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Register a new userConstraining reionization with the first measurement of the cross-correlation between the CMB optical-depth fluctuations and the Compton y-map
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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.
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We measure the cross-correlation of cosmic microwave background lensing convergence maps derived from Atacama Cosmology Telescope data with galaxy lensing convergence maps as measured by the Canada-France-Hawaii Telescope Stripe 82 Survey. The CMB-galaxy lensing cross power spectrum is measured for the first time with a significance of 4.2{sigma}, which corresponds to a 12% constraint on the amplitude of density fluctuations at redshifts ~ 0.9. With upcoming improved lensing data, this novel type of measurement will become a powerful cosmological probe, providing a precise measurement of the mass distribution at intermediate redshifts and serving as a calibrator for systematic biases in weak lensing measurements.
We calculate the cross-correlation function $langle (Delta T/T)(mathbf{v}cdot mathbf{n}/sigma_{v}) rangle$ between the kinetic Sunyaev-Zeldovich (kSZ) effect and the reconstructed peculiar velocity field using linear perturbation theory, to constrain the optical depth $tau$ and peculiar velocity bias of central galaxies with Planck data. We vary the optical depth $tau$ and the velocity bias function $b_{v}(k)=1+b(k/k_{0})^{n}$, and fit the model to the data, with and without varying the calibration parameter $y_{0}$ that controls the vertical shift of the correlation function. By constructing a likelihood function and constraining $tau$, $b$ and $n$ parameters, we find that the quadratic power-law model of velocity bias $b_{v}(k)=1+b(k/k_{0})^{2}$ provides the best-fit to the data. The best-fit values are $tau=(1.18 pm 0.24) times 10^{-4}$, $b=-0.84^{+0.16}_{-0.20}$ and $y_{0}=(12.39^{+3.65}_{-3.66})times 10^{-9}$ ($68%$ confidence level). The probability of $b>0$ is only $3.12 times 10^{-8}$ for the parameter $b$, which clearly suggests a detection of scale-dependent velocity bias. The fitting results indicate that the large-scale ($k leq 0.1,h,{rm Mpc}^{-1}$) velocity bias is unity, while on small scales the bias tends to become negative. The value of $tau$ is consistent with the stellar mass--halo mass and optical depth relation proposed in the previous literatures, and the negative velocity bias on small scales is consistent with the peak background-split theory. Our method provides a direct tool to study the gaseous and kinematic properties of galaxies.
We forecast the prospective constraints on the ionized gas model $f_{rm gas}(z)$ at different evolutionary epochs via the tomographic cross-correlation between kinetic Sunyaev-Zeldovich (kSZ) effect and the reconstructed momentum field at different redshifts. The experiments we consider are the Planck and CMB Stage-4 survey for CMB and the SDSS-III for the galaxy spectroscopic survey. We calculate the tomographic cross-correlation power spectrum, and use the Fisher matrix to forecast the detectability of different $f_{rm gas}(z)$ models. We find that for constant $f_{rm gas}$ model, Planck can constrain the error of $f_{rm gas}$ ($sigma_{f_{rm gas}}$) at each redshift bin to $sim 0.2$, whereas four cases of CMB-S4 can achieve $sigma_{f_{rm gas}} sim 10^{-3}$. For $f_{rm gas}(z)=f_{rm gas,0}/(1+z)$ model the error budget will be slightly broadened. We also investigate the model $f_{rm gas}(z)=f_{rm gas,0}/(1+z)^{alpha}$. Planck is unable to constrain the index of redshift evolution, but the CMB-S4 experiments can constrain the index $alpha$ to the level of $sigma_{alpha} sim 0.01$--$0.1$. The tomographic cross-correlation method will provide an accurate measurement of the ionized gas evolution at different epochs of the Universe.
Cosmic Microwave Background (CMB) is a powerful probe to study the early universe and various cosmological models. Weak gravitational lensing affects the CMB by changing its power spectrum, but meanwhile, it also carries information about the distribution of lensing mass and hence, the large scale structure (LSS) of the universe. When studies of the CMB is combined with the tracers of LSS, one can constrain cosmological models, models of LSS development and astrophysical parameters simultaneously. The main focus of this project is to study the cross-correlations between CMB lensing and the galaxy matter density to constrain the galaxy bias ($b$) and the amplitude scaling parameter ($A$), to test the validity of $Lambda$CDM model. We test our approach for simulations of the Planck CMB convergence field and galaxy density field, which mimics the density field of the Herschel Extragalactic Legacy Project (HELP). We use maximum likelihood method to constrain the parameters.
We report the measurement of the angular power spectrum of cross-correlation between the unresolved component of the Fermi-LAT gamma-ray sky-maps and the CMB lensing potential map reconstructed by the Planck satellite. The matter distribution in the Universe determines the bending of light coming from the last scattering surface. At the same time, the matter density drives the growth history of astrophysical objects, including their capability at generating non-thermal phenomena, which in turn give rise to gamma-ray emissions. The Planck lensing map provides information on the integrated distribution of matter, while the integrated history of gamma-ray emitters is imprinted in the Fermi-LAT sky maps. We report here the first evidence of their correlation. We find that the multipole dependence of the cross-correlation measurement is in agreement with current models of the gamma-ray luminosity function for AGN and star forming galaxies, with a statistical evidence of 3.0$sigma$. Moreover, its amplitude can in general be matched only assuming that these extra-galactic emitters are also the bulk contribution of the measured isotopic gamma-ray background (IGRB) intensity. This leaves little room for a big contribution from galactic sources to the IGRB measured by Fermi-LAT, pointing toward a direct evidence of the extragalactic origin of the IGRB.
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