The end of the Dark Ages in MOND

Abstract

We study the evolution of a spherically symmetric density perturbation in the Modified Newtonian Dynamics (MOND) model applied to the net acceleration over Hubble flow. The background cosmological model is a $\Lambda$-dominated, low-$\Omega_b$ Friedmann model with no Cold Dark Matter. We include thermal processes and non-equilibrium chemical evolution of the collapsing gas. We find that under these assumptions the first low-mass objects ($M \le 3\times 10^4 M_{\odot}$) may collapse already for $z\sim 30$, which is in quite good agreement with the recent WMAP results. A lower value of $a_0$ would lead to much slower collapse of such objects.