Singposts of shock waves in the metagalactic medium

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Explosions of quasars and young galaxies at large redshifts must cause propagation of blast waves in the metagalactic medium. The shock waves formed can, during the radiative cooling stage, produce dense cold spherical shells around the epicentres of explosions. But, even before that, at the stage of adiabatic expansion, each spherical shock-wave front, if it lies on one line-of-sight with a more distant quasar, can imprint into the quasar spectrum a specific absorption ‘doublet’ with a distance between the components (in the rest frame) Δλ0 ≲ 3 A. The Lα doublet components have a small but the same equivalent widthW0 ≲ 0.3 A, the ratioW0/Δλ0 weakly depending onW0 ifW0 is small. We demonstrate here that such absorption Lα doublets are really present among the ‘Lα forest’ in the absorption spectra of distant quasars which are, according to Sargentet al. (1980), of mostly intervening (and not intrinsic) origin. Further accumulation of data on absorption doublets, which can serve as direct indicators of metagalactic shock-waves, may provide valuable information about the physical conditions in the metagalactic gas at large redshifts.