EVOLUTION OF LYMAN-ALPHA CLOUDS AT LOW REDSHIFTS

We examine the evolution of an intergalactic gas cloud confined by the gravity of cold dark matter in the minihalo model. Assuming that the evolution of the diffuse ultraviolet (UV) flux follows a power law fun ction of the form (1+z)(alpha i) with a change in exponent at redshift z(c), and a constant comoving number density of gas clouds, we can re produce the evolution of the number of clouds per unit redshift at bot h high and low redshifts with alpha(L)=2 for z less than or equal to z (c) and alpha(H)=-4 (or -3) for z>z(c) with z(c)=1.9 (or 1.8). Such a small value of alpha(L) implies much more UV flux at low redshifts tha n is expected from the luminosity function of observed quasars. Moreov er, we find that the required intensity of this UV flux is consistent with observations of the Gunn-Peterson effect and of the continuum dep ression.