Day 1285

Thursday.  Friday.


1707.01108
ZOMG III: the effect of halo assembly on the satellite population
Gerald, Romano-Díaz, Borzyszkowski, Porciani

Use zoom hydro sims to investigate the properties of satellites within galaxy-sized DM haloes with different assembly histories.  Consider two classes of haloes at redshift z=0: 'stalled' haloes that assembled at z>1 and 'accreting' ones that are still forming nowadays.  Have previously shown that the stalled haloes are embedded within thick filaments of the cosmic web while the accreting ones lie where multiple thin filaments converge.  Find that satellites in the two classes have both similar and different properties.  Their mass spectra, radial count profiles, baryonic and stellar content, and the amount of material they shed are indistinguishable.  However, the mass fraction locked in satellites is substantially larger for the accreting haloes as they experience more mergers at late times.  The largest difference is found in the satellite kinematics.  Substructures fall towards the accreting haloes along quasi-radial trajectories whereas an important tangential velocity component is developed, before accretion, while orbiting the filament that surrounds the stalled haloes.  Thus, the velocity anisotropy parameter of the satellites (beta) is positive for the accreting heroes and negative for the stalled ones.  This signature enables us to tentatively categorize the Milky Way halo as stalled based on a recent measurement of beta.  Half of the haloes contain clusters of satellites with aligned orbital angular momenta corresponding to flattened structures in space.  These features are not driven by baryonic physics and are only found in haloes hosting grad-design spiral galaxies, independently of their assembly history.


1707.01285
Shear measurement bias: dependencies on methods, simulation parameters and measured parameters
Pujol, et al

Present a study of the dependencies of shear and ellipticity bias on simulation (input) and measured (output) parameters, noise, PSF anisotropy, pixel size and the model bias coming from two different independent shape estimators.  Use simulated images from Galsim based on the GREAT3 control-space-constant branch and measure ellipticity and shear bias from a model-firing method (gFIT) and a moment-based method (KSB).  Show the bias dependencies found on input and output parameters for both methods and identify the main dependencies and causes.  Find consistent results between the two methods (given the precision of the analysis) and important dependencies on orientation and morphology properties such as flux, size and ellipticity.  Show cases where shear bias and elliptical bias behave very different for the two methods due to the different nature of these measurements.  Also show that noise and pixelization play an important role on the bias dependencies on the output properties.  Find a large model bias for galaxies consisting of a bulge and a disk with different ellipticities or orientations.  Also see an important coupling between several properties on the bias dependencies.  Because of this, need to study several properties simultaneously in order to properly understand the nature of shear bias.