Gravitational lensing of the CMB by galaxy clusters

Abstract

Abstract. We adapt a non-linear filter proposed by Hu (2001) for detecting lensing of the CMB by large-scale structures to recover surface-density profiles of galaxy clusters from their localised, weak gravitational lensing effect on CMB fields. Shifting the band-pass of the filter to smaller scales, and normalising it such as to reproduce the convergence rather than the deflection angle, we find that the mean density profile of a sample of 100 clusters can be recovered to better than 10% from well within the scale radius to almost the virial radius. The kinetic Sunyaev-Zel'dovich effect is shown to be a negligible source of error. We test the filter applying it to data simulated using the characteristics of the Atacama Cosmology Telescope (ACT), showing that it will be possible to recover mean cluster profiles outside a radius of 1 corresponding to ACT's angular resolution.

Lensing reconstruction of cluster-mass cross correlation with cosmic microwave background polarization

“…The observed CMB polarization fields are also described by Eqs. (8), while σ pix and σ b in CMB polarization experiments may differ from those in CMB experiments for measuring temperature anisotropies.…”

“…The first estimates of each of the estimators from the uniform matter distribution are already close to the true convergence profile (thick solid). Having adopted the initial model without lensing effects, our improved quadratic estimators operate as standard quadratic estimators, and they are biased low when the lensing effect is large near the massive clusters [8][9][10], while the nonlinear effect is relatively mitigated for iTE, iTB, and iEB estimators, since the lensing contribution is par- tially canceled due to the oscillating nature of the cross power spectrum C C l and there is no B-mode polarization anisotropy C B l = 0. Next we take the estimate (thin line) of the convergence profile in the first trial as our initial convergence model for the next iteration, and we repeat the iteration process until the estimates converge.…”

“…However, it was shown that the standard method of using quadratic estimators is compromised [8] on cluster scales and needs additional free parameters [9] for calibration, as this method rests on the linear approximation in the lensing effect which breaks down near massive clusters. This problem was tackled by delensing the observed CMB temperature field and analyzing the likelihood of the delensed fields [10].…”

Measuring cluster masses with CMB lensing: a statistical approach

“…Seljak & Zaldarriaga (2000) considered instead the characteristic perturbation to the unlensed CMB temperature field, approximated locally as a pure gradient, induced by cluster lensing, an idea further studied by Holder & Kosowsky (2004) and Vale et al (2004). In an approach analogous to the first authors, Maturi et al (2005) built a filter nonlinear in CMB temperature to reconstruct the lensing convergence field around clusters as a means of studying their density profiles.…”

CMB lensing and the WMAP cold spot

“…The deflection field couples to the large scale gradients in the CMB and correlates the gradients with the small scale features. This property can be used to reconstruct the convergence profile of the lens, a subject that has been studied in detail over recent years [26][27][28][29][30][31][32][33][34]. In our case, since the lensing template has been already defined by fitting the temperature decrement of the Cold Spot, we can approach the problem in a simpler manner: given a deflection template α(r) = α(r)r, we ask how likely is it to be detected by a CMB experiment.…”