摘要：We discuss constraints on cosmic reionisation and their implications on a cosmic star formation rate (SFR) densityρSFRmodel; we study the influence of key-parameters such as the clumping factor of ionised hydrogen in the intergalactic medium (IGM)CH IIand the fraction of ionising photons escaping star-forming galaxies to reionise the IGMfesc. Our analysis has used SFR history data from luminosity functions, assuming that star-forming galaxies were sufficient to lead the reionisation process at high redshift. We have added two other sets of constraints: measurements of the IGM ionised fraction and the most recent result fromPlanckSatellite about the integrated Thomson optical depth of the cosmic microwave backgroundτPlanck. Our analysis shows that a reionisation beginning as early asz≥ 14 and persisting untilz~ 6 is a likely scenario. We also considered various possibilities for the evolution offescandCH IIwith redshift, and confront them with observational data cited above. We conclude that, if the model of a constant clumping factor is chosen, the fiducial value of three is consistent with observations; even if a redshift-dependent model is considered, the resulting optical depth is strongly correlated withCH IImean value atz> 7, an additional argument in favour of the use of a constant clumping factor. Similarly, a constant value of the escape fraction is favoured over a redshift-dependent model. When added as a fit parameter, we findfesc= 0.19 ± 0.04. However, this result strongly depends on the choice of magnitude limit in the derivation ofρSFR. Our fiducial analysis considers faint galaxies (Mlim= −13) and the result is a well constrained escape fraction of about 0.2, but whenMlim= −17, the number of galaxies available to reionise the IGM is not sufficient to match the observations, so that much higher values offesc, approaching 70%, are needed.
关键词：Key wordsendark ages, reionization, first stars
