Study On 21 Cm Signal Of High Redshift Quasars

In the modern cosmology theory,our Universe started with a Big Bang,and then experienced the rapid expansion stage.380,000 years later,baryons and photons decoupled,and produced the microwave background radiation(CMB),then the Universe entered the dark age.The cosmic reionization occurred after the first generation of stars and galaxies,? 1billion years after Big Bang.The primary density turbulence of the Universe made it possible to form galaxies,thus it is key point to understand the formation and evolution of high redshift stars,for the study of epoch of reionization.In this thesis,I would focus on the high redshift quasars(QSO)which is an important probe on studying the reionization,e.g.the observation of the QSO spectrum of Gunn-Peterson trough has proved that the cosmic reionization ended approximately at z?6.The QSO radiations such as ultraviolet(UV)photons and X-ray photons can gradually ionize and heat the neutral hydrogen in the surrounding,which enables a large ionization region(HII region)around QSO,with a large amount of neutral hydrogen in the IGM surrounding the HII region,thus one promising way to study the epoch of reionization is to measure the 21 cm radiation emitted by neutral hydrogen.In this thesis,I use ULAS J1120 + 0641 as a reference source,then study the 21 cm signal around the HII region using theoretical model and high-resolution numerical simulations.The results of high-resolution numerical simulations are used to fix the theoretical model that high redshift quasars(QSO)ionizing and heating neutral gas.I also predict the signal characteristics and signal/noise(S/N)ratios for Five-hundred meter Aperture Spherical Telescope(FAST)to observe such 21 cm radiation around the QSO.Our conclusions are summarized as:(1)the 21 cm frequency spectrum under the FAST field has full HII region for the QSO at z = 8 and with luminosity similar to ULAS J1120+0641,while has only a small trough for the QSO at z = 10 and with low luminosity;(2)the effect of finite light travel-time(FLTT)obviously changes the 21 cm frequency spectrum of high redshift QSOs,makes the transition curve at lower frequency much steeper than that at higher frequency;(3)the FAST telescope can observe the 21 cm radiation around the high redshift QSO with very high S/N ratio which as high as ?12,thus can identify the HII regions and the FLTT effect.