Moreover, it is remarkable to notice that measurements of CMB lensing are complementary to optical ones because they probe bigger volumes and have the advantage of a precisely known source redshift.
ACT, operating in Atacama desertIn the work summarized in this paper, the authors perform the computation of the power spectrum of the convergence field \kappa, thanks to an "optimal quadratic estimator" and using the Atacama Cosmology Telescope (ACT) data. This latter is a 6 meters telescope operating in the Atacama desert of Chile, at an altitude of 5200 meters. It uses three 1024-elements arrays of superconducting transition edge sensing bolometers, operating at 148, 218 and 277 GHz.
The study presented here is based on 6 patches (3 x 18 degree) observed at 148 GHz, properly filtered (especially avoiding atmosphere and point sources contamination). Lensing reconstruction is perform separately on each of these patches and the corresponding results are combined afterwards.
To compute the power spectrum of the field \kappa, the team propose the following optimal quadratic estimator:
where l, l, L, L′ are coordinates in Fourier space (under the flat-sky approximation), g defines filters that can be tuned to optimize signal-to-noise, N is a normalization term, and the second term "<..>Gaussian" is the Gaussian part of the four-point function.One of the main results is depicted on the following figure: it shows the convergence power spectrum estimation (red points) as measured by the ACT experiment (error bars are derived using Monte Carlo). The black solid line, corresponding to the best-fit WMAP+ACT cosmological model, turns out to be consistent with the measured points.
As mentionned in their conclusion, data from the Planck satellite should provide a much more precise measurement of the lensing power spectrum. Also, CMB polarization data from the next generation experiments will yield even more accurate measurements!Comments about this work are welcomed.
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