations of the Global signal and in addition the neutral fraction history. The emulator is pip installable and available at https://github.com/htjb/globalemu. GLOBALEMU will be used extensively by the REACH collaboration.", "alternate_bibcode": ["2021MNRAS.tmp.2500B", "2021arXiv210404336B"], "author": ["Bevins, H. T. J.", "Handley, W. J.", "Fialkov, A.", "de Lera Acedo, E.", "Javid, K."], "date": "2021-12-01T00:00:00Z", "doi": ["10.1093/mnras/stab2737", "10.48550/arXiv.2104.04336"], "first_author": "Bevins, H. T. J.", "issue": "2", "keyword": ["early Universe", "reionization", "first stars", "dark ages", "software: data analysis", "software: simulations", "Astrophysics - Cosmology and Nongalactic Astrophysics", "Astrophysics - Instrumentation and Methods for Astrophysics"], "pub": "Monthly Notices of the Royal Astronomical Society", "pubdate": "2021-12-00", "title": ["GLOBALEMU: a novel and robust approach for emulating the sky-averaged 21-cm signal from the cosmic dawn and epoch of reionization"]}, {"bibcode": "2021MNRAS.506.2041A", "abstract": "The H I 21 cm absorption line is masked by bright foregrounds and systematic distortions that arise due to the chromaticity of the antenna used to make the observation coupling to the spectral inhomogeneity of these foregrounds. We demonstrate that these distortions are sufficient to conceal the 21 cm signal when the antenna is not perfectly achromatic and that simple corrections assuming a constant spatial distribution of foreground power are insufficient to overcome them. We then propose a new physics-motivated method of modelling the foregrounds of 21 cm experiments in order to fit the chromatic distortions as part of the foregrounds. This is done by generating a simulated sky model across the observing band by dividing the sky into N regions and scaling a base map assuming a distinct uniform spectral index in each region. The resulting sky map can then be convolved with a model of the antenna beam to give a model of foregrounds and chromaticity parametrized by the spectral indices of the N regions. We demonstrate that fitting this model for varying N using a Bayesian nested sampling algorithm and comparing the results using the evidence allows the 21 cm signal to be reliably detected in data of a relatively smooth conical log spiral antenna. We also test a much more chromatic conical sinuous antenna and find this model will not produce a reliable signal detection, but in a manner that is easily distinguishable from a true detection.", "alternate_bibcode": ["2020arXiv201009644A", "2021MNRAS.tmp.1520A"], "author": ["Anstey, Dominic", "de Lera Acedo, Eloy", "Handley, Will"], "date": "2021-09-01T00:00:00Z", "doi": ["10.1093/mnras/stab1765", "10.48550/arXiv.2010.09644"], "first_author": "Anstey, Dominic", "issue": "2", "keyword": ["methods: data analysis", "dark ages", "reionization", "first stars", "early Universe", "Astrophysics - Instrumentation and Methods for Astrophysics"], "pub": "Monthly Notices of the Royal Astronomical Society", "pubdate": "2021-09-00", "title": ["A general Bayesian framework for foreground modelling and chromaticity correction for global 21 cm experiments"]}, {"bibcode": "2021MNRAS.505.2638R", "abstract": "Detection of millikelvin-level signals from the 'Cosmic Dawn' requires an unprecedented level of sensitivity and systematic calibration. We report the theory behind a novel calibration algorithm developed from the formalism introduced by the EDGES collaboration for use in 21-cm experiments. Improvements over previous approaches are provided through the incorporation of a Bayesian framework and machine learning techniques such as the use of Bayesian evidence to determine the level of frequency variation of calibration parameters that is supported by the data, the consideration of correlation between calibration parameters when determining their values, and the use of a conjugate-prior based approach that results in a fast algorithm for application in the field. In self-consistency tests using empirical data models of varying complexity, our methodology is used to calibrate a 50 \u03a9 ambient-temperature load. The RMS error between the calibration solution and the measured temperature of the load is 8 mK, well within the 1 \u03c3 noise level. Whilst the methods described here are more applicable to global 21-cm experiments, they can easily be adapted and applied to other applications, including telescopes such as HERA and the SKA.", "alternate_bibcode": ["2021MNRAS.tmp.1408R", "2020arXiv201114052R"], "author": ["Roque, I. L. V.", "Handley, W. J.", "Razavi-Ghods, N."], "date": "2021-08-01T00:00:00Z", "doi": ["10.1093/mnras/stab1453", "10.48550/arXiv.2011.14052"], "first_author": "Roque, I. L. V.", "issue": "2", "keyword": ["instrumentation: interferometers", "methods: statistical", "dark ages", "reionization", "first stars", "Astrophysics - Instrumentation and Methods for Astrophysics"], "pub": "Monthly Notices of the Royal Astronomical Society", "pubdate": "2021-08-00", "title": ["Bayesian noise wave calibration for 21-cm global experiments"]}, {"bibcode": "2021MNRAS.503..344S", "abstract": "We modelled the two major layer of Earth's ionosphere, the F-layer and the D-layer, by a simplified spatial model with temporal variance to study the chromatic ionospheric effects on global 21-cm observations. From the analyses, we found that the magnitude of the ionospheric disruptions due to ionospheric refraction and absorption can be greater than the expected global 21-cm signal, and the variation of its magnitude can differ, depending on the ionospheric conditions. Within the parameter space adopted in the model, the shape of the global 21-cm signal is distorted after propagating through the ionosphere, while its amplitude is weakened. It is observed that the ionospheric effects do not cancel out over time, and thus should be accounted for in the foreground calibration at each timestep to account for the chromaticity introduced by the ionosphere.", "alternate_bibcode": ["2020arXiv201110517S", "2021MNRAS.tmp..498S"], "author": ["Shen, Emma", "Anstey, Dominic", "de Lera Acedo, Eloy", "Fialkov, Anastasia", "Handley, Will"], "date": "2021-05-01T00:00:00Z", "doi": ["10.1093/mnras/stab429", "10.48550/arXiv.2011.10517"], "first_author": "Shen, Emma", "issue": "1", "keyword": ["atmospheric effects", "methods: data analysis", "Astrophysics - Instrumentation and Methods for Astrophysics", "Astrophysics - Cosmology and Nongalactic Astrophysics", "Astrophysics - Earth and Planetary Astrophysics"], "pub": "Monthly Notices of the Royal Astronomical Society", "pubdate": "2021-05-00", "title": ["Quantifying ionospheric effects on global 21-cm observations"]}, {"bibcode": "2021MNRAS.502.4405B", "abstract": "Maximally Smooth Functions (MSFs) are a form of constrained functions in which there are no inflection points or zero crossings in high-order derivatives. Consequently, they have applications to signal recovery in experiments where signals of interest are expected to be non-smooth features masked by larger smooth signals or foregrounds. They can also act as a powerful tool for diagnosing the presence of systematics. The constrained nature of MSFs makes fitting these functions a non-trivial task. We introduce MAXSMOOTH, an open-source package that uses quadratic programming to rapidly fit MSFs. We demonstrate the efficiency and reliability of MAXSMOOTH by comparison to commonly used fitting routines and show that we can reduce the fitting time by approximately two orders of magnitude. We introduce and implement with MAXSMOOTH Partially Smooth Functions, which are useful for describing elements of non-smooth structure in foregrounds. This work has been motivated by the problem of foreground modelling in 21-cm cosmology. We discuss applications of MAXSMOOTH to 21-cm cosmology and highlight this with examples using data from the Experiment to Detect the Global Epoch of Reionization Signature (EDGES) and the Large-aperture Experiment to Detect the Dark Ages (LEDA) experiments. We demonstrate the presence of a sinusoidal systematic in the EDGES data with a log-evidence difference of 86.19 \u00b1 0.12 when compared to a pure foreground fit. MSFs are applied to data from LEDA for the first time in this paper and we identify the presence of sinusoidal systematics. MAXSMOOTH is pip installable and available for download at https://github.com/htjb/maxsmooth.", "alternate_bibcode": ["2020arXiv200714970B", "2021MNRAS.tmp..209B"], "author": ["Bevins, H. T. J.", "Handley, W. J.", "Fialkov, A.", "de Lera Acedo, E.", "Greenhill, L. J.", "Price, D. C."], "date": "2021-04-01T00:00:00Z", "doi": ["10.1093/mnras/stab152", "10.48550/arXiv.2007.14970"], "first_author": "Bevins, H. T. J.", "issue": "3", "keyword": ["methods: data analysis", "dark ages", "reionization", "first stars", "early Universe", "Astrophysics - Cosmology and Nongalactic Astrophysics", "Astrophysics - Instrumentation and Methods for Astrophysics"], "pub": "Monthly Notices of the Royal Astronomical Society", "pubdate": "2021-04-00", "title": ["MAXSMOOTH: rapid maximally smooth function fitting with applications in Global 21-cm cosmology"]}]}}, "metadata": {"name": "REACH", "id": "QFTpllppSgS1zK9Z6lTVPQ", "description": "REACH papers", "num_documents": 30, "date_created": "2022-08-31T10:50:12.151695", "date_last_modified": "2025-01-06T09:59:23.199478", "permission": "write", "public": false, "num_users": 0, "owner": "da401"}, "updates": {"num_updated": 0, "duplicates_removed": 0, "update_list": [], "updated_notes": []}}