Numerous studies have established the theoretical potential of the 21cm bispectrum to boost our understanding of the Epoch of Reionization (EoR), and therefore early generation of stars and galaxies. In this paper we look at the impact of foregrounds and instrumental effects on the 21cm bispectrum and our ability to measure it. Unlike the power spectrum for which (in the absence of instrumental effects) there is a window clear of smooth-spectrum foregrounds in which the 21cm power spectrum may be detectable, there is no such "EoR window" for the bispectrum. Instead, on smaller scales EoR structure modulates that of the foregrounds (FG) to alter the EoR+FG bispectrum from that of the foregrounds in a complex manner. On larger scales the EoR structures are completely swamped by those of the foregrounds, and the EoR+FG bispectrum is entirely dominated by that of the foregrounds. It is therefore unlikely that the bispectrum will be useful in cases where we are observationally restricted to using foreground avoidance techniques. We also find that there is potential for instrumental effects to seriously corrupt the bispectrum, possibly even rendering the bispectrum useless for parameter estimation. On larger scales, foreground removal using GMCA is found to recover the EoR bispectrum to a reasonable level of accuracy (even better than the power spectrum for certain configurations). Further studies are necessary to understand the error and/or bias associated with foreground removal before the 21cm bispectrum can be practically applied in analysis of future data.
Redshifted 21cm signal is a promising tool to investigate the state of intergalactic medium (IGM) in the Cosmic Dawn (CD) and Epoch of Reionization(EoR). In our previous work (Shimabukuro et al 2015), we studied the variance and skewness to give a clear interpretation of 21cm power spectrum and found that skewness is a good indicator of the epoch when X-ray heating becomes effective. Thus, the non-Gaussian feature of the spatial distribution of the 21cm signal is expected to be useful to investigate the astrophysical effects in the CD and EoR. In this paper, in order to investigate such a non-…
We present the first application of the isosceles bispectrum to MCMC parameter inference from the cosmic 21-cm signal. We extend the MCMC sampler 21cmMC to use the fast bispectrum code, BiFFT, when computing the likelihood. We create mock 1000h observations with SKA1-low, using PyObs21 to account for uv-sampling and thermal noise. Assuming the spin temperature is much higher than that of the CMB, we consider two different reionization histories for our mock observations: fiducial and late-reionization. For both models we find that bias on the inferred parameter means and 1-$σ$ credible interva…
We study the spherically averaged bispectrum of the 21-cm signal from the Epoch of Reionization (EoR). This metric provides a quantitative measurement of the level of non-Gaussianity of the signal which is expected to be high. We focus on the impact of the light-cone effect on the bispectrum and its detectability with the future SKA-Low telescope. Our investigation is based on a single reionization light-cone model and an ensemble of 50 realisations of the 21-cm signal to estimate the cosmic variance errors. We calculate the bispectrum with a new, optimised direct estimation method, DviSukta w…
Measurements of the post-reionization 21-cm bispectrum $B_{\rm HI}(\mathbf{k_1},\mathbf{k_2},\mathbf{k_3})$ using various upcoming intensity mapping experiments hold the potential for determining the cosmological parameters at a high level of precision. In this paper we have estimated the 21-cm bispectrum in the $z$ range $1 \le z \le 6$ using semi-numerical simulations of the neutral hydrogen (${\rm HI}$) distribution. We determine the $k$ and $z$ range where the 21-cm bispectrum can be adequately modelled using the predictions of second order perturbation theory, and we use this to predict t…
The 21cm line brightness temperature brings rich information about Epoch of Reionizaton (EoR) and high-$z$ universe (Cosmic Dawn and Dark Age). While the power spectrum is a useful tool to investigate the EoR signal statistically, higher-order statistics such as bispectrum are also valuable because the EoR signal is expected to be highly non-Gaussian. In this paper, we develop a formalism to calculate the bispectrum contributed from the thermal noise taking array configularion of telescopes into account, by extending a formalism for the power spectrum \cite{2006ApJ...653..815M}. We apply our f…
We calculate the cosmic microwave background (CMB) bispectrum due to inhomogeneous reionization. We calculate all the terms that can contribute to the bispectrum that are products of first order terms on all scales in conformal Newtonian gauge. We also correctly account for the de-correlation between the matter density and initial conditions using perturbation theory up to third order. We find that the bispectrum is of local type as expected. For a reasonable model of reionization, in which the Universe is completely ionized by redshift z_{ri} ~ 8 with optical depth to the last scattering surf…
Redshift-space 21-cm bispectrum multipoles as an SKA-era gravity test in the post-reionization Universe
Indian Statistical Institute（印度统计研究所）；McGill University（麦吉尔大学）；Ciela—Montreal Institute for Astrophysical Data Analysis and Machine Learning（Ciela-蒙特利尔天体物理数据分析与机器学习研究所）
We compute the bispectra of the 21cm signal during the Epoch of Reionization for three different reionization scenarios that are based on a dark matter N-body simulation combined with a self-consistent, semi-numerical model of galaxy evolution and reionization. Our reionization scenarios differ in their trends of ionizing escape fractions ($f_\mathrm{esc}$) with the underlying galaxy properties and cover the physically plausible range, i.e. $f_\mathrm{esc}$ effectively decreasing, being constant, or increasing with halo mass. We find the 21cm bispectrum to be sensitive to the resulting ionizat…
The bispectrum can quantify the non-Gussianity present in the redshifted 21-cm signal produced by the neutral hydrogen (HI) during the epoch of reionization (EoR). Motivated by this, we perform a comprehensive study of the EoR 21-cm bispectrum using simulated signals. Given a model of reionization, we demonstrate the behaviour of the bispectrum for all unique triangles in $k$ space. For ease of identification of the unique triangles, we parametrize the $k$-triangle space with two parameters, namely the ratio of the two arms of the triangle ($n=k_2/k_1$) and the cosine of the angle between them…
The high-redshift 21 cm signal from the Epoch of Reionization (EoR) is a promising observational probe of the early universe. Current- and next-generation radio interferometers such as the Hydrogen Epoch of Reionization Array (HERA) and Square Kilometre Array (SKA) are projected to measure the 21 cm auto power spectrum from the EoR. Another observational signal of this era is the kinetic Sunyaev-Zel'dovich (kSZ) signal in the cosmic microwave background (CMB), which will be observed by the upcoming Simons Observatory (SO) and CMB-S4 experiments. The 21 cm signal and the contribution to the kSZ…
[Abridged] This PhD thesis was defended in September 2013 at Université Paris-Sud, France. It studies the non-Gaussianity (NG) of extragalactic foregrounds to the Cosmic Microwave Background (CMB). This is particularly important for the analysis of CMB data from the Planck satellite, in which I was involved. I studied in particular the extragalactic foregrounds tracing the Large Scale Structure (LSS) of the universe : radio and infrared point-sources and the thermal Sunyaev-Zel'dovich effect (tSZ). The motivations and summary of this thesis cannot be shortened into the length constraints of th…
Radio interferometric experiments aim to constrain the reionization model parameters by measuring the 21-cm signal statistics, primarily the power spectrum. However the Epoch of Reionization (EoR) 21-cm signal is highly non-Gaussian, and this non-Gaussianity encodes important information about this era. The bispectrum is the lowest order statistic able to capture this inherent non-Gaussianity. Here we are the first to demonstrate that bispectra for large and intermediate length scales and for all unique $k$-triangle shapes provide tighter constraints on the EoR parameters compared to the power…
We apply the Correlated Component Analysis (CCA) method on simulated data of the Square Kilometre Array, with the aim of accurately cleaning the 21 cm reionization signal from diffuse foreground contamination. The CCA has been developed for the Cosmic Microwave Background, but the application of the Fourier-domain implementation of this method to the reionization signal is straightforward. The CCA is a parametric method to estimate the frequency behaviour of the foregrounds from the data by using second-order statistics. We test its performance on foreground simulations of increasing complexit…
Understanding the properties of the galactic emission at millimetre wavelengths is important for studies of the cosmic microwave background (CMB). In this work we explore the bispectrum, the harmonic equivalent of the three point function, from galactic dust and synchrotron emission. We investigate these effects across a broad range of frequencies using the synchrotron dominated S-band Polarization All Sky Survey (SPASS) maps at 2.3 GHz, the Planck satellite maps (30-857 GHz) and dust dominated Infrared Astronomical Satellite (IRAS) maps at 3 THz. We measure bispectra of total intensity fields…
The epoch of reionization (EoR) 21-cm signal is expected to be highly non-Gaussian in nature and this non-Gaussianity is also expected to evolve with the progressing state of reionization. Therefore the signal will be correlated between different Fourier modes ($k$). The power spectrum will not be able capture this correlation in the signal. We use a higher-order estimator -- the bispectrum -- to quantify this evolving non-Gaussianity. We study the bispectrum using an ensemble of simulated 21-cm signal and with a large variety of $k$ triangles. We observe two competing sources driving the non-…
The bispectrum is a 3-point statistic with the potential to provide additional information beyond power spectra analyses of survey datasets. Radio telescopes which broadly survey the 21cm emission from neutral hydrogen (HI) are a promising way to probe LSS and in this work we present an investigation into the HI intensity mapping (IM) bispectrum using simulations. We present a model of the redshift space HI IM bispectrum including observational effects from the radio telescope beam and 21cm foreground contamination. We validate our modelling prescriptions with measurements from robust IM simul…
It is seen that foregrounds of 21cm Epoch of Reionization experiments, which are expected to have smooth spectral dependence, are dominant in a wedge shaped region of the Fourier space called as Foreground Wedge. A possible way forward to isolate the 21cm Epoch of Reionization (EoR) signal from the much larger foreground component is to focus on the remaining portion of the Fourier space called as the EoR window. There are in-fact three distinct regions in the Fourier space, (i) the Foreground wedge portion, (ii) the EoR window region which lies beyond Horizon wedge and (iii) the region in bet…
The amplitude of redshifted 21 cm fluctuations during the Epoch of Reionization (EoR) is expected to show a distinctive "rise and fall" behavior with decreasing redshift as reionization proceeds. On large scales (k <~ 0.1 Mpc^{-1}) this can mostly be characterized by evolution in the product of the mean 21 cm brightness temperature and a bias factor, b_21(z). This quantity evolves in a distinctive way that can help in determining the average ionization history of the intergalactic medium (IGM) from upcoming 21 cm fluctuation data sets. Here we consider extracting <T_21> b_21(z) using a combina…
Cosmic baryon evolution during the Cosmic Dawn and Reionization results in redshifted 21-cm spectral distortions in the cosmic microwave background (CMB). These encode information about the nature and timing of first sources over redshifts 30-6 and appear at meter wavelengths as a tiny CMB distortion along with the Galactic and extragalactic radio sky, which is orders of magnitude brighter. Therefore, detection requires precise methods to model foregrounds. We present a method of foreground fitting using maximally smooth (MS) functions. We demonstrate the usefulness of MS functions over tradit…
It is well-known that foreground subtraction in 21cm surveys removes large scale power. We investigate associated systematic biases. We show that removing line-of-sight fluctuations on large scales aliases into suppression of the 3D power spectrum across a broad range of scales. This bias can be eliminated by marginalizing over small k in the 1D power spectrum; however, the unbiased estimator will have unavoidably larger variance. We also show that Gaussian realizations of the power spectrum permit accurate and extremely rapid Monte-Carlo simulations for error analysis; repeated realizations o…
A possible way to disentangle the redshifted 21 cm signal of neutral hydrogen (HI) in the Epoch of Reionization (EoR) from the much larger astrophysical foregrounds is to restrict the analysis to a wedge-shaped region in the Fourier space. The foregrounds are confined to this wedge because of their smooth spectral properties which allows one to estimate the HI power spectrum in the foreground-free portion, known as the reionization window. The estimate of the spherically averaged power spectrum in the window, however, differs from the true value because of the line of sight anisotropies in the…
The nature of dark matter sets the timeline for the formation of first collapsed halos and thus affects the sources of reionization. Here, we consider two different models of dark matter: cold dark matter (CDM) and thermal warm dark matter (WDM), and study how they impact the epoch of reionization (EoR) and its 21-cm observables. Using a suite of simulations, we find that in the WDM scenarios, the structure formation on small scales gets suppressed resulting in a smaller number of low mass dark matter halos compared to the CDM scenario. Assuming that the efficiency of sources in producing ioni…
The intensity mapping of Ly-alpha emission during the epoch of reionization (EoR) will be contaminated by foreground emission lines from lower redshifts. We calculate the mean intensity and power spectrum of Ly-alpha emission at z~7, and estimate the uncertainties according to the relevant astrophysical processes. We find that the low-redshift emission lines from 6563 A H-alpha, 5007 A [OIII] and 3727 A [OII] will be the strong contaminants on the observed Ly-alpha power spectrum. We make use of both the star formation rate (SFR) and luminosity functions (LF) to estimate the mean intensity and…
Cross-correlation between the redshifted 21 cm signal and Lyman-α emitters (LAEs) is powerful tool to probe the Epoch of Reionization (EoR). Although the cross-power spectrum (PS) has an advantage of not correlating with foregrounds much brighter than the 21 cm signal, the galactic and extra-galactic foregrounds prevent detection since they contribute to the variance of the cross PS. Therefore, strategies for mitigating foregrounds are required. In this work, we study the impact of foreground avoidance on the measurement of the 21 cm-LAE cross-correlation. We then simulate the 21 cm observatio…
Many low-frequency radio interferometers are aiming to detect very faint spectral signatures from structures at cosmological redshifts, particularly of neutral Hydrogen using its characteristic 21 cm spectral line. Due to the very high dynamic range needed to isolate these faint spectral fluctuations from the very bright foregrounds, spectral systematics from the instrument or the analysis, rather than thermal noise, are currently limiting their sensitivity. Failure to achieve a spectral calibration with fractional inaccuracy $\lesssim 10^{-5}$ will make the detection of the critical cosmic si…
We present a measurement of the angular bispectrum of the millimeter-wave sky in observing bands centered at roughly 95, 150, and 220 GHz, on angular scales of $1^\prime \lesssim θ\lesssim 10^\prime$ (multipole number $1000 \lesssim l \lesssim 10000$). At these frequencies and angular scales, the main contributions to the bispectrum are expected to be the thermal Sunyaev-Zel'dovich (tSZ) effect and emission from extragalactic sources, predominantly dusty, star-forming galaxies (DSFGs) and active galactic nuclei. We measure the bispectrum in 800 $\mathrm{deg}^2$ of three-band South Pole Telesco…
The 21-cm signal from the epoch of reionization is non-Gaussian. Current radio telescopes are focused on detecting the 21-cm power spectrum, but in the future the Square Kilometre Array is anticipated to provide a first measurement of the bispectrum. Previous studies have shown that the position-dependent power spectrum is a simple and efficient way to probe the squeezed-limit bispectrum. In this approach, the survey is divided into subvolumes and the correlation between the local power spectrum and the corresponding mean density of the subvolume is computed. This correlation is equivalent to …
We explore possibility of using the three dimensional bispectra of the Ly-alpha forest and the redshifted 21-cm signal from the post-reionization epoch to constrain primordial non-Gaussianity. Both these fields map out the large scale distribution of neutral hydrogen and maybe treated as tracers of the underlying dark matter field. We first present the general formalism for the auto and cross bispectrum of two arbitrary three dimensional biased tracers and then apply it to the specific case. We have modeled the 3D Ly-alpha transmitted flux field as a continuous tracer sampled along 1D skewers …
A detection of the predicted anticorrelation between 21cm and either Ly-alpha or H-alpha from the Epoch of Reionization (EOR) would be a powerful probe of the first galaxies. While 3D intensity maps isolate foregrounds in low k_\parallel modes, infrared surveys cannot yet match the field of view and redshift resolution of radio intensity mapping experiments. In contrast, 2D (i.e., broad band) infrared intensity maps can be measured with current experiments and are limited by foregrounds instead of photon or thermal noise. We show 2D experiments can measure most of the 3D fluctuation power at k…
Predictions for the ability of 21-cm interferometric experiments to discriminate Epoch of Reionization (EoR) signal models are typically limited by the simplicity of data models, whereby foreground signals and characteristics of the instrument are often simplified or neglected.To move towards more realistic scenarios, we explore the effects of applying more realistic foreground and instrument models to the 21cm signal, and the ability to estimate astrophysical parameters with these additional complexities. We use a highly-optimized version of \textsc{21cmFAST}, integrated into \textsc{21cmMC},…
The GMRT Epoch of Reionization (EoR) experiment is an ongoing effort to measure the power spectrum from neutral hydrogen at high redshift. We have previously reported an upper limit of (70 mK)^2 at wavenumbers of k=0.65 h/Mpc using a basic piecewise-linear foreground subtraction. In this paper we explore the use of a singular value decomposition to remove foregrounds with fewer assumptions about the foreground structure. Using this method we also quantify, for the first time, the signal loss due to the foreground filter and present new power spectra adjusted for this loss, providing a revised …
The Squeezed Bispectrum from CHIME HI Emission and Planck CMB Lensing: Current Sensitivity and Forecasts
McGill University（麦吉尔大学）；Arizona State University（亚利桑那州立大学）；University of British Columbia（不列颠哥伦比亚大学）；National Research Council Canada（加拿大国家研究委员会）；Massachusetts Institute of Technology（麻省理工学院）
A proposed method for dealing with foreground emission in upcoming 21-cm observations from the epoch of reionization is to limit observations to an uncontaminated window in Fourier space. Foreground emission can be avoided in this way, since it is limited to a wedge-shaped region in $k_{\parallel}, k_{\perp}$ space. However, the power spectrum is anisotropic owing to redshift-space distortions from peculiar velocities. Consequently, the 21-cm power spectrum measured in the foreground avoidance window---which samples only a limited range of angles close to the line-of-sight direction---differs …
We perform a Fisher analysis to estimate the expected constraints on the Epoch of Reionization (EoR) model parameters (i.e., minimum virial temperature, the ionizing efficiency and the mean free path of ionizing photons) taking into account the thermal noise of the exisitting telescopes, MWA and LOFAR. We consider how the inclusion of the 21cm bispectrum improves the constraints compared to using the power spectrum alone. Assuming that we perfectly remove the foreground, we found that the bispectrum, which is calculated by the 21cmFAST code, can constrain the EoR model parameters more tightly …
The power spectrum of redshifted 21 cm emission brightness temperature fluctuations is a powerful probe of the Epoch of Reionization (EoR). However, bright foreground emission presents a significant impediment to its unbiased recovery from interferometric data. We build on the Bayesian power spectral estimation methodology introduced in Sims et al. 2016 and demonstrate that incorporating a priori knowledge of the spectral structure of foregrounds in the large spectral scale component of the data model enables significantly improved modelling of the foregrounds without increasing the model comp…
We present a sophisticated statistical point-source foreground model for low-frequency radio Epoch of Reionization (EoR) experiments using the 21 cm neutral hydrogen emission line. Motivated by our understanding of the low-frequency radio sky, we enhance the realism of two model components compared with existing models: the source count distributions as a function of flux density and spatial position (source clustering), extending current formalisms for the foreground covariance of 2D power spectral modes in 21 cm EoR experiments. The former we generalise to an arbitrarily broken power-law, an…
We show how cross-correlating a high redshift external tracer field, such as the 21cm neutral hydrogen distribution and product maps involving Cosmic Microwave Background (CMB) temperature and polarisation fields, that probe mixed bispectrum involving these fields, can help to determine the reionization history of the Universe, beyond what can be achieved from cross-spectrum analysis. Taking clues from recent studies for the detection of primordial non-Gaussianity (Munshi & Heavens 2010), we develop a set of estimators that can study reionization using a power spectrum associated with the bisp…
An obstacle to the detection of redshifted 21cm emission from the epoch of reionization (EoR) is the presence of foregrounds which exceed the cosmological signal in intensity by orders of magnitude. We argue that in principle it would be better to fit the foregrounds non-parametrically - allowing the data to determine their shape - rather than selecting some functional form in advance and then fitting its parameters. Non-parametric fits often suffer from other problems, however. We discuss these before suggesting a non-parametric method, Wp smoothing, which seems to avoid some of them. After o…
We use the binned bispectrum estimator to determine the bispectra of the dust, free-free, synchrotron, and AME galactic foregrounds using maps produced by the Commander component separation method from Planck 2015 data. We find that all of these peak in the squeezed configuration, allowing for potential confusion with in particular the local primordial shape. Applying an additional functionality implemented in the binned bispectrum estimator code, we then use these galactic bispectra as templates in an $f_\mathrm{NL}$ analysis of other maps. After testing and validating the method and code wit…
Experiments aimed at detecting highly-redshifted 21 centimeter emission from the Epoch of Reionization (EoR) are plagued by the contamination of foreground emission. A potentially important source of contaminating foregrounds may be Faraday-rotated, polarized emission, which leaks into the estimate of the intrinsically unpolarized EoR signal. While these foregrounds' intrinsic polarization may not be problematic, the spectral structure introduced by the Faraday rotation could be. To better understand and characterize these effects, we present a simulation of the polarized sky between 120 and 1…
The cosmic microwave background (CMB) temperature bispectrum is currently the most precise tool for constraining primordial non-Gaussianity (NG). The Planck temperature data tightly constrain the amplitude of local-type NG: $f_{\rm NL}^{\rm loc} = 2.5 \pm 5.7$. Here, we compute previously-neglected foreground biases in temperature-based $f_{\rm NL}^{\rm loc}$ measurements, due to the integrated Sachs-Wolfe (ISW) effect, gravitational lensing, the thermal and kinematic Sunyaev-Zel'dovich effects, and the cosmic infrared background. While standard analyses already subtract a significant bias on …
Observations of the 21-centimetre line of atomic hydrogen in the early Universe directly probe the history of the reionization of the gas between galaxies. The observations are challenging, though, because of the low expected signal strength (~10 mK), and contamination by strong (>100 K) foreground synchrotron emission in the Milky Way and extragalactic continuum sources2. If reionization happened rapidly, there should be a characteristic signature visible against the smooth foreground in an all-sky spectrum. Here we report an all-sky spectrum between 100 and 200 MHz, corresponding to the reds…
We apply two methods to estimate the 21~cm bispectrum from data taken within the Epoch of Reionisation (EoR) project of the Murchison Widefield Array (MWA). Using data acquired with the Phase II compact array allows a direct bispectrum estimate to be undertaken on the multiple redundantly-spaced triangles of antenna tiles, as well as an estimate based on data gridded to the $uv$-plane. The direct and gridded bispectrum estimators are applied to 21 hours of high-band (167--197~MHz; $z$=6.2--7.5) data from the 2016 and 2017 observing seasons. Analytic predictions for the bispectrum bias and vari…
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 …
Observations of the 21cm Epoch of Reionization (EoR) signal are dominated by Galactic and extragalactic foregrounds. The need for foreground removal has led to the development of two main techniques, often referred to as "foreground avoidance" and "foreground subtraction." Avoidance is associated with filtering foregrounds in Fourier space, while subtraction uses an explicit foreground model that is removed. Using 1088 hours of data from the 64-element PAPER array, we demonstrate that subtraction of a foreground model prior to delay-space foreground filtering results in a modest but measurable…
Intensity mapping of the HI 21 cm line and the CO 2.61 mm line from the epoch of reionization has emerged as powerful, complementary, probes of the high-redshift Universe. However, both maps and their cross-correlation are dominated by foregrounds. We propose a new analysis by which the signal is unbiased by foregrounds, i.e. it can be measured without foreground mitigation. We construct the antisymmetric part of the HI-CO cross-correlation, arising because the statistical fluctuations of two fields have different evolution in time. We show that the sign of this new signal can distinguish mode…
Characterizing the epoch of reionization (EoR) at $z\gtrsim 6$ via the redshifted 21 cm line of neutral Hydrogen (HI) is critical to modern astrophysics and cosmology, and thus a key science goal of many current and planned low-frequency radio telescopes. The primary challenge to detecting this signal is the overwhelmingly bright foreground emission at these frequencies, placing stringent requirements on the knowledge of the instruments and inaccuracies in analyses. Results from these experiments have largely been limited not by thermal sensitivity but by systematics, particularly caused by th…
The detection of the redshifted cosmological $21$~cm line signal requires the removal of the Galactic and extragalactic foreground emission, which is orders of magnitude brighter anywhere in the sky. Foreground cleaning methods currently used are efficient in removing spectrally smooth components. However, they struggle in the presence of not spectrally smooth contamination that is, therefore, potentially the most dangerous one. An example of this is the polarized synchrotron emission, which is Faraday rotated by the interstellar medium and leaks into total intensity due to instrumental imperf…
Observing the neutral hydrogen distribution across the Universe via redshifted 21cm line intensity mapping constitutes a powerful probe for cosmology. However, the redshifted 21cm signal is obscured by the foreground emission from our Galaxy and other extragalactic foregrounds. This paper addresses the capabilities of the BINGO survey to separate such signals. Specifically, this paper looks in detail at the different residuals left over by foreground components, shows that a noise-corrected spectrum is unbiased, and shows that we understand the remaining systematic residuals by analyzing nonze…
A number of current and future experiments aim to detect the reionization of neutral hydrogen by the first stars and galaxies in the Universe via the redshifted 21cm line. Using the \textsc{BlueTides} simulation, we investigate the measurement of an \textit{average} ionised region towards the beginning of reionization by stacking redshifted 21cm images around optically identified bright galaxies using mock observations. We find that with an SKA 1000 hour observation, assuming perfect foreground subtraction, a $5σ$ detection of a stacked HII region can be made with 30 images around some of the …
A critical challenge in measuring the power spectrum of 21cm emission from cosmic reionization is compensating for the frequency dependence of an interferometer's sampling pattern, which can cause smooth-spectrum foregrounds to appear unsmooth and degrade the separation between foregrounds and the target signal. In this paper, we present an approach to foreground removal that explicitly accounts for this frequency dependence. We apply the delay transformation introduced in Parsons & Backer (2009) to each baseline of an interferometer to concentrate smooth-spectrum foregrounds within the bounds…
Unaccounted for systematics from foregrounds and instruments can severely limit the sensitivity of current experiments from detecting redshifted 21~cm signals from the Epoch of Reionization (EoR). Upcoming experiments are faced with a challenge to deliver more collecting area per antenna element without degrading the data with systematics. This paper and its companions show that dishes are viable for achieving this balance using the Hydrogen Epoch of Reionization Array (HERA) as an example. Here, we specifically identify spectral systematics associated with the antenna power pattern as a signi…
We construct foreground simulations comprising spatially correlated extragalactic and diffuse Galactic emission components and calculate the `intrinsic' (instrument-free) two-dimensional spatial power spectrum and the cylindrically and spherically averaged three-dimensional k-space power spectra of the Epoch of Reionization (EoR) and our foreground simulations using a Bayesian power spectral estimation framework. This leads us to identify a model dependent region of optimal signal estimation for our foreground and EoR models, within which the spatial power in the EoR signal relative to foregro…
