6488( 4) - 12/16/98 11:31 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6488 Version: 4 Check-in Date: 16-Dec-1998 11:30:38 1.Proposal Title: AN ULTRA-FAINT GALAXY COUNT AND REDSHIFT SURVEY USING CLUSTER LENSES ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 6 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Ian Smail University of Durham CoI: Richard Ellis Institute of Astronomy Y CoI: Jean-Paul Kneib Institute of Astronomy N ------------------------------------------------------------------------------------ 5. Abstract The high surface density (~ 200 arcmin^-2) of the faintest sources revealed via ultra-deep CCD images suggests we may have detected a population of high redshift pre-galactic halos. The abundance, clustering and other properties of such sources would be valuable constraints on theories of structure formation. To verify the hypothesis redshifts and hence luminosities are required for sources well beyond the spectroscopic limits of even 10-m class telescopes. By using the gravitational distortion induced by foreground rich clusters, we demonstrate that it is possible to secure reliable distances at these limits by analysing the images of background sources viewed through a highly-constrained cluster lens. From HST images of a single cluster, the redshift distribution of ~ 60 objects to R=25 has already been determined. A further development is the use of lensing to provide constraints on source counts and redshifts to yet fainter limits, R~29, by analysing the location and abundance of highly-magnified `pairs'. The combination of both techniques, made possible only with HST, provides the only avenue towards constraining a pre-galactic halo population. We propose to apply both techniques to a further cluster enabling us to 1) compare our lensing-derived N(z) at R<=23 with spectroscopic results, 2) extend the inversion depth to R=26, and 3) analyse the frequency and geometry of faint pairs to constrain the distance and abundance of sources to R~29. ------------------------------------------------------------------------------------ 6488( 4) - 12/16/98 11:31 - [ 2] Observations Description ------------------------ Our observational strategy is similar to that successfully adopted for the Cycle 4 A2218 observations for which we have already undertaken the lensing inversion. Those observations totalled 3 orbits in F702W and were an excellent indication of the capabilities of both the telescope and the inversion method. However, a careful analysis of that data showed that we were compromised by the relatively high surface brightness limit imposed by the short exposure time -- which introduces biases into the object selection of the distorted arclets -- and equally importantly by residual flat-fielding errors from the small number of exposures available to stack. The robust inversion of these observations was thus limited to only R~25, too shallow to reach beyond the break in galaxy number counts. In this proposal we are attempting to probe the redshifts and luminosities of galaxies fainter than the break magnitude, reaching to R~26. We are thus requesting longer integration times to provide a fainter magnitude limit, a deeper limiting isophote for more robust object selection and to obtain more independent pointings to reduce contributions from flat-fielding errors. With 6 orbits per cluster and offsetting each pair of pointings by (1.0, 1.0) arcsec we can construct deeper and flatter images and provide a more robust arclet catalog. Our choice of the F702W is dictated by the need for the reddest possible high-sensitivity filter combination, this choice also provides commonality with our A2218 and AC114 exposures. Real Time Justification ----------------------- None. None. Spectroscopy of the brightest arc in this cluster has already been undertaken by ourselves. Extensive ground-based imaging, spectroscopic data for cluster members and deep ROSAT/ASCA observations are also available for this target. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ Data Distribution Paper Products: Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: Email: ------------------------------------------------------------------------------------ 6488( 4) - 12/16/98 11:31 - [ 3] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 ABELL2219 CLUSTER OF GALAXIES, RA=16H 40M 23.76S +/- 0.1S, 2000.0 Z=0.225 R = 25.5 GRAVITATIONAL LENS, DEC=+46D 42' 54.4" +/- 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) 2000.0 0.0 0.0 0.0 6488( 4) - 12/16/98 11:31 - [ 4] Visit: 01 Visit Priority: Visit Requirements: ORIENT 70D TO 95D GROUP 1, 2 WITHIN 60D 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 the field are split into three exposures each with a shift introduced of (1.0, 1.0) arcsec between each exposure in order to displace objects situated on CCD defects or on the seams of the pyramid. Thus, POS TARG +11.0,+11.0 corresponds to the second exposure, POS TARG +9.0,+9.0 to the third. CR-SPLIT=NO for all observations since in all cases there are sufficient multiple exposures to perform cosmic ray rejection. ORIENT range is 80 +15/-10 DEG to keep the target major axis aligned parallel to the X-axis of WF-4. 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. Observations now revised to split into two visits each of three exposures as per Biretta request 12/10/98. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 ABELL2219 WFPC2 IMAGE WFALL-F F702W CR-SPLIT=NO 1 2400 S EXPAND LOW-SKY POS TARG IX +10.0,+10.0 Comments: POS TARG +10,+10 PLACES TARGET COORDS AT APEX OF PYRAMID. ------------------------------------------------------------------------------------------------------------------------------------ 2 ABELL2219 WFPC2 IMAGE WFALL-F F702W CR-SPLIT=NO 1 2400 S EXPAND LOW-SKY POS TARG IX +11.0,+11.0 Comments: SHIFTED BY 1.0, 1.0 TO ALLOW REMOVAL OF CHIP DEFECTS ------------------------------------------------------------------------------------------------------------------------------------ 3 ABELL2219 WFPC2 IMAGE WFALL-F F702W CR-SPLIT=NO 1 2400 S EXPAND LOW-SKY POS TARG IX +9.0,+9.0 Comments: SHIFTED BY -1.0,-1.0 TO ALLOW REMOVAL OF CHIP DEFECTS ------------------------------------------------------------------------------------------------------------------------------------ 6488( 4) - 12/16/98 11:31 - [ 5] Visit: 02 Visit Priority: Visit Requirements: SAME ORIENT AS 1 GROUP 1, 2 WITHIN 60D 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,+11.0 to bring the center to close to the apex of the pyramid. Exposures for the field are split into three exposures each with a shift introduced of +/-1.0 arcsec between each exposure in order to displace objects situated on CCD defects or on the seams of the pyramid. Thus, POS TARG +11.0,+12.0 corresponds to the second exposure, POS TARG +9.0,+10.0 to the third. CR-SPLIT=NO for all observations since in all cases there are sufficient multiple exposures to perform cosmic ray rejection. ORIENT range is 80 +15/-10 DEG to keep the target major axis aligned parallel to the X-axis of WF-4. 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. Observations now revised to split into two visits each of three exposures as per Biretta request 12/10/98. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 11 ABELL2219 WFPC2 IMAGE WFALL-F F702W CR-SPLIT=NO 1 2400 S EXPAND LOW-SKY POS TARG IX +10.0,+11.0 Comments: POS TARG +10,+11 PLACES TARGET COORDS NEAR APEX OF PYRAMID. ------------------------------------------------------------------------------------------------------------------------------------ 12 ABELL2219 WFPC2 IMAGE WFALL-F F702W CR-SPLIT=NO 1 2400 S EXPAND LOW-SKY POS TARG IX +11.0,+12.0 Comments: SHIFTED BY 1.0, 1.0 TO ALLOW REMOVAL OF CHIP DEFECTS ------------------------------------------------------------------------------------------------------------------------------------ 13 ABELL2219 WFPC2 IMAGE WFALL-F F702W CR-SPLIT=NO 1 2400 S EXPAND LOW-SKY POS TARG IX +9.0,+10.0 Comments: SHIFTED BY -1.0,-1.0 TO ALLOW REMOVAL OF CHIP DEFECTS ------------------------------------------------------------------------------------------------------------------------------------ 6488( 4) - 12/16/98 11:31 - [ 6] Summary Form for Proposal 6488 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures WFALL-FIX ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENT 70D TO 95D GROUP 1, 2 WITHIN 60D EXPAND LOW-SKY POS TARG +10.0,+10.0 EXPAND LOW-SKY POS TARG +11.0,+11.0 EXPAND LOW-SKY POS TARG +9.0,+9.0 SAME ORIENT AS 1 GROUP 1, 2 WITHIN 60D EXPAND LOW-SKY POS TARG +10.0,+11.0 EXPAND LOW-SKY POS TARG +11.0,+12.0 EXPAND LOW-SKY POS TARG +9.0,+10.0 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F702W ------------------------------------------------------------------------------------------------------------------------------------ Target Names ABELL2219 ------------------------------------------------------------------------------------------------------------------------------------