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Register a new userMitigating the optical depth degeneracy using the kinematic Sunyaev-Zeldovich effect with CMB-S4
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The epoch of reionization is one of the major phase transitions in the history of the universe, and is a focus of ongoing and upcoming cosmic microwave background (CMB) experiments with improved sensitivity to small-scale fluctuations. Reionization also represents a significant contaminant to CMB-derived cosmological parameter constraints, due to the degeneracy between the Thomson-scattering optical depth, $tau$, and the amplitude of scalar perturbations, $A_s$. This degeneracy subsequently hinders the ability of large-scale structure data to constrain the sum of the neutrino masses, a major target for cosmology in the 2020s. In this work, we explore the kinematic Sunyaev-Zeldovich (kSZ) effect as a probe of reionization, and show that it can be used to mitigate the optical depth degeneracy with high-sensitivity, high-resolution data from the upcoming CMB-S4 experiment. We discuss the dependence of the kSZ power spectrum on physical reionization model parameters, as well as on empirical reionization parameters, namely $tau$ and the duration of reionization, $Delta z$. We show that by combining the kSZ two-point function and the reconstructed kSZ four-point function, degeneracies between $tau$ and $Delta z$ can be strongly broken, yielding tight constraints on both parameters. We forecast $sigma(tau) = 0.003$ and $sigma(Delta z) = 0.25$ for a combination of CMB-S4 and Planck data, including detailed treatment of foregrounds and atmospheric noise. The constraint on $tau$ is nearly identical to the cosmic-variance limit that can be achieved from large-angle CMB polarization data. The kSZ effect thus promises to yield not only detailed information about the reionization epoch, but also to enable high-precision cosmological constraints on the neutrino mass.
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Using high-resolution microwave sky maps made by the Atacama Cosmology Telescope, we for the first time present strong evidence for motions of galaxy clusters and groups via microwave background temperature distortions due to the kinematic Sunyaev-Zeldovich effect. Galaxy clusters are identified by their constituent luminous galaxies observed by the Baryon Oscillation Spectroscopic Survey, part of the Sloan Digital Sky Survey III. We measure the mean pairwise momentum of clusters, with a probability of the signal being due to random errors of 0.002, and the signal is consistent with the growth of cosmic structure in the standard model of cosmology.
We detect the kinematic Sunyaev-Zeldovich (kSZ) effect with a statistical significance of $4.2 sigma$ by combining a cluster catalogue derived from the first year data of the Dark Energy Survey (DES) with CMB temperature maps from the South Pole Telescope Sunyaev-Zeldovich (SPT-SZ) Survey. This measurement is performed with a differential statistic that isolates the pairwise kSZ signal, providing the first detection of the large-scale, pairwise motion of clusters using redshifts derived from photometric data. By fitting the pairwise kSZ signal to a theoretical template we measure the average central optical depth of the cluster sample, $bar{tau}_e = (3.75 pm 0.89)cdot 10^{-3}$. We compare the extracted signal to realistic simulations and find good agreement with respect to the signal-to-noise, the constraint on $bar{tau}_e$, and the corresponding gas fraction. High-precision measurements of the pairwise kSZ signal with future data will be able to place constraints on the baryonic physics of galaxy clusters, and could be used to probe gravity on scales $ gtrsim 100$ Mpc.
We present a new measurement of the kinetic Sunyaev-Zeldovich effect (kSZ) using Planck cosmic microwave background (CMB) and Baryon Oscillation Spectroscopic Survey (BOSS) data. Using the `LowZ North/South galaxy catalogue from BOSS DR12, and the group catalogue from BOSS DR13, we evaluate the mean pairwise kSZ temperature associated with BOSS galaxies. We construct a `Central Galaxies Catalogue (CGC) which consists of isolated galaxies from the original BOSS data set, and apply the aperture photometry (AP) filter to suppress the primary CMB contribution. By constructing a halo model to fit the pairwise kSZ function, we constrain the mean optical depth to be $bar{tau}=(0.53pm0.32)times10^{-4}(1.65,sigma)$ for `LowZ North CGC, $bar{tau}=(0.30pm0.57)times10^{-4}(0.53,sigma)$ for `LowZ South CGC, and $bar{tau}=(0.43pm0.28)times10^{-4}(1.53,sigma)$ for `DR13 Group. In addition, we vary the radius of the AP filter and find that the AP size of $7,{rm arcmin}$ gives the maximum detection for $bar{tau}$. We also investigate the dependence of the signal with halo mass and find $bar{tau}=(0.32pm0.36)times10^{-4}(0.8,sigma)$ and $bar{tau}=(0.67pm0.46)times10^{-4}(1.4,sigma)$ for `DR13 Group with halo mass restricted to, respectively, less and greater than its median halo mass, $10^{12}, h^{-1}{rm M}_{odot}$. For the `LowZ North CGC sample restricted to $M_{rm h} gtrsim 10^{14}, h^{-1}{rm M}_odot$ there is no detection of the kSZ signal because these high mass halos are associated with the high-redshift galaxies of the LowZ North catalogue, which have limited contribution to the pairwise kSZ signals.
The kinematic Sunyaev-Zeldovich (kSZ) effect -- the Doppler boosting of cosmic microwave background (CMB) photons scattering off free electrons with non-zero line-of-sight velocity -- is an excellent probe of the distribution of baryons in the Universe. In this paper, we measure the kSZ effect due to ionized gas traced by infrared-selected galaxies from the emph{unWISE} catalog. We employ the projected-field kSZ estimator, which does not require spectroscopic galaxy redshifts. To suppress non-kSZ foreground signals associated with the galaxies (e.g., dust emission and thermal SZ), this estimator requires cleaned CMB maps, which we obtain from emph{Planck} and emph{WMAP} data. Using a new asymmetric estimator that combines different foreground-cleaned CMB maps to maximize the signal-to-noise, we measure the kSZ$^2$-galaxy cross-power spectrum for three subsamples of the emph{unWISE} galaxy catalog, which peak at mean redshifts $z approx$ 0.6, 1.1, and 1.5, have average halo mass $sim 1$-$5times 10^{13}$ $h^{-1} M_{odot}$, and in total contain over 500 million galaxies. After marginalizing over CMB lensing contributions, we measure the amplitude of the kSZ signal $A_{rm kSZ^2} = 0.42 pm 0.31(stat.) pm 0.14(sys.)$, $5.02 pm 1.01(stat.) pm 0.47(sys.)$, and $8.23 pm 3.23(stat.) pm 1.60(sys.)$, for the three subsamples, where $A_{rm kSZ^2} = 1$ corresponds to our fiducial model. The combined kSZ detection S/N $>$ 5. We discuss possible explanations for the excess kSZ signal associated with the $z approx 1.1$ sample, and show that foreground contamination in the CMB maps is very unlikely to be the cause. Our measurements illustrate clearly that no baryons are missing on large scales at low redshifts.
In the standard hot cosmological model, the black-body temperature of the Cosmic Microwave Background (CMB), $T_{rm CMB}$, increases linearly with redshift. Across the line of sight CMB photons interact with the hot ($sim10^{7-8}$ K) and diffuse gas of electrons from galaxy clusters. This interaction leads to the well known thermal Sunyaev-Zeldovich effect (tSZ), which produces a distortion of the black-body emission law, depending on $T_{rm CMB}$. Using tSZ data from the ${it Planck}$ satellite it is possible to constrain $T_{rm CMB}$ below z=1. Focusing on the redshift dependance of $T_{rm CMB}$ we obtain $T_{rm CMB}(z)=(2.726pm0.001)times (1+z)^{1-beta}$ K with $beta=0.009pm0.017$, improving previous constraints. Combined with measurements of molecular species absorptions, we derive $beta=0.006pm0.013$. These constraints are consistent with the standard (i.e. adiabatic, $beta=0$) Big-Bang model.
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