Lens Galaxy Properties of SBS1520+530: Insights from Keck Spectroscopy and AO Imaging

TL;DR

This study combines archival HST, Keck spectroscopy, and AO imaging to refine the properties of the lens galaxy in SBS1520+530, revealing its morphology, environment, and a steeper mass profile than isothermal, with implications for lens modeling and galaxy interactions.

Contribution

The paper provides new high-precision lens galaxy properties, updates the lens redshift, and models the lens system considering environmental effects, which improves understanding of the lens mass profile.

Findings

Lens galaxy has elliptical morphology with possible disk features.

Updated lens redshift is approximately 0.761, though inconclusive.

Lens mass profile is steeper than isothermal, with alpha = 2.29.

Abstract

We report on an investigation of the SBS 1520+530 gravitational lens system and its environment using archival HST imaging, Keck spectroscopic data, and Keck adaptive-optics imaging. The AO imaging has allowed us to fix the lens galaxy properties with a high degree of precision when performing the lens modeling, and the data indicate that the lens has an elliptical morphology and perhaps a disk. The new spectroscopic data suggest that previous determinations of the lens redshift may be incorrect, and we report an updated, though inconclusive, value z_lens = 0.761. We have also spectroscopically confirmed the existence of several galaxy groups at approximately the redshift of the lens system. We create new models of the lens system that explicitly account for the environment of the lens, and we also include improved constraints on the lensing galaxy from our adaptive-optics imaging. Lens models created with these new data can be well-fit with a steeper than isothermal mass slope (alpha = 2.29, with the density proportional to r^-alpha) if H_0 is fixed at 72 km/s/Mpc; isothermal models require H_0 ~ 50 km/s/Mpc. The steepened profile may indicate that the lens is in a transient perturbed state caused by interactions with a nearby galaxy.