Mathematics – Logic
Scientific paper
Aug 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996phdt..........v&link_type=abstract
Ph.D. Thesis, Texas Univ., Austin, 1996.
Mathematics
Logic
4
Scientific paper
The gravitational instability of cosmological pancakes composed of both collisionless and baryonic matter in an Einstein-de Sitter universe is investigated numerically by Particle-Mesh and Smoothed Particle Hydrodynamics methods, to demonstrate that pancakes are unstable with respect to fragmentation and the formation of bound lumps. A "pancake" is defined here to be the nonlinear outcome of the growth of a 1D, sinusoidal, plane-wave, adiabatic density perturbation. We have studied the stability and fragmentation of pancakes subject to either symmetric (density) or antisymmetric (bending) perturbation modes with wavevector k perpendicular to the pancake wavelength k_p. We find: (1) For all k greater than k_p, the pancake surface density perturbation grows as a power law in time, with index alpha which is significantly larger than the value of 2/3 for a linear density fluctuation in the absence of the primary pancake. (2) The index alpha scales as k^n where n~0.2. (3) The onset of nonlinearity is signaled by a decline of growth rate and the production of bound overdense clumps. In 2D, "clumps" correspond to filaments. These filaments have azimuthally-averaged collisionless matter density profiles rho \prop rho^-n, n~1. In 3D, n~2.75 for the collisionless halos. (4) Clumps formed as a result of instability are biased (i.e their gas fraction exceeds Omega_b). (5) For the baryonic fluid, significant vorticity is generated behind curved, oblique pancake shocks, and as a result of a non-zero baroclinic term in the region of clumping. Simulations show that the first vortices to form have a spin angular momentum of a few times 10^31 lambda_p,Mpc cm^2s^-1 per unit mass where lambda_p,Mpc is the pancake wavelength in Mpc. This is sufficient to account for the observational value of 10^29-10^31 cm^2s^-1 for typical spiral galaxies. We also investigate the validity of the standard empirical method for determining galaxy cluter mass and baryonic fraction from X-ray brightness profiles by analyzing numerical gas dynamic simulations of the Cold Dark Matter (CDM) cosmogony by Adaptive Smoothed Particle Hydrodynamics. Such mass determinations previously indicated baryonic fractions in excess of BBN constraints and total masses smaller than estimated from gravitational lensing. We calculate the X-ray determined masses of simulated clusters using the standard assumption that clusters are isothermal spheres in hydrostatic equilibrium. We show that such X-ray determinations can often underestimate the cluster total mass by a factor of ~2 and overestimate the baryonic fraction, as a result of the presence of merging substructure and projection effects. This may help to reconcile the previous inconsistent mass estimates of X-ray clusters.
No associations
LandOfFree
Gravitational Instability in Cosmological Pancakes and X-ray Cluster Formation does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Gravitational Instability in Cosmological Pancakes and X-ray Cluster Formation, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Gravitational Instability in Cosmological Pancakes and X-ray Cluster Formation will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-774502