Probing cold dark matter subhalos with simulated ALMA observations of macrolensed sub-mm galaxies

TL;DR

This study uses simulated ALMA observations of strongly lensed sub-mm galaxies to detect dark matter subhalos, demonstrating the potential to identify subhalos down to 10^7 solar masses and exploring factors affecting detection sensitivity.

Contribution

The paper introduces a detailed simulation framework for detecting low-mass dark matter subhalos via ALMA lensing observations, analyzing detection limits and sensitivities across different bands and configurations.

Findings

Pseudo-Jaffe subhalos detectable down to 10^7 M_sun with 99% confidence.

Detection sensitivity varies with subhalo position and observational band.

Band 9 has the poorest sensitivity despite highest resolution.

Abstract

If the dark matter halos of galaxies contain large numbers of subhalos as predicted by the $\Lambda$CDM model, these subhalos are expected to appear in strong galaxy--galaxy lens systems as small--scale perturbations in individual images. We simulate observations of multiply--lensed sub--mm galaxies at $z\sim2$ as a probe of the dark matter halo of a lens galaxy at $z\sim0.5$. We present detection limits for dark substructures based on a visibility plane analysis of simulated Atacama Large Millimeter/submillimeter Array (ALMA) data in bands 7, 8 and 9. We explore two effects: local surface brightness anomalies on angular scales similar to the Einstein radius and the astrometric shift of macroimages. This improves the sensitivity of our lens modeling to the mass of the lens perturber. We investigate the sensitivity of the detection of low--mass subhalos to the projected position of the subhalo on the image plane as well as the source structure and inner density profile of the lens. We demonstrate that, using the most extended ALMA configuration, pseudo-Jaffe subhalos can be detected with 99% confidence down to $M = 10^7 M_\odot$. We show how the detection threshold for the three ALMA bands depends on the projected position of the subhalo with respect to the lensed images and conclude that, despite the highest nominal angular resolution, band 9 provides the poorest sensitivity due to observational noise. All simulations use the \emph{ALMA Full ops most extended} ALMA configuration setup in CASA.