Intergalactic shells at large redshift

Galactic explosions at large redshift may produce intergalactic shells, the interiors of which cool by inverse Compton scattering off the cosmic background radiation. These shells have characteristic angular size approx.1' at peak brightness; at z<2 they typically have radius 0.5 Mpc, velocity approx.50 km s-1, and metal abundance approx.10-4 of cosmic values. They radiate strongly in H I (Lyα), He II lambda304, and infrared fine-structure lines of C II and Si II. The redshifted emission from individual shells is at the current level of detectability. The predicted extragalactic background emission from many shells, strongly peaked toward the UV, sets and upper limit to the number of exploding sources at zapprox.10. Shell absorption lines of H I, C II, Si II, and Fe II may be seen at more recent epochs in quasar spectra. Each of these observations may probe otherwise invisible explosions in the early universe