The evolution of galaxies is driven by both external (e.g. environment, galaxy interactions) and internal (e.g. role of bar/bulges, stellar/AGN feedback) processes. My group studies nearby galaxies to understand the effect of these processes on their star formation, structure, kinematics, and evolution.
The Large and the Small Magellanic Clouds are together known as Magellanic Clouds. They are the nearest interacting system of low-mass galaxies and also the most massive satellites of the Milky Way. Its proximity (~ 55 kpc) allows to resolve individual stars and study different stellar populations within the system. They host a range of stellar populations, from young stars to stars as old as the Universe, and signatures of their interactions would have been imprinted on them. Using resolved stellar populations, we study these galaxies to understand the effect of low-mass galaxy interactions on their evolution. We use data from the Gaia and VISTA survey of the Magellanic Clouds system (VMC). I am a team member of the One Thousand and One Magellanic Cloud Fields (1001MC) survey within the 4MOST consortium. In our studies (Omkumar et al, James et al. Saroon & Subramanian, Dhanush et al.), we have found structural and kinematic signatures of recent interaction of the MCs.
According to the Λ cold dark matter model of galaxy formation, the hierarchical assembly process is scale-free, and interactions between galaxies in the entire mass range are expected. Dwarf galaxies are the dominant galaxy population at all redshifts, and the majority of mergers are expected to be between them. It is not clear whether their interactions can induce similar evolutionary changes as observed for massive galaxies. The effect of dwarf-dwarf interactions, in different environments, on their star formation properties is the area of our interest. Based on a study using GALEX FUV data, we found an enhancement in the star formation rate by a factor of 3.4 ± 1.2 for interacting systems compared to single dwarf galaxies in the stellar mass range of 107-108 M⊙. Our results indicate that dwarf-dwarf galaxy interactions can lead to an enhancement in their star formation rate (Subramanian et al. 2024). We are conducting a Far Ultraviolet Survey of dwarf galaxies in the Lynx Cancer Void using the Ultraviolet Imaging Telescope (UVIT) onboard AstroSat. I am also a team member of the AstroSat/UVIT Legacy Programme: a FUV Survey of Virgo Cluster Galaxies.
Molecular clouds in galaxies are structured hierarchically. The main mechanisms associated with this kind of spatial distribution are turbulence, magnetic fields, and self-gravity. Young stars and star clusters that form from these clouds inherit the spatial properties of the natal gas. Hierarchical, scale-free patterns are observed in the spatial distribution of unbound stars, embedded stars in clusters, star-forming HII regions, OB associations, young star clusters, etc. We study the spatial distribution of star-forming clumps in nearby galaxies to understand the physical mechanisms involved in star formation and the effect of galaxy properties and environment on the hierarchical nature of star formation. For this study, we use multi-wavelength data from UV to IR, specifically the collection of archival and proposal-based data from the UVIT. One of our recent studies, suggest that the global hierarchical properties of star formation in galaxies are not universal (Shashank et al. 2025).
The suppression of star formation in galaxies is known as quenching. It transforms blue, star-forming galaxies into red, passive galaxies and plays an important role in the evolution of galaxies. Several internal (AGN/stellar feedback, action of bar, bulges) and external processes (ram pressure stripping, major mergers, harassment, starvation, strangulation) have been proposed as mechanisms responsible for quenching. We study internal quenching mechanisms, especially the effect of structural components of spiral galaxies (like the bar and bulge) in quenching star formation, using multi-wavelength imaging and spectroscopic data. In a recent study, we found that in their later stages of evolution, bars turn the inner regions of galaxies redder, leading to quenching, with the effect being most prominent up to the ends of the bar and creating a region dominated by an older stellar population (Renu et al. 2025).