8705( 2) - 02/25/00 09:46 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 8705 Version: 2 Check-in Date: 25-Feb-2000 09:45:55 1.Proposal Title: External Shear in the Time-Delay Lens RX J0911+05 ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 9 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Jens Hjorth Copenhagen University Observatory CoI: Dr. Jean-Paul Kneib Observatoire Midi-Pyrenees N CoI: Ms. Ingunn Burud University of Liege N CoI: Mr. Andreas O. Jaunsen University of Oslo N CoI: Prof. Judy Cohen Caltech N ------------------------------------------------------------------------------------ 5. Abstract We propose to map the mass distribution in the vicinity of the multiple QSO system RX J0911+05 using weak gravitational lensing. This object has emerged as one of the most promising candidates for a cosmological determination of the Hubble constant using time delay measurements. There is evidence that a high-redshift cluster of galaxies (z = 0.77) acts as the source of a very large external shear (Gamma > 0.15), affecting the lens potential. Deep WFPC2 images will allow us to directly measure this shear from the distortions of faint background galaxies. Such data are essential for producing a reliable mass model of the system which, in combination with the newly measured time delay, will provide the best constrained mass model for a multiple QSO, hence leading to an accurate cosmological estimate of the Hubble constant. ------------------------------------------------------------------------------------ 8705( 2) - 02/25/00 09:46 - [ 2] Observations Description ------------------------ The weak lensing analysis of RX J0911+05 requires very deep imaging in addition to high spatial resolution. Only by exploiting the combination of high spatial resolution, low background, and stable PSF provided by the WFPC2 camera (Rhodes et al. 1999; Hoekstra et al. 1998) this goal can be achieved. We propose to use the WFPC2 to obtain the needed data. STIS is somewhat more sensitive but the WFPC2 allows a larger field to be studied which compensates for the smaller sensitivity when mapping a large area. We propose to obtain the data using two "red" filters, F606W and F814W which will allow color information to be obtained without compromising the sensitivity in detecting faint and distant galaxies. Furthermore, the filters can be carefully combined for the shear analysis. The QSO and the main cluster candidate will be centered on the WF chips. By comparison with the data on the rich z = 0.83 cluster MS1054-03 (Franx GO-7372; Hoekstra et al. 1999; 3 in F606W and 3 in F814W) and the z = 0.41 cluster Cl0939+47 (Seitz et al. 1996; 10-orbit exposure in F702W), we estimate that with a 10-orbit observation, we will be able to detect the shear signal down to 5 % in 15 independent points based on the average of the shape information of ~ 300 galaxies with 22.5 < R < 25.5 (based on the observed numbers in Cl0939+47, Seitz et al. 1996). This level of accuracy is required in order to accurately reconstruct the mass map (in a similar way as Seitz et al. 1996) with an uncertainty of about 10 %. A maximum-likelihood method that uses the position and magnitude of the bright galaxies as external constraints will be used to extract the mass distribution from the distortion of faint galaxies in a similar way as Natarajan et al. (1998). In such methods robust constraints can be put on the existence and the determination of the cluster mass distribution. The data will be obtained in a dithering pattern to remove cosmic rays and to improve resolution using the drizzle algorithm (cf. Hoekstra et al. 1999). Real Time Justification ----------------------- LOW-SKY: we require low sky observation mode in order to minimize the sky background which is critical in measuring the shape of the faintest galaxies, and thus to measure as precisely as possible the shear map. Multi-wavelength imaging observations will be performed quasi-simultaneously to the HST observations as part of our monitoring programs. This will be a useful test of the accuracy of our ground-based photometry. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 8705( 2) - 02/25/00 09:46 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 RXJ0911+05 CLUSTER OF GALAXIES, RA=09H 11M 27.50S +/- 0.1S, 2000.0 Z = 0.77 SURF(R) = 25 GRAVITATIONAL LENS, DEC=05D 50' 8.0" +/- 1" RICH CLUSTER Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 2000.0 0.0 0.0 0.0 8705( 2) - 02/25/00 09:46 - [ 4] Visit: 01 Visit Priority: Visit Requirements: ORIENT 80D TO 100D On Hold Comments: Additional Comments: Exposures for the field are split into five exposures each with a shift introduced of (0.75, 0.75) arcsec between each exposure in order to displace objects situated on CCD defects or on the seams of the pyramid. CR-SPLIT=NO for all observations since in all cases there are sufficient multiple exposures to perform cosmic ray rejection. ORIENT range is from 80 TO 100 DEG to keep the target major axis aligned parallel to the X-axis or Y-axis of the WFPC2. Final Target Postion may be slightly altered when the roll- angle is fixed to provide optimal coverage of the numerous lensed features in the cluster core. LOW-SKY is selected to provide a low sky background essential for identification of these very faint objects. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 RXJ0911+05 WFPC2 IMAGE WFALL-F F814W CR-SPLIT=NO,ATD-GAIN=7 1 2500 S LOW-SKY POS TARG -1.5, IX -1.5 Comments: SHIFTED TO ALLOW REMOVAL OF DEFECT ------------------------------------------------------------------------------------------------------------------------------------ 20 RXJ0911+05 WFPC2 IMAGE WFALL-F F814W CR-SPLIT=NO,ATD-GAIN=7 1 2500 S LOW-SKY POS TARG -0.75, IX -0.75 Comments: SHIFTED TO ALLOW REMOVAL OF DEFECT ------------------------------------------------------------------------------------------------------------------------------------ 30 RXJ0911+05 WFPC2 IMAGE WFALL-F F814W CR-SPLIT=NO,ATD-GAIN=7 1 2500 S LOW-SKY POS TARG 0.0, 0.0 IX Comments: SHIFTED TO ALLOW REMOVAL OF DEFECT ------------------------------------------------------------------------------------------------------------------------------------ 40 RXJ0911+05 WFPC2 IMAGE WFALL-F F814W CR-SPLIT=NO,ATD-GAIN=7 1 2500 S LOW-SKY POS TARG 0.75, IX 0.75 Comments: SHIFTED TO ALLOW REMOVAL OF DEFECT ------------------------------------------------------------------------------------------------------------------------------------ 50 RXJ0911+05 WFPC2 IMAGE WFALL-F F814W CR-SPLIT=NO,ATD-GAIN=7 1 2500 S LOW-SKY POS TARG 1.50, IX 1.50 Comments: SHIFTED TO ALLOW REMOVAL OF DEFECT ------------------------------------------------------------------------------------------------------------------------------------ 8705( 2) - 02/25/00 09:46 - [ 5] Visit: 02 Visit Priority: Visit Requirements: ORIENT -2D TO 2D FROM 01 On Hold Comments: Additional Comments: Exposures for the field are split into five exposures each with a shift introduced of (0.75, 0.75) arcsec between each exposure in order to displace objects situated on CCD defects or on the seams of the pyramid. CR-SPLIT=NO for all observations since in all cases there are sufficient multiple exposures to perform cosmic ray rejection. ORIENT range is from -2 To +2 DEG from visit 1 to allow to compare objects between the 2 different filters. Final Target Postion may be slightly altered when the roll-angle is fixed to provide optimal coverage of the numerous lensed features in the cluster core. LOW-SKY is selected to provide a low sky background essential for identification of these very faint objects. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 RXJ0911+05 WFPC2 IMAGE WFALL-F F606W CR-SPLIT=NO,ATD-GAIN=7 1 2500 S LOW-SKY POS TARG -1.5, IX -1.5 Comments: SHIFTED TO ALLOW REMOVAL OF DEFECT ------------------------------------------------------------------------------------------------------------------------------------ 20 RXJ0911+05 WFPC2 IMAGE WFALL-F F606W CR-SPLIT=NO,ATD-GAIN=7 1 2500 S LOW-SKY POS TARG -0.75, IX -0.75 Comments: SHIFTED TO ALLOW REMOVAL OF DEFECT ------------------------------------------------------------------------------------------------------------------------------------ 30 RXJ0911+05 WFPC2 IMAGE WFALL-F F606W CR-SPLIT=NO,ATD-GAIN=7 1 2500 S LOW-SKY POS TARG 0.00, IX 0.00 Comments: SHIFTED TO ALLOW REMOVAL OF DEFECT ------------------------------------------------------------------------------------------------------------------------------------ 40 RXJ0911+05 WFPC2 IMAGE WFALL-F F606W CR-SPLIT=NO,ATD-GAIN=7 1 2500 S LOW-SKY POS TARG 0.75, IX 0.75 Comments: SHIFTED TO ALLOW REMOVAL OF DEFECT ------------------------------------------------------------------------------------------------------------------------------------ 50 RXJ0911+05 WFPC2 IMAGE WFALL-F F606W CR-SPLIT=NO,ATD-GAIN=7 1 2500 S LOW-SKY POS TARG 1.50, IX 1.50 Comments: SHIFTED TO ALLOW REMOVAL OF DEFECT ------------------------------------------------------------------------------------------------------------------------------------ 8705( 2) - 02/25/00 09:46 - [ 6] Summary Form for Proposal 8705 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures WFALL-FIX ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=NO ATD-GAIN=7 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENT 80D TO 100D LOW-SKY POS TARG -1.5,-1.5 LOW-SKY POS TARG -0.75,-0.75 LOW-SKY POS TARG 0.0, 0.0 LOW-SKY POS TARG 0.75, 0.75 LOW-SKY POS TARG 1.50, 1.50 ORIENT -2D TO 2D FROM 01 LOW-SKY POS TARG 0.00, 0.00 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F814W F606W ------------------------------------------------------------------------------------------------------------------------------------ Target Names RXJ0911+05 ------------------------------------------------------------------------------------------------------------------------------------