ABSORPTION BY DISCRETE INTERGALACTIC CLOUDS - THEORY AND SOME APPLICATIONS

Using Markoff's method we have derived a general formalism to deal wit h the absorptions produced by randomly distributed discrete clouds, su ch as the QSO absorption-line systems. For a power-law H I column dens ity distribution we have calculated the optical depth distribution P(t au) by carrying out the integration of inverse Laplace transform along the steepest descent, and an analytical approximation of P(tau) has a lso been given. The two important parameters, i.e., the effective opti cal depth tau(eff) and the count reduction factor f(c), have been comp uted for the QSO absorption systems. We then use these results to deal with problems of the attenuation of ionizing background by QSO absorp tion-line systems, the difficulty of conducting the He II Gun-Peterson test, and the dust grain obscuration of distant quasars. The Lyman-co ntinuum absorption by QSO absorption-line systems not only reduces the intensity of the ionizing field significantly, but also tilts the int rinsic source spectrum to result in a flat background spectrum near nu (L). With a few reasonable approximations we have derived analytical e xpressions for J(nuL)(z(obs)). The QSO contribution is calculated to b e roughly constant for z(obs) greater-than-or-equal-to 2.2 with a valu e J(nuL) approximately 4 x 10(-22) ergs s-1 cm-2 Hz-1 sr-1, if a const ant comoving density for QSOs at z greater-than-or-equal-to 2.2 is ass umed.