Day 1144

Wednesday.

1608.08218
The origin of scatter in the stellar mass - halo mass relation of central galaxies in the EAGLE simulation
Matthew, Schaye, et al

Use the hydrosim EAGLE to study the magnitude and origin of the scatter in the stellar mass - halo mass relation for central galaxies.  Separate cause and effect by correlating stellar masses in the baryonic sim with halo properties in a matched DM only (DMO) sim.  The scatter in stellar mass increases with redshift and decreases with halo mass.  At z=0.1 it declines from 0.25 dex at M_200_DMO~1e11 Msun to 0.12 dex at M_200_DMO~1e13 Msun, but the trend is weak above 1e12 Msun.  For M200_DMO<1e12.5 Msun up to 0.04 dex of the scatter is due to scatter in the halo concentration.  At fixed halo mass, a larger stellar mass corresponds to a more concentrated halo.  This is likely because higher concentrations imply earlier formation times and hence more time for accretion and star formation, and/or because feedback is less efficient in haloes with higher binding energies.  The maximum circular velocity, V_max_DMO, and binding energy are therefore more fundamental properties than halo mass, meaning that they are more accurate predictors of stellar mass, and so provide fitting formulae for their relations with stellar mass.  However, concentration alone cannot explain the total scatter in the M_star - M200_DMO relation, and it does not explain the scatter in M_star - V_max_DMO.  Halo spin, sphericity, triaxiality, substructure and environment are also not responsible for the remaining scatter, which thus could be due to more complex halo properties or non-linear/stochastic baryonic effects.


1608.08603
VIS: the visible imager for Euclid
Cropper, et al

Euclid-VIS is the large format visible imager for the ESA Euclid space mission in their Cosmic Vision program, scheduled for launch in 2020.  Together with the NIR imaging within the NISP instrument, it forms the basis of the WL measurements of Euclid.  VIS will image in a single r+i+z band from 550-900 nm over a field of view of ~0.5 deg2.  By combining 4 exposures with a total of 2260 sec, VIS will reach to deeper than mAB=24.5 (10sigma) for sources with extent ~0.3 arcsec.  The image sampling is 0.1 arcsec.  VIS will provide deep imaging with a tightly controlled and stable PSF over a wide survey area of 15000 deg2 to measure the cosmic shear from nearly 1.5 billion galaxies to high levels of accuracy, from which the cosmo parameters will be measured.  In addition, VIS will also provide a legacy dataset with an unprecedented combination of spatial resolution, depth and area covering most of the extra-Galactic sky.  Here, present the results of the study carried out by the Euclid Consortium during the period up to the Critical Design Review.