Probing the inner kpc of massive galaxies with strong gravitational lensing

TL;DR

This paper explores the potential of using ALMA to detect and analyze demagnified central images in gravitational lensing of molecular lines, aiming to measure galaxy core properties and SMBH characteristics.

Contribution

It models lensing galaxies with detailed components and assesses the detectability of central images, providing new insights into measuring core sizes and SMBH masses.

Findings

Deep ALMA observations can detect central images at >3σ significance.

Large stellar cores allow accurate measurement of core size and SMBH mass.

Detection of binary SMBHs requires very long integrations and specific conditions.

Abstract

We examine the prospects of detecting demagnified images of gravitational lenses in observations of strongly lensed mm-wave molecular emission lines with ALMA. We model the lensing galaxies as a superposition of a dark matter component, a stellar component, and a central supermassive black hole and assess the detectability of the central images for a range of relevant parameters (e.g., stellar core, black hole mass, and source size). We find that over a large range of plausible parameters, future deep observations of lensed molecular lines with ALMA should enable detection of the central images at $\gtrsim 3\sigma$ significance. We use a Fisher analysis to examine the constraints that could be placed on these parameters in various scenarios and find that for large stellar cores, both the core size and the mass of the central SMBHs can be accurately measured. We also study the prospects for detecting binary SMBHs with such observations and find that only under rare conditions and with very long integrations ($\sim$40-hr) the masses of both SMBHs may be measured using the distortions of central images.