Day 799

Thursday.

1412.1081
Impact of anisotropic stress of free-streaming particles on gravitational waves induced by cosmological density perturbations
Saga, Ichiki, Sugiyama

GWs are inevitably induced at second-order in cosmo perturbations through NL couplings with first order scalar perturbations, whose existence is well established by recent cosmological observations.  So far, the evolution and the spectrum of the secondary induced GWs have been derived by taking into account the sources of GWs only from the product of first order scalar perturbations.  Investigate the effects of purely second-order anisotropic stresses of photons and neutrinos on the evolution of GWs, which have been omitted in the literature.  Present a full treatment of the Einstein-Boltzmann system to calculate the spectrum of GWs with anisotropic stress based on the formalism of the cosmo perturbation theory.  Find that photon anisotropic stress amplifies the amplitude of GWs by 150, whereas neutrino anisotropic stress suppress that of GWs by about 30 on small scales k>~1.0 h/Mpc.  The result is in marked contrast with the case at linear order, where the effect of isotropic stress is damping in amplitude of GWs.

1412.1094 The impact of cosmic variance on simulated weak lensing surveys
Kannawadi, Mandelbaum, Lackner

One major systematic uncertainty in WL is the calibration of WL shape distortions, or shears.  Most upcoming surveys plan to test several aspects of their shear estimation algorithms using sophisticated image simulations that include realistic galaxy populations based on high-resolution data from the HST.  However, existing datasets from HST over very small cosmological volumes, so cosmic variance could cause the galaxy populations in them to be atypical.  A narrow redshift slice from such surveys could e dominated by a single large overdensity or under density.  In this case, the morphology-density relation could alter the local galaxy populations and yield an incorrect calibration of shear estimates as a function of redshift.  Directly test this scenario using the COSMOS survey, the largest-area HST survey to date, and show how the statistical distributions of galaxy shapes and morphological parameters (e.g., Sersic n) are influenced by redshift-dependent cosmic variance.  The typical variation in RMS ellipticity due to environmental effects is 5% (absolute, not relative) for redshift bins of width Delta z = 0.05, which could result in uncertain shear calibration at the 1% level.  Conclude that the cosmic variance effects are large enough to exceed the systematic error budget of future surveys, but can be mitigated with careful choice of training dataset and sufficiently large redshift binning.


A bunch of ASTRO-H white papers, a JAXA/NASA X-ray satellite.


1412.1239
Cosmic evolution of dust in galaxies: methods and preliminary results
Bekki

Investigate the z evolution of dust properties, its dependences on initial conditions of galaxy formation, and physical correlations between dust, gas , and stellar contents at different z based on the original chemodynamical simulations of galaxy formation with dust growth and destruction.  In this preliminary investigation, first determine the reasonable ranges of the two most important parameters of dust evolution, i.e., the timescales of dust growth and destruction, by comparing the observed and simulated dust properties and molecular hydrogen H2 content of the Galaxy.  Then investigate the z-evolution of dust-to-gas-ratios (D) and, H2 gas fraction (f_H2), and gas-phase chemical abundances(e.g., A_O=12+log(O/H)) in the simulated disk and dwarf galaxies.  The principal results are as follows.  Both D and f_H2 can rapidly increase during the early dissipative formation of galactic disks (z~2-3) and the z-evolution of these depends on initial mass densities, spin parameters, and masses of galaxies.  The observed A_O-D relation can be qualitatively reproduced, but the simulated dispersion of D at a given A_O is smaller.  The simulated galaxies with larger total dust masses show larger H2 and stellar masses and higher f_H2.  Disk galaxies show negative radial gradients of D and the gradients are steeper for more massive galaxies.  Both dust-to-metal ratios and gas-phase [S/Fe] can be significantly different within a single galaxy and between different galaxies at different z, which means that fixed dust-to-metal ratios should not be used in investigating H2 contents and spectral energy distributions of galaxies.

1412.1432
Predicting Alpha Comae Berneices Time of eclipse I: A 26 year binary will eclipse within 2 weeks of 25 January 2015
Muterspaugh, Henry

As the title says.  Keep an eye out for the occultation!