Foreground Wedge Research Articles

Inferring astrophysical parameters using the 2D cylindrical power spectrum from reionisation

Abstract Enlightening our understanding of the first galaxies responsible for driving reionisation requires detecting the 21-cm signal from neutral hydrogen. Interpreting the wealth of information embedded in this signal requires Bayesian inference. Parameter inference from the 21-cm signal is primarily restricted to the spherically averaged power spectrum (1D PS) owing to its relatively straightforward derivation of an analytic likelihood function enabling traditional Monte-Carlo Markov-Chain (MCMC) approaches. However, in recent years, simulation-based inference (SBI) has become feasible which removes the necessity of having an analytic likelihood, enabling more complex summary statistics of the 21-cm signal to be used for Bayesian inference. In this work, we use SBI, specifically marginal neural ratio estimation to learn the likelihood-to-evidence ratio with Swyft, to explore parameter inference using the cylindrically averaged 2D PS. Since the 21-cm signal is anisotropic, the 2D PS should yield more constraining information compared to the 1D PS which isotropically averages the signal. For this, we consider a mock 1000 hr observation of the 21-cm signal using the SKA and compare the performance of the 2D PS relative to the 1D PS. Additionally, we explore two separate foreground mitigation strategies, perfect foreground removal and wedge avoidance. We find the 2D PS outperforms the 1D PS by improving the marginalised uncertainties on individual astrophysical parameters by up to ∼30 − 40 per cent irrespective of the foreground mitigation strategy. Primarily, these improvements stem from how the 2D PS distinguishes between the transverse, k⊥, and redshift dependent, k∥ information which enables greater sensitivity to the complex reionisation morphology.

Exploring the role of the halo mass function for inferring astrophysical parameters during reionisation

Abstract Detecting the 21-cm signal at z ≳ 6 will reveal insights into the properties of the first galaxies responsible for driving reionisation. To extract this information, we perform parameter inference with 3D simulations of the 21-cm signal embedded within a Bayesian inference pipeline. Presently, when performing inference, we must choose which sources of uncertainty to sample and which to hold fixed. Since the astrophysics of galaxies is much more uncertain than that of the underlying halo-mass function (HMF), we typically parameterise and model the former while fixing the latter. However, doing so may bias our inference of the galaxy properties. In this work, we explore the consequences of assuming an incorrect HMF and quantify the relative biases on our inferred astrophysical model parameters when considering the wrong HMF. We then relax this assumption by constructing a generalised five parameter HMF model and simultaneously recover it with our underlying astrophysical model. For this, we use 21CMFAST and perform Simulation-Based Inference using marginal neural ratio estimation to learn the likelihood-to-evidence ratio with Swyft. Using a mock 1000-hour observation of the 21-cm power spectrum from the forthcoming Square Kilometre Array, conservatively assuming foreground wedge avoidance, we find that assuming the incorrect HMF can bias the recovered astrophysical parameters by up to ∼3 − 4σ even when including independent information from observed luminosity functions. Using our generalised HMF model, although we recover our astrophysical parameters with a factor of ∼2 − 4 larger marginalised uncertainties, the constraints are unbiased, agnostic to the underlying HMF and therefore more conservative.

Modes of the Dark Ages 21 cm field accessible to a lunar radio interferometer.

At redshifts beyond [Formula: see text], the 21 cm line from neutral hydrogen is expected to be essentially the only viable probe of the three-dimensional matter distribution. The lunar far-side is an extremely appealing site for future radio arrays that target this signal, as it is protected from terrestrial radio frequency interference, and has no ionosphere to attenuate and absorb radio emission at low frequencies (tens of MHz and below). We forecast the sensitivity of low-frequency lunar radio arrays to the bispectrum of the 21 cm brightness temperature field, which can in turn be used to probe primordial non-Gaussianity generated by particular early universe models. We account for the loss of particular regions of Fourier space due to instrumental limitations and systematic effects, and predict the sensitivity of different representative array designs to local-type non-Gaussianity in the bispectrum, parametrized by [Formula: see text]. Under the most optimistic assumption of sample variance-limited observations, we find that [Formula: see text] could be achieved for several broad redshift bins at [Formula: see text] if foregrounds can be removed effectively. These values degrade to between [Formula: see text] and 0.7 for [Formula: see text] to [Formula: see text], respectively, when a large foreground wedge region is excluded. This article is part of a discussion meeting issue 'Astronomy from the Moon: the next decades (part 2)'.

Detecting the H i power spectrum in the post-reionization Universe with SKA-Low

ABSTRACT We present a survey strategy to detect the neutral hydrogen (H i) power spectrum at 5 < z < 6 using the SKA-Low radio telescope in presence of foregrounds and instrumental effects. We simulate observations of the inherently weak H i signal post-reionization with varying levels of noise and contamination with foreground amplitudes equivalent to residuals after sky model subtraction. We find that blind signal separation methods on imaged data are required in order to recover the H i signal at large cosmological scales. Comparing different methods of foreground cleaning, we find that Gaussian Process Regression (GPR) performs better than Principle Component Analysis (PCA), with the key difference being that GPR uses smooth kernels for the total data covariance. The integration time of one field needs to be larger than ∼250 h to provide large enough signal-to-noise ratio (SNR) to accurately model the data covariance for foreground cleaning. Images within the primary beam field-of-view give measurements of the H i power spectrum at scales $k\sim 0.02\, {\rm Mpc^{-1}}-0.3\, {\rm Mpc^{-1} }$ with SNR ∼2–5 in Δ[log(k/Mpc−1)] = 0.25 bins assuming an integration time of 600 h. Systematic effects, which introduce small-scale fluctuations across frequency channels, need to be ≲ 5 × 10−5 to enable unbiased measurements outside the foreground wedge. Our results provide an important validation towards using the SKA-Low array for measuring the H i power spectrum in the post-reionization Universe.

Towards optimal foreground mitigation strategies for interferometric H i intensity mapping in the low-redshift Universe

Abstract We conduct the first case study towards developing optimal foreground mitigation strategies for neutral hydrogen (H i) intensity mapping using radio interferometers at low redshifts. A pipeline for simulation, foreground mitigation, and power spectrum estimation is built, which can be used for ongoing and future surveys using MeerKAT and Square Kilometre Array Observatory. It simulates realistic sky signals to generate visibility data-given instrument and observation specifications, which is subsequently used to perform foreground mitigation and power spectrum estimation. A quadratic estimator formalism is developed to estimate the temperature power spectrum in visibility space. Using MeerKAT telescope specifications for observations in the redshift range, $z$ ∼ 0.25–0.30, corresponding to the MeerKAT International GHz Tiered Extragalactic Exploration (MIGHTEE) survey, we present a case study, where we compare different approaches of foreground mitigation. We find that component separation in visibility space provides a more accurate estimation of H i clustering when compared with foreground avoidance, with the uncertainties being 30 per cent smaller. Power spectrum estimation from image is found to be less robust with larger bias and more information loss when compared with estimation in visibility. We conclude that for the considered sub-band of $z$ ∼ 0.25–0.30, the MIGHTEE survey will be capable of measuring the H i power spectrum from $k\sim 0.5$ to $k\sim 10\, {\rm Mpc^{-1}}$ with signal-to-noise ratio being ∼3. We are the first to show that, at low redshift, component separation in visibility space suppresses foreground contamination at large line-of-sight scales, allowing measurement of H i power spectrum closer to the foreground wedge, crucial for data analysis towards future detections.

Optical depth to reionization from perturbative 21 cm clustering

The optical depth τ is the least well determined parameter in the standard model of cosmology, and one whose precise value is important for both understanding reionization and for inferring fundamental physics from cosmological measurements. We forecast how well future epoch of reionization experiments could constraint τ using a symmetries-based bias expansion that highlights the special role played by anisotropies in the power spectrum on large scales. Given a parametric model for the ionization evolution inspired by the physical behavior of more detailed reionization simulations, we find that future 21 cm experiments could place tight constraints on the timing and duration of reionization and hence constraints on τ that are competitive with proposed, space-based CMB missions provided they can measure k ≈ 0.1 h Mpc-1 with a clean foreground wedge across redshifts spanning the most active periods of reionization, corresponding to ionization fractions 0.2 ≲ x ≲ 0.8. Significantly improving upon existing CMB-based measurements with next-generation 21 cm surveys would require substantially longer observations (∼ 5 years) than standard \U0001d4aa(1000 hour) integration times. Precise measurements of smaller scales will not improve constraints on τ until a better understanding of the astrophysics of reionization is achieved. In the presence of noise and foregrounds even future 21 cm experiments will struggle to constrain τ if the ionization evolution deviates significantly from simple parametric forms.

Generating extremely large-volume reionization simulations

ABSTRACT Preparing for a first detection of the 21-cm signal during reionization by large-scale interferometer experiments requires rigorous testing of the data analysis and reduction pipelines. Validating that these do not erroneously add/remove features mimicking the signal (e.g. from side lobes or large-scale power leakage) requires simulations extending beyond the primary field of view. However, the Murchison Wide Field Array (MWA) with a field of view of ∼252 deg2 would require simulations spanning several Gpcs, which are currently infeasible. To address this, we developed a simplified version of the seminumerical reionization simulation code 21cmfast, sacrificing some physical accuracy (linear structure formation) in favour of extremely large volumes. We then constructed a 7.5 Gpc comoving volume specifically tailored to the binned spectral resolution of the MWA (∼1.17 cMpc), required for validating the pipeline used in the 2020 MWA 21-cm power spectrum (PS) upper limits. With this large-volume simulation, we then explored: (i) whether smaller volume simulations are biased by missing large-scale modes, (ii) non-Gaussianity in the cosmic variance uncertainty, (iii) biases in the recovered 21-cm PS following foreground wedge avoidance, and (iv) the impact of tiling smaller simulations to achieve large volumes. We found (i) no biases from missing large-scale power, (ii) significant contribution from non-Gaussianity, as expected, (iii) a 10–20 per cent overestimate of the 21-cm PS following wedge mode excision, and (iv) tiling smaller simulations underestimates the large-scale power and cosmic variance.

Detecting the non-Gaussianity of the 21-cm signal during reionization with the wavelet scattering transform

ABSTRACT Detecting the 21-cm hyperfine transition from neutral hydrogen in the intergalactic medium is our best probe for understanding the astrophysical processes driving the Epoch of Reionization (EoR). The primary means for a detection of this 21-cm signal is through a statistical measurement of the spatial fluctuations using the 21-cm power spectrum (PS). However, the 21-cm signal is non-Gaussian meaning the PS, which only measures the Gaussian fluctuations, is suboptimal for characterizing all of the available information. The upcoming Square Kilometre Array (SKA) will perform a deep, 1000 h observation over 100 deg2 specifically designed to recover direct images of the 21-cm signal. In this work, we use the Wavelet Scattering Transform (WST) to extract the non-Gaussian information directly from these 2D images of the 21-cm signal. The key advantage of the WST is its stability with respect to statistical noise for measuring non-Gaussian information, unlike the bispectrum whose statistical noise diverges. In this work, we specifically focus on introducing a novel method to isolate non-Gaussian information from an image and apply this methodology to individual mock 21-cm images to quantify the strength of the non-Gaussian information contained within a single image. For example, at 150 (177) MHz (z ∼ 8.5 and ∼7) for a fiducial reionization model we recover a signal to noise of ∼5 (8) for the non-Gaussian information assuming perfect foreground removal and ∼2 (3) assuming foreground wedge avoidance.

A 21-cm power spectrum at 48 MHz, using the Owens Valley Long Wavelength Array

ABSTRACT The Large-aperture Experiment to detect the Dark Age (LEDA) was designed to measure the 21-cm signal from neutral hydrogen at Cosmic Dawn, z ≈ 15–30. Using observations made with the ≈ 200 m diameter core of the Owens Valley Radio Observatory Long Wavelength Array (OVRO–LWA), we present a 2D cylindrical spatial power spectrum for data at 43.1–53.5 MHz (zmedian ≈ 28) incoherently integrated for 4 h, and an analysis of the array sensitivity. Power from foregrounds is localized to a ‘wedge’ within k⊥, $k_\parallel$ space. After calibration of visibilities using five bright compact sources including Vir A, we measure Δ2(k) ≈ 2 × 1012 mK2 outside the foreground wedge, where an uncontaminated cosmological signal would lie, in principle. The measured Δ2(k) is an upper limit that reflects a combination of thermal instrumental and sky noise, and unmodelled systematics that scatter power from the wedge, as will be discussed. By differencing calibrated visibilities for close pairs of frequency channels, we suppress foreground sky structure and systematics, extract thermal noise, and use a mix of coherent and incoherent integration to simulate a noise-dominated power spectrum for a 3000 h observation and z = 16−37. For suitable calibration quality, the resulting noise level, Δ2(k) ≈ 100 mK2 (k = 0.3 Mpc−1), would be sufficient to detect peaks in the 21-cm spatial power spectrum due to early Ly-α and X-ray sources, as predicted for a range of theoretical model parameters.

Forecasts on primordial non-Gaussianity from 21 cm intensity mapping experiments

We forecast the ability of dedicated 21 cm intensity mapping experiments to constraint primordial non-Gaussianity using power spectrum and bispectrum. We model the signal by including the non-linear biasing expansion through a generalized halo model approach. We consider the importance of foreground filtering scale and of the foreground wedge. We find that the current generation intensity mapping experiments like CHIME do not posses sufficient sensitivity to be competitive with the existing limits. On the other hand, upcoming experiments like HIRAX can improve the current constraints and the proposed PUMA experiment can substantially improve them, reaching sensitivities below σ(fNL)<5 for equilateral and orthogonal configurations and σ(fNL) < 1 for the local shape, if good foreground control is achieved.

The impact of non-Gaussianity on the Epoch of Reionization parameter forecast using 21-cm power-spectrum measurements

ABSTRACT Measurements of the Epoch of Reionization (EoR) 21-cm signal hold the potential to constrain models of reionization. In this paper, we consider a reionization model with three astrophysical parameters namely (1) the minimum halo mass that can host ionizing sources, Mmin, (2) the number of ionizing photons escaping into the IGM per baryon within the halo, Nion, and (3) the mean free path of the ionizing photons within the IGM, Rmfp. We predict the accuracy with which these parameters can be measured from future observations of the 21-cm power spectrum (PS) using the upcoming SKA-Low. Unlike several earlier works, we account for the non-Gaussianity of the inherent EoR 21-cm signal. Considering cosmic variance only and assuming that foregrounds are completely removed, we find that non-Gaussianity increases the volume of the 1σ error ellipsoid of the parameters by a factor of 133 relative to the Gaussian predictions, the orientation is also different. The ratio of the volume of error ellipsoids is 1.65 and 2.67 for observation times of 1024 and 10 000 h, respectively, when all the $\boldsymbol {k}$ modes within the foreground wedge are excluded. With foreground wedge excluded and for 1024 h, the 1D marginalized errors are (ΔMmin/Mmin, ΔNion/Nion, ΔRmfp/Rmfp) = (6.54, 2.71, 7.75) × 10−2 that are, respectively, $2 {{\ \rm per\ cent}}$, $5 {{\ \rm per\ cent}}$, and $23 {{\ \rm per\ cent}}$ larger than the respective Gaussian predictions. The impact of non-Gaussianity increases for longer observations, and it is particularly important for Rmfp.

Predictions for measuring the 21-cm multifrequency angular power spectrum using SKA-Low

ABSTRACT The light-cone effect causes the mean as well as the statistical properties of the redshifted 21-cm signal ${T_{\rm b}}(\hat{\boldsymbol {n}}, \nu)$ to change with frequency ν (or cosmic time). Consequently, the statistical homogeneity (ergodicity) of the signal along the line-of-sight (LoS) direction is broken. This is a severe problem particularly during the Epoch of Reionization (EoR) when the mean neutral hydrogen fraction ($\bar{x}_{\rm {H\,{\small I}}}$) changes rapidly as the Universe evolves. This will also pose complications for large bandwidth observations. These effects imply that the 3D power spectrum P(k) fails to quantify the entire second-order statistics of the signal as it assumes the signal to be ergodic and periodic along the LoS. As a proper alternative to P(k), we use the multifrequency angular power spectrum (MAPS) ${\mathcal {C}}_{\ell }(\nu _1,\nu _2)$, which does not assume the signal to be ergodic and periodic along the LoS. Here, we study the prospects for measuring the EoR 21-cm MAPS using future observations with the upcoming SKA-Low. Ignoring any contribution from the foregrounds, we find that the EoR 21-cm MAPS can be measured at a confidence level ≥5σ at angular scales ℓ ∼ 1300 for total observation time tobs ≥ 128 h across ∼44 MHz observational bandwidth. We also quantitatively address the effects of foregrounds on MAPS detectability forecast by avoiding signal contained within the foreground wedge in $({\boldsymbol {k}}_\perp , k_\parallel)$ plane. These results are very relevant for the upcoming large bandwidth EoR experiments as previous predictions were all restricted to individually analysing the signal over small frequency (or equivalent redshift) intervals.

Improved upper limits on the 21 cm signal power spectrum of neutral hydrogen at z ≈ 9.1 from LOFAR

ABSTRACTA new upper limit on the 21 cm signal power spectrum at a redshift of z ≈ 9.1 is presented, based on 141 h of data obtained with the Low-Frequency Array (LOFAR). The analysis includes significant improvements in spectrally smooth gain-calibration, Gaussian Process Regression (GPR) foreground mitigation and optimally weighted power spectrum inference. Previously seen ‘excess power’ due to spectral structure in the gain solutions has markedly reduced but some excess power still remains with a spectral correlation distinct from thermal noise. This excess has a spectral coherence scale of 0.25–0.45 MHz and is partially correlated between nights, especially in the foreground wedge region. The correlation is stronger between nights covering similar local sidereal times. A best 2-σ upper limit of $\Delta ^2_{21} \lt (73)^2\, \mathrm{mK^2}$ at $k = 0.075\, \mathrm{h\, cMpc^{-1}}$ is found, an improvement by a factor ≈8 in power compared to the previously reported upper limit. The remaining excess power could be due to residual foreground emission from sources or diffuse emission far away from the phase centre, polarization leakage, chromatic calibration errors, ionosphere, or low-level radiofrequency interference. We discuss future improvements to the signal processing chain that can further reduce or even eliminate these causes of excess power.

Reionisation &amp; Cosmic Dawn Astrophysics from the Square Kilometre Array: Impact of Observing Strategies

Abstract Interferometry of the cosmic 21-cm signal is set to revolutionise our understanding of the Epoch of Reionisation (EoR) and the Cosmic Dawn (CD). The culmination of ongoing efforts will be the upcoming Square Kilometre Array (SKA), which will provide tomography of the 21-cm signal from the first billion years of our Universe. Using a galaxy formation model informed by high-z luminosity functions, here we forecast the accuracy with which the first phase of SKA-low (SKA1-low) can constrain the properties of the unseen galaxies driving the astrophysics of the EoR and CD. We consider three observing strategies: (i) deep (1000h on a single field); (ii) medium-deep (100hr on 10 independent fields); and (iii) shallow (10hr on 100 independent fields). Using the 21-cm power spectrum as a summary statistic, and conservatively only using the 21-cm signal above the foreground wedge, we predict that all three observing strategies should recover astrophysical parameters to a fractional precision of ∼0.1 – 10 per cent. The reionisation history is recovered to an uncertainty of $\Delta z \mathrel {\lesssim}0.1$ (1σ) for the bulk of its duration. The medium-deep strategy, balancing thermal noise against cosmic variance, results in the tightest constraints, slightly outperforming the deep strategy. The shallow observational strategy performs the worst, with up to a ∼10 – 60 per cent increase in the recovered uncertainty. We note, however, that non-Gaussian summary statistics, tomography, as well as unbiased foreground removal would likely favour the deep strategy.

Reconstructing large-scale structure with neutral hydrogen surveys

Upcoming 21-cm intensity surveys will use the hyperfine transition in emission to map out neutral hydrogen in large volumes of the universe. Unfortunately, large spatial scales are completely contaminated with spectrally smooth astrophysical foregrounds which are orders of magnitude brighter than the signal. This contamination also leaks into smaller radial and angular modes to form a foreground wedge, further limiting the usefulness of 21-cm observations for different science cases, especially cross-correlations with tracers that have wide kernels in the radial direction. In this paper, we investigate reconstructing these modes within a forward modeling framework. Starting with an initial density field, a suitable bias parameterization and non-linear dynamics to model the observed 21-cm field, our reconstruction proceeds by {combining} the likelihood of a forward simulation to match the observations (under given modeling error and a data noise model) {with the Gaussian prior on initial conditions and maximizing the obtained posterior}. For redshifts z=2 and 4, we are able to reconstruct 21cm field with cross correlation, rc > 0.8 on all scales for both our optimistic and pessimistic assumptions about foreground contamination and for different levels of thermal noise. The performance deteriorates slightly at z=6. The large-scale line-of-sight modes are reconstructed almost perfectly. We demonstrate how our method also provides a technique for density field reconstruction for baryon acoustic oscillations, outperforming standard methods on all scales. We also describe how our reconstructed field can provide superb clustering redshift estimation at high redshifts, where it is otherwise extremely difficult to obtain dense spectroscopic samples, as well as open up a wealth of cross-correlation opportunities with projected fields (e.g. lensing) which are restricted to modes transverse to the line of sight.

The impact of non-Gaussianity on the error covariance for observations of the Epoch of Reionization (EoR) 21-cm power spectrum

Recent simulations show the Epoch of Reionization (EoR) 21-cm signal to be inherently non-Gaussian whereby the error covariance matrix |$\boldsymbol{\sf C}_{ij}$| of the 21-cm power spectrum (PS) contains a trispectrum contribution that would be absent if the signal were Gaussian. Using the binned power spectrum and trispectrum from simulations, here we present a methodology for incorporating these with the baseline distribution and system noise to make error predictions for observations with any radio-interferometric array. Here we consider the upcoming SKA-Low. Non-Gaussianity enhances the errors introducing a positive deviation Δ relative to the Gaussian predictions. Δ increases with observation time tobs and saturates as the errors approach the cosmic variance. Considering tobs = 1024 hours where a 5σ detection is possible at all redshifts 7 ≤ z ≤ 13, in the absence of foregrounds we find that the deviations are important at small k where we have |$\Delta \sim 40\!-\!100 {{\ \rm per\ cent}}$| at |$k \sim 0.04 \,\rm Mpc^{-1}$| for some of the redshifts and also at intermediate |$k \, (\sim 0.4 \,\rm Mpc^{-1})$| where we have |$\Delta \sim 200 {{\ \rm per\ cent}}$| at z = 7. Non-Gaussianity also introduces correlations between the errors in different k bins, and we find both correlations and anticorrelations with the correlation coefficient value spanning −0.4 ≤ rij ≤ 0.8. Incorporating the foreground wedge, Δ continues to be important (⁠|$\gt 50 {{\ \rm per\ cent}}$|⁠) at z = 7. We conclude that non-Gaussianity makes a significant contribution to the errors and this is important in the context of the future instruments that aim to achieve high-sensitivity measurements of the EoR 21-cm PS.

Anatomy of cosmic tidal reconstruction

Abstract 21-cm intensity surveys aim to map neutral hydrogen atoms in the universe through hyper-fine emission. Unfortunately, long-wavelength (low-wavenumber) radial modes are highly contaminated by smooth astrophysical foregrounds that are six orders of magnitude brighter than the cosmological signal. This contamination also leaks into higher radial and angular wavenumber modes and forms a foreground wedge. Cosmic tidal reconstruction aims to extract the large-scale signal from anisotropic features in the local small-scale power spectrum through non-linear tidal interactions; losing small-scale modes to foreground wedge will impair its performance. In this paper, we review tidal interaction theory and estimator construction, and derive the theoretical expressions for the reconstructed spectra. We show the reconstruction is robust against peculiar velocities. Removing low line-of-sight k modes, we demonstrate cross-correlation coefficient r is greater than 0.7 on large scales (k ≲ 0.1 h Mpc−1) even with a cut-off value $k^c_{\Vert }=0.1$h Mpc−1. Discarding wedge modes yields 0.3 ≲ r ≲ 0.5 and completely removes the dependency on $k^c_{\Vert }$. Our theoretical predictions agree with these numerical simulations.

High-redshift post-reionization cosmology with 21cm intensity mapping

We investigate the possibility of performing cosmological studies in the redshift range 2.5<z<5 through suitable extensions of existing and upcoming radio-telescopes like CHIME, HIRAX and FAST. We use the Fisher matrix technique to forecast the bounds that those instruments can place on the growth rate, the BAO distance scale parameters, the sum of the neutrino masses and the number of relativistic degrees of freedom at decoupling, N eff. We point out that quantities that depend on the amplitude of the 21cm power spectrum, like fσ8, are completely degenerate with ΩHI and bHI, and propose several strategies to independently constrain them through cross-correlations with other probes. Assuming 5% priors on ΩHI and bHI, kmax=0.2 h Mpc−1 and the primary beam wedge, we find that a HIRAX extension can constrain, within bins of Δ z=0.1: 1) the value of fσ8 at ≃4%, 2) the value of DA and H at ≃1%. In combination with data from Euclid-like galaxy surveys and CMB S4, the sum of the neutrino masses can be constrained with an error equal to 23 meV (1σ), while Neff can be constrained within 0.02 (1σ). We derive similar constraints for the extensions of the other instruments. We study in detail the dependence of our results on the instrument, amplitude of the HI bias, the foreground wedge coverage, the nonlinear scale used in the analysis, uncertainties in the theoretical modeling and the priors on bHI and Ω HI. We conclude that 21cm intensity mapping surveys operating in this redshift range can provide extremely competitive constraints on key cosmological parameters.

Measuring the reionization 21 cm fluctuations using clustering wedges

One of the main challenges in probing the reionization epoch using the redshifted 21 cm line is that the magnitude of the signal is several orders smaller than the astrophysical foregrounds. One of the methods to deal with the problem is to avoid a wedge-shaped region in the Fourier $k_{\perp} - k_{\parallel}$ space which contains the signal from the spectrally smooth foregrounds. However, measuring the spherically averaged power spectrum using only modes outside this wedge (i.e., in the reionization window), leads to a bias. We provide a prescription, based on expanding the power spectrum in terms of the shifted Legendre polynomials, which can be used to compute the angular moments of the power spectrum in the reionization window. The prescription requires computation of the monopole, quadrupole and hexadecapole moments of the power spectrum using the theoretical model under consideration and also the knowledge of the effective extent of the foreground wedge in the $k_{\perp} - k_{\parallel}$ plane. One can then calculate the theoretical power spectrum in the window which can be directly compared with observations. The analysis should have implications for avoiding any bias in the parameter constraints using 21 cm power spectrum data.

SPHERICAL HARMONIC ANALYSES OF INTENSITY MAPPING POWER SPECTRA

ABSTRACT Intensity mapping is a promising technique for surveying the large-scale structure of our universe from z = 0 to z ∼ 150, using the brightness temperature field of spectral lines to directly observe previously unexplored portions of our cosmic timeline. Examples of targeted lines include the 21 cm hyperfine transition of neutral hydrogen, rotational lines of carbon monoxide, and fine-structure lines of singly ionized carbon. Recent efforts have focused on detections of the power spectrum of spatial fluctuations, but have been hindered by systematics such as foreground contamination. This has motivated the decomposition of data into Fourier modes perpendicular and parallel to the line of sight, which has been shown to be a particularly powerful way to diagnose systematics. However, such a method is well-defined only in the limit of a narrow-field, flat-sky approximation. This limits the sensitivity of intensity mapping experiments, as it means that wide surveys must be separately analyzed as a patchwork of smaller fields. In this paper, we develop a framework for analyzing intensity mapping data in a spherical Fourier–Bessel basis, which incorporates curved sky effects without difficulty. We use our framework to generalize a number of techniques in intensity mapping data analysis from the flat sky to the curved sky. These include visibility-based estimators for the power spectrum, treatments of interloper lines, and the “foreground wedge” signature of spectrally smooth foregrounds.