Intrinsic Alignment Models for Precision Cosmology

Carnegie Mellon University, Pittsburgh PA

Investigators

Abstract

One of the key mysteries in modern cosmology is the nature of the dark energy that is responsible for the accelerated expansion rate of our Universe. Weak gravitational lensing, the coherent distortion of galaxy shapes due to deflection of light by mass, is the most promising observational method for uncovering the nature of dark energy. As a result, large upcoming surveys such as the Large Synoptic Survey Telescope (LSST) have been planned to measure weak lensing very precisely. The objective of this project is to provide accurate theoretical predictions that will eliminate a key source of uncertainty in weak lensing measurements and test their use in analysis of data from an ongoing sky survey. Work such as this, that will contribute to the solution of the biggest mystery in modern cosmology, will clearly promote the progress of science. As an additional benefit, the investigators will extend an existing, highly successful educational outreach program ("Space Public Outreach Team" or SPOT) to the Pittsburgh area, focusing on schools with a significant fraction of under-represented minorities. This project will have an impact both on K-12 education and undergraduate and graduate education. Weak gravitational lensing has great potential to solve some of the major outstanding issues in cosmology, such as the nature of dark energy. However, a major source of uncertainty is that these measurements are typically interpreted assuming that all coherent galaxy shape alignments are due to weak lensing, but unfortunately, galaxies do exhibit coherent "intrinsic alignments" with large-scale density fields. The alignments contaminate weak lensing measurements at a level that will significantly exceed the statistical error bars on weak lensing measurements with the LSST. This project has three main objectives. The first objective is to use large volume, extremely high resolution hydrodynamic simulations to further our understanding of the physics behind intrinsic alignments and build improved intrinsic alignments models. The second objective is to produce mock galaxy catalogs with intrinsic alignments for use in testing intrinsic alignments mitigation schemes. The final objective is to carry out cosmological weak lensing analysis including strategies to marginalize over intrinsic alignments using improved intrinsic alignment models that are motivated by state-of-the-art simulations, analytic theory, and observations.