Detectability of the 21-cm signal during the epoch of reionization with 21-cm Lyman α emitter cross-correlation – I

Abstract

Detection of the redshifted 21cm-line signal from neutral hydrogen in the intergalactic medium (IGM) during the Epoch of Reionization (EoR) is complicated by intense foregrounds such as galactic synchrotron and extragalactic radio galaxies. The 21cm-Lyman-α emitter(LAE) cross-correlation is one of the tools available to reduce the foreground effects because the foreground emission from such radio sources is statistically independent of LAE distribution. LAE surveys during the EoR at redshifts z = 6.6 and 7.3 are ongoing by the Subaru Hyper Suprime-Cam (HSC). Additionally, Prime Focus Spectrograph (PFS) will provide precise redshift information of the LAEs discovered by the HSC survey. In this paper, we investigate the detectability of the 21cm signal with the 21cm-LAE cross-correlation by using our improved reionization simulations. We also focus on the error budget and evaluate it quantitatively in order to consider a strategy to improve the signal-to-noise ratio. In addition, we explore an expansion of the LAE survey to suggest optimal survey parameters and show a potential to measure a characteristic size of ionized bubbles via the turnover scale of the cross-power spectrum. As a result, we find that the Murchison Widefield Array (MWA) has ability to detect the cross-power spectrum signal on large scales by combining LAE Deep field survey of HSC. We also show that the sensitivity is improved dramatically at small scales by adding redshift information from the PFS measurements. The Square Kilometre Array (SKA) has a potential to measure the turnover scale with an accuracy of 6 × 10 −3 Mpc −1 .

Probing delayed-end reionization histories with the 21-cm LAE cross-power spectrum

“…On scales smaller than the typical bubble size we expect to see correlation, with positive power contributions from pairs of pixels in the overdensities around LAEs, where the gas selfshields and must be ionized outside-in (Miralda-Escudé et al 2000). The general shape of our results is consistent with previous work Lidz et al 2009;Wiersma et al 2013;Vrbanec et al 2016;Kubota et al 2018) In more detail we see that for the original reionization histories -with reionization ending by z = 6 -there is no negative power in the left panel at z = 5.756. At these redshifts the large-scale IGM is ionized, and so we see only positive correlation resulting from the residual/self-shielded neutral gas in the overdensities that host LAEs.…”

The H i bias during the Epoch of Reionization

“…Of course, there will also some bias of the tracer sample with respect to the dark matter. Indeed, Sobacchi et al (2016) and Kubota et al (2018) have investigated the detectability of 21cm-LAE cross-correlation by combining the Subaru Hyper-Suprime Cam (HSC) Ultra-Deep field survey (Aihara et al 2018a,b) and the upcoming 21cm survey with LOFAR, MWA, or SKA-low. Measurement of the cross-correlation with the SKA-low is found very promising, and we expect the 21cm bias and its evolutionary features could be determined via such measurement in the SKA era.…”

Observations of the Lyman-α Universe

“…fully neutral IGM; top), medium (2 pMpc; middle), and large (10 pMpc; bottom), where pMpc stands for physical Mpc. Right: 21cm brightness temperature map at z = 6.6 predicted by numerical simulations (top; Kubota et al 2018). The blue regions of 0 mK correspond to the fully ionized regions.…”

“…For display purposes, the signs of the negative cross-power spectra (dotted lines) are changed to the positive signs. The data of center and right panels are adapted from Dijkstra et al (2007) and Kubota et al (2018), respectively, with permission.…”