Reionization and Cosmic Dawn: theory and simulations

Abstract

We highlight recent progress in the sophistication and diversification of cosmic dawn and reionization simulations. The application of these modeling tools to current observations has allowed us narrow down the timing of reionization, which we now know to within ∆z ∼ 1 for the bulk of reionization. The strongest constraints come from the optical depth to the CMB measured with the Planck satellite and the first detection of ongoing reionization from the spectra of the z = 7.1 QSOs ULASJ1120+0641. However, we still know virtually nothing about the astrophysical sources during the first billion years. The revolution in our understanding will be led by upcoming interferometric observations of the cosmic 21-cm signal. The properties of the sources and sinks of UV and X-ray photons are encoded in the 3D patterns of the signal. The development of Bayesian parameter recovery techniques, which tap into the wealth of the 21-cm signal, will soon usher in an era of precision astrophysical cosmology.

Probing Compensated Isocurvature with the 21-cm Signal during Cosmic Dawn

“…Including longer baselines significantly slows computation and adds negligible precision to the measurement at the redshifts used in this work. Each station 10 has diameter of 35 m giving SKA a core collecting area of 374444 m 2 accross a total bandwidth ranging [50,350] MHz. SKA is simulated for 6 hours per night for a tracked scan (different fields for 1 hour each) and as a drift scan.…”

“…Secondly, HERA [82,83], where stations are located in a filled hexagonal grid (11 along each side). Each station is 14 m in diameter giving a total collecting area of 50,953 m 2 accross a total bandwidth ranging [50,250] MHz. The antennae are taken to be at T rx = 100K.…”

“…During the cosmic dawn the first stars will produce a UV background, which will redshift into the Lyman-α line and couple the spin and kinetic temperatures of hydrogen in the intergalactic medium (IGM) via the Wouthuysen-Field effect [44][45][46]. Remnants of these first stars are likely to produce a diffuse background of ∼ 0.1 − 2 keV X-rays [47,48], heating the IGM before reionization progresses largely after z ∼ 10 [49][50][51]. As the tail-end of reionization is approached (z < 10), the effects of streaming velocities in the IGM on the 21-cm signal are reduced by Lyman-Werner feedback [42,52].…”