Properties of reionization-era galaxies from JWST luminosity functions and 21-cm interferometry

Abstract

Next generation observatories will enable us to study the first billion years of our Universe in unprecedented detail. Foremost among these are 21-cm interferometry with the Hydrogen Epoch of Reionization Arrays (HERA) and the Square Kilometre Array (SKA), and high-z galaxy observations with the James Webb Space Telescope (JWST). Taking a basic galaxy model, in which we allow the star formation rates and ionizing escape fractions to have a power-law dependence on halo mass with an exponential turnover below some threshold, we quantify how observations from these instruments can be used to constrain the astrophysics of high-z galaxies. For this purpose, we generate mock JWST LFs, based on two different hydrodynamical cosmological simulations; these have intrinsic luminosity functions (LFs) which turn over at different scales and yet are fully consistent with present-day observations. We also generate mock 21-cm power spectrum observations, using 1000h observations with SKA1 and a moderate foreground model. Using only JWST data, we predict up to a factor of 2-3 improvement (compared with HST) in the fractional uncertainty of the star formation rate to halo mass relation and the scales at which the LFs peak (i.e. turnover). Most parameters regulating the UV galaxy properties can be constrained at the level of ∼ 10% or better, if either (i) we are able to better characterize systematic lensing uncertainties than currently possible; or (ii) the intrinsic LFs peak at magnitudes brighter than M UV ∼ < −13. Otherwise, improvement over HST-based inference is modest. When combining with upcoming 21-cm observations, we are able to significantly mitigate degeneracies, and constrain all of our astrophysical parameters, even for our most pessimistic assumptions about upcoming JWST LFs. The 21-cm observations also result in an order of magnitude improvement in constraints on the EoR history.

Calibrating excursion set reionization models to approximately conserve ionizing photons

“…McGreer et al 2015;Planck Collaboration 2016;Pagano et al 2020). Furthermore, the galaxy scaling relations are consistent with results from hydrodynamic simulations (e.g., Xu et al 2016;Park et al 2020;Ma et al 2020) and semi-analytical galaxy formation models (e.g., Sun & Furlanetto 2016;Mutch et al 2016;Tacchella et al 2018;Behroozi et al 2019;Yung et al 2019). We briefly summarize the model here and its free parameters; interested readers can find more details in Park et al (2019).…”

Effect of the cosmological transition to metal-enriched star-formation on the hydrogen 21-cm signal

“…X-ray heating becomes relevant later (z 20, Cohen et al 2017Cohen et al , 2018 owing to the fact that it takes time for the first population of X-ray sources (such as X-ray binaries, Fragos et al 2013) to emerge. The impact of reionization on the 21-cm signal becomes apparent only at relatively late times (z 15 in Cohen et al 2017Cohen et al , 2018 with the appearance of massive galaxies which are efficient in ionizing the gas (e.g., Park et al 2020). It is, thus, expected that the Pop III-Pop II transition explored in this paper will mostly affect the 21-cm signal from the era of Ly-α coupling.…”

Implications of the z &gt; 5 Lyman-α forest for the 21-cm power spectrum from the epoch of reionization

“…The assumption TK TCMB is a plausible approximation at redshifts of our interest, since heating due to X-rays from first sources is expected to raise temperature of the neutral gas well above the TCMB by z ∼ 10 ( Bowman et al 2018;Ghara et al 2021). Some recent models have suggested that X-ray heating might be delayed to z < 10 (Fialkov et al 2014;Madau & Fragos 2017;Mirocha et al 2017;Cohen et al 2017;Park et al 2020;Mebane et al 2020). Our assumption (TS TCMB) will not be valid in such scenarios, but other than the redshift of heating transition (TK TCMB), the spin temperature fluctuations are only expected to enhance the power spectrum of 21-cm signal (Fialkov et al 2014;Mesinger et al 2014;Raste & Sethi 2018Ma et al 2021).…”