2006/03/21 by Zoltán Haiman, Zoltan Haiman, Greg L. Bryan · 4 citations
Physics and Astronomy · #Astrophysics and Star Formation Studies #Galaxies: Formation, Evolution, Phenomena #Gamma-ray bursts and supernovae #astro-ph
paper · pdf · doi:10.1086/506580
published as Astrophys.J.650:7-11,2006 · ApJL, submitted
arxiv created 2006/03/21 · openalex publication_date 2006/10/10 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
The primordial gas in the earliest dark matter halos, collapsing at redshifts around z=20, with masses Mhalo=106 Msun, and virial temperatures Tvir<104K, relied on the presence of molecules for cooling. Several theoretical studies have suggested that gas contraction and star-formation in these minihalos was suppressed by radiative, chemical, thermal, and dynamical feedback processes. The recent measurement by the Wilkinson Microwave Anisotropy Probe (WMAP) of the optical depth to electron scattering, tau=0.09+/-0.03, provides the first empirical evidence for this suppression. The new WMAP result is consistent with vanilla models of reionization, in which ionizing sources populate cold dark matter (CDM) halos down to a virial temperature of Tvir=104K. On the other hand, we show that in order to avoid overproducing the optical depth, the efficiency for the production of ionizing photons in minihalos must have been about an order of magnitude lower than expected and lower than the efficiency in large halos that can cool via atomic hydrogen (Tvir > 104K). This conclusion is insensitive to assumptions about the efficiency of ionizing photon production in the large halos, as long as reionization ends by z=6, as required by the spectra of bright quasars at z<6. Our conclusion is strengthened if the clumping of the ionized gas evolves with redshift, as suggested by semi-analytical predictions and three-dimensional numerical simulations.