JWST lensed quasar dark matter survey I: Description and First Results

TL;DR

This paper introduces a JWST survey measuring flux ratios of lensed quasars' warm dust emission to probe small-scale dark matter structures, achieving high precision and enabling detection of dark halos below galaxy formation scales.

Contribution

It presents a novel survey method using JWST MIRI to measure quasar flux ratios with high precision, sensitive to dark matter halos below galaxy formation scales.

Findings

Achieved 3% precision in flux ratio measurements.

Simulations indicate detection of 10^7 M_sun dark halos is feasible.

First results demonstrate the method's potential for dark matter studies.

Abstract

The flux ratios of gravitationally lensed quasars provide a powerful probe of the nature of dark matter. Importantly, these ratios are sensitive to small-scale structure, irrespective of the presence of baryons. This sensitivity may allow us to study the halo mass function even below the scales where galaxies form observable stars. For accurate measurements, it is essential that the quasar's light is emitted from a physical region of the quasar with an angular scale of milli-arcseconds or larger; this minimizes microlensing effects by stars within the deflector. The warm dust region of quasars fits this criterion, as it has parsec-size physical scales and dominates the spectral energy distribution of quasars at wavelengths greater than 10$\mu$m. The JWST Mid-Infrared Instrument (MIRI) is adept at detecting redshifted light in this wavelength range, offering both the spatial resolution and sensitivity required for accurate gravitational lensing flux ratio measurements. Here, we introduce our survey designed to measure the warm dust flux ratios of 31 lensed quasars. We discuss the flux-ratio measurement technique and present results for the first target, DES J0405-3308. We find that we can measure the quasar warm dust flux ratios with 3% precision. Our simulations suggest that this precision makes it feasible to detect the presence of 10$^7$ M$_\odot$ dark matter halos at cosmological distances. Such halos are expected to be completely dark in Cold Dark Matter models.