Investigating the relation between environment and internal structure of massive elliptical galaxies using strong lensing

TL;DR

This study uses strong lensing data to explore how the internal structure of massive elliptical galaxies relates to their environment, finding that certain structural offsets are unaffected by environment, which informs dark matter theories.

Contribution

It provides new insights into the relationship between galaxy internal structures and environment, especially regarding centroid and position angle offsets, using a sample of 15 strong lensing systems.

Findings

Centroid offset between mass and light is not correlated with environment.

Position angle offset correlates with local galaxy density under some definitions.

Residual shear in lens models is uncorrelated with environment, indicating modeling limitations.

Abstract

Strong lensing by massive galaxies probes their mass distribution, thus providing a window to study their internal structure, i.e., the distributions of luminous and dark matter. In this paper, we investigate the relation between the internal structure of massive elliptical galaxies and their environment using a sample of 15 strong lensing systems. We performed lens modeling for them using Lenstronomy and constrained the mass and light distributions of the deflector galaxies. We adopt the local galaxy density as a metric for the environment and test our results against several alternative definitions of it. We robustly find that the centroid offset between the mass and light is not correlated with the local galaxy density. This result supports using centroid offsets as a probe of dark matter theories since the environment's impact on it can be treated as negligible. Although we find a moderate to strong correlation between the position angle offset and the standard definition of the local galaxy density, consistent with previous studies, the correlation becomes weaker for alternative definitions of the local galaxy density. This result weakens the support for interpreting the position angle misalignment as having originated from interaction with the environment. Furthermore, we find the 'residual shear' magnitude in the lens model to be uncorrelated with the local galaxy density, supporting the interpretation of the residual shear originating, in part, from the inadequacy in modeling the angular structure of the lensing galaxy and not solely from the structures present in the environment or along the line of sight.