COSMOS-Web Brightest Group Galaxy (BGG) Cat.

This survey provides deep NIRCam imaging in four filters (F115W, F150W, F277W, F444W) in ~0.54deg^2^, enabling robust size and morphological measurements for ~1700 BGGs spanning ~12Gyr of cosmic history. High-resolution imaging enables consistent size measurements in the rest-frame optical across cosmic time through redshift-dependent filter selection.

We classified BGCS as star-forming and quiescent using both rest-frame NUV-r-J colors and redshift-dependent specific star formation rate thresholds. Our structural analysis shows: quiescent BGGs are more compact than star-forming counterparts across all redshifts, with steeper size-mass slopes (alpha_QG_~0.6-1.2 vs. alpha_SF_~0.0-0.3); the effective radius evolves as Re {prop.to} (1+z)^-alpha^, with alpha=0.96+/-0.07 for star-forming and alpha=1.24+/-0.09 for quiescent BGGs, implying stronger size growth in quenched systems; the corresponding growth factor at logM*=10.7 from z=3.7 to z=0.08 is ~4.4 for star-forming and ~6.6 for quiescent BGGs. the scatter in the size-mass relation increases toward high redshift, reaching ~0.3-0.4 dex at z>2, reflecting greater structural diversity.