Day 1065

Tuesday.


1603.03773
Microlensing by Kuiper, Oort, and Free-floating planets
Gould

Microlensing is generally thought to probe planetary systems only out to a few Einstein radii.  Microlensing events generated by bound planets beyond about 10 Einstein radii generally do not yield any trace of their hosts, and so would be classified as free floating planets (FFPs).  Show that it is already possible, using AO, to constrain the presence of potential hosts to FFP candidates at separations comparable to the Oort Cloud.  With next-generation telescopes, planets at Kuiper-Belt separations can be probed.  Next generation telescopes will also permit routine vetting for all FFP candidates, simply by obtaining second epochs 4-8 years after the event.  At present, the search for such hosts is restricted to within the "confusion limit" of theta_confus~250 mas, but future WFIRST observations will allow one to probe beyond this confusion limit as well.


1603.04152
Alignments of dark matter haloes with large-scale tidal fields: mass and redshift dependence
Chen, Wang, Mo, Shi

LS tidal field estimated directly from the distribution of DM haloes is used to investigate how halo shapes and spin vectors are aligned with the cosmic web.  The major, intermediate and minor axes of haloes are aligned with the corresponding tidal axes, and halo spin axes tend to be parallel with the intermediate axes and perpendicular to the major axes of tidal field.  The strengths of these alignments generally increase with halo mass and redshift, but the dependencies are only through the peak height nu.  The scaling relations of the alignment strengths with the value of nu indicate that the alignment strengths remain roughly constant when the structures within which the haloes reside are still in quasi-linear regime, but decreases as nonlinear evolution becomes more important.  Also calculate the alignments in projection so that the results can be compared directly with observations.  Finally, investigate the alignments of tidal tensors on large scales, and use the results to understand alignments of halo pairs separated at various distances.  The results suggest coherent structure of the tidal field is the underlying  reason for the alignments of haloes and galaxies seen in numerical simulations and in observations.


1603.04226
Generalized shear-ratio tests: a new relation between cosmological distances, and a diagnostic for a redshift-dependent multiplicative bias in shear measurements
Schneider

Derive a new relation between cosmological distances, valid in any (statistically) isotropic space-time and independent of cosmological parameters or even the validity of the field equation of GR.  In particular, this relation yields an equation between those distance ratios which are the geometrical factors determining the strength of the gravitational lensing effect of mass concentrations.  Considering a combination of WL shear ratios, based on lenses at two different redshifts, and sources at 3 different redshifts, derive a relation between shear-ratio tests which must be identically satisfied.  A redshift-dependent multiplicative bias in shear estimates will violate this relation, and thus can be probed by this generalized shear-ratio test. Combining the lensing effect for lenses at 3 different redshifts and 3 different source redshifts, a relation between shear ratios is derived which must be valid independent of a multiplicative bias.  Propose these generalized shear-ratio tests are a diagnostic for the presence of systematics in upcoming WL surveys.