We investigate the environmental dependence of star formation and the morphology of galaxies in the local universe based on a volume-limited sample constructed from the data of the Sloan Digital Sky Survey .
The sample galaxies ( 19,714 in total ) are restricted to the redshift range of 0.030 < z < 0.065 and the magnitude range of M _ { r } < M ^ { * } _ { r } +2 .
We investigate correlations between star formation , morphology , luminosity , local density , and richness of galaxy systems .
First , we focus on how galaxy properties change with local density .
Galaxies in dense environment are found to have suppressed star formation rates and early morphological types compared with those in the field .
Star formation and morphology show a ’ break ’ at the critical local density of \log \Sigma _ { crit } \sim 0.4 galaxies { \it h } _ { 75 } ^ { 2 } Mpc ^ { -2 } , which is in agreement with previous studies .
However , the break can be seen only for faint galaxies ( M ^ { * } _ { r } +1 < M _ { r } < M ^ { * } _ { r } +2 ) , and bright galaxies ( M _ { r } < M ^ { * } _ { r } +1 ) show no break .
Thus , galaxies of different luminosities are found to show different environmental dependencies .
Next , we examine dependencies on richness of galaxy systems .
Median properties of galaxies residing in systems with \sigma > 200 { km s ^ { -1 } } show no dependence on system richness , and most of the galaxies in those systems are non-star-forming early-type galaxies .
Star formation activities of galaxies are different from those of field galaxies even in systems as poor as \sigma \sim 100 { km s ^ { -1 } } .
This result suggests that environmental mechanisms that are effective only in rich systems , such as ram-pressure stripping of cold gas and harassment , have not played a major role in transforming galaxies into red early-type galaxies .
Strangulation and interactions between galaxiesm however , remain candidates of the driver of the environmental dependence .
In the dense environment in the local universe , the slow transformation of faint galaxies occurs to some extent , but the transformation of bright galaxies is not clearly visible .
We suggest that the evolution of bright galaxies is not strongly related to galaxy system , such as groups and clusters , while the evolution of faint galaxies is likely to be closely connected to galaxy system .