A New interpretation of chain galaxies at high redshift

Abstract

We propose a possible new model for the formation of chain galaxies at high redshift. Our model is summarized as follows. Step I: Successive merging of subgalactic gas clumps results in the formation of a galaxy with a mass of $10^{11-12} M_\odot$ at redshift $z \sim 5$. Step II: 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 hundreds of kpc. 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. Step III: Since the shell or the slab can be regarded as a gaseous sheet, filament-like gravitational instability is expected to occur. Step IV: Further gravitational instability occurs in each filament, leading to intense star formation along the filament. This is the chain galaxy phase. Step V: The filament collapses gravitationally into one spheroidal system like an elliptical galaxy within one dynamical timescale of the filament ($\sim 10^8$ 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 Ly$\alpha$ systems because their H {\sc i} column densities are expected to be $N_{\rm HI} \gtrsim 10^{19}$ cm$^{-2}$.