On the large-scale structure of galactic disks

The disk positions for galaxies of various morphological and nuclear-activity types (normal galaxies, QSO, Sy, E/S0, low-surface-brightness galaxies, etc.) on the μ₀-h (central surface brightness-exponential disk scale) plane are considered. The stellar disks are shown to form a single sequence on this plane $(SB_0 = 10^{ - 0.4\mu _0 } \propto h^{ - 1} )$ over a wide range of surface brightnesses (μ₀(I)≈12–25) and sizes (h≈10–100 kpc). The existence of this observed sequence can probably be explained by a combination of three factors: a disk-stability requirement, a limited total disk luminosity, and observational selection. The model by Mo et al. (1998) for disk formation in the CDM hierarchical-clustering scenario is shown to satisfactorily reproduce the salient features of the galaxy disk distribution on the μ₀-h plane.