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.

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Demonstrating the Tapered Gridded Estimator (TGE) for the Cosmological HI 21-cm Power Spectrum using 150 MHz GMRT observations

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3831 ◽

2020 ◽

Author(s):

Srijita Pal ◽

Somnath Bharadwaj ◽

Abhik Ghosh ◽

Samir Choudhuri

Keyword(s):

Power Spectrum ◽

Unbiased Estimate ◽

Power Spectra ◽

Neutral Hydrogen ◽

Statistical Error ◽

Temperature Fluctuations ◽

Radio Frequency Interference ◽

Rectangular Region ◽

Angular Power Spectrum ◽

The Mean

Abstract We apply the Tapered Gridded Estimator (TGE) for estimating the cosmological 21-cm power spectrum from 150 MHz GMRT observations which corresponds to the neutral hydrogen (HI) at redshift z = 8.28. Here TGE is used to measure the Multi-frequency Angular Power Spectrum (MAPS) Cℓ(Δν) first, from which we estimate the 21-cm power spectrum P(k⊥, k∥). The data here are much too small for a detection, and the aim is to demonstrate the capabilities of the estimator. We find that the estimated power spectrum is consistent with the expected foreground and noise behaviour. This demonstrates that this estimator correctly estimates the noise bias and subtracts this out to yield an unbiased estimate of the power spectrum. More than $47\%$ of the frequency channels had to be discarded from the data owing to radio-frequency interference, however the estimated power spectrum does not show any artifacts due to missing channels. Finally, we show that it is possible to suppress the foreground contribution by tapering the sky response at large angular separations from the phase center. We combine the k modes within a rectangular region in the ‘EoR window’ to obtain the spherically binned averaged dimensionless power spectra Δ2(k) along with the statistical error σ associated with the measured Δ2(k). The lowest k-bin yields Δ2(k) = (61.47)2 K2 at k = 1.59 Mpc−1, with σ = (27.40)2 K2. We obtain a 2 σ upper limit of (72.66)2 K2 on the mean squared HI 21-cm brightness temperature fluctuations at k = 1.59 Mpc−1.

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21-cm power spectrum and ionization bias as a probe of long-mode modulated non-Gaussian sky

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz2037 ◽

2019 ◽

Vol 488 (4) ◽

pp. 5941-5951

Author(s):

Shahram Khosravi ◽

Amirabbas Ghazizadeh ◽

Shant Baghram

Keyword(s):

Power Spectrum ◽

Background Radiation ◽

Neutral Hydrogen ◽

Hydrogen Distribution ◽

Microwave Background ◽

Power Asymmetry ◽

Angular Power Spectrum ◽

Long Wavelength ◽

Microwave Background Radiation ◽

Non Gaussian

ABSTRACT The observed hemispherical power asymmetry in cosmic microwave background radiation can be explained by long-wavelength mode (long-mode) modulation. In this paper, we study the possibility of detecting this effect in the angular power spectrum of the 21-cm brightness temperature. For this task, we study the effect of the neutral hydrogen distribution on the angular power spectrum. This is done by formulating the bias parameter of the ionized fraction to the underlying matter distribution. We also discuss the possibility that the long-mode modulation is accompanied by a primordial non-Gaussianity of local type. In this case, we obtain the angular power spectrum with two effects of primordial non-Gaussianity and long-mode modulation. Finally, we show that the primordial non-Gaussianity enhances the long-mode modulated power of the 21-cm signal via the non-Gaussian scale-dependent bias up to four orders of magnitude. Accordingly, observations of the 21-cm signal with upcoming surveys, such as the Square Kilometer Array (SKA), will probably be capable of detecting hemispherical power asymmetry in the context of long-mode modulation.

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A decadal cirrus clouds climatology from ground-based and spaceborne lidars above the south of France (43.9° N–5.7° E)

Atmospheric Chemistry and Physics ◽

10.5194/acp-13-6951-2013 ◽

2013 ◽

Vol 13 (14) ◽

pp. 6951-6963 ◽

Cited By ~ 19

Author(s):

C. Hoareau ◽

P. Keckhut ◽

V. Noel ◽

H. Chepfer ◽

J.-L. Baray

Keyword(s):

Observation Time ◽

Cirrus Clouds ◽

Cirrus Cloud ◽

Upper Troposphere ◽

Cloud Parameters ◽

Cloud Properties ◽

Total Observation Time ◽

The Mean ◽

Ground Based Lidar ◽

Total Observation

Abstract. This study provides an analysis of cirrus cloud properties at midlatitude in the southern part of France from ground-based and spaceborne lidars. A climatology of cirrus cloud properties and their evolution over more than 12 yr is presented and compared to other mid-latitude climatological studies. Cirrus clouds occur ~37% of the total observation time and remain quasi-constant across seasons with a variation within ~5% around the mean occurrence. Similar results are obtained from CALIOP and the ground-based lidar, with a mean difference in occurrence of ~5% between both instruments. From the ground-based lidar data, a slight decrease in occurrence of ~3% per decade is observed but found statistically insignificant. Based on a clustering analysis of cirrus cloud parameters, three distinct classes have been identified and investigations concerning their origin are discussed. Properties of these different classes are analysed, showing that thin cirrus in the upper troposphere represent ~50% of cloud cover detected in summer and fall, decreasing by 15–20% for other seasons.

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Spherically Restricted Random Hyperbolic Diffusion

Entropy ◽

10.3390/e22020217 ◽

2020 ◽

Vol 22 (2) ◽

pp. 217 ◽

Cited By ~ 2

Author(s):

Philip Broadbridge ◽

Alexander Kolesnik ◽

Nikolai Leonenko ◽

Andriy Olenko ◽

Dareen Omari

Keyword(s):

Power Spectrum ◽

Random Fields ◽

Spectral Measure ◽

Convergence Rates ◽

Initial Conditions ◽

Angular Power Spectrum ◽

Numerical Studies ◽

Random Initial Conditions ◽

Mean Square Convergence ◽

The Mean

This paper investigates solutions of hyperbolic diffusion equations in R 3 with random initial conditions. The solutions are given as spatial-temporal random fields. Their restrictions to the unit sphere S 2 are studied. All assumptions are formulated in terms of the angular power spectrum or the spectral measure of the random initial conditions. Approximations to the exact solutions are given. Upper bounds for the mean-square convergence rates of the approximation fields are obtained. The smoothness properties of the exact solution and its approximation are also investigated. It is demonstrated that the Hölder-type continuity of the solution depends on the decay of the angular power spectrum. Conditions on the spectral measure of initial conditions that guarantee short- or long-range dependence of the solutions are given. Numerical studies are presented to verify the theoretical findings.

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Detailed study of ELAIS N1 field with the uGMRT – II. Source properties and spectral variation of foreground power spectrum from 300–500 MHz observations

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz2533 ◽

2019 ◽

Vol 490 (1) ◽

pp. 243-259 ◽

Cited By ~ 6

Author(s):

Arnab Chakraborty ◽

Nirupam Roy ◽

Abhirup Datta ◽

Samir Choudhuri ◽

Kanan K Datta ◽

...

Keyword(s):

Power Spectrum ◽

Spectral Characteristics ◽

Low Frequency ◽

Neutral Hydrogen ◽

Galactic Nuclei ◽

Detailed Comparison ◽

Spectral Variation ◽

Angular Power Spectrum ◽

Star Forming ◽

First Time

ABSTRACT Understanding the low-frequency radio sky in depth is necessary to subtract foregrounds in order to detect the redshifted 21 cm signal of neutral hydrogen from the cosmic dawn, the epoch of reionization and the post-reionization era. In this second paper of the series, we present the upgraded Giant Metrewave Radio Telescope (uGMRT) observation of the ELAIS N1 field made at 300–500 MHz. The image covers an area of ∼1.8 deg2 and has a central background rms noise of ∼ 15 μJy beam−1. We present a radio source catalogue containing 2528 sources (with flux densities > 100 μJy) and normalized source counts derived from that. A detailed comparison of detected sources with previous radio observations is shown. We discuss flux-scale accuracy, positional offsets, spectral index distribution and correction factors in source counts. The normalized source counts are in agreement with previous observations of the same field, as well as model source counts from the Square Kilometre Array Design Study simulation. It shows a flattening below ∼1 mJy that corresponds to a rise in populations of star-forming galaxies and radio-quiet active galactic nuclei. For the first time, we estimate the spectral characteristics of the angular power spectrum or multi-frequency angular power spectrum of diffuse Galactic synchrotron emission over a wide frequency bandwidth of 300–500 MHz from radio interferometric observations. This work demonstrates the improved capabilities of the uGMRT.

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Combined lensed estimator to probe the post reionization H i power spectrum

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab2480 ◽

2021 ◽

Author(s):

Urvashi Arora ◽

Prasun Dutta

Keyword(s):

Power Spectrum ◽

Galaxy Clusters ◽

Galaxy Cluster ◽

Observation Time ◽

Statistical Distribution ◽

Nearby Galaxy ◽

Gravitational Lenses ◽

Total Observation Time ◽

Total Observation

Abstract In the post-reionization era, the baryons assembled into the protogalaxies and eventually the present population of the galaxies evolved through merger and evolution. In this work, we discuss a possible probe of the statistical distribution and evolution of the H i density in the post reionization era. We introduce an estimator of the H i power spectrum from the post reionization universe by observing it through the strong gravitational lenses by the nearby galaxy cluster. We also analytically calculate the uncertainties associated with the estimates of the post-EoR power spectrum for the discussed estimator. We access the efficacy of this estimator in the context of 19 galaxy clusters for which the lensing potential has been estimated earlier by various authors. We find that by combining the lensed power spectrum through eight of these cluster lenses, it is possible to estimate the post-reionization H i power spectrum at five-sigma significance for angular multipoles <4000 for a uGMRT observation of 16 MHz bandwidth from redshifts of 1.25, 1.5 with a total of 400 hours of observation. With the same setup, for a redshift of 3.0, we need 200 hours of total observation time. The estimator also suppresses the diffused galactic foreground, though, the latter is still a dominant contributor to the overall signal and hence need to be estimated and mitigated. We discuss the merits and demerits of the estimator.

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A decadal cirrus clouds climatology from ground-based and spaceborne lidars above south of France (43.9° N–5.7° E)

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-13-6379-2013 ◽

2013 ◽

Vol 13 (3) ◽

pp. 6379-6417 ◽

Cited By ~ 1

Author(s):

C. Hoareau ◽

P. Keckhut ◽

V. Noel ◽

H. Chepfer ◽

J.-L. Baray

Keyword(s):

Clustering Analysis ◽

Observation Time ◽

Cirrus Clouds ◽

Cirrus Cloud ◽

Upper Troposphere ◽

Cloud Parameters ◽

Total Observation Time ◽

The Mean ◽

Ground Based Lidar ◽

Total Observation

Abstract. This study provides an analysis of cirrus clouds properties at midlatitude in the southern part of France from ground-based and spaceborne lidars. A climatology of cirrus clouds properties and their evolution over more than 12 yr is presented and compared to other mid-latitude climatological studies. Cirrus clouds occur ~ 37% of the total observation time and remain quasi-constant across seasons with a variation within ~ 5% around the mean occurrence. Similar results are obtained from CALIOP and the ground-based lidar, with a mean difference in occurrence of ~ 5% between both instruments. From the ground-based lidar data, a slight decrease in occurrence of ~ 3% per decade is observed but found statistically insignificant. Based on a clustering analysis of cirrus cloud parameters, three distinct classes have been identified and investigations concerning their origin are discussed. Properties of these different classes are analysed, showing that thin cirrus in the upper troposphere represent ~ 50% of cloud cover detected in summer and fall, decreasing by 15–20% for other seasons.

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An Accurate Reconstruction of CMB E Mode Signal over Large Angular Scales using Prior Information of CMB Covariance Matrix in ILC Algorithm

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3935 ◽

2020 ◽

Author(s):

Ujjal Purkayastha ◽

Vipin Sudevan ◽

Rajib Saha

Keyword(s):

Power Spectrum ◽

Linear Combination ◽

Covariance Matrix ◽

Large Scale ◽

Prior Information ◽

Future Generation ◽

Temperature Anisotropy ◽

Satellite Mission ◽

Angular Power Spectrum ◽

Accurate Reconstruction

Abstract Recently, the internal-linear-combination (ILC) method was investigated extensively in the context of reconstruction of Cosmic Microwave Background (CMB) temperature anisotropy signal using observations obtained by WMAP and Planck satellite missions. In this article, we, for the first time, apply the ILC method to reconstruct the large scale CMB E mode polarization signal, which could probe the ionization history, using simulated observations of 15 frequency CMB polarization maps of future generation Cosmic Origin Explorer (COrE) satellite mission. We find that the clean power spectra, from the usual ILC, are strongly biased due to non zero CMB-foregrounds chance correlations. In order to address the issues of bias and errors we extend and improve the usual ILC method for CMB E mode reconstruction by incorporating prior information of theoretical E mode angular power spectrum while estimating the weights for linear combination of input maps (Sudevan & Saha 2018b). Using the E mode covariance matrix effectively suppresses the CMB-foreground chance correlation power leading to an accurate reconstruction of cleaned CMB E mode map and its angular power spectrum. We compare the performance of the usual ILC and the new method over large angular scales and show that the later produces significantly statistically improved results than the former. The new E mode CMB angular power spectrum contains neither any significant negative bias at the low multipoles nor any positive foreground bias at relatively higher mutlipoles. The error estimates of the cleaned spectrum agree very well with the cosmic variance induced error.

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Statistical modelling of the cosmological dispersion measure

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab170 ◽

2021 ◽

Vol 502 (2) ◽

pp. 2615-2629

Author(s):

Ryuichi Takahashi ◽

Kunihito Ioka ◽

Asuka Mori ◽

Koki Funahashi

Keyword(s):

Dark Matter ◽

Correlation Function ◽

Probability Distribution ◽

Power Spectrum ◽

Free Electron ◽

Statistical Modelling ◽

Dispersion Measure ◽

Host Galaxies ◽

Angular Power Spectrum ◽

Bias Factor

ABSTRACT We have investigated the basic statistics of the cosmological dispersion measure (DM)—such as its mean, variance, probability distribution, angular power spectrum, and correlation function—using the state-of-the-art hydrodynamic simulations, IllustrisTNG300, for the fast radio burst cosmology. To model the DM statistics, we first measured the free-electron abundance and the power spectrum of its spatial fluctuations. The free-electron power spectrum turns out to be consistent with the dark matter power spectrum at large scales, but it is strongly damped at small scales (≲ Mpc) owing to the stellar and active galactic nucleus feedback. The free-electron power spectrum is well modelled using a scale-dependent bias factor (the ratio of its fluctuation amplitude to that of the dark matter). We provide analytical fitting functions for the free-electron abundance and its bias factor. We next constructed mock sky maps of the DM by performing standard ray-tracing simulations with the TNG300 data. The DM statistics are calculated analytically from the fitting functions of the free-electron distribution, which agree well with the simulation results measured from the mock maps. We have also obtained the probability distribution of source redshift for a given DM, which helps in identifying the host galaxies of FRBs from the measured DMs. The angular two-point correlation function of the DM is described by a simple power law, $\xi (\theta) \approx 2400 (\theta /{\rm deg})^{-1} \, {\rm pc}^2 \, {\rm cm}^{-6}$, which we anticipate will be confirmed by future observations when thousands of FRBs are available.

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