A UV and optical study of star formation and AGN activity using the UVIT and MUSE

Abstract

The cold gas accretion and merging of galaxies are two important physical mechanisms which contribute to the building up of galaxies at various epochs of the universe. Thus, it is crucial to understand the role of gas accretion and interactions/mergers on star formation (SF) activity in the present era. This thesis focuses on understanding SF and AGN activity in extended UV disk and interacting galaxies. Extended UV Disk Galaxies (XUV) show UV emission in their extended outer disk. The presence of UV emission reveals recent SF activity in the outer disk, which is linked with the cold gas accretion. The UV emission in the outer disk of XUV galaxies provides a new perspective on the evolutionary growth of the galactic disk. The interactions also play a major role in the evolution of galaxies. They are the main drivers of galaxy evolution. Galaxy interactions and mergers can modify the properties of galaxies, such as their gas and stellar masses, chemical content, morphology, kinematic and dynamical properties. Galaxy interactions/mergers can also lead to dual or triple AGN systems. The enhanced AGN feedback in such systems can heat the intracluster medium in clusters and enrich the circumgalactic medium around galaxies. Feedback processes such as jets or intense quasar outflows from AGN can affect the evolution of the galaxy. Thus, multiwavelength data is important to understand these systems. We take advantage of the unprecedented capabilities of MUSE and UVIT to carry out a highly detailed spatially and spectrally resolved study of SF rate, SF histories, metallicity and AGN activity in galaxies. We have focused on understanding the properties of inner and outer disk star-forming complexes in three face-on spirals type-1 XUV galaxies. We have focussed on understanding, what fuels the SF in the outer disk. We have also focused on understanding the spatially resolved properties of interacting galaxies. The galaxies are gas-rich and show signatures of recent SF activity in FUV and Hα images. The FUV band of the Ultraviolet Imaging Telescope (UVIT) has a resolution of 1 ′′, which allows us to trace star-forming regions in interacting galaxies with a relatively high spatial resolution from 200 pc to around 800 pc at the distance of the galaxies in the sample. The galaxies show SF in the tidal arm and in the disk regions. During the interaction of gas-rich galaxies, the tidal forces enhance cloud collision and gas compression, which triggers SF. The galaxies had undergone multiple bursts of SF in the past and show rising SF at their current phase. The galaxies also show higher sSFR in the spiral arms than interarm regions, which is expected, as spiral arms are the sites of higher gas and stellar concentration.