Improved mass constraints for two nearby strong-lensing elliptical galaxies from Hubble Space Telescope Imaging

TL;DR

This study uses new Hubble Space Telescope imaging to refine mass measurements of two nearby strong-lensing elliptical galaxies, revealing new structures and reducing uncertainties in their lensing mass estimates.

Contribution

The paper provides improved lensing mass constraints for two elliptical galaxies by utilizing high-resolution HST imaging and relative magnification data, reducing uncertainties significantly.

Findings

Lensing mass of SNL-1 increased by 7% to 9.49×10^{10} M_sun.

Lensing mass of SNL-2 increased by 9% to 12.59×10^{10} M_sun.

Reduced mass uncertainty from 5-10% to 2-3%.

Abstract

We analyse newly obtained Hubble Space Telescope (HST) imaging for two nearby strong lensing elliptical galaxies, SNL-1 (z = 0.03) and SNL-2 (z = 0.05), in order to improve the lensing mass constraints. The imaging reveals previously unseen structure in both the lens galaxies and lensed images. For SNL-1 which has a well resolved source, we break the mass-vs-shear degeneracy using the relative magnification information, and measure a lensing mass of 9.49 $\pm$ 0.15 $\times$ 10$^{10}$ M$_{\odot}$, a 7 per cent increase on the previous estimate. For SNL-2 the imaging reveals a bright unresolved component to the source and this presents additional complexity due to possible AGN microlensing or variability. We tentatively use the relative magnification information to constrain the contribution from SNL-2's nearby companion galaxy, measuring a lensing mass of 12.59 $\pm$ 0.30 $\times$ 10$^{10}$ M$_{\odot}$, a 9 per cent increase in mass. Our improved lens modelling reduces the mass uncertainty from 5 and 10 per cent to 2 and 3 per cent respectively. Our results support the conclusions of the previous analysis, with newly measured mass excess parameters of 1.17 $\pm$ 0.09 and 0.96 $\pm$ 0.10 for SNL-1 and SNL-2, relative to a Milky-Way like (Kroupa) initial mass function.