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 su bgalactic gas clumps results in the formation of a galaxy with a mass of 10 (11)-10(12) M-. at redshift z similar to 5. (2) Subsequently, supernova exp losions 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 thi s radius may be smaller than the typical separation between galaxies, inter actions of shells may also occur, resulting in the formation of a large-sca le gaseous slab. (3) Since the shell or the slab can be regarded as a gaseo us sheet, filament-like gravitational instability is expected to occur. (4) Further gravitational instability occurs in each filament, leading to inte nse star formation along the filament. This is the chain galaxy phase. (5) The filament collapses gravitationally into one spheroidal system like an e lliptical galaxy within one dynamical timescale of the filament (similar to 10(8) yr). Therefore, it seems quite difficult to find remnants of chain g alaxies. We also discuss that shocked shells driven by superwinds may be re sponsible for some Lyman limit systems and damped Ly alpha systems because their H I column densities are expected to be N-HI greater than or similar to 10(19) cm(-2).