CMB lensing reconstruction biases in cross-correlation with large-scale structure probes

The cross-correlation between cosmic microwave background (CMB) gravitational lensing and large-scale structure tracers will be an important cosmological probe in the coming years. Quadratic estimators provide a simple and powerful (if suboptimal) way to reconstruct the CMB lensing potential and are widely used. For Gaussian fields, the cross-correlation of a quadratic-estimator CMB lensing reconstruction with a tracer is exactly unbiased if the power spectra are known and consistent analytic lensing mode response functions are used. However, the bispectrum induced by non-linear large-scale structure growth and post-Born lensing can introduce an additional bias term (NL(3/2)) in the cross-correlation spectrum, similar to the NL(3/2) bias in the auto-spectrum demonstrated in recent works. We give analytic flat-sky results for the cross-correlation bias using approximate models for the post-Born and large-scale structure cross-bispectra, and compare with N-body simulation results using ray-tracing techniques. We show that the bias can be at the 5–15% level in all large-scale structure cross-correlations using small-scale CMB temperature lensing reconstruction, but is substantially reduced using polarization-based lensing estimators or simple foreground-projected temperature estimators. The relative magnitude of these effects is almost three times higher than in the CMB lensing auto-correlation, but is small enough that it can be modelled to sufficient precision using simple analytic models. We show that NL(3/2) effects in cross-correlation will be detected with high significance when using data of future surveys and could affect systematic effects marginalization in cosmic shear measurements mimicking galaxy intrinsic alignment

QSOs sigposting cluster size halos as gravitational lenses: halo mass, projected mass density profile and concentration at z 3c0.7

Magnication bias is a gravitational lensing eect that is normally overlooked because it is considered sub-optimal in comparison with the lensing shear. Thanks to the demonstrated optimal characteristics of the sub-millimetre galaxies (SMGs) for lensing analysis, in this work we were able to measure the magnication bias produced by a sample of QSOs acting as lenses, 0:2 < z < 1:0, on the SMGs observed by Herschel at 1:2 < z < 4:0. Two dierent methodologies were successfully applied: the traditional cross-correlation function approach and the Davis-Peebles estimator through stacking technique. The second one was found to be more robust for analysing the strong lensing regime (< 2030 arcsec in our case) and provides the possibility to take into account the positional errors of the sources in our samples. From the halo modelling of the cross-correlation function, the halo mass where the QSOs acting as lenses are located was estimated to be greater than log10 (Mmin=M) > 13:6+0:9 0:4, also conrmed by the mass density prole analysis (M200c 1014M). These mass values indicate that we are observing the lensing eect of a cluster size halo signposted by the QSOs, as in previous studies of the magnication bias. Moreover, we were able to estimate the lensing convergence, (), for our magnication bias measurements down to a few kpcs. The derived mass density prole is in good agreement with a Navarro-Frank-White (NFW) prole. We also attempt an estimation of the halo mass and the concentration parameters, obtaining MNFW = 1:0+0:4 0:2 1014M and C = 3:5+0:5 0:3. This concentration value is rather low and it would indicate that the cluster halos around these QSOs are unrelaxed. However, higher concentration values still provides a compatible t to the data

Observing patchy reionization with future CMB polarization experiments

We study the signal from patchy reionization in view of the future high accuracy polarization measurements of the Cosmic Microwave Background (CMB). We implement an extraction procedure of the patchy reionization signal analogous to CMB lensing. We evaluate the signal to noise ratio (SNR) for the future Stage IV (S4) CMB experiment. The signal has a broad peak centered on the degree angular scales, with a long tail at higher multipoles. The CMB S4 experiment can effectively constrain the properties of reionization by measuring the signal on degree scales. The signal amplitude depends on the properties of the structure determining the reionization morphology. We describe bubbles having radii distributed log-normally. The expected S/N is sensitive to the mean bubble radius: R = 5 Mpc implies S/N 48 4, R = 10 Mpc implies S/N 48 20. The spread of the radii distribution strongly affects the integrated SNR, that changes by a factor of 102when \u3c3lnrgoes from 2 to 3. Future CMB experiments will thus place important constraints on the physics of reionization