Day 1284

Wednesday.


1707.01020
Astrometric accuracy during the past 2000 years
Høg

The great development of astrometry accuracy since the observations by Hipparchus about 150 BC was documented in 2008 in the first version of the present report.  This report is updated, e.g. with recent information on the catalogues before 1800 AD.  The development has often been displayed in diagrams showing the accuracy versus time.  A new such diagram is provided in a figure and in a .png file (section 2) and this information will presumably be the main interest for most readers.  For the specialist reader, a detailed documentation is provided in order to give confidence in the diagram and to show how the knowledge about astrometric accuracy has improved in the recent 20 years.  The history of these diagrams is illustrated in the appendix.


1707.01072
Effects of self-calibration of intrinsic alignment on cosmological parameter constraints from future cosmic shear surveys
Yao, Ischak, Lin, Troxel

IA of galaxies have been recognized as one of the most serious contaminates to WL.  These systematics need to be isolated and mitigated in order for ongoing and future lensing surveys to tech their full potential.  The IA self-calibration (SC) method was shown in previous studies to be able to reduce the GI contamination by up to a factor of 10 for the 2pt and 3pt correlations.  The SC method does not require to assume an IA model in its working and can extract the GI signal from the sample photo-z survey offering the possibility to test and understand structure formation scenarios and their relationship to IA models.  In this paper, study the effects of the IA SC mitigation method on the precision and accuracy of cosmo parameter constraints from future cosmic shear surveys LSST, WFIRST and Euclid.  Perform analytical and numerical calculations to estimate the loss of precision and the residual bias in the best fit cosmo parameters after the self-calibration is performed.  Take into account uncertainties from photometric z and the galaxy bias.  Find that the confidence contours are slightly inflated from applying the SC method itself while a significant increase is due to the inclusion of the photo-z uncertainties.  The bias of cosmological parameters is reduced from several-sigma, when IA is not corrected for, to below 1-sigma after SC is applied.  These numbers are comparable to those resulting from applying the method of marginalizing over IA model parameters despite the fact that the two methods operate very differently.  Conclude that implementing the SC for these future cosmic-shear surveys will not only allow one to efficiently mitigate the GI contaminant but also help to understand their modeling and link to structure formation.