  To investigate the environment effects on size growth of galaxies, we study
the size-mass relation across a broad range of environment with a vast sample
of approximately 32 million galaxies at z < 0.5 from the DESI Legacy Imaging
Surveys. This sample is divided into 3 subsamples representing galaxies within
three different environments: brightest cluster galaxies (BCGs), other cluster
galaxies, and field galaxies. The BCGs in our large sample are dominated by
quiescent galaxies (QGs), while only a minority (~13%) of BCGs are star-forming
galaxies (SFGs). To demonstrate the influence of environment on size growth, we
attempt to observe the difference in size-mass relation for these three
subsamples. In general, the slope differences between QGs and SFGs within
various environments are significant, and tend to be greater at higher
redshifts. For the mass-complete subsamples at z < 0.5, BCGs are found to have
the highest slope of size-mass relation, and no difference in size-mass
relation is found between cluster members and field galaxies. To assess whether
the observed slope differences stem from the variations in environment or mass
distribution, we construct the mass-matched subsamples for QGs and SFGs. As a
result, both QGs and SFGs show negligible difference in slope of size-mass
relation among the galaxies within three distinct environments, indicating that
stellar mass is the most fundamental factor driving the size evolution at z <
0.5, though the mass growth mode for QGs and SFGs may have been affected by
galaxy environment.
