BCCP Seminars

Friday, October 3
INPA/Cosmology/BCCP seminar
Location: LBNL 50-5026 – 12 p.m.
Speaker: Yin Li, Chicago
Title: “The power spectrum super-sample effect”
Abstract: The impact of density fluctuations with wavelengths larger than a survey must be considered when extracting cosmological information from power spectrum measurements. These modes change the power spectrum in the same way as a change in the cosmological background does. Using a handful of separate universe simulations, we accurately capture this effect in terms of response of the matter power spectrum to a single mode — the mean density fluctuation in the survey volume. The unknown amplitude of this mean density mode contributes to a (typically dominant) error in the matter power spectrum estimators. Alternatively, it can also be simply included in parameter estimation and forecasts by treating the mean density fluctuation as an additional cosmological parameter. Parameter degeneracies arise since the response of the power spectrum to the mean density mode and cosmological parameters share similar properties in changing the growth of structure and dilating the scale of features.

Tuesday, October 7

Location: UCB, Hearst Field Annex B-1 – 1:10 pm
Speaker: Benedikt Diemer, Chicago  
Title: “The (non-)universality of halo density profiles”
Abstract: The density profiles of dark matter halos are an essential input for models of galaxy formation, as well as for the interpretation of numerous observations such as weak and strong lensing signals. The profiles are commonly thought to follow a simple, universal shape, and only depend on two parameters, mass and concentration. Using a large suite of cosmological simulations, I will show that the outer halo density profiles depend on an additional parameter, the mass accretion rate, and present an accurate new fitting formula that takes this dependence into account. I will further discuss the question of universality, and show that the definition of the halo boundary plays a crucial role. Similarly, halo concentrations are usually described as a universal function of mass and redshift. Instead, I will present a model in which concentration depends on an additional parameter: the local slope of the matter power spectrum. I will demonstrate that this model accurately (to better than 10-15%) describes simulated concentrations over a large range of redshifts, halo masses and cosmological parameters, and is in excellent agreement with the recent observations of the CLASH cluster survey.