Evolution of the angular power spectrum of scattered radiation from a point source upon propagation in a turbid medium

2004 ◽  
Vol 96 (5) ◽  
pp. 804-809 ◽  
Author(s):  
V. G. Gavrilenko ◽  
A. V. Sorokin ◽  
G. V. Jandieri ◽  
V. G. Jandieri
Keyword(s):  
Power Spectrum ◽  
Point Source ◽  
Scattered Radiation ◽  
Turbid Medium ◽  
Angular Power Spectrum

scholarly journals The angular power spectrum measurement of the Galactic synchrotron emission using the TGSS survey

2017 ◽  
Vol 12 (S333) ◽  
pp. 157-161
Author(s):  
Samir Choudhuri ◽  
Somnath Bharadwaj ◽  
Sk. Saiyad Ali ◽  
Nirupam Roy ◽  
H. T. Intema ◽  
...  
Keyword(s):  
Synchrotron Radiation ◽  
Power Spectrum ◽  
Point Source ◽  
Power Law ◽  
Point Sources ◽  
Synchrotron Emission ◽  
Angular Power Spectrum ◽  
Spectrum Measurement ◽  
Upper Limit ◽  
Sky Survey

AbstractCharacterizing the diffuse Galactic synchrotron emission (DGSE) at arcminute angular scales is needed to remove this foregrounds in cosmological 21-cm measurements. Here, we present the angular power spectrum (Cℓ) measurement of the diffuse Galactic synchrotron emission using two fields observed by the TIFR GMRT Sky Survey (TGSS). We apply 2D Tapered Gridded Estimator (TGE) to estimate the Cℓ from the visibilities. We find that the residual data after subtracting the point sources is likely dominated by the diffuse Galactic synchrotron radiation across the angular multipole range 240 ≤ ℓ ≲ 500. We fit a power law to the measured Cℓ over this ℓ range. We find that the slopes in both fields are consistent with earlier measurements. For the second field, however, we interpret the measured Cℓ as an upper limit for the DGSE as there is an indication of a significant residual point source contribution.

scholarly journals The CMB angular power spectrum via component separation: a study on Planck data

2019 ◽  
Vol 624 ◽  
pp. A67
Author(s):  
C. Umiltà ◽  
J. F. Cardoso ◽  
K. Benabed ◽  
M. Le Jeune
Keyword(s):  
Power Spectrum ◽  
Point Source ◽  
Cosmological Parameters ◽  
Point Sources ◽  
Blind Separation ◽  
Microwave Background ◽  
Angular Power Spectrum ◽  
Planck Data ◽  
Small Scales ◽  
Source Emission

Aims. We investigate the extent to which foreground-cleaned cosmic microwave background (CMB) maps can be used to estimate cosmological parameters at small scales. Methods. We use the SMICA method, a blind separation technique that works directly at the spectral level. In this work we focus on the small scales of the CMB angular power spectrum, which are chiefly affected by noise and extragalactic foregrounds, such as point sources. We adapt SMICA to use only cross-spectra between data maps, thus avoiding the noise bias. In this study, performed using both simulations and Planck 2015 data, we fit for extragalactic point sources by modelling them as shot noise of two independent populations. Results. In simulations, we correctly recover the point-source emission law, and obtain a CMB angular power spectrum that has an average foreground residual of one fifth of the CMB power at ℓ ≥ 2200. With Planck data, the recovered point-source emission law corresponds to external estimates, with some offsets at the highest and lowest frequencies, possibly due to frequency decoherence of point sources. The CMB angular power spectrum residuals are consistent with what we find in simulations. The cosmological parameters obtained from the simulations and the data show offsets up to 1σ on average from their expected values. Biases on cosmological parameters in simulations represent the expected level of bias in Planck data. Conclusions. The results on cosmological parameters depend on the detail of the foreground residual contamination in the spectrum, and therefore a tailored modelling of the likelihood foreground model is required.

ON THE LINEAR FILTERS FOR POINT SOURCE EXTRACTION OF THE PLANCK MISSION

2005 ◽  
Vol 14 (07) ◽  
pp. 1251-1272
Author(s):  
LUNG-YIH CHIANG ◽  
PAVEL D. NASELSKY ◽  
IGOR D. NOVIKOV
Keyword(s):  
Power Spectrum ◽  
Point Source ◽  
A Priori ◽  
Point Sources ◽  
Noise Power ◽  
Linear Filters ◽  
Angular Power Spectrum ◽  
Beam Shape ◽  
Compact Source ◽  
Source Extraction

The manifestation of point sources in the upcoming Planck maps is a direct reflection of the properties of the pixelized antenna beam shape for each frequency, which is related to the scan strategy, pointing accuracy, noise properties and map-making algorithm. In this paper we firstly compare analytically two filters for the Planck point source extraction, namely, the adaptive top-hat filter (ATHF) and the theoretically-optimal filter (TOF). Our analyses are based on the premise that the required experiment parameters of the TOF are assumed to be already known: the CMB and noise power spectrum and a circular Gaussian beam shape and size. Whereas, the ATHF does not need any a priori knowledge. The analyses show that the TOF is optimal in terms of the gain after the parameter inputs. We simulate the Planck HFI 100 GHz channel with elliptical beam in rotation to test the efficiency of the TOF and the ATHF. We also apply the ATHF on the WMAP Q-band map and the derived map (the foreground-cleaned map by Tegmark, de Oliveira Costa & Hamilton) from the WMAP one-year data. The uncertainties on the angular power spectrum will hamper the efficiency of the TOF. The ATHF is computationally efficient in tackling more realistic data such as the following effects: an elliptical beam with slow precession and the change of the beam ellipticity ratio due to possible mirror degradation. The ATHF is well suited for the construction of the Planck Early Release Compact Source Catalogue.

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

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.

scholarly journals Statistical modelling of the cosmological dispersion measure

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.

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

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.

scholarly journals Validating a novel angular power spectrum estimator using simulated low frequency radio-interferometric data

New Astronomy ◽  
2017 ◽  
Vol 57 ◽  
pp. 94-103 ◽  
Author(s):  
Samir Choudhuri ◽  
Nirupam Roy ◽  
Somnath Bharadwaj ◽  
Sk. Saiyad Ali ◽  
Abhik Ghosh ◽  
...  
Keyword(s):  
Power Spectrum ◽  
Low Frequency ◽  
Angular Power Spectrum

scholarly journals Improved Diffuse Foreground Subtraction with the ILC Method: CMB Map and Angular Power Spectrum UsingPlanckandWMAPObservations

2017 ◽  
Vol 842 (1) ◽  
pp. 62 ◽  
Author(s):  
Vipin Sudevan ◽  
Pavan K. Aluri ◽  
Sarvesh Kumar Yadav ◽  
Rajib Saha ◽  
Tarun Souradeep
Keyword(s):  
Power Spectrum ◽  
Angular Power Spectrum
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