The First Compact Objects in the $\Lambda$-dominated Universe

Abstract

We calculate the evolution of a low-mass ($M\le 10^5{M}_{\odot }$) spherically symmetric density perturbation in the ${\Omega }_b{h}^2=0.02$, ${\Omega }_M=0.35$, ${\Omega }_{\Lambda }=0.65$, $h=0.72$ Universe. The results are compared with the ones that assume no cosmological constant and the flat, dark matter dominated Universe. We include thermal processes and non-equilibrium chemical evolution of the collapsing gas. We find that direct formation of bound objects with such masses by $z=8$ is unlikely so in fact they may form only through fragmentation of greater objects. This is in stark contrast to the $\Omega =1$ pure CDM cosmology, where low-mass objects form abundantly at redshits $z>10$.

LaTeX 2e, 7 pages, 9 figures, to appear in MNRAS, uses mn2e style (included) with graphicx and natbib (included) packages