Probing the Star-formation Activities of Galaxies Residing in Void and Filaments using AstroSat

Abstract

The distribution of galaxies around the cosmic web is in-homogeneous. On megaparsec scales, galaxies cluster together to form groups and galaxy clusters which are located at the intersection of long filaments. A vast region between the galaxy clusters, known as the void, contains relatively fewer galaxies. The clusters, groups, voids, and filaments constitute the large-scale structures (LSSs) of the Universe. The LSSs may leave a characteristic imprint on the photometric and chemical properties of the constituent galaxies. Apart from the environment, the stellar mass of galaxies also strongly influences galaxy evolution. This work aims to understand the intertwined effect of environment and stellar mass on galaxies residing in different LSSs. We primarily work with proposed Ultraviolet Imaging Telescope (UVIT)/AstroSat deep imaging observations. The imaging surveys cover small portions of a few LSSs, i.e., the voids and filaments situated 300 Mpc from us. We present a total of six void galaxies and 18 filament galaxies having FUV observation based on the deep UV imaging survey. Of these, nine galaxies are newly detected in our observation. We calculate star formation rates and colors, model spectral energy distribution (SED) using multi-band fluxes, and dissect the structural properties of the detected galaxies. Our analysis reveals a dominant fraction of bluer galaxies over the red ones in the void region probed while we detected equal number of star-forming and non star-forming galaxies in filaments. We find that the large-scale environment weakly impacts the ongoing star formation in galaxies. We studied the star formation properties of the most massive galaxy, I Zw 81 detected in our void galaxy sample. The 2D structural decomposition of the galaxy revealed the presence of multiple components such as a nuclear point source, a bar, a ring, and an inner exponential disk followed by an outer low surface brightness disk. The star formation inside the lenticular galaxy is concentrated within the central few kpc region enclosing the bar. The galaxy hosts a low-luminosity AGN which does not impact the central star formation. We report that the minor merger interaction enhances star formation in the galaxy and perhaps aids bar formation. The results are peculiar from the standpoint of a massive barred lenticular galaxy. Our study on the filament galaxies confirms the influence of the environment on their evolution. The number density of high-mass and passive galaxies increases near the filament axis. We do not detect FUV emission in galaxies within 0.4 Mpc from the filament axis. The mass-assembly mode of filament galaxies shows stronger dependence on their environment than stellar mass. We uncover extended-UV emission in a few filament galaxies, which hints towards the possibility of cold-mode gas accretion in the LSS.