Spectroscopical Confirmation and Lens Modeling of a Complex Strong Lensing System Produced by a Close Galaxy Pair at $z_d=0.79$

TL;DR

This study confirms a complex strong lensing system involving a close galaxy pair at redshift 0.79, modeling its mass distribution and dark matter content, and analyzing the source galaxies at redshift 2.16.

Contribution

It provides detailed lens modeling and mass analysis of a unique galaxy pair lens system, highlighting its potential for studying galaxy interactions and dark matter.

Findings

Two elliptical galaxies form the lens with specific Einstein radii.

Dark matter constitutes approximately 82% of the total mass within the critical curve.

The system includes two disk galaxies and a point source, useful for merger studies.

Abstract

We report the spectroscopic confirmation and lens modeling of the complex strong-lens system J0233-0205, in which the deflector consists of a pair of galaxies at zd = 0.790 +/- 0.022, the background source lies at zs = 2.160 +/- 0.002, and the circularized Einstein radius is thetaE = 1.680 arcsec +/- 0.003 arcsec. Our lens modeling requires two lens components, namely two elliptical galaxies with Einstein radii of 0.669 arcsec +/- 0.002 arcsec and 0.735 arcsec +/- 0.002 arcsec, respectively, and a projected separation of 0.513 arcsec (about 3.832 kpc), as well as three source components: two disk galaxies separated by 0.4965 arcsec (about 3.712 kpc), plus a point-like component closely aligned with one of the disks. From a joint lensing and stellar-population analysis, we infer a total stellar mass within the critical curve of the lens pair of (1.956 +/- 0.418) x 10^11 solar masses and a total enclosed mass of (1.107 +/- 0.008) x 10^12 solar masses, corresponding to a projected dark-matter fraction of 82 +/- 4%. The stellar masses of the two lens galaxies are (8.548 +/- 2.128) x 10^10 solar masses and (1.525 +/- 0.295) x 10^11 solar masses, implying dark-matter fractions within the z-band effective radius of 57 +/- 11% and 70 +/- 6%, respectively. The small separation of the lens pair, together with its relatively high deflector redshift, makes J0233-0205 a potentially ideal laboratory for probing the mass distribution and dark-matter content of close galaxy pairs. In addition, the two disk galaxies and the associated point-like source make this system valuable for investigating the merger process in the source plane.