A calibration of the stellar mass fundamental plane at z ~ 0.5 using the micro-lensing induced flux ratio anomalies of macro-lensed quasars

TL;DR

This study uses micro-lensing flux ratio anomalies in macro-lensed quasars at z~0.5 to calibrate the stellar mass fundamental plane, providing a novel way to measure stellar mass surface densities in early type galaxies.

Contribution

It introduces a method that leverages micro-lensing effects in X-ray observations to normalize the stellar mass fundamental plane, accounting for faint stellar remnants and brown dwarfs.

Findings

Median normalization factor F = 1.23 for stellar masses

Confidence range 0.77 < F < 2.10

Method sensitive to individual stellar gravitational potential graininess

Abstract

We measure the stellar mass surface densities of early type galaxies by observing the micro-lensing of macro-lensed quasars caused by individual stars, including stellar remnants, brown dwarfs and red dwarfs too faint to produce photometric or spectroscopic signatures. Instead of observing multiple micro-lensing events in a single system, we combine single epoch X-ray snapshots of ten quadruple systems, and compare the measured relative magnifications for the images with those computed from macro-models. We use these to normalize a stellar mass fundamental plane constructed using a Salpeter IMF with a low mass cutoff of 0.1 solar mass and treat the zeropoint of the surface mass density as a free parameter. Our method measures the graininess of the gravitational potential produced by individual stars, in contrast to methods that decompose a smooth total gravitational potential into two smooth components, one stellar and one dark. We find the median likelihood value for the normalization factor F by which the Salpeter stellar masses must be multiplied is 1.23, with a one sigma confidence range, dominated by small number statistics, of 0.77 < F < 2.10