Durham astronomers discover two rare diamonds in the sky

When by chance a distant quasar lies directly behind a foreground massive galaxy the effect of strong gravitational lensing can produce multiple images of the background quasar. This effect was originally predicted by Albert Einstein in his general theory of relativity. The first doubly-imaged lensed quasar was discovered in 1979 by Walsh et al.

In exceedingly rare cases, when there is a very precise alignment of the galaxy and the quasar, four images of the background quasar are observed in a diamond-shaped configuration. The famous Einstein Cross, a quadruply-imaged lensed quasar, was reported in 1985 by Huchra et al.

Such objects are extremely valuable astrophysically as they can be exploited to study in great detail the foreground massive galaxy, including the dark matter content, and can be used to provide a robust independent measurement of the expansion rate of the Universe.

During work to refine the target input catalogue for the forthcoming Taipan Galaxy Survey of the southern hemisphere, Durham astronomers serendipitously discovered two of these very rare diamond-shaped systems in the Pan-STARRS PS1 image survey. Below the PS1 images show the two new diamonds with the quasar’s multiple images labeled as A to D and the foreground massive galaxies as G (very faint) and G1+G2 (double galaxy).

The figure shows the two lensing systems in giy data, with labels A–D denoting the lensed quasar images, and and G and H labels for the foreground massive galaxies.

The 2M1134-2103 system (on the left) is a z = 2.77 quasar quadruply lensed by a very faint foreground galaxy of currently unknown redshift.
The 2M1310-1714 system (on the right) is a z = 1.98 quasar quadruply lensed by a z = 0.29 foreground double galaxy.

The two newly discovered lensing systems

Link to the original research paper: arxiv.org/abs/1711.02674, or Lucey et al. 2018, MNRAS, 476, 927.

The Taipan Galaxy Survey is described in da Cunha et al. 2017, PASA, 34, 47 and at www.taipan-survey.org.

Contacts from CEA, Durham:

Russell Smith

John Lucey