The Hidden Fortress: Structure and substructure of the complex strong lensing cluster SDSS J1029+2623

TL;DR

This study uses HST and weak lensing data to analyze the complex mass distribution of the galaxy cluster SDSS J1029+2623, revealing a bimodal structure, a significant mass discrepancy with X-ray estimates, and detailed lensing properties.

Contribution

It provides a detailed strong and weak lensing analysis of SDSS J1029+2623, highlighting its bimodal mass distribution and the impact of merger-related shock heating on mass estimates.

Findings

Bimodal mass distribution confirmed in the cluster.

Mass estimate from lensing is about half of the X-ray mass, indicating merger effects.

High concentration parameter c_vir=25.7 suggests a dense core.

Abstract

We present Hubble Space Telescope (HST) ACS and WFC3 observations of SDSS J1029+2623, a three-image quasar lens system produced by a foreground cluster at z=0.584. Our strong lensing analysis reveals 6 additional multiply imaged galaxies. We confirm the complex nature of the mass distribution of the lensing cluster, with a bimodal distribution which deviates from the Chandra X-ray SB distribution. The Einstein radius is estimated to be \theta_E=15.2" \pm 0.5" for the quasar redshift of z=2.197. We derive a radial mass distribution from the combination of strong lensing, HST/ACS weak lensing, and Subaru/Suprime-cam weak lensing analysis results, finding a best-fit virial mass of M_vir=(1.5+0.40-0.35) \times 10^14 h^-1 M_sun and a concentration parameter of c_vir=25.7+14.1-7.5. The lensing mass estimate at the outer radius is smaller than the X-ray mass estimate by a factor of ~2. We ascribe this large mass discrepancy to shock heating of the intracluster gas during a merger, which is also suggested by the complex mass and gas distributions and the high value of the concentration parameter. In the HST image, we also identify a probable galaxy, GX, in the vicinity of the faintest quasar image C. The inclusion of GX explains the anomalous flux ratios between the quasar images. The morphology of the highly elongated quasar host galaxy is also well reproduced. The best-fit model suggests large total magnifications of 30 for the quasar and 35 for the quasar host galaxy, and has an AB time delay consistent with the measured value. (Abridged)