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Register a new userA Projected Estimate of the Reionization Optical Depth Using the CLASS Experiments Sample-Variance Limited E-Mode Measurement
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We analyze simulated maps of the Cosmology Large Angular Scale Surveyor (CLASS) experiment and recover a nearly cosmic-variance limited estimate of the reionization optical depth $tau$. We use a power spectrum-based likelihood to simultaneously clean foregrounds and estimate cosmological parameters in multipole space. Using software specifically designed to constrain $tau$, the amplitude of scalar fluctuations $A_s$, and the tensor-to-scalar ratio $r$, we demonstrate that the CLASS experiment will be able to estimate $tau$ within a factor of two of the full-sky cosmic variance limit allowed by cosmic microwave background polarization measurements. Additionally, we discuss the role of CLASSs $tau$ constraint in conjunction with gravitational lensing of the CMB on obtaining a $gtrsim4sigma$ measurement of the sum of the neutrino masses.
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CMB full-sky temperature data show a hemispherical asymmetry in power nearly aligned with the Ecliptic. In real space, this anomaly can be quantified by the temperature variance in the northern and southern Ecliptic hemispheres, with the north displaying an anomalously low variance while the south appears consistent with expectations from the best-fitting theory, LCDM. While this is a well-established result in temperature, the low signal-to-noise ratio in current polarization data prevents a similar comparison. Even though temperature and polarization are correlated, polarization realizations constrained by temperature data show that the lack of variance is not expected to be present in polarization data. Therefore, a natural way of testing whether the temperature result is a fluke is to measure the variance of CMB polarization components. In anticipation of future CMB experiments that will allow for high-precision large-scale polarization measurements, we study how variance of polarization depends on LCDM parameters uncertainties by forecasting polarization maps with Plancks MCMC chains. We find that, unlike temperature variance, polarization variance is noticeably sensitive to present uncertainties in cosmological parameters. This comes mainly from the current poor constraints on the reionization optical depth, tau, and the fact that tau drives variance at low multipoles. In this work we show how the variance of polarization maps generically depends on the cosmological parameters. We demonstrate how the improvement in the tau measurement seen between Plancks two latest data releases results in a tighter constraint on polarization variance expectations. Finally, we consider even smaller uncertainties on tau and how more precise measurements of tau can drive the expectation for polarization variance in a hemisphere close to that of the cosmic-variance-limited distribution.
The Epoch of Reionization (EoR) depends on the complex astrophysics governing the birth and evolution of the first galaxies and structures in the intergalactic medium. EoR models rely on cosmic microwave background (CMB) observations, and in particular the large-scale E-mode polarization power spectra (EE PS), to help constrain their highly uncertain parameters. However, rather than directly forward-modelling the EE PS, most EoR models are constrained using a summary statistic -- the Thompson scattering optical depth, $tau_e$. Compressing CMB observations to $tau_e$ requires adopting a basis set for the EoR history. The common choice is the unphysical, redshift-symmetric hyperbolic tangent (Tanh) function, which differs in shape from physical EoR models based on hierarchical structure formation. Combining public EoR and CMB codes, 21cmFAST and CLASS, here we quantify how inference using the $tau_e$ summary statistic impacts the resulting constraints on galaxy properties and EoR histories. Using the last Planck 2018 data release, we show that the marginalized constraints on the EoR history are more sensitive to the choice of the basis set (Tanh vs physical model) than to the CMB likelihood statistic ($tau_e$ vs PS). For example, EoR histories implied by the growth of structure show a small tail of partial reionization extending to higher redshifts. However, biases in inference using $tau_e$ are negligible for the Planck 2018 data. Using EoR constraints from high-redshift observations including the quasar dark fraction, galaxy UV luminosity functions and CMB EE PS, our physical model recovers $tau_e=0.0569^{+0.0081}_{-0.0066}$.
We compute the expected sensitivity on measurements of optical depth to reionization for a ground-based experiment at Teide Observatory. We simulate polarized partial sky maps for the GroundBIRD experiment at the frequencies 145 and 220 GHz. We perform fits for the simulated maps with our pixel-based likelihood to extract the optical depth to reionization. The noise levels of polarization maps are estimated as 110 $mumathrm{K~arcmin}$ and 780 $ mumathrm{K~arcmin}$ for 145 and 220 GHz, respectively, by assuming a three-year observing campaign and sky coverages of 0.537 for 145 GHz and 0.462 for 220 GHz. Our sensitivities for the optical depth to reionization are found to be $sigma_tau$=0.030 with the simulated GroundBIRD maps, and $sigma_tau$=0.012 by combining with the simulated QUIJOTE maps at 11, 13, 17, 19, 30, and 40 GHz.
We propose a new reionization probe that uses cosmic microwave background (CMB) observations; the cross-correlation between fluctuations in the CMB optical depth which probes the integrated electron density, $deltatau$, and the Compton $y$-map which probes the integrated electron pressure. This cross-correlation is much less contaminated than the $y$-map power spectrum by late-time cluster contributions. In addition, this cross-correlation can constrain the temperature of ionized bubbles while the optical-depth fluctuations and kinetic SZ effect can not. We measure this new observable using a Planck $y$-map as well as a map of optical-depth fluctuations that we reconstruct from Planck CMB temperature data. We use our measurements to derive a first CMB-only upper limit on the temperature inside ionized bubbles, $T_{rm b}lesssim 7.0times10^5,$K ($2,sigma$). We also present future forecasts, assuming a fiducial model with characteristic reionization bubble size $R_{rm b}=5,$Mpc and $T_{rm b}=5times10^4,$K. The signal-to-noise ratio of the fiducial cross-correlation using a signal dominated PICO-like $y$-map becomes $simeq7$ with CMB-S4 $deltatau$ and $simeq13$ with CMB-HD $deltatau$. For the fiducial model, we predict that the CMB-HD $-$ PICO cross-correlation should achieve an accurate measurement of the reionization parameters; $T_{rm b}simeq 49800^{+4500}_{-5100},$K and $R_{rm b}simeq 5.09^{+0.66}_{-0.79},$Mpc. Since the power spectrum of the electron density fluctuations is constrained by the $deltatau$ auto spectrum, the temperature constraints should be only weakly model-dependent on the details of the electron distributions and should be statistically representative of the temperature in ionized bubbles during reionization. This cross-correlation could, therefore, become an important observable for future CMB experiments.
The reionization optical depth is the most poorly determined of the six $Lambda$CDM parameters fit to CMB anisotropy data. Instrumental noise and systematics have prevented uncertainties from reaching their cosmic variance limit. At present, the datasets providing the most statistical constraining power are the WMAP, Planck LFI, and Planck HFI full-sky polarization maps. As the reprocessed HFI data with reduced systematics are not yet publicly unavailable, we examine determinations of $tau$ using 9-year WMAP and 2015 Planck LFI data, with an emphasis on characterizing potential systematic bias resulting from foreground template and masking choices. We find evidence for a low-level systematic in the LFI polarization data with a roughly common-mode morphology across the LFI frequencies and a spectrum consistent with leakage of intensity signal into the polarization channels. We demonstrate significant bias in the optical depth derived when using the LFI 30 GHz map as a template to clean synchrotron from WMAP data, and recommend against use of the 2015 LFI 30 GHz polarization data as a foreground template for non-LFI datasets. We find an inconsistency betwe
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