Two-component mass models of the lensing galaxy in the quadruply imaged supernova iPTF16geu

TL;DR

This paper develops two-component mass models for the lensing galaxy in supernova iPTF16geu, resolving previous modeling puzzles and providing more realistic galaxy mass distributions that fit observed lensing features.

Contribution

It introduces two-component, offset mass models inspired by local elliptical galaxies, improving the explanation of microlensing and mass-light alignment issues in the lensing system.

Findings

Models achieve better microlensing fits without shallow density slopes.

Mass centroid aligns with light distribution in the models.

Lopsided mass distributions resemble observed galaxy structures.

Abstract

The first resolved, multiply imaged supernova Type Ia, iPTF16geu, was observed 4 years ago, five decades after such systems were first envisioned. Because of the unique properties of the source, these systems hold a lot of promise for the study of galaxy structure and cosmological parameters. However, this very first example presented modelers with a few puzzles. It was expected that to explain image fluxes a contribution from microlensing by stars would be required, but to accommodate the magnitude of microlensing, the density slope of the elliptical power law lens model had to be quite shallow, $\rho_{2D} \propto r^{-0.7}$. Furthermore, the center of mass had to be displaced from that of observed light by ~0.1 kpc, and the position angle of light distribution was misaligned with that of mass by ~40 degrees. In this paper we present mass models that resolve the first two problems, and suggest a resolution of the third. Motivated by observations of local ellipticals, and some recent analysis of galaxy-scale lenses, our mass models consist of two offset (baryonic) mass components. The resulting mass distributions have a single centroid, but are lopsided, and have isodensity contours that are not purely elliptical and not self-similar with radius. For many of our models the microlensing requirements are modest, and the ring formed by the extended supernova host galaxy resembles the observed one.