Astrophysics Colloquium: Alexie Leauthaud (UCSC) PAB

Mar 09, 2017 - 11:00 am to 12:00 pm
Campus, Varian 355 *note change in location this week*

Lensing is Low: Cosmology, Galaxy Formation, or New Physics?

A fundamental goal in observational cosmology is to understand the link between the luminous properties of galaxies and the dark matter halos in which they reside. Weak lensing, which relies simply on the laws of gravity, is a unique method that can be used to directly probe the dark matter components of galaxies. In this talk, I will present new high signal-to-noise weak lensing measurements for galaxies from the BOSS “CMASS" sample. By comparing this signal with predictions from mock catalogs trained to match observables including the stellar mass function and the projected and two dimensional clustering of BOSS galaxies, I will show that the clustering of CMASS, together with standard models of the galaxy-halo connection, robustly predicts a lensing signal that is 20-40\% larger than observed. I will discuss several effects that may explain this mis-match including, a low value of the amplitude of low redshift structure compared to Planck2015, assembly bias, the effects of baryons on the matter distribution, and the effects of massive neutrinos. Towards the end of this talk, I will show some early results from the new Hyper Suprime Cam (HSC) survey, an ambitious multi-wavelength (g,r,i,z,y) weak-lensing program to map out 1500 square degrees of the sky with the 8.2m Subaru Telescope to i∼26 mag.