10589( 4) - 05/08/05 15:02 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 10589 Version: 4 Check-in Date: 08-May-2005 19:01:55 1.Proposal Title: The highest redshift Einstein ring: probing a dark matter halo at z=1 and galaxy morphology at z=3.8 ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle 4. Parallel Pointing Tolerance GO 14 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: Dr. Remi A. Cabanac Canada-France-Hawaii Telescope Corporation CoI: Dr. David Valls-Gabaud Observatoire Midi-Pyrenees N CoI: Dr. Christopher Lidman European Southern Observatory - Chile N ------------------------------------------------------------------------------------ 6. Abstract 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. ------------------------------------------------------------------------------------ 10589( 4) - 05/08/05 15:02 - [ 2] Observations Description ------------------------ 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. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 10589( 4) - 05/08/05 15:02 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 FOR-J0332- GALAXY, EINSTEIN RING, RA=03H32M59.9400S +/- 0.3", J2000 V = 24.2+/-0.5 3557-F814W GRAVITATIONAL LENS, DEC=-35D57'51.70" +/- 0.3" Rc 22.2 +/-0.1 Igunn 21.7+/-0.1 HIGH REDSHIFT GALAXY, ELLIPTICAL Coordinate Source: GUIDE_STAR_CATALOG Comments: Coordinates come from the WCS info of a VLT/FORS2 fits image header. Subarcsec accuracy on GCS2. 10589( 4) - 05/08/05 15:02 - [ 4] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type ACS-HRC-DITHER-BOX Pattern_Purpose DITHER Number_Of_Points 4 Point_Spacing 0.15 Line_Spacing 0.098 Coordinate_Frame POS-TARG Pattern_Orient 19.89 Angle_Between_Sides 63.5 Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ 10589( 4) - 05/08/05 15:02 - [ 5] Visit: 01 Visit Priority: Visit Requirements: PCS MODE FINE; SCHED 30% On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 FOR-J0332-3 ACS/HRC ACCUM HRC F814W 1 600 S PATTERN 1 1 557-F814W ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ FOR-J0332-3557-F81 1 ACS/HRC ACCUM HRC F814W 1 none none 1 1 N/A 4W FOR-J0332-3557-F81 1 ACS/HRC ACCUM HRC F814W 1 none none 2 1 N/A 4W FOR-J0332-3557-F81 1 ACS/HRC ACCUM HRC F814W 2 none none 1 1 N/A 4W FOR-J0332-3557-F81 1 ACS/HRC ACCUM HRC F814W 2 none none 2 1 N/A 4W FOR-J0332-3557-F81 1 ACS/HRC ACCUM HRC F814W 3 none none 1 1 N/A 4W FOR-J0332-3557-F81 1 ACS/HRC ACCUM HRC F814W 3 none none 2 1 N/A 4W FOR-J0332-3557-F81 1 ACS/HRC ACCUM HRC F814W 4 none none 1 1 N/A 4W FOR-J0332-3557-F81 1 ACS/HRC ACCUM HRC F814W 4 none none 2 1 N/A 4W 10589( 4) - 05/08/05 15:02 - [ 6] Summary Form for Proposal 10589 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures HRC ------------------------------------------------------------------------------------------------------------------------------------ Configurations ACS/HRC ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PCS MODE FINE; SCHED 30% PATTERN 1 1 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names FOR-J0332-3557-F814W ------------------------------------------------------------------------------------------------------------------------------------