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

Pal, Srijita; Bharadwaj, Somnath; Ghosh, A.; Choudhuri, Samir

doi:10.1093/mnras/staa3831

Cited by 15 publications

(7 citation statements)

References 65 publications

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“…Moreover, the antenna-based gains are functions of both time and frequency; the residual gain is expected to have correlated frequency dependence. Such frequency-correlated calibration errors couple the foreground power beyond the foreground wedge into the EoR window region of the 2-D power spectrum space (Barry et al 2016;Ewall-Wice et al 2017;Byrne et al 2019;Pal et al 2021). At present, we are working towards expanding the formalism presented in this paper to estimate bias and variance in power spectrum estimate when visibility correlation in different frequencies is considered.…”

Section: Discussionmentioning

confidence: 99%

Calibration requirements for Epoch of Reionization 21-cm signal observations -- II. Analytical estimation of the bias and variance with time-correlated residual gains

Kumar,

Dutta,

Choudhuri

et al. 2022

Preprint

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Observation of redshifted 21-cm signals from neutral hydrogen holds the key to understanding the structure formation and its evolution during the reionization and postreionization era. Apart from the presence of orders of magnitude larger foregrounds in the observed frequency range, the instrumental effects of the interferometers combined with the ionospheric effects present a considerable challenge in the extraction of 21-cm signals from strong foregrounds. The systematic effects of time and frequency correlated residual gain errors originating from the measurement process introduce a bias and enhance the variance of the power spectrum measurements. In this work, we study the effect of time-correlated residual gain errors in the presence of strong foreground. We present a method to produce analytic estimates of the bias and variance in the power spectrum. We use simulated observations to confirm the efficacy of this method and then use it to understand various effects of the gain errors. We find that as the standard deviation in the residual gain errors increases, the bias in the estimation supersedes the variance. It is observed that an optimal choice of the time over which the gain solutions are estimated minimizes the risk. We also find that the interferometers with higher baseline densities are preferred instruments for these studies.

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Section: Discussionmentioning

confidence: 99%

Calibration requirements for Epoch of Reionization 21-cm signal observations -- II. Analytical estimation of the bias and variance with time-correlated residual gains

Kumar,

Dutta,

Choudhuri

et al. 2022

Preprint

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“…Considering a fixed antenna pair, the baseline U is held fixed at the value corresponding to the central frequency 𝜈 𝑐 . The details of the visibility based TGE are given in Paper I (also Bharadwaj et al 2018 andPal et al 2021). Here we briefly summarize the salient features of the formalism, and extend it to consider the polarization.…”

Section: The Tge For Mapsmentioning

confidence: 99%

“…Bharadwaj et al (2018) further developed upon this to introduce a MAPS-based TGE which first estimates the MAPS, and, from it, the PS, effectively dealing with the missing frequency channels in the visibility data while preserving all the qualities mentioned above. Pal et al (2021) have used the MAPS-based TGE to estimate the MAPS and PS of the redshifted H signal from EoR using an 8 MHz GMRT data set observed at 153 MHz.…”

Section: Introductionmentioning

confidence: 99%

Towards $21$-cm intensity mapping at $z=2.28$ with uGMRT using the tapered gridded estimator II: Cross-polarization power spectrum

Elahi¹,

Bharadwaj²,

Ghosh³

et al. 2023

Preprint

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Neutral hydrogen (H ) 21-cm intensity mapping (IM) offers an efficient technique for mapping the large-scale structures in the universe. We introduce the 'Cross' Tapered Gridded Estimator (Cross TGE), which cross-correlates two cross-polarizations (RR and LL) to estimate the multi-frequency angular power spectrum (MAPS) 𝐶 ℓ (Δ𝜈). We expect this to mitigate several effects like noise bias, calibration errors etc., which affect the 'Total' TGE which combines the two polarizations. Here we apply the Cross TGE on a 24.4 MHz bandwidth uGMRT Band 3 data centred at 432.8 MHz aiming H IM at 𝑧 = 2.28. The measured 𝐶 ℓ (Δ𝜈) is modelled to yield maximum likelihood estimates of the foregrounds and the spherical power spectrum 𝑃(𝑘) in several 𝑘 bins. Considering the mean squared brightness temperature fluctuations, we report a 2𝜎 upper limit Δ 2 𝑈 𝐿 (𝑘) ≤ (58.67) 2 mK 2 at 𝑘 = 0.804 Mpc −1 which is a factor of 5.2 improvement on our previous estimate based on the Total TGE. Assuming that the H traces the underlying matter distribution, we have modelled 𝐶 ℓ (Δ𝜈) to simultaneously estimate the foregrounds and [Ω H 𝑏 H ] where Ω H and 𝑏 H are the H density and linear bias parameters respectively. We obtain a best fit value of [Ω H 𝑏 H ] 2 = 7.51 × 10 −4 ± 1.47 × 10 −3 which is consistent with noise. Although the 2𝜎 upper limit [Ω H 𝑏 H ] 𝑈 𝐿 ≤ 0.061 is ∼ 50 times larger than the expected value, this is a considerable improvement over earlier works at this redshift.

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“…A salient feature of this estimator is that it only uses the available data, and it is not necessary to make any assumption regarding the data values in the missing frequency channels. In a recent paper Pal et al (2021) (hereafter Paper II) have demonstrated the capabilities of the TGE by using the TGE to estimate 𝑃(𝑘 ⊥ , 𝑘 ) from a 150 MHz GMRT observational data where 47% of the frequency channels are flagged due to Radio Frequency Interference (RFI). They obtain a 2𝜎 upper limit of (72.66) 2 K 2 on the mean squared H 21-cm brightness temperature fluctuations at 𝑘 = 1.59 Mpc −1 .…”

Section: Introductionmentioning

confidence: 99%

Towards 21-cm intensity mapping at z = 2.28 with uGMRT using the tapered gridded estimator I: Foreground avoidance

Pal

Elahi

Bharadwaj

et al. 2022

Monthly Notices of the Royal Astronomical Society

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The post-reionization (z ≤ 6) neutral hydrogen (H i ) 21-cm intensity mapping signal holds the potential to probe the large scale structures, study the expansion history and constrain various cosmological parameters. Here we apply the Tapered Gridded Estimator (TGE) to estimate P(k⊥, k∥) the power spectrum of the z = 2.28 (432.8 MHz) redshifted 21-cm signal using a 24.4 MHz sub-band drawn from uGMRT Band 3 observations of European Large-Area ISO Survey-North 1 (ELAIS-N1). The TGE allows us to taper the sky response which suppresses the foreground contribution from sources in the periphery of the telescope’s field of view. We apply the TGE on the measured visibility data to estimate the multi-frequency angular power spectrum (MAPS) Cℓ(Δν) from which we determine P(k⊥, k∥) using maximum-likelihood which naturally overcomes the issue of missing frequency channels (55 % here). The entire methodology is validated using simulations. For the data, using the foreground avoidance technique, we obtain a 2 σ upper limit of Δ2(k) ≤ (133.97)2 mK2 for the 21-cm brightness temperature fluctuation at k = 0.347 Mpc−1. This corresponds to $[\Omega _{\rm H\, {\small I}~}b_{\rm H\, {\small I}~}] \le 0.23$, where $\Omega _{\rm H\, {\small I}~}$ and $b_{\rm H\, {\small I}~}$ respectively denote the cosmic H i mass density and the H i bias parameter. A previous work has analyzed 8 MHz of the same data at z = 2.19, and reported Δ2(k) ≤ (61.49)2 mK2 and $[\Omega _{\rm H\, {\small I}~} b_{\rm H\, {\small I}~}] \le 0.11$ at k = 1 Mpc−1. The upper limits presented here are still orders of magnitude larger than the expected signal corresponding to $\Omega _{\rm H\, {\small I}~} \sim 10^{-3}$ and $b_{\rm H\, {\small I}~} \sim 2$.

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

Cited by 15 publications

References 65 publications

Calibration requirements for Epoch of Reionization 21-cm signal observations -- II. Analytical estimation of the bias and variance with time-correlated residual gains

Calibration requirements for Epoch of Reionization 21-cm signal observations -- II. Analytical estimation of the bias and variance with time-correlated residual gains

Towards $21$-cm intensity mapping at $z=2.28$ with uGMRT using the tapered gridded estimator II: Cross-polarization power spectrum

Towards 21-cm intensity mapping at z = 2.28 with uGMRT using the tapered gridded estimator I: Foreground avoidance

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