We use a semi-analytical model to study the impact of reionization, and the associated radiative feedback, on galaxy formation. Two feedback models have been considered: (i) a standard prescription, according to which star formation is totally suppressed in galaxies with circular velocity below a critical threshold (model CF06) and (ii) a characterization based on the filtering scale (model G00), allowing for a gradual reduction of the gas available for star formation in low-mass galaxies. In model CF06, reionization starts at z <~ 15-20 and is 85 per cent complete by z ~ 10; at the same z, the ionized fraction is 16 per cent in model G00. The models match SDSS constraints on the evolution of the neutral hydrogen fraction at z < 7, but predict different Thomson optical depths, τe = 0.1017 (CF06) and 0.0631 (G00); such values are within 1σ of the Wilkinson Microwave Anisotropy Probe three-year determination. Both models are in remarkable good agreement with additional existing data [evolution of Lyman-limit systems, cosmic star formation history, high-z galaxy counts, intergalactic medium (IGM) thermal history], which therefore cannot be used to discriminate among different feedback models. Deviations among radiative feedback prescriptions emerge when considering the expected HI 21-cm background signal, where a ~15 mK absorption feature in the range 75-100 MHz is present in model G00 and a global shift of the emission feature preceding reionization towards larger frequencies occurs in the same model. Single dish observations with existing or forthcoming low-frequency radio telescopes can achieve mK sensitivity, allowing the identification of these features provided that foregrounds can be accurately subtracted.
Detectable signatures of cosmic radiative feedback
FERRARA, ANDREA;
2008
Abstract
We use a semi-analytical model to study the impact of reionization, and the associated radiative feedback, on galaxy formation. Two feedback models have been considered: (i) a standard prescription, according to which star formation is totally suppressed in galaxies with circular velocity below a critical threshold (model CF06) and (ii) a characterization based on the filtering scale (model G00), allowing for a gradual reduction of the gas available for star formation in low-mass galaxies. In model CF06, reionization starts at z <~ 15-20 and is 85 per cent complete by z ~ 10; at the same z, the ionized fraction is 16 per cent in model G00. The models match SDSS constraints on the evolution of the neutral hydrogen fraction at z < 7, but predict different Thomson optical depths, τe = 0.1017 (CF06) and 0.0631 (G00); such values are within 1σ of the Wilkinson Microwave Anisotropy Probe three-year determination. Both models are in remarkable good agreement with additional existing data [evolution of Lyman-limit systems, cosmic star formation history, high-z galaxy counts, intergalactic medium (IGM) thermal history], which therefore cannot be used to discriminate among different feedback models. Deviations among radiative feedback prescriptions emerge when considering the expected HI 21-cm background signal, where a ~15 mK absorption feature in the range 75-100 MHz is present in model G00 and a global shift of the emission feature preceding reionization towards larger frequencies occurs in the same model. Single dish observations with existing or forthcoming low-frequency radio telescopes can achieve mK sensitivity, allowing the identification of these features provided that foregrounds can be accurately subtracted.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
