9135( 3) - 07/05/01 12:03 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 9135 Version: 3 Check-in Date: 05-Jul-2001 12:02:56 1.Proposal Title: A New High-z Galaxy Cluster with Extraordinary Lensed Arcs From Multiple Sources ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 10 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Mike Gladders University of Toronto CoI: Dr. Henk Hoekstra University of Toronto (as of Oct. 2000) N CoI: Prof. Erica Ellingson University of Colorado N CoI: Prof. Howard Yee University of Toronto N CoI: Dr. Hanadi AbdelSalam University of Gronegin N ------------------------------------------------------------------------------------ 5. Abstract In the course of the Red-Sequence Cluster Survey (a 100 deg^2 optical imaging survey), we have discovered a stunning new example of strong lensing by a relatively high redshift (z~0.7) cluster. This lens system has more bright arcs, with better cluster azimuthal coverage than examples of lower z lenses previously imaged by HST (e.g., Abell 370, CL2244- 0221), and is the only known lens at z>0.6 with such significant lensing. At least 4 separate arcs are detected in our initial survey data, at 3-4 different cluster-centric radii and hence likely corresponding to at least 3 different background sources at 3 different redshifts. Moreover, these arcs are relatively bright (R_c~21.5-24.2) and hence redshifts should be readily obtainable using 8m class telescopes. The proposed HST WFPC2 imaging, in conjunction with proposed VLT spectroscopy, offers an unprecedented opportunity to measure the core mass distribution of a cluster at such a high redshift. In combination with requested coordinated Chandra X- ray imaging, this will enable a direct comparison of the dark matter and baryonic components of the cluster, and enable a measure of cosmology via sources at different z. Furthermore, the arcs are bright enough to allow a detailed look at several high-z galaxies, via image reconstruction of the unlensed sources (only possible with HST images) and detailed spectroscopy. ------------------------------------------------------------------------------------ 9135( 3) - 07/05/01 12:03 - [ 2] Observations Description ------------------------ paragraph We require data that are deep enough to obtain structural information for galaxies at z~0.7 (the cluster galaxies) as well as for the arcs. We also wish to go significantly deeper than the ground-based discovery data, because of the likelihood of finding additional fainter arcs. Additional arcs seem certain to exist, given that there are more faint than bright background sources in general, and given that RCS0224-0002 has a demonstrated propensity for producing strong lensing. Two filters are required both because of the use of color in identifying the source objects for arcs, and for interpreting the nature of the lensed sources. We request images in the F606W and F814W filters. F606W roughly matches the R filter used in the ground based imaging and so is certain to be sensitive to the background arcs. F814W is somewhat bluer than the z' ground based image, but due to HST's much lower sky background should allow a much deeper integration than the z' filter in order to properly see the arcs at longer wavelengths. The choice of F606W and F814W is in part mandated by the need to properly sample the 4000 Angstrom break at the cluster z, so as to facilitate the identification of early-type cluster members via photometric methods. We request integration times of 7200 and 14400 seconds in F606W and F814W respectively, equivalent to 9 orbits in total. With this integration, we will be able to obtain a S/N ratio of 1 per pixel at surface brightness of 26.5 (F606W) and 26.1 (F814W) mag/sq arcsec. This will be sufficient for measuring morphological structure and the detailed surface brightness of the arcs, since most structure will be considerably larger than a single pixel, and will be sufficiently deeper than the ground based imaging data (limiting 5Sigma mags of R_c~25.2 and z'~23.8 for point sources) so as to enable a search for fainter arcs. These total exposure times are comparable to those previously allocated by HST on WFPC-2 for studies of lower z cluster lenses (e.g., CL2244-0221 - see Figure 2, and Abell 370) despite the significantly higher z of the lens, because the ground-based data indicate that the brightest arcs are likely of comparable surface brightness. Note also that in order to improve the resolution, individual exposures (6 (F606W) or 12 (F814W) in total with a CR- SPLIT in each orbit) will be done with partial pixel shifts to allow ``drizzling''. The improved sampling from drizzling is critical to understanding the detailed morphology of the arcs, which assists in matching arc images to particular background sources and is critical in interpreting cosmological results. Real Time Justification ----------------------- We are requesting a 15 Ksec Chandra ACIS-I observation of this cluster. As discussed above, a preliminary mass estimate from the strong lensing yields a velocity dispersion for the cluster in the range 1050-1250 km s^-1. The expected X-ray temperature is thus in the range 8-10 keV. Scaling from Chandra observations by us and others of high redshift clusters and assuming galactic absorption from Colden, PIMMS yields an ACIS-I count rate of about 0.1 ct/sec from this source. Assuming a 9 keV Raymond-Smith spectrum with abundance of 0.2 solar, XSPEC predicts that a 15 Ksec exposure will allow us to to determine the X-ray temperature to about +/- 0.8 (10\ Substructure in the core region resulting in a 30\ surface luminosity over a scale of 50 kpc will be detectable at a 3-sigma confidence level in a 15 Ksec integration. Together, the spatial and spectral X-ray measurements will allow us to independently check the assumptions in modeling the mass distribution via strong lensing-- in particular, the cluster velocity dispersion/global potential well depth and the possibility of core substructure. We attach this request to our HST proposal because it directly tests the assumptions we must make in modeling the strong lensing observations from HST. A much deeper ACIS observation (up to 100 Ksec, and hence inappropriate here) will be proposed for AO3 in order to derive a detailed core mass distribution (including the effects of possible temperature gradients) and explore any substructure which may be indicated by our initial observation. The Chandra data obtained from this proposal can easily be co- added to any future data to increase the depth. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 9135( 3) - 07/05/01 12:03 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 RCS0224-0002 CLUSTER OF GALAXIES, RA=02H 24M 34.06S +/- 0.5", DEC= J2000 R = 23.0+/-1.0 RICH CLUSTER, HIGH -00D 2' 30.9" +/- 0.5" REDSHIFT CLUSTER, GRAVITATIONAL LENS Coordinate Source: OTHER_SOURCE 9135( 3) - 07/05/01 12:03 - [ 4] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type WFPC2-LINE Pattern_Purpose DITHER Number_Of_Points 2 Point_Spacing 0.3535 Coordinate_Frame POS-TARG Pattern_Orient 45 Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ 9135( 3) - 07/05/01 12:03 - [ 5] Visit: 01 Visit Priority: Visit Requirements: ORIENT 220D TO 20D 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 RCS0224-000 WFPC2 IMAGE WF3 F606W CR-SPLIT=NO 1 1100 S PATTERN 1 10 2 ------------------------------------------------------------------------------------------------------------------------------------ 20 RCS0224-000 WFPC2 IMAGE WF3 F606W CR-SPLIT=NO 1 1100 S PATTERN 1 20 POS TARG .5, 2 .5 ------------------------------------------------------------------------------------------------------------------------------------ 21 RCS0224-000 WFPC2 IMAGE WF3 F606W CR-SPLIT=NO 1 1100 S PATTERN 1 21 POS TARG -.5 2 ,-.5 ------------------------------------------------------------------------------------------------------------------------------------ 9135( 3) - 07/05/01 12:03 - [ 6] Visit: 02 Visit Priority: Visit Requirements: SAME ORIENT AS 01 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 RCS0224-000 WFPC2 IMAGE WF3 F814W CR-SPLIT=NO 1 1100 S PATTERN 1 10 2 ------------------------------------------------------------------------------------------------------------------------------------ 20 RCS0224-000 WFPC2 IMAGE WF3 F814W CR-SPLIT=NO 1 1100 S PATTERN 1 20 POS TARG .5, 2 .5 ------------------------------------------------------------------------------------------------------------------------------------ 21 RCS0224-000 WFPC2 IMAGE WF3 F814W CR-SPLIT=NO 1 1100 S PATTERN 1 21 POS TARG -.5 2 ,-.5 ------------------------------------------------------------------------------------------------------------------------------------ 9135( 3) - 07/05/01 12:03 - [ 7] Visit: 03 Visit Priority: Visit Requirements: SAME ORIENT AS 01 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 RCS0224-000 WFPC2 IMAGE WF3 F814W CR-SPLIT=NO 1 1100 S PATTERN 1 10 2 ------------------------------------------------------------------------------------------------------------------------------------ 20 RCS0224-000 WFPC2 IMAGE WF3 F814W CR-SPLIT=NO 1 1100 S PATTERN 1 20 POS TARG .5, 2 .5 ------------------------------------------------------------------------------------------------------------------------------------ 21 RCS0224-000 WFPC2 IMAGE WF3 F814W CR-SPLIT=NO 1 1100 S PATTERN 1 21 POS TARG -.5 2 ,-.5 ------------------------------------------------------------------------------------------------------------------------------------ 9135( 3) - 07/05/01 12:03 - [ 8] Summary Form for Proposal 9135 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures WF3 ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENT 220D TO 20D PATTERN 1 10 PATTERN 1 20 POS TARG .5,.5 PATTERN 1 21 POS TARG -.5,-.5 SAME ORIENT AS 01 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F606W F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names RCS0224-0002 ------------------------------------------------------------------------------------------------------------------------------------