Dark Matter in Draco and Bo"otes I: Hints of a Core in an Ultra-Faint Dwarf from Simulation-Based Inference
Tri Nguyen, Lina Necib, Ting S. Li, Justin Read, Andrés Bañares-Hernández, Claude-André Faucher-Giguère, Kohei Hayashi, Kevin McKinnon, Andrew B. Pace, Nathan R. Sandford, Hao Yang
astro-ph.GA, astro-ph.HE
Submitted: 2026-06-24
Comments: 33 + 8 pages, 13 + 8 figures, 5 tables, submitted to MNRAS
Code: https://github.com/trivnguyen/jgnn
License: http://creativecommons.org/licenses/by/4.0/
The gist: The density profiles of dwarf spheroidal galaxies are among the most sensitive probes of dark matter physics, yet extracting them from noisy stellar kinematics remains a fundamental obstacle.
Terminology
Abstract
The density profiles of dwarf spheroidal galaxies are among the most sensitive probes of dark matter physics, yet extracting them from noisy stellar kinematics remains a fundamental obstacle. We present GraphNPE, a simulation-based inference method for dynamical mass modeling that incorporates measurement uncertainties and spectroscopic selection functions in the forward model. Using mock data, we show that methods relying solely on line-of-sight velocity dispersion are biased toward cuspy density profiles, even in the absence of the mass-anisotropy degeneracy. By accessing higher-order velocity moments, particularly line-of-sight kurtosis, GraphNPE breaks key degeneracies and recovers density profiles with substantially less bias. We apply GraphNPE to Draco and Bo"otes I using MMT/Hectochelle and DESI for Draco, and the S5 survey for Bo"otes I. For each, we report density profiles and dark matter J - and D-factors. For Draco, GraphNPE yields consistent results across datasets, marginally preferring a cuspy inner profile (rho 150 about 1.6-1.9 times 10 8, M, kpc-3) in agreement with literature. On DESI, however, second-order Jeans modeling fits the dispersion but fails to reproduce the kurtosis, demonstrating higher-order moments are essential. For Bo"otes I, limited statistical power prevents definitive determination of the inner slope. GraphNPE recovers rho 150 = 0.36+0.15-0.11 times 10 8, M, kpc-3, significantly lower than literature and consistent with a cored inner profile. This places Bo"otes I among the lowest density dwarfs at comparable stellar masses.
Sources
- Convolutional Neural Networks on Graphs with Fast Localized Spectral Filtering
- Neural Spline Flows
- Fast Graph Representation Learning with PyTorch Geometric
- Adam: A Method for Stochastic Optimization
- SGDR: Stochastic Gradient Descent with Warm Restarts
- Forecasting Dark Matter Subhalo Constraints from Stellar Streams using Implicit Likelihood Inference
- The Local Volume Database: a library of the observed properties of nearby dwarf galaxies and star clusters
- Normalizing Flows for Probabilistic Modeling and Inference
- Multi-component, axisymmetric dynamical models of dSphs based on distribution functions: inferences on dark matter and intermediate-mass black holes in Draco and Ursa Minor
- PyTorch: An Imperative Style, High-Performance Deep Learning Library
- It's Not Just Star Formation: A trend of low dark matter densities in the Andromeda dwarf galaxy system
- Aggressively-Dissipative Dark Dwarfs: The Effects of Atomic Dark Matter on the Inner Densities of Isolated Dwarf Galaxies
- Performance of AAOmega: the AAT multi-purpose fibre-fed spectrograph
- Tailored mass estimators for Milky Way dwarf Spheroidals
- Validating Bayesian Inference Algorithms with Simulation-Based Calibration
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