Beyond collective fluctuations: probing micro-image swarms in lensed quasars with intensity interferometry

TL;DR

This paper explores using intensity interferometry to measure micro-image swarm sizes in lensed quasars, aiming to extract detailed information about stellar and dark matter substructures.

Contribution

It proposes a novel application of intensity interferometry to analyze micro-image swarms in lensed quasars, advancing observational techniques in gravitational lensing.

Findings

Micro-image swarm features can be studied in visibility space.

Observations are feasible for the brightest lensed quasars with current and future tech.

Intensity interferometry can reveal stellar and dark matter substructure details.

Abstract

Each strongly lensed image of a quasar behind a lensing galaxy (or galaxy cluster) is composed of a swarm of micro-images. This is a result of microlensing due to stellar-scale substructure in the lens. The presence of microlenses forms a network of micro-caustics, and a source transiting these micro-caustics gives rise to variation in observed strongly lensed images. These micro-image swarms are currently observable only through collective intensity fluctuations, which hide the underlying information on the stellar (and compact dark matter, if any) mass functions within the swarm. To unlock the information present in micro-image swarms, it is necessary to explore new techniques. In this work, we study the prospects of determining the micro-image swarm size in lensed quasar images using the intensity interferometry (i.e., the Hanbury Brown & Twiss effect). We consider QSO 2237+0305 and PS J0147+4630, two of the brightest lens quasars in the sky, and study micro-image swarm features in visibility space for both macro-minimum and macro-saddle-point images. At the end, we argue that, with ongoing and expected technical advances, observations of micro-image swarms are plausible, at least for the brightest lensed quasars.