Wide-Field Science – Regular
Jonathan Blazek / Northeastern University, PI
The Nancy Grace Roman Space Telescope brings exciting new capabilities for cosmology. The High-Latitude Wide-Area Survey on the Wide-Field Instrument will provide the positions and shapes of hundreds of millions of galaxies, and over ten million galaxy spectra, from which analysis of weak gravitational lensing and galaxy clustering will form a main pillar of cosmology studies.
Despite its tremendous statistical power, the ultimate success of Roman will depend on our understanding of a range of astrophysical, observational, and instrumental effects. With current cosmology projects, we have already reached the point where cosmological constraints are determined by these systematic uncertainties. While observing from space reduces several challenges induced by the atmosphere, the impact of astrophysical effects is unavoidable. of particular interest to this proposal are galaxy “intrinsic alignments” (IA), correlations in the true shapes of galaxies as influenced by their local environment and formation. Galaxy IA induces observed correlations between galaxy shapes that mimic the weak lensing signal we are trying to measure. IA is one of the most significant astrophysical systematics for Roman and other future cosmology projects – without properly accounting for it, analyses can be significantly biased. Conversely, if sufficiently understood, IA can provide a new probe of cosmology and astrophysics.
The constraining power of Roman makes it critical that IA and other astrophysical effects are understood to a high degree of accuracy. At the same time, Roman’s depth means that we are probing galaxies that are fainter and more distant than those reached in current surveys, and we are thus more reliant on other approaches to predict their behavior. This proposal aims to address this challenge, using a combination of observational data, simulations, and analytic modeling to achieve three key objectives. First, we will combine current measurements to predict the plausible range of IA scenarios and the impact on Roman cosmology. These results will allow us to determine optimal modeling strategies. Second, we will provide simulation tools and proof-of-concept simulated Roman galaxy catalogs with realistic IA, to be used for pipeline validation and as an input for community-wide simulation efforts. Third, we will determine how to utilize IA as a new physical probe with Roman data.
The methods employed in this proposed research include analyzing existing observational data, processing numerical simulations, and analytic modeling. Forecasts will be done as realistic analysis of synthetic Roman data vectors. The simulation component will utilize “gravity-only” simulations, avoiding several challenges that arise when using hydrodynamics. We will refine and employ a method that is able to populate simulated dark matter structure with realistic galaxies, including alignments. These simulated galaxies will improve our understanding of galaxy IA and their impact on Roman analyses. We will also use them to develop a simulation-based model of IA and to improve and test analytic modeling in the context of Roman. Finally, these simulation and modeling tools will be used to develop new analyses for Roman that will utilize observed galaxy shapes to probe both astrophysics (e.g. galaxy formation) and fundamental physics (e.g. inflation and dark matter interactions).
This proposal is highly responsive to the criteria of this WFS opportunity and to NASA science goals more broadly. It will enable core Roman cosmology analyses through better understanding and treatment of IA, including guidance to the relevant Project Infrastructure Team(s). It will expand the potential scientific impact of WFI data, including opportunities to learn about both astrophysics and fundamental physics of the Universe. It will provide simulation products and software that enable projects and collaboration across the Roman science community.