The Third Image of the Large-Separation Lensed Quasar SDSS J1029+2623

TL;DR

This paper reports the discovery of a third lensed image of a quasar in a galaxy cluster, supporting the prediction that large-separation lensed quasars often involve naked cusp configurations, which are rare in galaxy-scale lenses.

Contribution

It provides the first identification of a third image in the unique quasar lens SDSS J1029+2623, and supports the theoretical prediction of naked cusp lensing in large-separation quasar lenses.

Findings

Discovery of a third lensed quasar image with similar spectral features.

Evidence for a naked cusp lens configuration based on mass modeling.

Support for the cold dark matter model prediction regarding large-separation lenses.

Abstract

We identify a third image in the unique quasar lens SDSS J1029+2623, the second known quasar lens produced by a massive cluster of galaxies. The spectrum of the third image shows similar emission and absorption features, but has a redder continuum than the other two images which can be explained by differential extinction or microlensing. We also identify several lensed arcs. Our observations suggest a complicated structure of the lens cluster at z~0.6. We argue that the three lensed images are produced by a naked cusp on the basis of successful mass models, the distribution of cluster member galaxies, and the shapes and locations of the lensed arcs. Lensing by a naked cusp is quite rare among galaxy-scale lenses but is predicted to be common among large-separation lensed quasars. Thus the discovery can be viewed as support for an important theoretical prediction of the standard cold dark matter model.