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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.

I will talk about some recent results on the nature of radio emission in low luminosity or radio-quiet AGN. I will discuss the magnetic field structures as well as episodic AGN activity seen in the outflows of these AGN and how they impact their surroundings. SKA, with its much improved sensitivity, is expected to revolutionise our understanding of these low luminosity AGN.

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 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.

In this talk I will describe recent work done by the MIST Global 21-cm experiment. The focus will be on sky observations conducted from the Canadian High Arctic and on efforts to calibrate these observations with high accuracy.

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.

The observations of the redshifted 21-cm signal contain a wealth of cosmological and astrophysical information. The study of this signal from the high redshift Universe provides a unique opportunity to learn about the properties of the first stars and galaxies. However, the problem is particularly challenging due to the presence of foregrounds and system noise. In this talk, I will talk about different statistical estimators to measure the cosmological 21-cm signal from radio interferometric observations. Also, I will present our recent results towards detecting this faint 21-cm signal using the uGMRT and the MWA low-frequency observations.

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.

The study of the Universe's large-scale structure and evolution has entered a new era with the emergence of neutral hydrogen intensity mapping as a powerful observational technique. HI intensity mapping (IM) offers a unique and innovative approach to cosmological research by probing the distribution of neutral hydrogen on vast scales. This technique uses radio telescopes like MeerKAT to detect the cumulative 21cm emission from neutral hydrogen. In this talk, I will introduce our current HI IM experiment with MeerKAT in the post-reionization universe and discuss our recent breakthroughs in the field. Additionally, I will present the on-the-fly (OTF) interferometric imaging capabilities with MeerKAT. Our aim is to explore cosmology through single-dish HI intensity mapping while simultaneously generating continuum images via the interferometer. This technique allows for commensal observing for both intensity mapping and interferometric imaging. We plan to survey an extensive 10,000 square degrees in the UHF band, achieving a sensitivity of 25 uJy/beam rms and a resolution of 13’’. Our partial observations have achieved an image sensitivity of approximately 140 uJy, with a goal of reaching 30 uJy using existing data. These advanced techniques are propelling the joint studies of cosmology and radio astronomy to new heights, and with the emergence of the Square Kilometre Array (SKA), the future of this field looks exceptionally promising.