One of the key science goals for the most sensitive telescopes, both current and upcoming, is the detection of the redshifted 21-cm signal from the Cosmic Dawn and Epoch of Reionization. The success of detection relies on accurate foreground modelling for their removal from data sets. This paper presents the characterization of astrophysical sources in the Lockman Hole region. Using 325-MHz data obtained from the Giant Metrewave Radio Telescope, a 6° × 6° mosaiced map is produced with an rms reaching 50 μJy per beam. A source catalogue containing 6186 sources is created, and the Euclidean normalized differential source counts have been derived from it, consistent with previous observations as well as simulations. A detailed comparison of the source catalogue is also made with previous findings – at both lower and higher frequencies. The angular power spectrum (APS) of the diffuse Galactic synchrotron emission is determined for three different Galactic latitudes using the tapered gridded estimator. The values of the APS lie between ∼1 and ∼100 mK2. Fitting a power law of the form Aℓ−β gives values of A and β varying across the latitudes considered. This paper demonstrates, for the first time, the variation of the power-law index for diffuse emission at very high Galactic locations. It follows the same trend that is seen at locations near the Galactic plane, thus emphasizing the need for low-frequency observations for developing better models of the diffuse emission.

We investigate the effect of radio-frequency interference (RFI) excision in estimating the cosmological H i 21 cm power spectrum. Flagging of RFI-contaminated channels results in a nonuniform sampling of the instrumental bandpass response. Hence, the Fourier transformation of visibilities from frequency to delay domain contaminates the higher foreground-free delay modes, and separating the spectrally fluctuating H i signal from spectrally smooth foregrounds becomes challenging. We have done a comparative analysis between two algorithms, one-dimensional CLEAN and least-squares spectral analysis (LSSA), which have been used widely to solve this issue in the literature. We test these algorithms using the simulated SKA-1 Low observations in the presence of different RFI flagging scenarios. We find that, in the presence of random flagging of data, both algorithms perform well and can mitigate the foreground leakage issue. But CLEAN fails to restrict the foreground leakage in the presence of periodic and periodic plus broadband RFI flagging and gives an extra bias to the estimated power spectrum. However, LSSA can restrict the foreground leakage for these RFI flagging scenarios and gives an unbiased estimate of the H i 21 cm power spectrum. We have also applied these algorithms to observations with the upgraded GMRT and found that both CLEAN and LSSA give consistent results in the presence of realistic random flagging scenarios for this observed data set. This comparative analysis demonstrates the effectiveness and robustness of these two algorithms in estimating the H i 21 cm power spectrum from data sets affected by different RFI scenarios.

Observation of the redshifted 21-cm signal from Cosmic Dawn and Epoch of Reionization is a challenging endeavor in observational cosmology. Presence of orders of magnitude brighter astrophysical foregrounds and various instrumental systematics increases the complexity of these observations. This work presents an end-to-end pipeline dealing with synthetic interferometric data of sensitive radio observations . The mock sky model includes the redshifted 21-cm signal and astrophysical foregrounds. The effects of calibration error and position error in the extraction of the redshifted 21-cm power spectrum has been simulated. The effect of the errors in the image plane detection of the cosmological signal has also been studied. A comparative analysis for array configurations like the SKA1-Low, MWA and HERA has been demonstrated. The calibration error tolerance of the arrays, under some assumptions about the nature of the systematic components, is optimally found to be $\sim 0.01{{\%}}$ for the detection of the signal. For position errors, an offset of ⪆ 5″ makes the residual foregrounds obscure the target signal. These simulations also imply that in the SKA-1 Low performs marginally better than the others in the image domain, while the same is true for MWA in the power spectrum domain. This is one of the first studies that compares performance of various radio telescopes operating under similar observing conditions towards detecting the cosmological signal. This end-to-end pipeline can also be extended to study effects of chromatic primary beam, radio frequency inferences, foregrounds with spectral features, etc.

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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 HI 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 hours to provide large enough signal-to-noise ratio 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 ∼ 0.02 Mpc−1 − 0.3 Mpc−1 with signal-to-noise ratio ∼2 − 5 in Δ[log(k/Mpc−1)] = 0.25 bins assuming an integration time of 600 hours. 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.