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Register a new userA Detection of CMB-Cluster Lensing using Polarization Data from SPTpol
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Added by
Srinivasan Raghunathan
Publication date
2019
fields
Physics
and research's language is
English
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We report the first detection of gravitational lensing due to galaxy clusters using only the polarization of the cosmic microwave background (CMB). The lensing signal is obtained using a new estimator that extracts the lensing dipole signature from stacked images formed by rotating the cluster-centered Stokes $Q/U$ map cutouts along the direction of the locally measured background CMB polarization gradient. Using data from the SPTpol 500 deg$^{2}$ survey at the locations of roughly 18,000 clusters with richness $lambda ge 10$ from the Dark Energy Survey (DES) Year-3 full galaxy cluster catalog, we detect lensing at $4.8sigma$. The mean stacked mass of the selected sample is found to be $(1.43 pm 0.4) times 10^{14} {rm M_{odot}}$ which is in good agreement with optical weak lensing based estimates using DES data and CMB-lensing based estimates using SPTpol temperature data. This measurement is a key first step for cluster cosmology with future low-noise CMB surveys, like CMB-S4, for which CMB polarization will be the primary channel for cluster lensing measurements.
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We use cosmic microwave background (CMB) temperature maps from the 500 deg$^{2}$ SPTpol survey to measure the stacked lensing convergence of galaxy clusters from the Dark Energy Survey (DES) Year-3 redMaPPer (RM) cluster catalog. The lensing signal is extracted through a modified quadratic estimator designed to be unbiased by the thermal Sunyaev-Zel{}dovich (tSZ) effect. The modified estimator uses a tSZ-free map, constructed from the SPTpol 95 and 150 GHz datasets, to estimate the background CMB gradient. For lensing reconstruction, we employ t
We perform the first simultaneous Bayesian parameter inference and optimal reconstruction of the gravitational lensing of the cosmic microwave background (CMB), using 100 deg$^2$ of polarization observations from the SPTpol receiver on the South Pole Telescope. These data reach noise levels as low as 5.8 $mu$K-arcmin in polarization, which are low enough that the typically used quadratic estimator (QE) technique for analyzing CMB lensing is significantly sub-optimal. Conversely, the Bayesian procedure extracts all lensing information from the data and is optimal at any noise level. We infer the amplitude of the gravitational lensing potential to be $A_phi,{=},0.949,{pm},0.122$ using the Bayesian pipeline, consistent with our QE pipeline result, but with 17% smaller error bars. The Bayesian analysis also provides a simple way to account for systematic uncertainties, performing a similar job as frequentist bias hardening, and reducing the systematic uncertainty on $A_phi$ due to polarization calibration from almost half of the statistical error to effectively zero. Finally, we jointly constrain $A_phi$ along with $A_{rm L}$, the amplitude of lensing-like effects on the CMB power spectra, demonstrating that the Bayesian method can be used to easily infer parameters both from an optimal lensing reconstruction and from the delensed CMB, while exactly accounting for the correlation between the two. These results demonstrate the feasibility of the Bayesian approach on real data, and pave the way for future analysis of deep CMB polarization measurements with SPT-3G, Simons Observatory, and CMB-S4, where improvements relative to the QE can reach 1.5 times tighter constraints on $A_phi$ and 7 times lower effective lensing reconstruction noise.
We present measurements of the $E$-mode polarization angular auto-power spectrum ($EE$) and temperature-$E$-mode cross-power spectrum ($TE$) of the cosmic microwave background (CMB) using 150 GHz data from three seasons of SPTpol observations. We report the power spectra over the spherical harmonic multipole range $50 < ell leq 8000$, and detect nine acoustic peaks in the $EE$ spectrum with high signal-to-noise ratio. These measurements are the most sensitive to date of the $EE$ and $TE$ power spectra at $ell > 1050$ and $ell > 1475$, respectively. The observations cover 500 deg$^2$, a fivefold increase in area compared to previous SPTpol analyses, which increases our sensitivity to the photon diffusion damping tail of the CMB power spectra enabling tighter constraints on LCDM model extensions. After masking all sources with unpolarized flux $>50$ mJy we place a 95% confidence upper limit on residual polarized point-source power of $D_ell = ell(ell+1)C_ell/2pi <0.107,mu{rm K}^2$ at $ell=3000$, suggesting that the $EE$ damping tail dominates foregrounds to at least $ell = 4050$ with modest source masking. We find that the SPTpol dataset is in mild tension with the $Lambda CDM$ model ($2.1,sigma$), and different data splits prefer parameter values that differ at the $sim 1,sigma$ level. When fitting SPTpol data at $ell < 1000$ we find cosmological parameter constraints consistent with those for $Planck$ temperature. Including SPTpol data at $ell > 1000$ results in a preference for a higher value of the expansion rate ($H_0 = 71.3 pm 2.1,mbox{km},s^{-1}mbox{Mpc}^{-1}$ ) and a lower value for present-day density fluctuations ($sigma_8 = 0.77 pm 0.02$).
We present a demonstration of delensing the observed cosmic microwave background (CMB) B-mode polarization anisotropy. This process of reducing the gravitational-lensing generated B-mode component will become increasingly important for improving searches for the B modes produced by primordial gravitational waves. In this work, we delens B-mode maps constructed from multi-frequency SPTpol observations of a 90 deg$^2$ patch of sky by subtracting a B-mode template constructed from two inputs: SPTpol E-mode maps and a lensing potential map estimated from the $textit{Herschel}$ $500,mu m$ map of the CIB. We find that our delensing procedure reduces the measured B-mode power spectrum by 28% in the multipole range $300 < ell < 2300$; this is shown to be consistent with expectations from theory and simulations and to be robust against systematics. The null hypothesis of no delensing is rejected at $6.9 sigma$. Furthermore, we build and use a suite of realistic simulations to study the general properties of the delensing process and find that the delensing efficiency achieved in this work is limited primarily by the noise in the lensing potential map. We demonstrate the importance of including realistic experimental non-idealities in the delensing forecasts used to inform instrument and survey-strategy planning of upcoming lower-noise experiments, such as CMB-S4.
We present a search for anisotropic cosmic birefringence in 500 deg$^2$ of southern sky observed at 150 GHz with the SPTpol camera on the South Pole Telescope. We reconstruct a map of cosmic polarization rotation anisotropies using higher-order correlations between the observed cosmic microwave background (CMB) $E$ and $B$ fields. We then measure the angular power spectrum of this map, which is found to be consistent with zero. The non-detection is translated into an upper limit on the amplitude of the scale-invariant cosmic rotation power spectrum, $L(L+1)C_L^{alphaalpha}/2pi < 0.10 times 10^{-4}$ rad$^2$ (0.033 deg$^2$, 95% C.L.). This upper limit can be used to place constraints on the strength of primordial magnetic fields, $B_{1 rm Mpc} < 17 {rm nG} $ (95% C.L.), and on the coupling constant of the Chern-Simons electromagnetic term $g_{agamma} < 4.0 times 10^{-2}/H_I $ (95% C.L.), where $H_I$ is the inflationary Hubble scale. For the first time, we also cross-correlate the CMB temperature fluctuations with the reconstructed rotation angle map, a signal expected to be non-vanishing in certain theoretical scenarios, and find no detectable signal. We perform a suite of systematics and consistency checks and find no evidence for contamination.
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