ICTS

Detecting the redshifted 21-cm signal from the Cosmic Dawn and Epoch of Reionization remains one of the most ambitious challenges in radio cosmology, due in large part to the overwhelming foreground contamination that can obscure the faint cosmological signal. In this talk, I will present recent progress in foreground mitigation strategies within the SKA context, with a focus on machine learning–based Gaussian Process Regression (ML-GPR) techniques. I will show how ML-GPR enables robust, flexible foreground removal and highlight its application to both LOFAR and NenuFAR observations. Beyond methodology, I will discuss the critical role of deep field selection, how environmental, instrumental, and sky-based factors impact foreground mitigation and signal recovery. Finally, I will report on the results from our team, DOTSS-21, in the SKA Data Challenge 3a (SDC3a), where we tested our pipeline on realistic simulated SKA data, demonstrating the potential and current limitations of ML-GPR–based approaches for upcoming SKA observations.

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The Canadian Hydrogen Intensity Mapping Experiment (CHIME) is a drift-scan radio interferometer located at the Dominion Radio Astrophysical Observatory (DRAO) in Penticton, British Columbia, Canada. CHIME, operating between 400 and 800 MHz, will map the redshifted 21 cm emission of neutral hydrogen between redshifts z = 0.8 − 2.5 across the northern sky. The 21cm line is a tracer of the large-scale structure of matter, whose statistics encode a well-understood standard ruler, the baryon acoustic oscillation scale. By detecting and tracking the evolution of this scale with redshift, CHIME aims to constrain the expansion history of the Universe over this crucial redshift epoch when the overall energy density of the Universe is expected to have become dominated by dark energy.

However, measuring this cosmological signal is challenging due to bright astrophysical foregrounds, which are about 4-5 orders of magnitude brighter than the cosmological HI signal.

In principle, these two signals can be separated due to their different spectral features, in which, the foreground signal is smooth in frequency, whereas the cosmological signal has spectral structure. However, this separation requires an instrument calibration at the sub-percent level accuracy. Recently, the CHIME collaboration reported the detection of cosmological 21 cm emission from a large-scale structure between redshift 0.78 and 1.43 in cross-correlation with eBOSS galaxy and quasar catalogs. In this cross-correlation measurement, a high-pass filter is applied to the frequency axis of each map pixel to remove foregrounds, which results in a measurement of the cosmological signal at the non-linear scales. I will discuss recent results in measuring the 21 cm signal in auto-correlation and some of the challenges that we have encountered. I will describe the improvements in the data processing and various data quality cuts required to measure the signal in auto-correlation. I will show the first results of the power spectrum using CHIME data.

21-cm intensity mapping is a promising technique to probe large-scale structures in our Universe. To measure the 21-cm intensity mapping signal, we have carried out a deep radio continuum observation of the ELAIS-N1 field using the SKA pathfinder instrument uGMRT. We have used uGMRT’s high angular resolution and wide bandwidth (300-500 MHz) to make a deep image of the field, from which, we identified and removed the compact sources. We found that the residual foregrounds are still several orders of magnitude brighter than the expected 21-cm signal. In a series of subsequent works, we have systematically developed novel techniques to remove the residual foregrounds and reach the system noise. The methodology includes sidelobe suppression, RFI handling, a foreground removal technique that is robust against signal loss and the necessary ingredients for a wide bandwidth data analysis. With a mere 25 hours of observation, we have found an upper limit which is just 10 times above the expected 21-cm signal. This stringent upper limit has led us to 50 more hours of observations with uGMRT, which, combined with the refined pipeline, is expected to provide a substantial improvement and a much tighter constraint. The techniques and these results will underpin future observations with SKA.

MeerKLAS, the MeerKAT Large Area Synoptic Survey, aims to survey large areas of the sky with MeerKAT in order to probe cosmology using the single dish HI intensity mapping (IM) technique. The MeerKLASS project provides an additional wide continuum survey capability alongside the single-dish HI IM survey by utilizing the ‘On-the-Fly’ (OTF) mapping technique. The target is to cover 10,000 sq. deg on the UHF band with 35 uJy rms and 15’’ resolution. This OTF interferometric imaging technique enables commensal observing for intensity mapping and interferometric imaging. The target sky area will cover most of the Southern sky, overlapping with several optical/NIR wide galaxy surveys and providing an invaluable legacy dataset. We have successfully implemented an end-to-end pipeline that produces continuum images from fast scanning MeerKLASS observations. In this presentation, I will focus on the development of the MeerKLASS OTF imaging pipeline. OTF imaging comes with its own set of challenges, such as flux errors due to smearing caused by the motion of the pointing centre on the sky. I shall discuss how we have mitigated the challenges in the OTF pipeline and the consequences. The final data product for the OTF-MeerKLASS survey consists of deep continuum images obtained by combining all the data from repeated scans of the same sky patch. Finally I shall discuss early science results for the survey such as source count, clustering and multi-wavelength analysis of the OTF catalog radio sources from L and UHF-band. In future, with many fold data acquisition by the MeerKLASS survey we expect to embark on the search for slow transients and I plan to briefly discuss the prospect of such analysis. Lessons from these techniques will be valuable for the upcoming SKA-mid observations.

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The power spectrum of H I 21-cm radiation is a key probe for studying the large-scale structure of the universe and the processes of galaxy formation and evolution. However, one of the major observational challenges is the contamination by foregrounds that are orders of magnitude brighter than the redshifted 21-cm signal in the same frequency range. Foreground contamination complicates calibration, introducing residual errors that bias power spectrum estimates and add systematics. In this work, we assess the efficacy of 21-cm power spectrum estimation using uGMRT Band-3 observations of the ELAIS-N1 field. By analyzing the statistics of residual gain errors and applying additional flagging based on these statistics, we demonstrate a significant reduction in bias and systematics. Our results show that systematics at lower angular scales (ℓ < 6000) primarily arise from residual gain errors and that standard deviation consistently exceeds the bias in power spectrum estimates. We estimate that approximately 2000 hours of on-source observation time is required to detect the 21-cm signal at a redshift of 2.55 with 3-σ significance at ℓ ≈ 3000.

Additionally, we explore the impact of frequency-dependent gain calibration errors on the EoR window in the k⊥-k∥ plane, finding significant contamination due to these errors. We also develop an analytical formula for the wedge structure, allowing wedge characterization directly from MAPS without simulations. These advancements provide critical insights into overcoming challenges in 21-cm cosmology for uGMRT and SKA-like telescopes. Further analysis of residual gain effects on multifrequency angular power spectra will be presented in a companion study.

I will introduce 21cmFASTv4, a new version of the public simulation package for interpreting multi-tracer observations of the first billion years. 21cmFASTv4 features a new, efficient halo finder as well as a flexible semi-empirical framework to connect galaxies to host halos. Built with Bayesian inference in mind, it allows for self-consistent forward models of multiple tracer fields (e.g. 21cm, galaxies, CMB anisotropies, line intensity maps). I show some recent examples of the power of this approach, including quantifying which galaxy surveys are the most promising for a cross-correlation with 21cm, and characterizing galaxies using recent JWST observations.

Observations of the redshifted 21-cm signal measure the state of the intergalactic medium. However, forward modelling of this signal depends mostly on parameters of the sources and thus inference frameworks put constraints on source properties. Given the considerable uncertainties on the properties of the sources of reionization, it would be good to be able to infer IGM properties from 21-cm observations. In this talk I will address our recent attempts at developing such a model.

The formation of the first stars in the Universe remains a key challenge in cosmology, requiring a multi-wavelength observational strategy across a range of facilities. Telescopes like the James Webb Space Telescope (JWST) enable direct observation of early galaxies, while upcoming radio telescopes such as the SKA will capture the hydrogen signal from the early Universe. Interpreting the extensive datasets from these facilities demands sophisticated theoretical models that balance detailed physics with computational efficiency, supported by advanced statistical methods to probe the parameter space. In this talk, we will discuss recent advancements in modelling the high-redshift Universe, along with the evolution of machine learning-driven statistical techniques. Together, these developments are essential for bridging the gap between theoretical predictions and observations, enabling a deeper understanding of cosmic evolution with next-generation observational capabilities.

Morphological summary statistics, such as Minkowski functionals, Betti numbers and Minkowski tensors, provide a route to carry out cosmological data analysis which is complementary to traditional mode decomposition based statistics such as the power spectrum. We summarize the properties of these statistics and demonstrate their information content by using the gravitational evolution of matter and 21-cm brightness temperature as physical examples.

The redshifted global 21-cm signal from the Cosmic Dawn has not been detected confidently to date. Beyond bright astrophysical foregrounds, there are three important challenges to signal detection, namely Radio Frequency Interference (primarily from FM transmitters), ionospheric effects, and modification of antenna properties by objects in the near-field. PRATUSH is a ProPosed lunar orbiter experiment, to observe the radio sky in the lunar farside where all the three challenges above are alleviated. I will discuss the PRATUSH design Philosophy, current status, Phase-I operations in Earth Orbit, and next steps.

During the Epoch of Reionisation (EoR), the ultraviolet radiation from the first stars and galaxies ionised the neutral hydrogen of the intergalactic medium, which itself can emit radiation through the 21 cm hyperfine transition. Due to this, the 21 cm signal is a direct probe of the first stars in the early Universe and a key science goal for the future Square Kilometre Array (SKA). However, observing and interpreting this signal is a notoriously difficult task.

Another high-potential probe is the patchy kinetic Sunyaev-Zel'dovich effect (pkSZ). Induced by the scattering of Cosmic Microwave Background (CMB) photons with a medium of free electrons produced during the EoR, the effect altered the small-scale CMB temperature anisotropies, imprinting information on the growth of ionising bubbles from the first galaxies. While measurements of the pkSZ angular power spectrum by Reichardt et al. (2021) have reported a 3σ constraint of D^pkSZ (l=3000) = 3.0 ± 1.0 μK2, the results are also subject to modelling uncertainties.

In this talk, we propose a simple yet effective parametric model that establishes a formal connection between the 21 cm and pkSZ power spectra. Using this model to jointly fit mock 21 cm and pkSZ data points, we confirm that these two observables exhibit complementary characteristics, leading to significantly improved constraints on reionisation compared to analysing each data set separately. Our findings demonstrate that a few well-informed low-redshift (eg., z < 8) measurements of the 21 cm power spectrum at k ≈ 0.1 cMpc^-1 and pkSZ power spectra can precisely determine the reionisation history of the Universe.

Therefore, even in the early stages of observations with the SKA, we can begin to constrain cosmic reionisation by performing a combined analysis of the 21 cm power spectrum with the pkSZ observations.

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The first stars - the chemically pristine Population III - likely started forming at z~20-30, but may have continued to form in pockets of chemically pristine gas down to at least z~6. Both the initial mass distribution of these stars and their formation history are currently largely unconstrained, but the James Webb Space Telescope (JWST) has the potential to detect Population III star clusters, galaxies and in some cases even individual Population III stars at z<15. With future 21 cm observations, it may be possible to constrain the nature of these stars at even higher redshifts, and when combined, a coherent picture of Population III stars from the epoch of cosmic dawn and until the end of the reionization era could be within reach. Here, I will offer my perspective on what kind of observational limits on the nature of Population III stars one is likely to get from JWST data in coming years, and how one may envision such constraints connecting to the clues to the puzzle that SKA will deliver.

With the increased sensitivity and field of view of SKA pathfinders, dynamic radio imaging (imaging the time axis) is becoming a burgeoning field, yielding rich new discoveries of transients and variable sources. MeerKAT is capable of reaching sub-150 uJy image rms in an 8s integration, which opens up studies of variability on much shorter timescales than was possible with previous radio interferometers. This also has important implications for interferometric SETI, since any potential technosignatures would be a subset of such transient events.

At the same time, imaging at such short timescales introduces its own substantial challenges. Instrumental effects that tend to average out in a traditional long synthesis observation can become limiting for dynamic imaging if not addressed correctly. I will discuss these challenges and present MeerKAT dynamic imaging of Jupiter’s radiation belts, which have led to the serendipitous discovery of a pulsar-class object named the PARROT (pulsar with abnormal refraction recurring on odd timescales).

This work has led to the development of (and given the name to) a more general dynamic imaging pipeline, developed in collaboration with the Breakthrough Listen initiative. The PARROT pipeline is capable of detecting short-duration transients in imaging data, and yielding light curves and dynamic spectra for thousands of field sources en masse. We are already starting to use it to “mine” existing archival MeerKAT data, yielding a couple of new discoveries. The longer-term plan is to develop the PARROT pipeline to a state where it can be run in real-time, commensally with any MeerKAT imaging observation. This would open the door to transient event triggers -- something that has never been done with a radio interferometer before.    

The MeerKAT Exploration of Relics, Giant Halos, and Extragalactic Radio Sources (MERGHERS) survey is a multi-semester MeerKAT programme targeting a homogeneously selected sample of galaxy clusters with the aim of probing the cosmic and mass evolution of diffuse cluster radio emission, such as radio halos and radio relics. Almost all statistical cluster samples studied for diffuse radio emission are restricted to low-redshift, high-mass clusters due to historical telescope sensitivity limitations. MERGHERS is designed in statistically complete tiers, to build up to a large statistically significant cluster sample across wide redshift and mass ranges, as yet unprobed at mid-MHz and GHz ranges. The MERGHERS target samples are extracted from the Atacama Cosmology Telescope’s fifth data release catalogue (ACT DR5), where galaxy clusters are detected via the Sunyaev-Zel’dovich effect, providing a mass-selected sample with a well defined selection function. The MERGHERS pilot study (Knowles et al. 2021) consisted of 13 ACT clusters and served as an observing strategy testbed, to ensure potential problems with limited uv-coverage could be adequately addressed before the full program began. The pilot study, which focused on likely merging clusters based on the projected separation between the SZ peak and the cluster’s brightest cluster galaxy, produced several new diffuse emission detections and confirmed the observational strategy moving forward. The first tier of the MERGHERS project focuses on a statistical sample of 25 massive ACT DR5 clusters in the redshift range 0.4 < z < 0.6, selected while being blind to the cluster dynamical state so as not to bias observed diffuse emission occurrence rates. The second tier data, lowering the mass range within the same redshift bin has also been observed, taking the current statistical sample up to 56 systems. In this talk I will discuss the observational results of the first tier MERGHERS sample, and highlight some interesting serendipitous findings in the preliminary tier two images.

Galaxy clusters and superclusters are among the youngest structures forming in the Universe. The intra-cluster medium (ICM) and inter-galactic medium (IGM) are both unique plasmas that host magnetic fields and cosmic rays. Radio band observations provide the probes to these, so-called non thermal components, via the detectable synchrotron radiation. The particle acceleration mechanisms involve the role of shocks and turbulence in the magnetized plasma that can be probed with radio band continuum and polarization observations. I will present our work on studying turbulence and shocks in the high redshift, massive galaxy cluster El Gordo and the Saraswati supercluster with the precursors and pathfinders of the SKA. I will discuss our findings on the evolution of radio galaxies in superclusters and the properties of intra-cluster turbulence using radio and X-ray observations and provide a perspective on the exciting possibilities with the SKA.

The radiation emitted by the first galaxies in our Universe ionised the hydrogen in the intergalactic medium (IGM) during the first billion years, ushering in the Epoch of Reionisation. How did this last major phase transition that governed the evolution of the galaxies we see today happen? Was it driven by the few bright or numerous faint galaxies?
Current and upcoming optical, near-infrared and radio surveys, with e.g. the Roman Space Telescope and the Square Kilometre Array, will tackle these questions: 21cm emission maps will trace the evolving distribution of ionised regions, while galaxy surveys will sketch the ionising sources and their distribution. Most importantly, combining these maps of the ionising sources and the ionisation topology opens up the possibility of constraining the ionising properties of the galaxies that are too faint to be observed. Various works have explored the benefits of synergising surveys of the 21cm signal and emission line galaxies (e.g. Lyman-alpha emitters), finding that the corresponding cross-correlation functions and power spectra trace the overall ionisation state of the IGM.
I will discuss the characteristic signatures of 21cm-galaxy cross-correlations, explaining how they trace the ionisation history and morphology and which type of 21cm and galaxy surveys can constrain these reionisation scenario characteristics.

Understanding the evolution of active galactic nuclei (AGN) and host galaxies across cosmic epochs is one of the key science drivers of extragalactic surveys. Although, obscuration poses a challenge to detect the complete population of AGN across cosmic epochs. The merger induced dust-obscured galaxies (DOGs) are supposedly potential hosts of AGN. However, detection of AGN in DOGs is challenging due to high absorption of optical, UV and X-ray emission arising from the AGN. Radio emission is insensitive to dust obscuration, and hence, radio continuum surveys are efficient means to detect radio AGN hosted in DOGs. I shall discuss the role of multi-frequency radio continuum surveys in uncovering the AGN population in obscured environments up to large redshifts, and therefore, shedding new insights to the cosmic evolution of AGN.

Radio galaxies associated with active galactic nuclei (AGN) have traditionally been classified into two types: Fanaroff-Riley I (FR I) and Fanaroff-Riley II (FR II). The classification is based on radio morphology but correlates strongly with their luminosities, which are separated by a sharp dividing line. However, recent observations with the most sensitive radio telescopes like LOFAR, MeerKAT, uGMRT, and JVLA are challenging this distinction. High-resolution and high-sensitivity studies have revealed that the sharp line may actully be broader band, with the luminosities of some FR I and FR II on ”wrong” side. Adding to this complexity is the discovery of Hybrid Morphology Radio Sources (HyMoRS) that show FR I morphology on one side of the active nucleus and FR II morphology on the other.
We present results from a study which used GMRT to image a sample of HyMoRS identified from the MeerKAT Galaxy Cluster Legacy Survey (MGCLS). These sources were selected based on the following criteria:
(i) difference between AGN and host galaxy cluster spectroscopic redshifts < 1000 km/s (ii) angular size > 4 arcmin, and (iii) declination 0-50 degree. The selected sources are situated at varying distances from the cluster center. Initial findings suggest a link between the host cluster environment and the occurrence of HyMoRS morphology.

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Cosmic inflation is currently the most promising paradigm for explaining the fine-tuned initial conditions of the standard Big Bang model. A class of inflation models that involves bursts of particle productions during inflation predicts bump-like features on the power spectrum of primordial density perturbations. This talk will present the imprints of these primordial features on the cosmological 21 cm signal at the high-redshift universe. Using semi-numerical simulations, we demonstrate that the 21 cm signal measurements with the average profile and power spectrum can provide unique constraints on inflationary models that predict such features. Furthermore, we discuss how to distinguish the effects of reionization parameters from the imprints of primordial features on the 21 cm signal, offering insights into both early universe physics and cosmic reionization.

Photons between the Lyman-α and Lyman-limit frequencies, produced in the large scale structures during the Cosmic Dawn, redshift into the neutral IGM and undergo multiple scatterings by the HI atoms, coupling the HI spin temperature to the gas kinetic temperature. However, during this process the Lyman-α photons also exchange energy with the medium. The photons which redshift into the Lyman-α line (continuum photons) heat up the medium, while the photons which are injected at the line centre (injected photons) cause cooling, assuming the profile near Lyman-α line centre to be in quasi-static equilibrium. However, we find that the time-scale to reach this equilibrium are often under-estimated in the literature. Thermal feedback due to evolving IGM temperature delays this equilibrium. Additionally, the life time of the first stars in the Universe (PopIII stars) is comparable to the time scales for reaching quasi-static equilibrium (1–10 Myr). In our analysis we have also found a new equilibrium profile for the continuum photons which is reached on the expansion time scales (∼100 Myr). We also calculate the final equilibrium temperature of the IGM for a combination of continuum and injected photons. However, this balance shifts when the source switches off, and the residual photons in the IGM can heat the medium above the equilibrium temperatures. In this talk I will discuss times scales for the temperature evolution of the IGM during Cosmic Dawn and it’s effect on the 21-cm signal.

The Epoch of Reionization (EoR) and Cosmic Dawn (CD) play pivotal roles in the structural evolution of the Universe within its initial billion years. The characteristics of the Intergalactic Medium (IGM) during the EoR and CD are yet to be firmly established through observation. One of the primary objectives of current and upcoming radio telescopes, such as EDGES, SARAS, MWA, and SKA, is to detect the redshifted HI 21-cm signal. However, these experiments face challenges due to systematic errors and heavily rely on the precision of foreground removal. Additionally, at lower frequencies, the Earth's ionosphere significantly distorts the signal by creating direction-dependent effects. Hence, it is crucial to comprehend the effect of each source of corruption when employing non-parametric techniques for accurately detecting the 21cm signal. Our study uses Artificial Neural Networks (ANN) and Markov Chain Monte Carlo (MCMC) to extract the HI 21-cm power spectrum and its associated parameters from the observed sky signal. This encompasses the HI signal, actual foregrounds, calibration and position errors, and systematic effects. The trained model improves ground-based data findings for upcoming radio interferometric studies such as SKA, MWA, and HERA, aiding in understanding position and calibration error tolerance levels across different arrays and their impact on parameter estimation.

The morphology of the 21-cm signal emitted by the neutral hydrogen present in the intergalactic medium (IGM) during the Epoch of Reionization (EoR) depends both on the properties of the sources of ionizing radiation and on the underlying physical processes within the IGM. Variation in the morphology of the 21-cm signal due to the different sources of the EoR is expected to have a significant impact on the 21-cm bispectrum, which is one of the crucial observable statistics that can evaluate the non-Gaussianity present in the signal and which can be estimated from radio interferometric observations by SKA. We present the 21-cm bispectrum for different reionization scenarios, assuming different simulated models for the sources. We also demonstrate how well the bispectrum can distinguish between different 21-cm signal morphologies arising due to the differences in the reionization scenarios, which will help us shed light on the nature of the sources of ionizing photons.

Line-intensity mapping (LIM) is expected to be a promising tool for probing the Epoch of Reionization (EoR) via detecting the integrated flux of line emissions from the galaxies and the diffuse IGM. However, contaminants such as the instrumental noise of the LIM surveys will affect the observable summary statistics and degrade the detectability of the LIM signal. One possible method to tackle this is to cross-correlate with a different tracer of the high redshift universe, such as the HI 21cm signal from the neutral IGM. In this work, we forecast the CO-21cm cross-power spectrum from the EoR and its detectability. We consider a 21cm survey with AARTFAAC and a CO emission survey by COMAP, with an overlap of 12 deg^2 of the survey area. We use the outputs of a combination of N-body and radiative transfer simulations to obtain the mock 21cm and CO signals. Considering the planned COMAP-pathfinder survey, which will detect the CO(2-1) signal from the EoR and 2400 hours of observation time on AARTFAAC, the weakest CO emission model is detectable with ~2sigma significance in cross-correlation. Finally, for the planned COMAP-EoR survey, set to detect the CO(1-0) signal from the EoR, one might achieve close to ~3sigma detection significance for the weakest CO emission model. We also find that the CO-21cm cross-power spectrum from the EoR can contrast a wide range of CO emission models. Therefore, cross-correlation can improve the prospects of detecting high redshift LIM signals probing the EoR.

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Cosmic dawn and epoch of reionization, the period during which the first stars and galaxies formed and reionized the universe, can be studied using the 21-cm line transition of the neutral hydrogen atom. The sky-averaged global 21-cm signal component corresponding to 6 < z < 34 is redshifted to metre wavelengths and lies between 40 to 200 MHz.

However, detecting this signal poses significant challenges due to strong foreground emissions and systematic effects introduced by antenna instrumentation. The antenna's primary beam and impedance, which also depend on the properties of the observing environment, play an influential role in distorting the signal. In this presentation, we explore the intricate relationship between antenna properties and signal detectability. We identify key parameters influencing signal detection and estimate biases across different 21-cm signal models. We use realistic simulations of SARAS antenna characteristics. Our analysis finds correlations between beam chromaticity and spectral profile biases. We also find stringent requirements for transfer function corrections, which can otherwise prohibit detection prospects. We finally explore a range of critical parameters that allow robust signal detection.

Furthermore, we share insights from recent RFI surveys and SARAS deployments in the Trans-Himalayan region of Ladakh and the Andaman Islands. This includes an overview of the Radio Frequency Interference (RFI) environment at the surveyed sites and the methodologies used for data reduction and analysis. Our findings underscore the importance of site-specific environmental factors in enhancing detection prospects for the global 21-cm signal

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The current cosmology paradigm favours the Lambda cold dark matter (L-CDM) model. So far, the cosmological simulations based on the L-CDM parameters have revealed the best visual picture of our Universe as a 3-D filamentary network of matter distribution called the cosmic web. Galaxy clusters are seen to form at the nodes of this network, while the smaller structures reside in the filaments. The simulation predicts a thin and warm (~10^6 K) intergalactic medium known as the Warm Hot Intergalactic Medium (WHIM). However, observational validation of this scenario is inconclusive, especially the detection of diffuse intergalactic medium that channelled towards the clusters. Since the expected diffuse radio emission from filaments is extremely weak, it largely remained undetected. In this talk, I will discuss the recent developments in the field. How the simulation works have motivated comprehensive search of objects in quest of unraveling cosmic-web. In this context, I will also show how our recent work on development of an improved search algorithm have successfully produced a comprehensive list of promising interacting systems from galaxy redshift surveys. Interestingly, as predicted, we found that the bulk of cases show cluster interaction along the prominent cosmic filaments of galaxy distribution (i.e., the proxy for Dark Matter filaments), with the most violent ones at their nodes. Moreover, some of these regions found to trace the imprint of interactions in their multi-band signatures such as, diffuse cluster emissions in radio or X-rays. I will also discuss about the future prospect of detection with newly commissioned radio telescope arrays and more so in the SKA era.

Radio observations are essential for studying galaxy formation and evolution, yet analyzing low-frequency interferometric data is challenging due to radio frequency interference (RFI) contamination and other system issues. To streamline this process, we developed GARUDA, an automated pipeline for analyzing GMRT data, employing AI/ML-based algorithms for efficient RFI identification and artifact removal. GARUDA enables fast and consistent data reduction, handling ~10-12 GB GSB data in 20-30 minutes and ~400 GB GWB data in under three hours on standard servers. In this presentation, I will discuss GARUDA’s capabilities and showcase results, including some of the deepest GMRT radio continuum images at the L-band, HI emission in galaxies, and one of the most sensitive galactic HI absorption lines (using frequency switching observation with GWB).

21-cm Cosmology from Dark Ages

Radio continuum emission is a highly promising tool for tracing star formation activity across cosmic time and environments, by virtue of being unbiased by dust and reaching high angular resolution in interferometric imaging. I will discuss recent results, but also some of the challenges associated with using GHz continuum surveys to characterize the evolution of the star-forming galaxy population from the final Gyr of the EoR to the present day.

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Despite its great success, the LCDM model faces several theoretical and observational challenges. In this review, we explore some of the alternative models and investigate their possible detectable imprints on the 21-cm observations.

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The next generation of extragalactic surveys will reveal the full diversity of the galaxy assembly process: from environment-dependent evolution to the build-up of mass inside galaxies, and with a complete accounting of all relevant processes/constituents ensured by multi-wavelength coverage. Observations at radio wavelengths carry a unique potential in that they can probe star-formation activity and cold gas content, i.e. place constraints on both galaxy growth rates and the fuel for future galaxy growth. With the construction of the Square Kilometre Array (SKA), radio astronomy will enter a new era; high-sensitivity, high-resolution and dust-unbiased radio imaging will provide a confusion-free census of star formation and black hole activity, regardless of whether these occur in dust-obscured or optically thin regions. I will review the high-priority science cases developed by the SKA extragalactic continuum science working group and outline the challenges brought about by our still only partial understanding of some of the astrophysical mechanisms producing radio emission (e.g. the relation between star formation rate and radio continuum luminosity).
Thanks to an order of magnitude increase in survey speed compared to existing radio telescopes, SKA surveys will detect millions of galaxies. I will summarize how - in addition to advancing our understanding of the drivers of the cosmic star-formation history - commensal survey design will ensure that information on galaxy shapes, redshifts, spatial distribution and polarization can be used for cosmological studies and to trace the evolution of magnetic fields in galaxies and the cosmic web.

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