Day 747

Thursday.  Friday.

1409.5130
The impact of sprious shear on cosmological parameter estimates from weak lensing observables
Petri, May, Haiman, Kratochvil

Residual errors in shear measurements, after corrections for instrument systematic and atmospheric effects, can impact cosmological parameter derived from WL observations.  Combine convergence maps from ray-tracing sims with random realization of serious shear with a PS estimated from LSST.  This allows to quantify the errors and biases on the triplet (Omega_m, w, sigma_8) derived from the PS, as well as from 3 different sets of non-Gaussian statistics of the lensing convergence field: Minkowski functionals (MF), low-order moments (LM), and peak counts (PK).  Main results are: (i) find an order of magnitude smaller biases from the PS than in previous work.  (ii) the PS and LM yield biases much smaller than the morphological statistics (MF, PK).  (iii) For strictly Gaussian spurious shear with integrated amplitude as low as its current estimate of sigma^2_sys~1e-7, biases from the PS and LM would be unimportant even for a survey with the statistical power of LSST.  However, find that for surveys larger than ~100 deg^2, non-Gaussianity in the noise (not included in the analysis) will likely be important and must be quantified to assess the biases.  (iv) The morphological statistics (MF, PK) introduce important biases even for Gaussian noise, which must be corrected in large surveys.  The biases are in different directions in (Omega_m, w, sigma_8) parameter space, allowing self-calibration by combining multiple statistics.  Results warrant follow-up studies with more extensive lensing simulations and more accurate spurious shear estimates.

1409.5197
A theoretical estimate of intrinsic ellipticity bispectra induced by angular momenta alignments
Merkel, Schaefer

Results from sims suggest that 3rd order measures might be even stronger affected by IA.  Investigate the (angular) bispectrum of IA.  Describe IA by a physical alignment model, which makes use of tidal torque theory.  Derive expressions for the various combinations of intrinsic and gravitationally induced ellipticities, i.e., III- GII- and GGI-alignments, and com are results to the shear bispectrum, the GGG-term.  The latter is computed using hyper-extended perturbation theory.  Considering equilateral and squeezed configurations, find that for a Euclid-like survey IA (III-alignemtns) start to dominate on angular scales smaller than 20 arcmin and 13 arcmin, respectively.  This sensitivity to the configuration-space geometry may allow to exploit the cosmological information contained in both the intrinsic and gravitationally induced ellipticity field.  On smallest scales (l~3000) III-alignments exceed the lensing signal by at least one order of magnitude.  The amplitude of the GGI-alignments is the weakest.  It stays below that of the shear field on all angular scales irrespective of the wave-vector configuration.

1409.5228
The physical origin of the universal accretion history of dark matter haloes
Correa, Wyithe, Schaye, Duffy

Assume extended Press-Schechter formalism; then explore the relation between the structure of the inner DM halos and halo mass history using a suite of cosmological, hydrodynamical simulations.  Confirm that the formation time, defined as the time when the virial mass of the main progenitor equals the mass enclosed within the scale radius, correlates strongly with concentration.  Provide a fitting formula for the relation between concentration and formation time, from which we show analytically that the scatter in formation time determines the scatter in concentration.  Based on the analytic and numerical work, conclude that the concentration is determined by the halo mass history, and show by simple modeling that one can be determined from the other.  Since halo concentrations are characterized by their mass histories, and the latter are described by the initial density perturbations and the growth rate, establish the physical link between halo concentrations and the initial density perturbation field.  Finally, model the halo mass history as M(z)=M0(1+z)^{alpha}e^{beta z} and find a direct correlation between the parameters alpha, beta and concentration.  Provide fitting formulas for the halo mass history and accretion rate as a function of halo mass, and demonstrate how halo mass history changes according to the adopted mass definition and cosmology.