Comparing Lensing and Stellar Orbital Models of a Nearby Massive Strong-Lens Galaxy

TL;DR

This study compares mass estimates from stellar dynamical models and lensing techniques for the nearby galaxy SNL-1, finding strong agreement and providing insights into its intrinsic shape, orbital structure, and implications for galaxy modeling.

Contribution

It presents a detailed comparison of dynamical and lensing mass estimates for SNL-1, highlighting the galaxy's shape, orbital anisotropy, and the impact of orientation on lensing configurations.

Findings

Dynamical and lensing mass estimates agree within 5%.

SNL-1 has a triaxial, oblate-like shape in the center and spherical at larger radii.

The galaxy's orbital structure transitions from isotropic to radially-biased outward.

Abstract

Exploiting the relative proximity of the nearby strong-lens galaxy SNL-1, we present a critical comparison of the mass estimates derived from independent modelling techniques. We fit triaxial orbit-superposition dynamical models to spatially-resolved stellar kinematics, and compare to the constraints derived from lens modelling of high-resolution photometry. From the dynamical model, we measure the total (dynamical) mass enclosed within a projected aperture of radius the Einstein radius to be $\log_{10} M_{\mathrm{Ein.}} = 11.00 \pm 0.02$, which agrees with previous measurements from lens modelling to within $5\%$. We then explore the intrinsic (de-projected) properties of the best-fitting dynamical model. We find that SNL-1 has approximately-constant, intermediate triaxiality at all radii. It is oblate-like in the inner regions (around the Einstein radius) and tends towards spherical at larger radii. The stellar velocity ellipsoid gradually transforms from isotropic in the very central regions to radially-biased in the outskirts. We find that SNL-1 is dynamically consistent with the broader galaxy population, as measured by the relative fraction of orbit `temperatures' compared to the CALIFA survey. On the mass--size plane, SNL-1 occupies the most-compact edge given its mass, compared to both the MaNGA and SAMI surveys. Finally, we explore how the observed lensing configuration is affected by the orientation of the lens galaxy. We discuss the implications of such detailed models on future combined lensing and dynamical analyses.