The program is a simple orbit ACS HRC DITHER of a gravitational lens ----- Submission 1 (Tue Apr 26 02:11:24 GMT 2005) ----- Phase II Proposal 10589 (10589) successfully submitted. ----- Submission 2 (Thu May 05 20:50:26 GMT 2005) ----- Second submission Assigned ID: 547 ----- Submission 1 (Fri Jan 21 23:38:01 GMT 2005) ----- Phase I Proposal 547 (lens_c14) successfully submitted. ----- Submission 3 (Sat Jan 22 00:42:59 GMT 2005) ----- The occurence of nearly complete Einstein rings is very low, but their importance cannot be overstated : in comparison with configurations which have a few images, Einstein rings provide a full characterisation of the dark matter halo when combined with measures of the velocity dispersion gradient in the lens. The projected gravitational potential is vastly constrained by the polar information given by the shape of the ring at different position angles. Our discovery of the highest redshift Einstein ring so far, a configuration where the lens is an elliptical galaxy at z=0.986 and the source a post-starburst Lyman break galaxy at z=3.77, yields several intriguing results. The modelling of the ring, which streches some 260 degrees around the lens, points to a very slow evolution in the mass-to-light ratio, as indicated by its position with respect to the fundamental plane of nearby ellipticals. This is at odds with the results obtained by the few lenses existing at this redshift. The M/L ratio within the effective radius is consistent with the one produced by stellar populations, indicating that the dark matter is not dominant at this radius. To fully characterise the dark matter halo of this unique elliptical at a look-back time of 50% of the current age of the universe, we require both a measure of the gradient in velocity dispersion and a high-resolution image of the ring. The former will be measured by our forthcoming VLT medium-resolution spectroscopy, while the later can only be provided by the ACS onboard HST. The presence of a counter-image which is radially elongated, combined with the shape of the main ring will lead to the first reconstructed projected potential of an isolated dark halo at z=1, with unprecedented accuracy. In addition, the exquisite image quality provided by the ACS will allow us to reconstruct the imaged source, providing the first ever high-resolution morphology of a Lyman-break galaxy at z=3.77.

This is a very simple one orbit visit with ACS WFC in F814W of a gravitational lensing system. Default dithering with ACS-WFC-DITHER-BOX template. COSMOLOGY 0 false 0.0 false false false false false SUPPORTED GALAXY EINSTEIN RING GRAVITATIONAL LENS HIGH REDSHIFT GALAXY ELLIPTICAL Coordinates come from the WCS info of a VLT/FORS2 fits image header. Subarcsec accuracy on GCS2. Rc 22.2 +/-0.1 Igunn 21.7+/-0.1 FORJ0332-3557 J2000 03 32 59.9400 -35 57 51.70 J2000 ACS/HRC Imaging No No F814W POS-TARG DITHER 0.15 LINE 0.098 false false 63.5 4 19.89 ACS-HRC-DITHER-BOX 1 false /tmp/OPVisit12167.xml 1115325913113 (Tic-Visit :proposal-id 10589 :visit-id "01" :proposal-version -1 :trans-version "20050323" :date "05-May-2005 11:45:13.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "27" :si-bright-earth-limb-angle 20.0 :data-volume 147216 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 10589 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 10589 :visit-id "01" :orbit-number 1 :pcs-time 367 :si-vis-utilization 2918 :al-overhead-at-end 0 :internal-dur-at-end 199 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3310 :pcs-gap 0 ) true 1 0 /tmp/OPVisit24470.xml 1115076524098