Scanning for dark matter subhaloes in Hubble Space Telescope imaging of 54 strong lenses

Abstract

The cold dark matter (DM) model predicts that every galaxy contains thousands of DM subhaloes;ãlmostãll other DM models includeã physical process that smoothsãway the subhaloes. The subhaloesãre invisible, but could be detected via strong gravitational lensing, if they lie on the line of sight toã multiply imaged background source,ãnd perturb itsãpparent shape. We presentã predominantlyãutomated strong lensãnalysis framework,ãnd scan for DM subhaloes in Hubble Space Telescope imaging of 54 strong lenses. We identify five DM subhalo candidates, including two especially compelling candidates (one pre viously kno wn in SLACS0946 + 1006) whereã subhalo is fa v ouredãfterãll of our tests for systematics. We find that the detectability of subhaloes depends upon theãssumed parametric form for the lens galaxy's mass distribution, especially its degree ofãzimuthal freedom. Using separate components for DMãnd stellar mass reveals two DM subhalo candidatesãnd remo v es four false positives compared to the single power-law mass model that is common in the literature. We identify 45 lenses without substructures, the number of which is key to statistical testsãble to rule out models of, for example, warm or self-interacting DM. Our fullãnalysis resultsãreãvailableãt ht tps://github.com/Jammy2211/aut olens subhalo.