Cosmological Strong Lensing: A Public Comparison of Theory with New Data Across Mass and Redshift

University Of Chicago, Chicago IL

Investigators

Abstract

This project will simulate elements of cosmology and compare those to observations, in particular using strong gravitational fields that act as lenses. The goal is to understand whether gravitational lenses can be used to understand the cosmological properties. What makes this project possible is the growing sample of strong gravitational lenses. These lenses are massive galaxies and clusters of galaxies that are so large they bend light coming from a more distant background object and passing near the lensing object. Studying these lenses and the lensed objects will allow the researchers to study the mass of the galaxies and clusters, the amount of dark matter, the distant object and space between the source, the lens, and us, and to determine fundamental properties of the universe. The main question to be answered by this project is: Do the properties of the most massive objects in the universe, which are acting as lenses, match those from astronomer's predictions from simulations of the unverse? If so, they can be used to understand more fundamental problems. If not, astronomers will have a better understanding of what needs to be done to their simulations to improve them. This project is possible now due to an increase in the number of observed lensing objects. In addition to the scientific portion of the project, the PI to increase diversity among American scientists by working with six Deaf undergraduate students from the National Technical Institute for the Deaf, as summer co-op students at the University of Chicago. By engaging them in scientific research early in their academic careers, this project aims to open career paths that they would otherwise be unable to tread. The students will develop a mobile app as a portal for "citizen science"; and the project engages the broader public by enabling participation in the visual classifications central to the scientific analysis. Unlike prior efforts in citizen science in astronomy, this program aims to reach citizens through their now most commonly used electronic tools (tablets and phones) and by casting much of the interaction in a more "game-like" setting using an app, rather than webpages. The students will be encouraged to participate in outreach activities, particularly to the broader Deaf public in Chicago, with the aim of sparking interest in STEM studies in yet younger citizens. This project clearly relates to NSF's mission to promote the progress of science. In addition, the "Broader Impact" portion of the project does this, and advances the national health, prosperity and welfare by helping to develop interest in, and educating, STEM activities among the next generation of diverse individuals. Cosmological simulations are becoming the backbone of analysis for a wide range of extragalactic data. These analyses are numerous, spanning our efforts to understand all observable discrete extragalactic objects, integrated direct backgrounds from X- rays to the radio, and the influence of all that structure on the observed cosmic microwave background, as well as the scientific exploitation of that wide range of signals. Simulations are central to the planning and deployment of major new facilities and experiments. As simulations develop in complexity and scope, and impact, it is paramount that they are rigorously tested against a broad range of observables. This testing is critical as a check of algorithms and simulation contents, and as a test of the physics that the simulations evince. Strong lensing by the most massive halos (from galaxies and clusters of galaxies) in the universe is a unique point of connection between cosmological simulations, and the real cosmos. Robustly predicting strong lensing, given a simulation, requires only some fairly simple ray tracing. By comparing the two largest samples of massive strong lenses against the largest existing simulations, this proposal will address unambiguously a long-standing doubt in the literature: Namely that the correspondence between real and simulated universes in this regime is poor. If the proposed comparisons refute this long-suggested concern, a major challenge to the existing model and the simulations that evoke it will be effectively retired. Conversely, if this long held problem is reinforced, then the proposed detailed examination of the statistics of lensing will illuminate why, and how simulations must be advanced to ensure correspondence. Either result will move this field forward, significantly. Comparisons between simulations and observed real samples will be made across many lens and lensing properties, testing the match or lack thereof in multiple ways, across the entire relevant redshift column, and two decades in halo mass. Such an analysis has never before been possible or attempted, and is possible only now due to rapid advances in both real strong lensing samples, and simulations.