First Results on Dark Matter Substructure from Astrometric Weak Lensing

Area of Science:

• Astrophysics
• Cosmology
• Particle Physics

Background:

• Low-mass dark matter structures are predicted to lack baryonic matter.
• These pristine substructures offer a unique testbed for dark matter microphysics and early universe fluctuations.
• Small-scale structures in the Milky Way are ideal for studying dark matter properties.

Purpose of the Study:

• To conduct the first search for Galactic dark matter (DM) subhalos using time-domain astrometric weak gravitational lensing.
• To establish constraints on the substructure fraction of dark matter in the Milky Way.
• To develop and validate a data analysis pipeline for detecting DM subhalos.

Main Methods:

• Utilized a matched-filter template for local lensing corrections to stellar proper motion in the Magellanic Clouds.
• Developed a data analysis pipeline for sample selection, background subtraction, and outlier management.
• Identified a unique signature for DM lenses using anomalous parallax templates for confirmation.

Main Results:

• Presented constraints on the substructure fraction (f_l) as f_l≲5 at 90% C.L. and f_l≲2 at 50% C.L. for compact lenses (radii < 1 pc).
• Achieved best sensitivity for lens masses around 10^7-10^8 solar masses.
• Demonstrated the potential for robust discovery with full time-series data.

Conclusions:

• The time-domain astrometric weak lensing technique is a promising method for discovering Galactic DM subhalos.
• Future astrometric datasets, like Gaia, will significantly improve sensitivity, potentially reaching f_l≲10^-3 for massive point-like objects.
• The method will enable sensitivity to lighter and/or more extended subhalos.