Main sequence of star formation and colour bimodality considering galaxy environment

Abstract

This study involves the use of friend-of-friend method on the volume limited samples constructed from the Sloan Digital Sky Survey Data Release 12 (SDSS DR12) to classify the galaxies into isolated and non-isolated environments hence to investigate the influence of the galaxy environment on the main sequence of star formation, and colour bimodality. We classified the galaxies into the luminous volume-limited sample with $-22.5\le M_r\le -20.5$ (mag), and the faint volume-limited sample with $-20.5\le M_r\le -18.5$ (mag). Using the WHAN diagnostic diagram we assigned the samples into star-forming, strong AGN, weak AGN, and retired galaxies based on their environment (isolated and non-isolated). The friend-of-friend method was successful in producing consistent results regarding the stellar mass-SFR and stellar mass-colour known relations. Apart from that the decrease in the slope of the main sequence for star-forming galaxies by 0.04 dex and intercept by 0.39 dex for the luminous sample was observed while the faint sample a decrease of 0.08 dex in slope and 0.74 dex in intercept was observed between isolated and non-isolated galaxies. A significant difference on the number of galaxies between isolated and non-isolated galaxies within, above and below the main sequence by 7.47%, 28.51%, 14.59% for the luminous sample while for the faint sample by 16.15%, 32.60%, 35.23% on average, respectively are observed. A significant difference in the number of galaxies in the blue cloud, green valley, and red sequence by 10.30%, 20.61%, 5.74% for luminous sample while for faint sample by 28.46%, 41.36%, 8.95% on average, respectively was observed. The study concludes that the galaxy environment influences the shaping and positioning of galaxies along the star formation main sequence and colour bimodality.