Speaker:  Seshadri Nadathur (Helsinki, Finland)

Absract:

Most of the volume of the universe is made up of under-dense regions or “voids”. The shapes, abundances, gravitational effects on light propagation and dynamics of voids have all been suggested as potential tests of the LCDM model, non-Gaussianities and modified gravity theories. I will start by discussing the crucial question of how exactly to define and identify “voids” in galaxy surveys, and describe a public catalogue that is free of spurious contamination. Using this catalogue and a very large simulation I will address the problem of the stacked integrated Sachs-Wolfe signal observed from voids (and superclusters), which has appeared to contradict LCDM, and a possible resolution of this mystery. Finally, I will discuss how to measure void density profiles and show that they are independent of void size and tracer galaxy population. This self-similarity and universality provides an exciting new tool with which to use voids for future cosmological tests.