Astrometric Weak Lensing with Gaia DR3 and Future Catalogs: Searches for Dark Matter Substructure

TL;DR

This paper searches for dark matter substructures through astrometric weak lensing using Gaia DR3 data, setting constraints on their abundance and proposing methods for future detection with Gaia DR4 and star-star lensing techniques.

Contribution

It introduces a novel astrometric weak lensing analysis to detect dark matter subhalos and forecasts future sensitivity improvements with upcoming Gaia data releases.

Findings

Excluded substructure fractions of order unity for halos with $10^{7}$ to $10^{9}$ solar masses

Forecasted sensitivity to lower mass substructures with Gaia DR4 data

Proposed a star-star lensing stacking technique for future studies

Abstract

Small-scale dark matter structures lighter than a billion solar masses are an important probe of primordial density fluctuations and dark matter microphysics. Due to their lack of starlight emission, their only guaranteed signatures are gravitational in nature. We report on results of a search for astrometric weak lensing by compact dark matter subhalos in the Milky Way with Gaia DR3 data. Using a matched-filter analysis to look for correlated imprints of time-domain lensing on the proper motions of background stars in the Magellanic Clouds, we exclude order-unity substructure fractions in halos with masses $M_{l}$ between $10^{7} \, M_{\odot}$ and $10^{9} \, M_{\odot}$ and sizes of one parsec or smaller. We forecast that a similar approach based on proper accelerations across the entire sky with data from Gaia DR4 may be sensitive to substructure fractions of $f_{l} \gtrsim 10^{-3}$ in the much lower mass range of $10 \, M_{\odot} \lesssim M_{l} \lesssim 3 \times 10^{3} \, M_{\odot}$. We further propose an analogous technique for stacked star-star lensing events in the regime of large impact parameters. Our first implementation is not yet sufficiently sensitive but serves as a useful diagnostic and calibration tool; future data releases should enable average stellar mass measurements using this stacking method.