This award will support a study of the effects of baryonic matter on cosmological constraints on dark energy as derived from future weak lensing surveys. Large-scale numerical simulations of cosmological structure formation will be performed that treat the physics of baryons in detail. The information garnered from the simulation programs will be used to develop the techniques that will be needed to make optimal use of future photometric surveys to constrain the properties of dark energy and the process of galaxy formation.
Broader impacts of this work include research training for a graduate student. All simulation data, processed data products, analysis tools and software developed as part of this project will be made available freely to the scientific community. Simulation visualizations and results will be discussed as part of regular public lecture series at the Allegheny Observatory and will be incorporated into the Carnegie Science Center Girls Science & Math Project to build interest in astrophysical sciences.
Over the previous fifteen years, experimental data have repeatedly confirmed that the expansion of the universe is accelerating. This result is surprising because one would expect gravity to decelerate the cosmological expansion. The cause of the acceleration is not known, but has been given the name "dark energy." Exploring the nature of the dark energy is a high priority for astronomers and physicists because it seems to point toward a new form of matter and/or new laws of physics. A number of astronomical facilities are preparing to perform surveys that may shed light on the nature of dark energy. One of the most promising experimental techniques that may be used to diagnose the properties of dark energy is the gravitational lensing of galaxies. The effect is a distortion in the images of distant galaxies caused by the gravitation of intervening matter. This project was concerned with enabling informative determinations of the properties of dark energy from current and forthcoming astronomical data. To utilize these data, theoretical predictions are needed with which the data can be compared. Gravitational lensing signals are difficult to predict with sufficient precision to exploit forthcoming data fully. This work helped to established specific requirements of survey data and improved predictions for lensing signals in an effort to maximize the scientific gains from current and future surveys. Consequently, this project is part of the necessary work that must be done in support of the science goals of a number of large-scale astronomical facilities. The project proceeded in several steps. First, mock lensing data were generated and used to establish experimental requirements necessary to determine dark energy properties precisely. Second, simulations of cosmological structure formation were analyzed in order to understand lensing signatures in detail and in order to establish a framework for making more faithful theoretical predictions for the lensing effect that could be compared with data. The novel aspect of our work was to include the influence of galaxies and inter-galactic gas in predictions of the gravitational lensing signal. Third, complementary data on galaxy properties, the properties of supernova explosions, and other astronomical phenomena were explored as a means of extracting complementary information from survey data that could help physicists and astronomers to improve current understanding of both the formation of galaxies and the nature of the dark energy. The goals of this project were largely achieved. In the course of this work, several deficiencies of previous theoretical models of the large-scale structure of the universe were identified and modifications to the standard theoretical calculations that show significant promise for analyzing survey data were proposed. It is quite likely that these techniques will enable a variety of astronomical surveys to determine the properties of the dark energy more reliably, but further testing is necessary in order to be assured that this is the case. This work resulted in a number of peer-reviewed publications describing our methods and results. Our final manuscripts are currently being prepared for peer review and will describe comprehensive tests of our methods for using the lensing signature to determine the properties of the dark energy. Our work required the development of software necessary to perform these analyses. This software is now available freely to other scientists through a web interface. Over the course of the work, the PI was engaged in an active program of graduate student education and mentoring as well as public education and outreach. Educational activities related to this work included public lectures, demonstrations at local schools, and participation in programs aimed at improving science education. Much of this undertaking constituted the doctoral dissertation work of a graduate student at the University of Pittsburgh. The student successfully defended his thesis in the summer of 2012 and is continuing his work at the Fermi National Accelerator Laboratory in Illinois.
