MOLECULAR SIGNALS FROM PRIMORDIAL CLOUDS AT HIGH-REDSHIFT

The possibility of detecting cosmological signals from the postrecombi nation universe is one of the main aims of modern cosmology. In a prev ious paper we emphasized the role that elastic resonant scattering thr ough WH molecules can have in dumping primary cosmic background radiat ion (CBR) anisotropies and raising secondary signals. Here we extend o ur analysis to all the evolutionary stages of a primordial cloud, star ting with the linear phase, through the turnaround, and to the nonline ar collapse. We have done calculations for protoclouds in a cold dark matter (CDM) scenario and, more generally, for a set of clouds with va rious masses and various turnaround redshifts, in this case without re ferring to any particular structure formation scenario. We found that the first phase of collapse, for t/t(free-fall) = 0.05-0.2 is the best one for simultaneous detection of the first two LiH rotational lines. The observational frequency falls between 30 and 250 GHz, and the lin e width Delta nu/nu is between 10(-5) and 10(-4). As far as we know, t his is the most favorable process to detect primordial clouds before t hey begin star formation processes.