Event calendar file
State of the Universe
Implications of the z ~ 5 Lyman-alpha forest for the 21-cm power spectrum from EoR
by Dr. Jankee Raste
Friday, February 12, 2021
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| Description |
Most ongoing experiments targeting to detect the neutral hydrogen (HI) 21-cm signal from Epoch of Reionization (EoR) aims to look for the signal at redshifts well above 6. This strategy is motivated by the traditional assumption that reionization ends at z ~ 6. However, recent observations of Lyman-alpha absorption troughs in spectra of high redshift QSOs suggest large spatial fluctuations of HI gas within the intergalactic medium (IGM) at redshifts z = 5–6. These observations, combined with the Cosmic Microwave Background (CMB) Thomson scattering optical depth observed by Planck Collaboration prefer a significantly delayed reionization scenario in which the reionization is 50% complete at redshifts as low as z ~ 7. In these models, reionization ends at z ~ 5, with large 100-Mpc "islands" of cold, neutral hydrogen persisting in the IGM well below z = 6. We study the effect of these neutral hydrogen islands on the 21-cm power spectrum by analyzing outputs of a state-of-the-art radiative transfer simulation of the IGM calibrated to the CMB and Lyman-alpha forest data. We calculate the power spectra of the 21-cm signal from these simulations and compare them with a more traditional reionization model in which reionization is completed by z = 6.7. Contrary to previous models, we find that thanks to the late end of reionization the 21-cm power continues at be high at z = 5-6 and this signal should be detectable by upcoming radio interferometric projects (HERA and SKA1- LOW) for reasonable integration times, assuming optimistic foreground models. We argue that the redshift range z = 5-6 is very attractive for 21-cm experiments due to easier thermal noise characteristics and synergies with abundant multi-wavelength observations. |
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