Heating of Intergalactic Gas Near Growing Black Holes During the Hydrogen Reionization Epoch

Abstract

Black holes growing during Eddington accretion emit a large number of ultraviolet and x-ray photons which can influence the ionization and thermal state of the surrounding intergalactic gas before the onset of the hydrogen reionization epoch in the universe. This radiation heats the gas beyond the temperature of the relict radiation (cosmic microwave background CMB) TCMB (z) to a red shift z ~ 8 –12 within 0.1-3 Mpc of a black hole with initial mass ~300 M⨀ formed at z ~ 20-50 and growing with radiation efficiency e ~ 0.15 – 0.075. The size of the gas regions in which the degree of ionization of hydrogen is higher than the residual value after recombination, i.e., greater than 10-4, approaches the same levels. More substantial heating and ionization of the gas takes place in a smaller volume. In the vicinity of 30-300 kpc, for the same black hole parameters, it is heated to above 104 K or almost an order of magnitude greater than around a black hole with almost constant mass. The radiative flux from growing black holes is sufficient for complete (above 99%) production of ionized hydrogen and doubly ionized helium within 3-10 kpc of the parent minihalo. The recombination time for hydrogen in the ionization zones surrounding the black holes exceeds the local age of the universe for z ≲ 10. These zones, which occupy several kiloparsecs, can become seeds for the next reionization of the universe. It turns out that extended regions with sizes of hundreds of kiloparsecs where radiation from growing black holes substantially changes the evolution of the intergalactic gas will radiate in the 21 cm line of atomic hydrogen, since the gas in these zones essentially remains neutral at a temperature exceeding that of the CMB.