Overview
The Roman Space Telescope is expected to observe \(\mathcal{O}(10^5)\) galaxy-galaxy strong gravitational lenses, providing high angular resolution images of galaxy-galaxy strong gravitational lenses that can be used to probe the nature of dark matter at sub-galactic scales (Daylan and Birrer 2023, Wedig et al. 2025).
The Roman Data Challenge for Dark Matter Substructure with Galaxy-Galaxy Strong Gravitational Lenses provides realistic simulated Roman images of strong lenses with various dark matter substructure populations and challenges the community to test out substructure detection and characterization pipelines.
We have simulated datasets of Roman strong lenses using the mejiro package (Wedig et al. 2025). mejiro uses SLSim to simulate a population of galaxy-galaxy strong gravitational lenses, then adds substructure populations from pyHalo and instrumental effects with GalSim and STPSF. Participants may also generate their own simulated data using mejiro on the Roman Research Nexus by following the instructions on the Running mejiro page.
This data challenge aims to achieve the following:
- Explore optimal approaches for strong lensing substructure analysis
- Assess how much dark matter information will be available in the Roman survey
- Assess which lenses in the Roman survey will be most promising to perform robust analyses on
- Incentivize scalable methodology to be able to work on Roman-scale datasets
- Support and maintain a research community focused on substructure studies using Roman
Scientific Motivation
Although Cold Dark Matter (CDM) is a widely successful model for predicting the large-scale structure of the Universe, its shortcomings become apparent when used to predict properties of small-scale structures. Examples include the missing satellite problem, where CDM predicts more satellite galaxies than observed, the cusp-core problem, where CDM predicts a higher density of dark matter at the center of galaxies than observed, and more (Perivolaropoulos and Skara 2022). To explain these discrepancies, other dark matter models have been brought forth, such as the warm dark matter and self-interacting dark matter models. Thus, our aim is to analyze dark matter through strong gravitational lenses, which can allow us to place constraints on these alternative dark matter models.
Additional Possible Paths of Inquiry
- Einstein radius of main deflector
- Total Halo Mass enclosed in Einstein radius
- Upper/lower bounds on halo mass
- Upper/lower bounds on number of halos
- Sigma_sub, half mode mass, mean number of halos
- Locating largest/most massive halos
- Given halo locations, determine halo concentration
Timeline
| Date | Event |
|---|---|
| October 2025 | Rung 0 begins |
| May 2026 | Rung 1 begins |
| Summer 2026 | Rung 2 begins |
Contact Us
Feedback and questions are welcome, and should be sent to roman_data_challenge_submissions@stonybrook.edu. Additionally, we are active in the #strong-lensing channel in the Roman Space Telescope Slack.