2024ApJ...966..168L

We study the size and structure of globular cluster (GC) systems of 118 early-type galaxies from the NGVS, MATLAS, and ACSVCS surveys. Fitting Sérsic profiles, we investigate the relationship between effective radii of GC systems (R_e,gc) and galaxy properties. GC systems are 2-4 times more extended than host galaxies across the entire stellar mass range of our sample (10^8.3M_⊙ < M_* < 10^11.6M_⊙). The relationship between R_e,gc and galaxy stellar mass exhibits a characteristic “knee” at a stellar mass of M_p ≃ 10^10.8, similar to the galaxy R_e-stellar mass relationship. We present a new characterization of the traditional blue and red GC color subpopulations, describing them with respect to host galaxy $(g^{\prime} -i^{\prime} )$ color (Δ_gi): GCs with similar colors to their hosts have a “red” Δ_gi, and those significantly bluer GCs have a “blue” Δ_gi. The GC populations with red Δ_gi, even in dwarf galaxies, are twice as extended as the stars, suggesting that formation or survival mechanisms favor the outer regions. We find a tight correlation between R_e,gc and the total number of GCs, with intrinsic scatter ≲0.1 dex spanning two and three orders of magnitude in size and number, respectively. This holds for both red and blue subpopulations, albeit with different slopes. Assuming that N_GC,Total correlates with M₂₀₀, we find that the red GC systems have effective radii of roughly 1%-5% R₂₀₀, while the blue GC systems in massive galaxies can have sizes as large as ∼10% R₂₀₀. Environmental dependence on R_e,gc is also found, with lower-density environments exhibiting more extended GC systems at fixed mass.