Strong Lensing in the CFHTLS - Images

A gallery of gravitational arcs

This mosaic shows a subset of the sample of new gravitational lenses discovered in the CFHTLS and illustrating the broad range of masses probed by the excellent images gathered at CFHT.

In addition to the very massive clusters and compact galaxies, a large number of intermediate mass lenses are seen for the first time.

High resolution image

© Canada-France-Hawaii Telescope Corporation 2006

A galaxy group lens

This example of a galaxy group lens in the CFHTLS-SL2S, called SL2SJ021408-053532, shows a very complex arc structure (in blue).

Such complex arc geometries allow us to probe the details of the dark matter profiles associated with the group of yellow galaxies in the center of the image.

© Canada-France-Hawaii Telescope Corporation 2006

Giant arcs around a massive cluster galaxy


This is a spectacular example of giant arcs around a massive cluster galaxy (SL2SJ085446-012137).

Such multiple arc configurations are rare and very powerful to probe the substructures of dark matter within large clusters.

The small white spot on top of the bright blue arc is actually a satellite galaxy inducing its own distortion on the arc. Such a unique configuration imposes very strong constraints on the offset between luminous and dark matter.

© Canada-France-Hawaii Telescope Corporation 2006

A very bright ringlet configuration

This very bright ringlet configuration (SL2SJ021737-051329) is actually a group of multiple images of a single source, called cusp arcs, merged together in a single arc on the ground-based images.

High resolution images from space telescopes, free of atmospheric distortions, are required to discriminate the individual images.

Such strongly magnified rings are especially important for the study of the evolution of dark matter with time and allow astronomers to study instrinsically faint sources using the lens as a "gravitational telescope".

© Canada-France-Hawaii Telescope Corporation 2006

A piece of History

Abel 370 in 1985

This picture if the first image of a giant gravitational arc, found in a massive nearby cluster calleb Abel 370.

This image has been taken in 1985 at CFHT through an R filter, using the first CCD camera made available to the observers at the observatory. Called RCA1, this camera boosted a matrix of 320x512 pixels (!) with a resolution of 0.8 arcsecond/pixel.

This image introduced the astronomers to the rich realm of strong gravitational lensing of galaxies by massive foreground clumps of dark matter.

It first appeared in January 1987, 20 years ago, in the following article:
Soucail, G., Fort, B., Mellier, Y., & Picat, J. P. 1987, Astronomy and Astrophysics A blue ring-like structure, in the center of the A 370 cluster of galaxies

The gravitational lensing origin of the arc was recognized ten months later in:
Soucail, G., Mellier, Y., Fort, B., Mathez, G., & Hammer, F. 1987, Astronomy and Astrophysics Further data on the blue ring-like structure in A 370

© Canada-France-Hawaii Telescope Corporation 2006

Another piece of History

Abel 370 in 1990

Taken five years later with the camera RCA2, this image illustrates the rapid progress of the CCD technology in a short time, ending with today's mosaics like MegaCam and its 340 MegaPixels...

This image is a composite of deep images taken in three colors: B, R and I.

Here is the same image with a slightly higher resolution

© Canada-France-Hawaii Telescope Corporation 2006

CFHT - The telescope with MegaPrime/MegaCam

The Canada-France-Hawaii telescope structure is based on an equatorial mount design, with one of the axis of rotation set parallel to the axis of the Earth¹s rotation. The mirror cell (the white circular structure at the bottom of the telescope, seen just above the person giving the scale on this photograph) holds and protects the most precious element: the 3.6-meter diameter mirror.
Light from distant objects enters the dome through the slit, bounces back from the mirror such that it will focus, and create a crisp image at the prime focus, MegaPrime, where the image is captured by MegaCam, CFHT's wide-field digital camera (340 MegaPixels!) .
By today's standards, the CFHT telescope is a heavy structure compared to the diameter of its mirror: the total mass of the telescope is 325 tons, with 250 tons for the mobile section alone. Yet the telescope can point to any location in the sky with an accuracy of 3 thousandths of a degree - and can follow astronomical objects with an even better accuracy, thanks to an automated guiding mechanism that compensates for the apparent motion of the sky due to the Earth's rotation.

High Resolution image

© Canada-France-Hawaii Telescope Corporation 2006

Copyright policy and credits related to all press release materials

All images on this page are to be used exclusively for the purpose of media announcements
related to Strong Lensing in the CFHT Legacy Survey (Dec 2006)
For any other use, please seek authorization from CFHT's PR officer .