The discrepancy between Einstein mass and dynamical mass for SIS and power-law mass models

TL;DR

This study examines the discrepancy between lensing and dynamical masses in strong gravitational lensing systems, finding a significant 20.7% difference for SIS models that increases with redshift, likely due to mass contamination and modeling assumptions.

Contribution

It provides a quantitative analysis of mass discrepancies in lensing systems using Bayesian methods and compares different mass models, highlighting the impact of line-of-sight contamination.

Findings

Einstein mass exceeds dynamical mass by 20.7% in SIS models.

Discrepancy increases with the redshift of lensing galaxies.

Mass contamination and measurement errors contribute to the discrepancy.

Abstract

We investigate the discrepancy between the two-dimensional projected lensing mass and the dynam- ical mass for an ensemble of 97 strong gravitational lensing systems discovered by the Sloan Lens ACS (SLACS) Survey, the BOSS Emission-Line Lens Survey (BELLS), and the BELLS for GALaxy-Ly{\alpha} EmitteR sYs- tems (BELLS GALLERY) Survey. We fit the lensing data to obtain the Einstein mass, and use the velocity dispersion of the lensing galaxies provided by the Sloan Digital Sky Survey (SDSS) to get the projected dynamical mass within the Einstein radius by assuming the power-law mass approximation. The discrepancy is found to be obvious and quantified by Bayesian analysis. For the singular isothermal sphere (SIS) mass model, we obtain that the Einstein mass is 20.7% more than the dynamical mass, and the discrepancy increases with the redshift of the lensing galaxies. For more general power-law mass model, the discrepancy still exists within 1{\sigma} credible region. The main reason of the the discrepancy could be mass contamination, including all invisible masses along the line of sight. In addition, the measurement errors and the approximation of the mass models could lead to part of the discrepancy.