A New Interpretation of Chain Galaxies at High Redshift

We propose a possible new model for the formation of chain galaxies at high redshift. Our model is summarized as follows. (1) Successive merging of subgalactic gas clumps results in the formation of a galaxy with a mass of 10¹¹-10¹² M_solar at redshift z~5. (2) Subsequently, supernova explosions occur inside the galaxy and then blow out as a galactic wind (or a superwind). This wind expands into the intergalactic space and then causes a large-scale shell with a radius of several hundred kiloparsecs. Since this radius may be smaller than the typical separation between galaxies, interactions of shells may also occur, resulting in the formation of a large-scale gaseous slab. (3) Since the shell or the slab can be regarded as a gaseous sheet, filament-like gravitational instability is expected to occur. (4) Further gravitational instability occurs in each filament, leading to intense star formation along the filament. This is the chain galaxy phase. (5) The filament collapses gravitationally into one spheroidal system like an elliptical galaxy within one dynamical timescale of the filament (~10⁸ yr). Therefore, it seems quite difficult to find remnants of chain galaxies. We also discuss that shocked shells driven by superwinds may be responsible for some Lyman limit systems and damped Lyα systems because their H I column densities are expected to be N_HI>~10¹⁹ cm^-2.