A multi-wavelength study of the gravitational lens COSMOS J095930+023427

TL;DR

This study combines multi-wavelength data to analyze the mass distribution and environment of the gravitational lens COSMOS J095930+023427, revealing a high dark matter fraction and a galaxy group at z~0.7.

Contribution

It provides a robust lensing analysis of COSMOS J095930+023427 using multiple models and data sources, highlighting the dark matter fraction and the galaxy group's influence.

Findings

Dark matter fraction within Einstein radius is between 0.71 and 0.79.

External shear indicates presence of a galaxy group at z~0.7.

X-ray luminosity measurement aligns with weak lensing mass estimates.

Abstract

We present a multi-wavelength study of the gravitational lens COSMOS J095930+023427 (z=0.89), together with the associated galaxy group located at $z\sim0.7$ along the line of sight and the lensed background galaxy. The source redshift is currently unknown, but estimated to be at $z_s \sim 2$. The analysis is based on the available public HST, Subaru, Chandra imaging data, and VLT spectroscopy. The lensing system is an early-type galaxy showing a strong [OII] emission line, and produces 4 bright images of the distant background source. It has an Einstein radius of 0.79", about 4 times large than the effective radius. We perform a lensing analysis using both a Singular Isothermal Ellipsoid (SIE) and a Peudo-Isothermal Elliptical Mass Distribution (PIEMD) for the lensing galaxy, and find that the final results on the total mass, the dark matter (DM) fraction within the Einstein radius and the external shear due to a foreground galaxy group are robust with respect of the choice of the parametric model and the source redshift (yet unknown). We measure the luminous mass from the photometric data, and find the DM fraction within the Einstein radius $f_{\rm DM}$ to be between $0.71\pm 0.13$ and $0.79 \pm 0.15$, depending on the unknown source redshift. Meanwhile, the non-null external shear found in our lensing models supports the presence and structure of a galaxy group at $z\sim0.7$, and an independent measurement of the 0.5-2 keV X-ray luminosity within 20" around the X-ray centroid provides a group mass of $M=(3-10)\times 10^{13}$ M$_{\odot}$, in good agreement with the previous estimate derived through weak lensing analysis.