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\leq M_r \leq -20.5$ (mag), and the faint volume-limited sample with $-20.5 \leq M_r \leq -18.5$ (mag). Using the WHAN diagnostic diagram we assignedthe 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.