Simulating Roman+Gaia Combined Astrometry, Parallaxes, and Proper Motions

TL;DR

This paper introduces a simulation tool for predicting combined astrometric precision of Gaia and Roman missions, aiding in survey planning and strategy optimization.

Contribution

A new, generalizable simulation tool for combining astrometric data from Gaia and Roman, with detailed modeling of Roman survey strategies and uncertainties.

Findings

Roman-Gaia combined data can achieve Gaia-DR3 quality PMs down to G=26.5 mag.

Roman survey strategy impacts astrometric precision, especially for the HLWAS.

Multi-year Roman-only baseline is necessary for meaningful proper motion uncertainties.

Abstract

The next generation of high-precision astrometry is rapidly approaching thanks to ongoing and upcoming missions like Euclid, LSST, and RST. We present a new tool (available at https://github.com/KevinMcK95/gaia_roman_astrometry) to simulate the astrometric precision that will be achieved when combining Gaia data with Roman images. The statistics that underpin this method generalize to combinations of astrometric datasets from any telescope. We construct realistic Roman position uncertainties as a function of filter, magnitude, and exposure time, which are combined with Gaia precisions and user-defined Roman observing strategies to predict the expected uncertainty in position, parallax, and proper motion (PM). We also simulate the core Roman surveys to assess their end-of-mission astrometric capabilities, finding that the High Latitude and Galactic Bulge Time Domain Surveys will deliver Gaia-DR3-quality PMs down to G=26.5 mag and G=29.0 mag, respectively. Due to its modest number of repeat observations, we find that the astrometry of the High Latitude Wide Area Survey (HLWAS) is very sensitive to particular choices in observing strategies. We compare possible HLWAS strategies to highlight the impact of parallax effects and conclude that a multi-year Roman-only baseline is required for useful PM uncertainties (<100 mas/yr). This simulation tool is actively being used for ongoing Roman proposal writing to ensure astrometric requirements for science goals will be met. Subsequent work will expand this tool to include simulated observations from other telescopes to plan for a future where all surveys and datasets are harnessed together.