The correlation of high-redshift galaxies with the thermal Sunyaev–Zel’dovich effect traces reionization

Abstract

We explore a potential new probe of reionization: the cross-correlation of high-redshift galaxies with maps of the thermal Sunyaev–Zel’dovich (tSZ) effect. We consider two types of high-redshift galaxies: Lyman break galaxies (LBGs) and Lyman-α emitters (LAEs). LBGs and LAEs will be detected in large numbers at high redshift (z ≈ 4–7) by ongoing and future surveys. We consider a future LBG sample from The Rubin Observatory Legacy Survey of Space and Time, and a selection of LAEs modelled after the Subaru SILVERRUSH programme, but covering a much larger sky fraction. The tSZ effect is sensitive to a line-of-sight integral of the ionized gas pressure, and is measured across large patches of sky using multifrequency cosmic microwave background (CMB) surveys. We consider forecast tSZ maps from CMB Stage 4 and more futuristic observations. Using a suite of hydrodynamical simulations, we show that LBGs and LAEs are correlated with the tSZ signal from reionization. The cross-spectra between LBGs/LAEs with tSZ maps contain information about the reionization history of the Universe, such as the distribution of bubble sizes, and could be used to directly measure the timing of reionization. The amplitude of the signal is small, however, and its detectability is hindered by low-redshift contributions to tSZ maps and by instrumental noise. If the low-redshift contribution to the observed tSZ signal is suppressed by masking of massive haloes, a combination of overlapping futuristic CMB and galaxy surveys could probe this signal.

Retrieving cosmological information from small-scale CMB foregrounds

“…In order to break degeneracies between parameters, detect systematics, and allow a fruitful analysis of available data sets, a consistent analysis of the different observables of reionisation seems to be a promising avenue. Indeed, several works have already demonstrated the potential offered by a combined analysis of astrophysical and CMB data (e.g., Millea & Bouchet 2018;Qin et al 2020;Chatterjee et al 2021;Baxter et al 2021;Sato-Polito et al 2021;La Plante et al 2022), 21 cm andCMB data (e.g., Tashiro et al 2011;Alvarez 2016;Ma et al 2018;Hotinli & Johnson 2022;La Plante et al 2020;Billings et al 2021;Choudhury et al 2021;Ahn & Shapiro 2021;Bégin et al 2022), or different types of CMB data (e.g., Planck Collaboration XLVII 2016; Alvarez et al 2021;Namikawa et al 2021;Paul et al 2021;Roy et al 2021).…”

Constraining reionization with the first measurement of the cross-correlation between the CMB optical-depth fluctuations and the Compton y-map

“…Ref. [19] proposes to use the cross-correlation between tSZ and high-redshift galaxies for another reionization probe. Alternatively, the kinetic SZ (kSZ) effect generated by the radial motion of ionized bubbles during reionization could be detected by future CMB experiments, which will potentially constrain the redshift and duration of reionization [20][21][22][23].…”

Prospects for kSZ$^2$-Galaxy Cross-Correlations during Reionization

“…Baxter et al (2021) study the cross-correlation between the tSZ signal and reionization-era galaxy surveys. The tSZ fluctations from the EoR contain interesting information about the thermal state of the IGM during reionization but, as discussed in that work, are weaker than the kSZ anisotropies from reionization considered here.…”