Giant Low-Surface Brightness Galaxies in the Global Picture of Galaxy Formation and Evolution

Abstract

Giant low-surface brightness galaxies (gLSBGs) challenge standard merger-driven galaxy assembly models due to their large, dynamically cold disks, with radii often larger than 100~kpc and dynamical masses exceeding ${\sim}10^{12}$~\Ms. We identify $60$ gLSBGs, including a volume-complete subsample of $35$ galaxies out to $z=0.1$ in the 120~sq.deg. area. Using new and archival photometric and spectroscopic data, we homogeneously analyze their structural properties and derive central velocity dispersions. We update the gLSBG volume density estimate in the local Universe to $(3.6 \pm 0.6) \cdot 10^{-5}~\text{Mpc}^{-3}$. This number corresponds to about 1 in 4000 galaxies in the $g$-band luminosity range $0.14-1.37 \cdot 10^{11}~L_{\odot}$ out to $z=0.1$, which is consistent with EAGLE cosmological simulations but 3.8 times lower than the corresponding value in TNG100. Central surface brightness and scalelength of the gLSB disks scale with the luminosity of the central component, becoming fainter and flatter as the central component grows more luminous, suggesting rapid disk formation rather than the inside-out growth typical of high surface brightness late-type galaxies. Many gLSBGs also show extended UV counterparts in GALEX, strengthening their connection to XUV-disk galaxies. Finally, comparison with superluminous spirals shows that even complete gas-to-star conversion cannot transform a typical gLSBG into a superspiral, owing to their lower total baryonic mass.