LY-ALPHA CLOUDS - ISOLATED STRUCTURES IN COLD DARK MATTER COSMOGONY

Formation of low-mass objects is inevitable in a cold dark matter (CDM) cosmogony. Objects that exist in near-mean background density environments are most likely to survive destruction. Such objects will also not exhibit strong clustering. Models have been proposed seeking to identify these isolated low-mass condensates as Lyα cloud candidates. However, the accompanying estimates of quantities such as the epoch of formation, the number density of candidate objects, etc., are not based on characteristics of isolated density peaks. Isolated density peaks result primarily from power in a narrow band at the mass scale of the structures. In this paper, we introduce a filter designed to study isolated density fluctuations. We use the filter to identify Lyα cloud candidates in a biased CDM model. We find that the number density of cloud candidates at Z = 2.5 is too small to account for the observed number of lines. If Lyα clouds have their origins in primordial density fluctuations, the CDM power spectrum does not have sufficient power on subgalactic scales to account for the observed structures.