Abstract
ABSTRACT In this work, we use the astraeus (seminumerical rAdiative tranSfer coupling of galaxy formaTion and Reionization in N-body dArk mattEr simUlationS) framework that couples galaxy formation and reionization in the first billion years. Exploring a number of models for reionization feedback and the escape fraction of ionizing radiation from the galactic environment (fesc), we quantify how the contribution of star-forming galaxies (with halo masses $M_\mathrm{ h}\gt 10^{8.2}\, {\rm \rm M_\odot }$) to reionization depends on the radiative feedback model, fesc, and the environmental overdensity. Our key findings are: (i) for constant fesc models, intermediate-mass galaxies (with halo masses of $M_\mathrm{ h}\simeq 10^{9-11}\, {\rm \rm M_\odot }$ and absolute UV magnitudes of MUV ∼ −15 to −20) in intermediate-density regions (with overdensity log10(1 + δ) ∼ 0−0.8 on a 2 comoving Mpc spatial scale) drive reionization; (ii) scenarios where fesc increases with decreasing halo mass shift, the galaxy population driving reionization to lower mass galaxies ($M_\mathrm{ h}\lesssim 10^{9.5}\, {\rm \rm M_\odot }$) with lower luminosities (MUV ≳ −16) and overdensities [log10(1 + δ) ∼ 0−0.5 on a 2 comoving Mpc spatial scale]; (iii) reionization imprints its topology on the ionizing emissivity of low-mass galaxies ($M_h\lesssim 10^{9}\, {\rm \rm M_\odot }$] through radiative feedback. Low-mass galaxies experience a stronger suppression of star formation by radiative feedback and show lower ionizing emissivities in overdense regions; (iv) a change in fesc with galaxy properties has the largest impact on the sources of reionization and their detectability, with the radiative feedback strength and environmental overdensity playing a sub-dominant role; (v) James Webb Space Telescope-surveys (with a limiting magnitude of MUV = −16) will be able to detect the galaxies providing ${\sim}60{-}70{{\ \rm per\ cent}}$ (${\sim}10{{\ \rm per\ cent}}$) of reionization photons at z = 7 for constant fesc models (scenarios where fesc increases with decreasing halo mass).
Highlights
The Epoch of Reionization marks a pivotal time in the history of our Universe when the photons emitted by the first stars and galaxies permeate and gradually ionize the intergalactic medium (IGM)
While the factor fg modifying the initial gas mass reservoir accounts for the effects of radiative feedback, the effective star formation rate accounts for the suppressed star formation in low-mass haloes (Mh 109.5 M ) due to gas being heated and ejected from a galaxy by supernovae type II (SNII) explosions from star formation in the current and, since we account for massdependent stellar lifetimes Padovani & Matteucci (1993), all previous time-steps
For all constant fesc models, we find the ionizing photon contribution to be dominated by Mh = 109−10 M haloes during the first half of reionization and by Mh = 109−10 M and increasingly Mh = 1010−11 M haloes during the second half of reionization
Summary
The Epoch of Reionization marks a pivotal time in the history of our Universe when the photons emitted by the first stars and galaxies permeate and gradually ionize the intergalactic medium (IGM). We investigate how SN and radiative feedback or the escape fraction of ionizing photons can redistribute the ionizing photon contribution within the galaxy population, and whether these processes affect the ionizing emissivities of galaxies in different parts of the cosmic web differently, i.e. do galaxies contribute different amounts of ionizing photons depending on whether they lie in overdense or underdense regions To answer these questions, we analyse a set of self-consistent, seminumerical simulations of galaxy evolution and reionization that were run within the ASTRAEUS framework (Hutter et al 2021).
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