5935( 6) - 12/20/95 14:13 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 5935 Version: 6 Check-in Date: ********** 1.Proposal Title: Gravitational Imaging in Well-Constrained Clusters: Absolute Masses and Faint Galaxy Redshifts ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle Galaxies & Clusters GO 5 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: Ian Smail OCIW CoI: Richard Ellis Institute for Astronomy N CoI: Jean-Paul Kneib Institute for Astronomy N ------------------------------------------------------------------------------------ 6. Abstract The shear of faint galaxy images arising from gravitational lensing by foreground massive clusters provides important constraints on the distribution and total amount of mass in the clusters. Furthermore, in a few rare clusters, the lensing models may be sufficiently well-constrained by arcs and multiple images to yield robust redshift estimates for faint galaxies well beyond reach of current spectrographs. Ground- based telescopes suffer systematic degradations which reduce the detected shear by factors of ~2-3. Detecting the unadulterated shear pattern with HST will yield an absolute calibration of ground-based results and confirm or otherwise the high cluster mass/light ratios obtained so far. We propose deep WFPC-2 imaging of two of the most well-studied clusters for this purpose. Both have the rare distinction of having lensed features of known redshift which strongly constrain the absolute mass. When calibrated with the HST shear, not only will more reliable mass maps result, but the lensing equations can be inverted to provide statistical distances for large numbers of very faint field galaxies. These will be invaluable in studies of galaxy evolution and for subsequent lensing applications in other clusters. ------------------------------------------------------------------------------------ 5935( 6) - 12/20/95 14:13 - [ 2] Observations Description ------------------------ To fully exploit HST's unique capabilities for our proposed lensing study we require continous coverage of a sizeable area in the centre of each of our cluster. The area coverage must be contiguous and cover a field sufficient to adequately measure the morphology of the cluster mass to allow a robust inversion of the distribution in the redshift analysis. Moreover we require enough arclets in the outer regions to overcome noise in the weak shear pattern arising from the intrinsic orientations and shapes of faint galaxies. To accomplish this we have chosen four overlapping pointings. providing nearly complete coverage to a radius of 1.0-1.5 Mpc (H_o=50), and allowing for overlap, a ~20 arcmin^2 field. From ground-based images in sub-arcsecond seeing the induced shear at the 1.0 Mpc radius is 10--15% which determines the accuracy of the final mass reconstruction is the surface density of background galaxies. We propose to sample the mass map via a grid of 20 cells with 0.5 arcmin spacing. To get a signal/noise>3, we require an rms noise in the shear per cell of better than 3% an unfeasibly high surface density of background galaxies. However, the elimination of atmospheric seeing increases our shear sensitivity so that only 20--30 galaxies are required per cell using HST, corresponding to a surface density of ~50 galaxies arcmin^-2. We choose the F702W filter as it is the most efficient filter to reach a high surface density of background sources in the shortest time. Additionally, a long wavelength passband is the most appropriate for deep redshift surveys (c.f.\\ Lilly 1993). A galaxy surface density of 50 arcmin^-2 is reached at a limiting magnitude of R_702=25.5. A deep limiting isophote is essential to ensure each faint image is sufficiently resolved for its shear to be reliably measured. We calculate that ~30 pixels above the 2 Sigma isophote in an R=25.5 galaxy will yield an orientation and ellipticity to the precision required from the considerations discussed above. Scaling from the deepest MDS blank field observations (available to RSE), this limiting isophote is found to be Mu_R = 30.2 mag pixel^-2. For a 2 Sigma detection of 30 pixels at this isophote, we calculate an exposure time of 17 ksec (6 orbits). With four pointings in the cluster and we are thus requesting a total of 24 orbits. We will additionally employ offsetting of each exposure by a small shift (1.0 arcsec) to further reduce the effects of flatfield errors. These deep exposures will provide high signal/noise mass maps in this cluster to ~1.5 Mpc with a resolution of 150-200 kpc in the outskirts and ~50 kpc in the core regions. The frames will also provide a sample of around 1000 field galaxies in the cluster for the redshift inversion. Real Time Justification ----------------------- None. Calibration Justification ------------------------- None. Extensive ground-based imaging (UBVRIK) and spectroscopic data plus satellite X-ray images for the target have already been taken and analysed. Additional Comments ------------------- According to the convention for WFPC2, coordinates as given in the FIXED TARGETS positions are shifted by POS TARG +10.0,+10.0 to bring the center to the apex of the pyramid. Exposures for a given field and are split into three groups with a shift introduced of +1.0 arcseconds in either X or Y, in order to displace objects situated on CCD defects or on the seams of the pyramid. Thus, POS TARG +11.0,+10.0 corresponds to the second group, POS TARG +10.0,+11.0 to the third. CR-SPLIT=NO for all observations since in all cases there are sufficient multiple exposures to perform cosmic ray rejection. Another very important factor is to to keep the ORIENT ANGLE the *SAME* for all exposures at POS1--POS4 in the cluster. This will simplify coadding the images and mosaicing the four different positions in the cluster together. ------------------------------------------------------------------------------------ 5935( 6) - 12/20/95 14:13 - [ 3] Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_address Ship Via: UPS Email: , ------------------------------------------------------------------------------------ 5935( 6) - 12/20/95 14:13 - [ 4] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 AC114-POS1 CLUSTER OF GALAXIES, RA=22H 56M 01.91S +/- 0.1S, DEC= 1950.0 Z=0.31 R = 25.5 GRAVITATIONAL LENS, -35D 05' 05.4" +/- 2" V-R = 1.5 RICH CLUSTER Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 1950.0 0.0 0.0 0.0 2 AC114-POS2 CLUSTER OF GALAXIES, RA=22H 56M 01.96S +/- 0.1S, DEC= 1950.0 Z=0.31 R = 25.5 GRAVITATIONAL LENS, -35D 03' 16.5" +/- 2" V-R = 1.5 RICH CLUSTER Comments: Exact position to be confirmed when roll-angle for AC114-POS1 is fixed in scheduling. Position may shift by +/-10 arcsec to retain chip alignment between the four pointings. Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 1950.0 0.0 0.0 0.0 3 AC114-POS3 CLUSTER OF GALAXIES, RA=22H 56M 10.59S +/- 0.1S, DEC= 1950.0 Z=0.31 R = 25.5 GRAVITATIONAL LENS, -35D 05' 06.0" +/- 2" V-R = 1.5 RICH CLUSTER Comments: Exact position to be confirmed when roll-angle for AC114-POS1 is fixed in scheduling. Position may shift by +/-10 arcsec to retain chip alignment between the four pointings. Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 1950.0 0.0 0.0 0.0 4 AC114-POS4 CLUSTER OF GALAXIES, RA=22H 55M 53.17S +/- 0.1S, DEC= 1950.0 Z=0.31 R = 25.5 GRAVITATIONAL LENS, -35D 03' 16.1" +/- 2" V-R = 1.5 RICH CLUSTER Comments: Exact position to be confirmed when roll-angle for AC114-POS1 is fixed in scheduling. Position may shift by +/-10 arcsec to retain chip alignment between the four pointings. Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 1950.0 0.0 0.0 0.0 5935( 6) - 12/20/95 14:13 - [ 5] Visit: 01 Visit Requirements: ORIENT 89.75D TO 90.25D GROUP 1-4 WITHIN 10D On Hold Comments: Additional Comments: According to the convention for WFPC2 coordinates as given in the FIXED TARGETS positions are shifted by POS TARG +10.0,+10.0 to bring the center to the apex of the pyramid. Exposures for a given field and are split into three groups with a shift introduced of +1.0 arcseconds in either X or Y, in order to displace objects situated on CCD defects or on the seams of the pyramid. Thus, POS TARG +11.0,+10.0 corresponds to the second group, POS TARG +10.0,+11.0 to the third. CR-SPLIT=NO for all observations since in all cases there are sufficient multiple exposures to perform cosmic ray rejection. Another very important factor is to to keep the ORIENT ANGLE the *SAME* for all exposures at POS1--POS4 This will simplify coadding the images and mosaicing the four different positions in the cluster together. ORIENT range is 90 +10/-10 DEG due to bright stars outside the field. ( 90D +/- 10D = range of 80D to 100D as specified in the program's visit level requirements. ) NOTE: This was modified to a smaller range of 89.75D to 90.25D in order to help in generation of accurate plan windows after ORIENT was fixed at 90D in SOGS. This change and the subsequent re-PIPing was done at the request of the LRP Group. The actual period for scheduling at 90D is also only ~4 days long, from 3 January, 1996 - 7 January, 1996, but the LRP Group person said that the GROUP WITHIN 10D(ays) did not need to be changed to GROUP WITHIN 4D(ays), so that has been left "as is"... RAL - 11 October, 1995 Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 AC114-POS1 WFPC2 IMAGE WFALL- F702W CR-SPLIT=NO 2 2300S EXPAND POS TARG +10.0,+10.0 FIX Comments: POS TARG +10,+10 PLACES TARGET COORDS AT APEX OF PYRAMID ------------------------------------------------------------------------------------------------------------------------------------ 2 AC114-POS1 WFPC2 IMAGE WFALL- F702W CR-SPLIT=NO 2 2300S EXPAND POS TARG +11.0,+10.0 FIX Comments: SHIFTED BY 1.0,0.0 TO ALLOW REMOVAL OF CHIP DEFECTS ------------------------------------------------------------------------------------------------------------------------------------ 3 AC114-POS1 WFPC2 IMAGE WFALL- F702W CR-SPLIT=NO 2 2300S EXPAND POS TARG +10.0,+11.0 FIX Comments: SHIFTED BY 0.0,1.0 TO ALLOW REMOVAL OF CHIP DEFECTS ------------------------------------------------------------------------------------------------------------------------------------ 5935( 6) - 12/20/95 14:13 - [ 6] Visit: 02 Visit Requirements: SAME ORIENT AS 1 On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 4 AC114-POS2 WFPC2 IMAGE WFALL- F702W CR-SPLIT=NO 2 2300S EXPAND POS TARG +10.0,+10.0 FIX Comments: POS TARG +10,+10 PLACES TARGET COORDS AT APEX OF PYRAMID ------------------------------------------------------------------------------------------------------------------------------------ 5 AC114-POS2 WFPC2 IMAGE WFALL- F702W CR-SPLIT=NO 2 2300S EXPAND POS TARG +11.0,+10.0 FIX Comments: SHIFTED BY 1.0,0.0 TO ALLOW REMOVAL OF CHIP DEFECTS ------------------------------------------------------------------------------------------------------------------------------------ 6 AC114-POS2 WFPC2 IMAGE WFALL- F702W CR-SPLIT=NO 2 2300S EXPAND POS TARG +10.0,+11.0 FIX Comments: SHIFTED BY 0.0,1.0 TO ALLOW REMOVAL OF CHIP DEFECTS ------------------------------------------------------------------------------------------------------------------------------------ 5935( 6) - 12/20/95 14:13 - [ 7] Visit: 03 Visit Requirements: SAME ORIENT AS 1 On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 7 AC114-POS3 WFPC2 IMAGE WFALL- F702W CR-SPLIT=NO 2 2300S EXPAND POS TARG +10.0,+10.0 FIX Comments: POS TARG +10,+10 PLACES TARGET COORDS AT APEX OF PYRAMID ------------------------------------------------------------------------------------------------------------------------------------ 8 AC114-POS3 WFPC2 IMAGE WFALL- F702W CR-SPLIT=NO 2 2300S EXPAND POS TARG +11.0,+10.0 FIX Comments: SHIFTED BY 1.0,0.0 TO ALLOW REMOVAL OF CHIP DEFECTS ------------------------------------------------------------------------------------------------------------------------------------ 9 AC114-POS3 WFPC2 IMAGE WFALL- F702W CR-SPLIT=NO 2 2300S EXPAND POS TARG +10.0,+11.0 FIX Comments: SHIFTED BY 0.0,1.0 TO ALLOW REMOVAL OF CHIP DEFECTS ------------------------------------------------------------------------------------------------------------------------------------ 5935( 6) - 12/20/95 14:13 - [ 8] Visit: 04 Visit Requirements: SAME ORIENT AS 1 On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 AC114-POS4 WFPC2 IMAGE WFALL- F702W CR-SPLIT=NO 2 2300S EXPAND POS TARG +10.0,+10.0 FIX Comments: POS TARG +10,+10 PLACES TARGET COORDS AT APEX OF PYRAMID ------------------------------------------------------------------------------------------------------------------------------------ 11 AC114-POS4 WFPC2 IMAGE WFALL- F702W CR-SPLIT=NO 2 2300S EXPAND POS TARG +11.0,+10.0 FIX Comments: SHIFTED BY 1.0,0.0 TO ALLOW REMOVAL OF CHIP DEFECTS ------------------------------------------------------------------------------------------------------------------------------------ 12 AC114-POS4 WFPC2 IMAGE WFALL- F702W CR-SPLIT=NO 2 2300S EXPAND POS TARG +10.0,+11.0 FIX Comments: SHIFTED BY 0.0,1.0 TO ALLOW REMOVAL OF CHIP DEFECTS ------------------------------------------------------------------------------------------------------------------------------------ 5935( 6) - 12/20/95 14:13 - [ 9] Summary Form for Proposal 5935 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category Galaxies & Clusters ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENT 89.75D TO 90.25D GROUP 1-4 WITHIN 10D EXPAND POS TARG +10.0,+10.0 EXPAND POS TARG +11.0,+10.0 EXPAND POS TARG +10.0,+11.0 SAME ORIENT AS 1 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F702W ------------------------------------------------------------------------------------------------------------------------------------ Target Names AC114-POS1 AC114-POS2 AC114-POS3 AC114-POS4 ------------------------------------------------------------------------------------------------------------------------------------