2026ApJ...998...19S

Giant low-surface-brightness galaxies (gLSBGs) are rare objects with disk radii up to 160 kpc and dynamical masses of up to the order of 10¹²M_⊙. Their very existence challenges currently accepted theories of galaxy formation and evolution, as it is difficult to build such large, dynamically cold disks through mergers without destroying them. We present deep MUSE mosaic observations of two nearby gLSBGs with compact elliptical satellites: UGC 1382, which hosts a globally counterrotating gaseous disk, and AGC 192040, which does not. We analyze properties of ionized gas and present spatially resolved maps of kinematics and metallicity, as well as stellar population analysis for the central regions of the galaxies. The radial gradients of gas-phase metallicities are flat for both galaxies. Our observational data indicate that both galaxies experienced mergers several Gyr ago. However, the scenarios of the formation of giant disks appear to be slightly different for these two systems. For AGC 192040, we propose gas accretion from the filament or from the cooling hot halo gas followed by a merger with a companion on a prograde orbit at an intermediate mass ratio. For UGC 1382, multiple gas-rich mergers with companions on retrograde orbits are preferred by the data.