GALAXY EVOLUTION AT HIGH REDSHIFT: OBSCURED STAR FORMATION, GRB RATES, COSMIC REIONIZATION, AND MISSING SATELLITES

Abstract

We provide a holistic view of galaxy evolution at high redshifts z ≳ 4, which incorporates the constraints from various astrophysical/cosmological probes, including the estimate of the cosmic star formation rate (SFR) density from UV/IR surveys and long gamma-ray burst (GRBs) rates, the cosmic reionization history following the latest Planck measurements, and the missing satellites issue. We achieve this goal in a model-independent way by exploiting the SFR functions derived by Mancuso et al. on the basis of an educated extrapolation of the latest UV/far-IR data from HST / Herschel , and already tested against a number of independent observables. Our SFR functions integrated down to a UV magnitude limit M UV  ≲ −13 (or SFR limit around 10 −2 M ⊙ yr −1 ) produce a cosmic SFR density in excellent agreement with recent determinations from IR surveys and, taking into account a metallicity ceiling Z ≲ Z ⊙ /2, with the estimates from long GRB rates. They also yield a cosmic reionization history consistent with that implied by the recent measurements of the Planck mission of the electron scattering optical depth τ es  ≈ 0.058; remarkably, this result is obtained under a conceivable assumption regarding the average value f esc  ≈ 0.1 of the escape fraction for ionizing photons. We demonstrate via the abundance-matching technique that the above constraints concurrently imply galaxy formation becoming inefficient within dark matter halos of mass below a few 10 8 M ⊙ ; pleasingly, such a limit is also required so as not to run into the missing satellites issue. Finally, we predict a downturn of the Galaxy luminosity function faintward of M UV  ≲ −12, and stress that its detailed shape, to be plausibly probed in the near future by the JWST , will be extremely informative on the astrophysics of galaxy formation in small halos, or even on the microscopic nature of the dark matter.