Precision Epoch of Reionization studies with next-generation CMB experiments

TL;DR

The paper demonstrates that combining arcminute-scale CMB polarization from AdvACT with Planck temperature data enables a high-precision prediction of the primordial TT spectrum and a clean extraction of the kSZ signal at small scales. This approach yields a $0.5\%$-level TT prediction at high $\ell$, a $15\sigma$ detection of homogeneous kSZ, and tight reionization constraints via patchy kSZ ($\sigma(z_{\rm re})=1.1$, $\sigma(\Delta z_{ m re})=0.2$). It also shows that these results are robust to lensing and modest cosmological extensions, and that extending measurements to lower multipoles could further tighten $\tau$ and reionization parameters. The work highlights the crucial role of arcminute-scale polarization and multi-frequency foreground cleaning for advancing our understanding of reionization and small-scale CMB physics.

Abstract

Future arcminute resolution polarization data from ground-based Cosmic Microwave Background (CMB) observations can be used to estimate the contribution to the temperature power spectrum from the primary anisotropies and to uncover the signature of reionization near $\ell=1500$ in the small angular-scale temperature measurements. Our projections are based on combining expected small-scale E-mode polarization measurements from Advanced ACTPol in the range $300<\ell<3000$ with simulated temperature data from the full Planck mission in the low and intermediate $\ell$ region, $2<\ell<2000$. We show that the six basic cosmological parameters determined from this combination of data will predict the underlying primordial temperature spectrum at high multipoles to better than $1\%$ accuracy. Assuming an efficient cleaning from multi-frequency channels of most foregrounds in the temperature data, we investigate the sensitivity to the only residual secondary component, the kinematic Sunyaev-Zel'dovich (kSZ) term. The CMB polarization is used to break degeneracies between primordial and secondary terms present in temperature and, in effect, to remove from the temperature data all but the residual kSZ term. We estimate a $15 σ$ detection of the diffuse homogeneous kSZ signal from expected AdvACT temperature data at $\ell>1500$, leading to a measurement of the amplitude of matter density fluctuations, $σ_8$, at $1\%$ precision. Alternatively, by exploring the reionization signal encoded in the patchy kSZ measurements, we bound the time and duration of the reionization with $σ(z_{\rm re})=1.1$ and $σ(Δz_{\rm re})=0.2$. We find that these constraints degrade rapidly with large beam sizes, which highlights the importance of arcminute-scale resolution for future CMB surveys.

Figures (9)

• Figure 1: Temperature (blue) and polarization (purple) quadrupole transfer functions. The solid lines show the transfer functions corresponding to the Planck 2013 base_planck_lowl_lowLike_highL best-fit cosmological model, while the bands show the transfer functions computed for $\Omega_bh^2$ at the left- and right-most $2\sigma$ range allowed by the Planck data. This shows how particularly the polarization transfer function constrains the cosmological model, allowing one to predict the temperature transfer function (and thus the angular power spectrum) using EE data.
• Figure 2: Simulated Planck temperature and AdvACT polarization observations with relative noise levels.
• Figure 3: Posterior distributions of the base $\Lambda$CDM cosmological parameters derived from simulated Planck temperature data alone (orange), AdvACT EE data (blue), and their combination (purple).
• Figure 4: Left: Predicted contribution to the temperature power spectrum from primordial anisotropies obtained from the Planck TT + AdvACT EE cosmology. We report the 1$\sigma$ band uncertainty of the mean extracted temperature and, for a better visualization, the same band enlarging the errors by a factor of 30. Right: zoom on the 1$\sigma$ band uncertainty after subtracting the mean extracted $\hat{C}^{TT}_{\ell}$ per $\hat{C}^{TT}_{\ell}$, i.e. the fractional error in the recovered $\hat{C}^{TT}_{\ell}$. We compare the Planck TT + AdvACT EE predicted error on $\hat{C}^{TT}_{\ell}$ with the same error band obtained using AdvACT EE only cosmology. At small scales, $\ell>2200$, the estimate is dominated by AdvACT.
• Figure 6: Residual power in the simulated AdvACT TT + kSZ components with respect to the predicted TT from the Planck TT + AdvACT EE cosmology. The blue lines are one realization of the data including homogeneous (dark blue) or patchy (light blue) terms, while the purple band is the error on the predicted TT spectrum derived in the previous Section. At multipoles $\ell>1500$ the kSZ signal is well above the error on the predicted primordial TT spectrum.