COLLISIONAL VERSUS COLLISIONLESS MATTER - A ONE-DIMENSIONAL ANALYSIS OF GRAVITATIONAL CLUSTERING

We present the results of a series of one-dimensional N-body and hydro dynamical simulations which have been used for testing the different c lustering properties of baryonic and dark matter in an expanding backg round. The numerical code is based on the piecewise parabolic method. Initial Gaussian random density perturbations with a power-law spectru m P(k)proportional to k(n) are assumed. We analyse the distribution of density fluctuations and thermodynamical quantities for different spe ctral indices n and discuss the statistical properties of clustering i n the corresponding simulations. At large scales the final distributio n of the two components is very similar while at small scales the dark matter presents a lumpiness which is not found in the baryonic matter . The amplitude of density fluctuations in each component depends on t he spectral index n but that of the baryonic matter is always larger t han the one in the dark component. This result is also confirmed by th e behaviour of the bias factor, defined as the ratio between the rms o f baryonic and dark matter fluctuations at different scales, which is larger than unity in all the models we have considered. The final temp eratures depend on the initial spectral index: the highest values (10( 8) K) are obtained for n = -1, and are in proximity to high-density re gions. In the other models, the typical post-shock temperatures are sm aller (10(5)-10(7) K).