Day 732

Thursday.

1408.6284
Weak lensing corrections to tSZ-lensing cross correlation
Tröster, Van Waerbeke

The cross correlation between the thermal tSZ effect and gravitational lensing in the wide field has recently been measured.  It can be used to probe the distribution of the diffuse gas in large scale structure, as well as inform us about the missing baryons.  As for any lensing -based quantity, higher order lensing effects can potentially affect the signal.  Extend previous higher order lensing calculations to the case of tSZ-lensing cross correlations.  Derive terms analogous to corrections due to the Born approximation, lens-lens coupling, and reduced shear up to fourth order in the Newtonian potential.  Redshift distortions and vector modes are shown to be negligible at this order.  Find that the dominant correction due to the reduced shear exceeds percent-level only at multipoles of ell>3000.

1408.6297
Statistical and systematic uncertainties in pixel-based source reconstruction algorithms for gravitational lensing
Tagore, Keeton

Gravtiational lens modeling of spatially resolved sources is a challenging inverse problem with many observational constraints and model parameters.  Examine established pixel-based source reconstruction algorithms for de-lensing the source and constraining lens model parameters.  Using test data for four canonical lens configurations, explore statistical and systematic uncertainties associated with gridding, source regularization, interpolation errors, noise, and telescope pointing.  Specifically, compare two gridding schemes in the source plane: a fully adaptive grid that follows the lens mapping but is irregular, and an adaptive Cartesian grid.  Also consider regularization schemes that minimize derivatives of the source (using two finite difference methods) and introduce a scheme that minimizes deviations from an analytic source profile.  Careful choice of gridding and regularization can reduce "discreteness noise" in the chi2 surface that is inherent in the pixel-based methodology.  With a gridded source, some degree of interpolation is unavoidable, and errors due to interpolation need to be taken into account (especially for high SN data).  Different realizations of the noise and telescope pointing lead to slightly different values for lens model parameters, and the scatter between different "observations" can be comparable to or larger than the model uncertainties themselves.  The same effects create scatter in the lensing magnification at the level of a few percent for a peak SN ratio of 10, which decreases as the data quality improves.