6004( 4) - 10/27/95 16:32 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6004 Version: 4 Check-in Date: ********** 1.Proposal Title: Direct Measurement of The Mass Distribution in the Rich Cluster Abell 1689 ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle Galaxies & Clusters GO 5 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: Tony Tyson AT&T Bell Laboratories CoI: Phil Fischer Bell Laboratories N CoI: Puragra Guhathakurta University of California, Santa Cruz N CoI: Jordi Miralda Institute for Advanced Study N ------------------------------------------------------------------------------------ 6. Abstract We propose to obtain a map of the mass, including the dark matter, in the core of the richest galaxy cluster, Abell 1689 at z=0.18. The only way to do this is to take very deep images of the cluster and measure the gravitational lens distortion of the blue background galaxy population. The confirmation of distortions in the lensed background galaxies inferred from very deep ground-based observations will allow us to produce a high quality map of the cluster mass distribution over a range of scales from 10 kpc to 1 Mpc, revealing the nature of the non-singular mass core. The detailed shape of this mass core inside 100 kpc will contain information on the nature of the dark matter and the scenario for sub-structure formation in clusters of galaxies. Background galaxies in the range B=24-- 26 are very compact (r<0.5 arcsec) and, in order to constrain lens models, it is essential to measure both the width and the length of the distorted galaxies---accurate width measurement is virtually impossible with ground-based resolution. ------------------------------------------------------------------------------------ 6004( 4) - 10/27/95 16:32 - [ 2] Observations Description ------------------------ We need to measure the width of the blue radial spikes in the core region of the cluster, in the presence to the red light from the superposed bright ellipticals. Given the tangential "pinch" distortion of these spikes, together with the conservation of surface brightness, we need to go to 27.5 -- 28 B mag/sq.arcsec surface brightness at 2-sigma. We will do 2 color imaging with WFPC2. The filters best suited to do this are the F555W and F814W filters. The faint blue galaxies which we wish to image have a spectrum in the optical similar to an F0 star (as expected from galaxy evolution models). We will image the radial spikes and arcs at a V magnitude of 26. The colors of the arcs imply from Table 6.1 of the WFPC2 handbook an AB correction of 0.06 magnitudes at 450nm and 0.05 magnitudes at 700nm. The seeing- deconvolved CFHT data and the HST Cy 4 MDS data give a mean half-light radius of 0.5 arcsec for galaxies around magnitude V=24--25 with considerable scatter. We infer from this a 50 WFPC2 pixel area for half the light at magnitude 26. Using equations 6.1 and Tables 6.1 and 6.2 we infer 293 electrons in 2000 seconds for a 26 V magnitude galaxy at 450nm and 652e for the same galaxy and integration time at 702nm. We calculate signal to noise per pixel since we are doing surface photometry. Note that ellipse fitting averages pixels and will increase our signal to noise. Assuming a flat profile for the galaxies we get 3e/pixel/2000s at 450nm although based on extrapolations from the MDS survey data it could be as much as 7e/pixel/2000s. For the sky background at high ecliptic lattitudes (tables 6.1 and 6.3) we infer 30e/pix/2000s. Calculating signal to noise based on the data above we infer that we get a S/N of 0.5 in 2000s seconds per pixel inside the half light radius. We thus need 20 orbits to get a signal to noise of 3 per pixel at the half light point. Note however that there are many sources inside the WFC field at magnitude 26 and we do get signal from pixels inside the half light radius. We have compared the throughput for the F450W and F550W filters; while the arclets have more flux at 450nm than at 550nm, the system throughput is higher with the F550W. These effects roughly cancel, implying that we need roughly 20 orbits in either filter; however the availability of better flats in the F550W tips the balance to the F550W filter. We also need longer wavelength data; while we requested R data in the Phase 1 proposal, we now prefer the I band (F814W) due to several factors: the change from F450W to F550W for the blue filter mandates a redder red filter, and the possibility of exchanging data with Kaiser et al (F814W). [We originally requested 4 orbits in F702W in order to adequately photometer the very red elliptical galaxies near these blue arcs and spikes.] These red galaxies will be modeled and subtracted using software developed for this purpose on our ground-based data. We will take 1-2 exposures per orbit to try to achieve sky-limited data while having enough frames to eliminate radiation events. The exposures will be stepped in integral pixels to aid in the elimination of hot pixels. Most of the steps will be large enough to move small galaxies and arclets off themselves, aiding the cleaned image reconstruction. We have optimized the roll angle for maximum product of schedulability and arc coverage (using our ground-based data as a guide). Real Time Justification ----------------------- none Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 6004( 4) - 10/27/95 16:32 - [ 3] Data Distribution Media: 8MM Blocking Factor: 10 Ship To: Philippe Fischer*830 Dennison Building*University of Michigan*Ann Arbor, MI 48109 Ship Via: UPS Email: tyson@physics.att.com , ------------------------------------------------------------------------------------ 6004( 4) - 10/27/95 16:32 - [ 4] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 ABELL1689 CLUSTER OF GALAXIES, RA=13H 11M 31.16S +/- 1S, DEC=- 2000 Z=0.18 V=16 +/- 0.5 SURF(V)=24.0 +/- 1.0 RICH CLUSTER, 01D 20' 22.6" +/- 1" GRAVITATIONAL LENS 6004( 4) - 10/27/95 16:32 - [ 5] Visit: 01 Visit Requirements: PCS MODE Fine ORIENT 92D TO 92D 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 ------------------------------------------------------------------------------------------------------------------------------------ 1 ABELL1689 WFPC2 IMAGE PC1-FIX F814W CR-SPLIT=NO 1 1000S POS TARG -14.0,-14.5 ------------------------------------------------------------------------------------------------------------------------------------ 2 ABELL1689 WFPC2 IMAGE PC1-FIX F814W CR-SPLIT=NO 1 1000S POS TARG -14.5,-14.5 ------------------------------------------------------------------------------------------------------------------------------------ 3 ABELL1689 WFPC2 IMAGE PC1-FIX F555W CR-SPLIT=NO 1 2600S POS TARG -14.5,-14.5 ------------------------------------------------------------------------------------------------------------------------------------ 4 ABELL1689 WFPC2 IMAGE PC1-FIX F555W CR-SPLIT=NO 1 2600S POS TARG -14.5,-14.0 ------------------------------------------------------------------------------------------------------------------------------------ 5 ABELL1689 WFPC2 IMAGE PC1-FIX F555W CR-SPLIT=NO 1 2600S POS TARG -14.0,-14.0 ------------------------------------------------------------------------------------------------------------------------------------ 6 ABELL1689 WFPC2 IMAGE PC1-FIX F555W CR-SPLIT=NO 1 2600S POS TARG -14.0,-14.5 ------------------------------------------------------------------------------------------------------------------------------------ 7 ABELL1689 WFPC2 IMAGE PC1-FIX F555W CR-SPLIT=NO 1 2600S POS TARG -14.5,-15.0 ------------------------------------------------------------------------------------------------------------------------------------ 8 ABELL1689 WFPC2 IMAGE PC1-FIX F555W CR-SPLIT=NO 1 2600S POS TARG -15.0,-14.5 ------------------------------------------------------------------------------------------------------------------------------------ 9 ABELL1689 WFPC2 IMAGE PC1-FIX F555W CR-SPLIT=NO 1 2600S POS TARG -15.0,-15.0 ------------------------------------------------------------------------------------------------------------------------------------ 6004( 4) - 10/27/95 16:32 - [ 6] Visit: 02 Visit Requirements: PCS MODE Fine ORIENT 92D TO 92D 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 ------------------------------------------------------------------------------------------------------------------------------------ 1 ABELL1689 WFPC2 IMAGE PC1-FIX F814W CR-SPLIT=NO 1 1000S POS TARG -14.0,-14.0 ------------------------------------------------------------------------------------------------------------------------------------ 2 ABELL1689 WFPC2 IMAGE PC1-FIX F814W CR-SPLIT=NO 1 1000S POS TARG -14.5,-14.0 ------------------------------------------------------------------------------------------------------------------------------------ 3 ABELL1689 WFPC2 IMAGE PC1-FIX F555W CR-SPLIT=NO 1 2600S POS TARG -15.5,-15.5 ------------------------------------------------------------------------------------------------------------------------------------ 4 ABELL1689 WFPC2 IMAGE PC1-FIX F555W CR-SPLIT=NO 1 2600S POS TARG -14.0,-15.0 ------------------------------------------------------------------------------------------------------------------------------------ 5 ABELL1689 WFPC2 IMAGE PC1-FIX F555W CR-SPLIT=NO 1 2600S POS TARG -15.0,-14.0 ------------------------------------------------------------------------------------------------------------------------------------ 6 ABELL1689 WFPC2 IMAGE PC1-FIX F555W CR-SPLIT=NO 1 2600S POS TARG -14.5,-15.5 ------------------------------------------------------------------------------------------------------------------------------------ 7 ABELL1689 WFPC2 IMAGE PC1-FIX F555W CR-SPLIT=NO 1 2600S POS TARG -15.5,-14.5 ------------------------------------------------------------------------------------------------------------------------------------ 8 ABELL1689 WFPC2 IMAGE PC1-FIX F555W CR-SPLIT=NO 1 2600S POS TARG -15.5,-15.0 ------------------------------------------------------------------------------------------------------------------------------------ 9 ABELL1689 WFPC2 IMAGE PC1-FIX F555W CR-SPLIT=NO 1 2600S POS TARG -15.0,-15.5 ------------------------------------------------------------------------------------------------------------------------------------ 6004( 4) - 10/27/95 16:32 - [ 7] Visit: 03 Visit Requirements: PCS MODE Fine ORIENT 92D TO 92D 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 ------------------------------------------------------------------------------------------------------------------------------------ 1 ABELL1689 WFPC2 IMAGE PC1-FIX F814W CR-SPLIT=NO 1 1000S POS TARG -14.5,-15.0 ------------------------------------------------------------------------------------------------------------------------------------ 2 ABELL1689 WFPC2 IMAGE PC1-FIX F814W CR-SPLIT=NO 1 1000S POS TARG -15.0,-14.5 ------------------------------------------------------------------------------------------------------------------------------------ 3 ABELL1689 WFPC2 IMAGE PC1-FIX F555W CR-SPLIT=NO 1 2600S POS TARG -13.5,-14.5 ------------------------------------------------------------------------------------------------------------------------------------ 4 ABELL1689 WFPC2 IMAGE PC1-FIX F555W CR-SPLIT=NO 1 2600S POS TARG -14.0,-15.5 ------------------------------------------------------------------------------------------------------------------------------------ 5 ABELL1689 WFPC2 IMAGE PC1-FIX F555W CR-SPLIT=NO 1 2600S POS TARG -15.5,-14.0 ------------------------------------------------------------------------------------------------------------------------------------ 6004( 4) - 10/27/95 16:32 - [ 8] Summary Form for Proposal 6004 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category Galaxies & Clusters ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PCS MODE Fine ORIENT 92D TO 92D POS TARG -14.0,-14.5 POS TARG -14.5,-14.5 POS TARG -14.5,-14.0 POS TARG -14.0,-14.0 POS TARG -14.5,-15.0 POS TARG -15.0,-14.5 POS TARG -15.0,-15.0 POS TARG -15.5,-15.5 POS TARG -14.0,-15.0 POS TARG -15.0,-14.0 POS TARG -14.5,-15.5 POS TARG -15.5,-14.5 POS TARG -15.5,-15.0 POS TARG -15.0,-15.5 PCS MODE Fine ORIENT 92D TO 92D SAME ORIENT AS 1 POS TARG -13.5,-14.5 POS TARG -14.0,-15.5 POS TARG -15.5,-14.0 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F814W F555W ------------------------------------------------------------------------------------------------------------------------------------ Target Names ABELL1689 ------------------------------------------------------------------------------------------------------------------------------------