Search Talks

Dark matter plays a major role in the equilibrium of galaxy disks, especially the outer disks of galaxies where the stellar disk surface density declines. The hydrostatic equilibrium of the HI disk in these regions can be used to probe the dark matter distribution within the disk. In this presentation we show that the disk dark matter in nearly face-on galaxies can be probed with sensitive HI velocity dispersion observations. Alternatively, the HI disk thickness in edge-on galaxies can be used to estimate the disk dark matter. We show that both methods have assumptions and advantages/disadvantages. Assuming a form of the halo potential, we show that the disk dark matter can be used to probe the halo shape. We apply our methods to nearby galaxies and show that smaller dwarf galaxies appear to be more dark matter dominated and their halo shapes appear to be oblate, whereas massive galaxies have more spherical halos. We also discuss how HI velocity dispersion can explore the dark matter distribution of very close, low luminosity satellites such as Leo-T. The halo shape can affect galaxy disk properties, such as the stellar velocity dispersion and disk surface density, which in turn affects bar formation, gas kinematics and star formation in galaxy disks, all of which are important for galaxy evolution. Our study thus demonstrates the importance of SKA HI surveys to probe the dark matter distribution in galaxies. We discuss how the SKA sensitivity will allow us to probe HI and dark matter at much larger distances compared to present studies.

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.

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.

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.