Lyman Alpha Emitters and the 21cm Power Spectrum as Probes of Density-Ionization Correlation in the Epoch of Reionization

Abstract

Due to the large cross section of Ly𝛼 photons with hydrogen, Lyman Alpha Emitters (LAEs) are sensitive to the presence of neutral hydrogen in the intergalactic medium (IGM) during the Epoch of Reionization (EoR): the period in the Universe's history where neutral hydrogen in the IGM is ionized. The correlation of the ionized regions in the IGM with respect to the underlying intrinsic LAEs has a pronounced effect on the number of observed LAEs and their apparent clustering. As a result, observations of LAEs during the EoR can be used as a probe of the EoR morphology. Here we build on previous works where we parametrize the density-ionisation correlation during the EoR, and study how the observed number density and angular correlation function (ACF) of LAEs depends on this parametrization. Using Subaru measurements of the number density of LAEs and their ACF at z = 6.6, we place constraints on the EoR morphology. We find that measurements of LAEs at z = 6.6 alone cannot distinguish between different density-ionization models at 68% credibility. However, adding information regarding the number density, and ACF, of LAEs at 𝑧 = 6.6 to 21cm power spectrum measurements using the hydrogen Epoch of Reionization Array (HERA) at the midpoint of reionization can rule out uncorrelated and outside-in reionization at 99% credibility.

Constraining the 21cm brightness temperature of the IGM at $z$=6.6 around LAEs with the Murchison Widefield Array

“…More recently, simulations of the 21 cm field around early galaxies has illuminated the topology of reionisation (Elbers & van de Weygaert 2019;Chen et al 2019;Kakiichi et al 2016;Hutter et al 2021;Sobacchi et al 2016;Pagano & Liu 2021), and the evolution of the size and distribution of ionised regions around UV-bright sources (Lin et al 2016). Heneka et al (2017) used radiative transfer simulations to map the diffuse and galactic Ly-𝛼 emission to 21 cm maps, showing a good agreement on smoothing scales of a few megaparsecs, confirming the anti-correlation of earlier work (e.g.…”