Annual Report_Abridged - Second Version - FINAL

22 programme assume that the underlying model of the Universe is well-approximated by the Lambda-cold dark matter (LCDM) framework. Aseem Paranjape and his collaborators have developed an analysis technique that allows the BAO feature to be used in a model-independent manner, i.e., the same analysis is simultaneously applicable in constraining not only LCDM but also other classes of `modified gravity' or `dark energy' models. The new technique relies on basic physical aspects of cosmological structure formation shared by a wide class of models including and beyond LCDM, combined with a simple data-driven description of the BAO feature using polynomials which is embedded in a fully Bayesian analysis framework. The new technique thus opens the door to using the BAO feature to its full capacity as a probe of primordial cosmology. DwarfGalaxies Giant galaxies, like our Milky Way and its neighbour Andromeda, are surrounded by tens of dwarf galaxies - irregular in shape and often forming stars. Looking back in time, we see that galaxies were smaller and more irregular. How these dwarf galaxies assemble their stars and evolve is still one of the outstanding questions of galaxy formation. A recent study using AstroSat shows how the star-forming clumps in the outskirts of a dwarf galaxy migrate towards the central region due to dynamical friction and contribute to its growth in mass and luminosity. The discovery of this process in several dwarf galaxies has been made for the first time by the research group led by Kanak Saha at IUCAA in collaboration with Indian university students and international scientists. The resolving power of Astrosat's UltraViolet Imaging Telescope and AstroSat UV Deep Field (AUDF) imaging has been the key to spotting such extremely blue, young star-forming clumps that in-spiral inside the optical boundary within a billion years (much shorter than a galaxy's lifetime) timescale to grow these galaxies. One of the key challenging tasks has been to establish the detection of these. Another key research activity of the Galaxy group at IUCAA is to search for extended UV emission in the outskirts of dwarf galaxies, some of which are seen now at a stage when our universe was less than half its current age. In parallel, the group is actively hunting for such distant dwarf galaxies (at redshift z>1) that might have contributed to the reionization history of the universe. Theoretical SolarPhysics Two important goals of solar physics are to understand its dynamomechanismand to be able to make an early prediction of energetic events, such as coronal mass ejections and solar flares, which directly influence the terrestrial life. These phenomena are powered by magnetic fields which are generatedwithin the Sun. Moreover, the Sun supports a wide variety of waves that carry useful information about the inhomogeneous solar structure. Based on simulations of turbulent magneto-convection we study the generation of concentrated magnetic fields in a self-consistent manner, and also analyse observational data to look for imprints of subsurfacemagnetic fields on helioseismic modes. We find that the solar surface gravity or the f-mode displays strengthening about two days prior to active region (AR) formation and thus it provides a new precursor for AR formation. This has implications for space weather forecasting and can potentially be important for constraining dynamo paradigms