Early Structure Formation and Reionization in a Warm Dark Matter Cosmology

Details Early Structure Formation and Reionization in a Warm Dark Matter Cosmology Early Structure Formation and Reionization in a Warm Dark Matter Cosmology

2003-03-28

arxiv.org/abs/astro-ph/0303622v2

Astrophys.J.591:L1-L4,2003

Astronomy and Astrophysics

Astrophysics

Minor revision and citation updated. Version accepted by ApJL

Scientific paper

10.1086/376963

We study first structure formation in Lambda-dominated universes using large cosmological N-body/SPH simulations. We consider a standard LCDM model and a LWDM model in which the mass of the dark matter particles is taken to be m_X=10 keV. The linear power spectrum for the LWDM model has a characteristic cut-off at a wavenumber k=200 /Mpc, suppressing the formation of low mass (< 10^6 Msun) nonlinear objects early on. The absence of low mass halos in the WDM model makes the formation of primordial gas clouds with molecular hydrogen very inefficient at high redshifts. The first star-forming gas clouds form at z~21 in the WDM model, considerably later than in the CDM counterpart, and the abundance of these gas clouds differs by an order of magnitude between the two models. We carry out radiative transfer calculations by embedding massive Population III stars in the gas clouds. We show that the volume fraction of ionized gas rises up close to 100% by z=18 in the CDM case, whereas that of the WDM model remains extremely small at a level of a few percent. Thus the WDM model with m_X=10 keV is strongly inconsistent with the observed high optical depth by the WMAP satellite.

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