The concerted impact of galaxies and QSOs on the ionization and thermal state of the intergalactic medium

Abstract

We present a detailed analysis of the ionization and thermal structure of the intergalactic medium (IGM) around a high-redshift QSO using a large suite of cosmological, multifrequency radiative transfer (RT) simulations, exploring the contribution from galaxies as well as the QSO, and the effect of X-rays and secondary ionization. We show that in high-z QSO environments both the central QSO and the surrounding galaxies concertedly control the reionization morphology of hydrogen and helium and have a non-linear impact on the thermal structure of the IGM. A QSO imprints a distinctive morphology on H II regions if its total ionizing photon budget exceeds that of the surrounding galaxies since the onset of hydrogen reionization; otherwise, the morphology shows little difference from that of H II regions produced only by galaxies. In addition, the spectral shape of the collective radiation field from galaxies and QSOs controls the thickness of the I-fronts. While a UV-obscured QSO can broaden the I-front, the contribution from other UV sources, either galaxies or unobscured QSO, is sufficient to maintain a sharp I-front. X-rays photons from the QSO are responsible for a prominent extended tail of partial ionization ahead of the I-front. QSOs leave a unique imprint on the morphology of He II/He III regions. We suggest that, while the physical state of the IGM is modified by QSOs, the most direct test to understand the role of galaxies and QSOs during reionization is to perform galaxy surveys in a region of sky imaged by 21 cm tomography.

Constraints on high-J CO emission lines in z ∼ 6 quasars

“…(e.g., Pallottini et al 2017a,b) and radiative transfer of X-ray photons (e.g., Kakiichi et al 2017), thus hampering a realistic comparison with observations.…”

Radiative transfer of ionizing radiation through gas and dust: the stellar source case

“…The next project we plan to approach using the implementation presented here is investigating non-equilibrium ionization by Active Galactic Nuclei (AGN), complementing the work done in Kakiichi et al (2017) with dust. Such sources allow studying X-ray effects since they emit large numbers of photons at high energies, where the dust cross section gains importance in comparison with the gas cross section.…”

Observing the Redshifted 21 cm Signal around a Bright QSO at z ∼ 10

“…We analyze the results of hydrodynamical and radiative transfer (RT) simulations (Kakiichi et al 2017) to study the 21 cm signal around a bright QSO at z ∼ 10 and its detectability with SKA1-low and LOFAR. The RT calculations include ionizing photons both from the QSO and the galaxies surrounding it.…”