Day 656

Wednesday.

1405.2921
Introducing the Illustris project: simulating the coevolution of dark and visible matter in the Universe
Vogelsberger, Genel, Springel, Torrey, Sijacki, Xu, Snyder, Nelson, Hernquist

Illustris Project: a series of large-scale hydro-sim of galaxy formation.  Highest resolution: (100Mpc)^3, DM resolution 6.3e6Msun, and initial baryonic matter mass resolution of 1.3e6Msun.  At z=0, softening scales of 710 pc, and the smallest hydro gas cells have extent of 48 pc.  Follow dynamical evolution of 2x1820^3 resolution elements and in addition passively evolve 1820^3 MC tracer particles reaching a total particle count of 18 billion.  The galaxy formation model includes primordial and metal-line cooling with self-shielding corrections, stellar evolution, stellar feedback, gas recycling, chemical enrichment, SMBH growth, and feedback from AGN.  At z=0 the simulation volume contains about 40k well-resolved galaxies covering a diverse range of morphologies and colors including early-type, late-type and irregular galaxies.  The simulation reproduces the cosmic SFR density, the galaxy luminosity function, and baryon conversion efficiency at z=0.  It also qualitatively captures the impact of galaxy environment on the red fractions of galaxies.  The internal velocity structure of selected well-resolved disk galaxies obeys the stellar and baryonic TF relation together with flat circular velocity curves.  In the well-resolved regime the simulation reproduces the observed mix of early-type and late-type galaxies.  Model predicts a halo mass dependent impact of baryonic effects on the halo MF and the masses of haloes caused by feedback form SN and AGN.

1405.2923
Orientation bias of optically selected galaxy clusters and its impact on stacked weak lensing analyses
Dietrich, et al

WL measurements of averaged shear profiles of galaxy clusters binned by some proxy for cluster mass are commonly converted to cluster mass estimates under the assumption that these cluster stacks have spherical symmetry.  Test whether this assumption holds for optically selected clusters binned by estimated optical richness.  Using mock catalogues from N-body sims populated with galaxies, ran a quite of optical cluster finders and estimated their optical richness.  Binned galaxy clusters by true cluster mass and estimated optical richness and measure the ellitpicity of these stacks.  Find that the processes of optical cluster selection and richness estimation are biased, leading to stacked structures that are elongated along the LoS.  Show that WL alone cannot measure the size of this orientation bias.  WL masses of stacked optically selected clusters are overestimated by 3-6% when clusters can be uniquely associated with haloes.  This effect is large enough to lead to significant biases in the cosmological parameters derived from large surveys like the DES, if not calibrated via simulations or fitted simultaneously.  This bias probably also contributes to the observed discrepancy between the observed and predicted SZ signal of optically-selected clusters.