Inferring the astrophysics of reionization and cosmic dawn from galaxy luminosity functions and the 21-cm signal

Abstract

The properties of the first galaxies, expected to drive the Cosmic Dawn (CD) and the Epoch of Reionization (EoR), are encoded in the 3D structure of the cosmic 21-cm signal. Parameter inference from upcoming 21-cm observations promises to revolutionize our understanding of these unseen galaxies. However, prior inference was done using models with several simplifying assumptions. Here we introduce a flexible, physicallymotivated parametrization for high-z galaxy properties, implementing it in the public code 21cmfast. In particular, we allow their star formation rates and ionizing escape fraction to scale with the masses of their host dark matter halos, and directly compute inhomogeneous, sub-grid recombinations in the intergalactic medium. Combining current Hubble observations of the rest-frame UV luminosity function (UV LFs) at high-z with a mock 1000h 21-cm observation using the Hydrogen Epoch of Reionization Arrays (HERA), we constrain the parameters of our model using a Monte Carlo Markov Chain sampler of 3D simulations, 21cmmc. We show that the amplitude and scaling of the stellar mass with halo mass is strongly constrained by LF observations, while the remaining galaxy properties are constrained mainly by 21-cm observations. The two data sets compliment each other quite well, mitigating degeneracies intrinsic to each observation. All eight of our astrophysical parameters are able to be constrained at the level of ∼ 10% or better. The updated versions of 21cmfast and 21cmmc used in this work are publicly available.

Probing small scale primordial power spectrum with 21cm line global signal

“…Nevertheless despite some degenerate effects on the 21cm global signal among the amplitude of primordial fluctuations and astrophysical parameters, they can be removed by combining other observations. Actually a recent analysis [22] has shown that the combination of 21cm power spectrum and UV luminosity function can severely constrain some of the astrophysical parameters, which can reduce the degeneracy.…”

“…The 21cm signal is observed as an absorption when T S is lower than T CMB , and becomes an emission once the gas is heated sufficiently by the X-ray photons and T s gets larger than T CMB . For the analysis in this paper, we use the latest version of 21cmFAST [22,23] for calculating the 21cm line global signal, which we briefly describe here. The 21cmFAST solves the reionization, the evolution of the spin temperature and evaluate the 21cm brightness temperature distribution.…”

“…In particular, the X-ray luminosity per star formation rate and the power law index of X-ray would significantly change the position of absorption trough, which are degenerate with the effect caused by the small scale amplitude of primordial power spectrum. However, these parameters would be strictly constrained by luminosity function and 21cm power spectrum [22], which can remove the degeneracy between the small scale amplitude and astrophysical parameters.…”

Physical Cosmology from the 21 cm Line

“…More complex astrophysical processes can also enable such a period as well -for example, strong photoheating feedback can delay reionization relative to X-ray heating [47]. Whether this is more than speculation remains uncertain: calibrating the X-ray luminosity of star-forming galaxies to local measurements suggests that the reionization epoch may overlap with the X-ray heating epoch [48,57], but if the EDGES measurement is confirmed, heating must actually occur very early in the Cosmic Dawn, well before reionization is complete.…”

Astrophysics from the 21 cm Background

“…Many efforts are now underway to simulate galaxy formation using ab initio cosmological simulations [153,130,63,108,54], rather than using analytic or semianalytic models. However, doing so self-consistently in statistically representative volumes is exceedingly computationally challenging, as a result, semi-analytic and semi-empirical prescriptions for star formation in reionization modeling remain the norm in 21-cm modeling codes [94,110,101]. Though such approaches lack the spatial resolution to model individual galaxies or even groups of galaxies, including some information about the galaxy population permits joint modeling of 21-cm observables as well as high-z galaxy luminosity functions, stellar mass functions, and so on, and thus open up the possibility of tightening constraints on the properties of galaxies using a multi-wavelength approach.…”