12362( 2) - 20-Sep-2010 11:21:05 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 12362 Version: 2 Check-in Time: 20-Sep-2010 11:21:05 STScI Edit Number: 0 Title The Bullet Cluster Reloaded? An in-depth study of two post-collision cluster mergers ------------------------------------------------------------------------------------ Type Cycle GO 18 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Harald Ebeling University of Hawaii CoI: Dr. Alastair C. Edge University of Durham N CoI: Dr. Johan Richard University of Durham N CoI: Mr. Cheng-Jiun Ma University of Hawaii N CoI: Dr. Andrew Mann University of Hawaii N CoI: Dr. Marceau Limousin Laboratoire d'Astrophysique de Marseille N CoI: Prof. Jean-Paul Kneib Laboratoire d'Astrophysique de Marseille N CoI: Prof. Priyamvada Natarajan Yale University N ------------------------------------------------------------------------------------ Abstract Detailed X-ray/lensing studies of the massive X-ray selected galaxy clusters 1E0657-56 (the "Bullet Cluster") and MACSJ0025.4-1222 have exploited the segregation of collisional and collisionless matter in cluster mergers to obtain first constraints on the self-interaction cross section of dark matter. We here propose a similar study of two newly discovered very X-ray luminous galaxy clusters from the MACS sample that have been confirmed as linear, post-collision mergers of similar or higher mass. The proposed ACIS-I and HST/ACS observations will allow an accurate mapping of collisional (X-ray gas) and collisionless matter (galaxies and, presumably, dark matter) and thus yield improved constraints on the properties of dark matter. ------------------------------------------------------------------------------------ Observations Description ------------------------ The depth of the proposed observations is dictated by the requirements of an accurate measurement of the gravitational shear field. Resolved colour information from non-overlapping passbands is critical for the secure identification of faint, multiply imaged background objects and thus an unambiguously determined lens model, as well as for the elimination of unlensed galaxies in the cluster and the foreground, which cause a dilution of the measured shear. We note that several strong-lensing features have already been tentatively identified in the existing HST snapshot. The weak-lensing analysis of the large-scale mass distribution will be conducted in the F814W passband which provides the greatest depth. Since this requires high-precision measurements of the ellipticity of faint background galaxies across the full field of view, we request LOW SKY mode. Earth glow would drastically reduce the sensitivity of these observations by raising the limiting magnitude, and thus lower the number of background galaxies for which accurate shape measurements can be obtained. A single pointing with ACS will suffice since the mass-sheet degeneracy of the weak-lensing shear field can be broken with strong-lensing constraints. However, coverage of the full ACS/WFC field of view is critical to probe the gravitational shear field to a radius of at least 400 kpc. We request 12362( 2) - 20-Sep-2010 11:21:05 - [ 2] SAME ORIENTATION for all observations, as random orientations of the ACS field of view for observations in different passbands would severely compromise the availability of colour information (important to mitigate dilution of the weak-shear signal from unlensed foreground and cluster galaxies) in the outer cluster regions. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 12362( 2) - 20-Sep-2010 11:21:05 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 MACSJ0553.4- CLUSTER OF GALAXIES, RA=05H53M24.0000S +/- 0.1", J2000 V = 14 +/- 0.1 3342 GRAVITATIONAL LENS, DEC=-33D42'30.00" +/- 0.1" RICH CLUSTER, SHOCK FRONT Reference Frame: ICRS Comments: ------------------------------------------------------------------------------------------------------------------------------------ 12362( 2) - 20-Sep-2010 11:21:05 - [ 4] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type ACS-WFC-DITHER-LINE ACS-WFC-DITHER-LINE Pattern_Purpose DITHER DITHER Number_Of_Points 2 3 Point_Spacing 3.011 0.138 Line_Spacing Coordinate_Frame POS-TARG POS-TARG Pattern_Orient 85.28 32.99 Angle_Between_Sides Center_Pattern YES YES Pattern_Comments: 6-position dither ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 2 Primary_Pattern Secondary_Pattern Pattern_Type ACS-WFC-DITHER-LINE ACS-WFC-DITHER-LINE Pattern_Purpose DITHER DITHER Number_Of_Points 2 2 Point_Spacing 3.011 0.138 Line_Spacing Coordinate_Frame POS-TARG POS-TARG Pattern_Orient 85.28 32.99 Angle_Between_Sides Center_Pattern YES YES Pattern_Comments: 4-position dither ------------------------------------------------------------------------------------------------------------------------------------ 12362( 2) - 20-Sep-2010 11:21:05 - [ 5] Visit: 01 Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 MACSJ0553.4 ACS/WFC ACCUM WFC F435W CR-SPLIT=NO 1 742 S LOW-SKY; PATTERN 1 1 -3342 ------------------------------------------------------------------------------------------------------------------------------------ 2 MACSJ0553.4 ACS/WFC ACCUM WFC F814W CR-SPLIT=NO 1 762 S LOW-SKY; PATTERN 1 2 -3342 ------------------------------------------------------------------------------------------------------------------------------------ 3 MACSJ0553.4 ACS/WFC ACCUM WFC F606W CR-SPLIT=NO 1 523 S LOW-SKY; PATTERN 2 3 -3342 ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ MACSJ0553.4-3342 1 ACS/WFC ACCUM WFC F435W 1 1 none none 1 N/A MACSJ0553.4-3342 1 ACS/WFC ACCUM WFC F435W 1 2 none none 1 N/A MACSJ0553.4-3342 1 ACS/WFC ACCUM WFC F435W 1 3 none none 1 N/A MACSJ0553.4-3342 1 ACS/WFC ACCUM WFC F435W 2 1 none none 2 N/A MACSJ0553.4-3342 1 ACS/WFC ACCUM WFC F435W 2 2 none none 2 N/A MACSJ0553.4-3342 1 ACS/WFC ACCUM WFC F435W 2 3 none none 2 N/A MACSJ0553.4-3342 2 ACS/WFC ACCUM WFC F814W 1 1 none none 3 N/A MACSJ0553.4-3342 2 ACS/WFC ACCUM WFC F814W 1 2 none none 3 N/A MACSJ0553.4-3342 2 ACS/WFC ACCUM WFC F814W 1 3 none none 3 N/A MACSJ0553.4-3342 2 ACS/WFC ACCUM WFC F814W 2 1 none none 4 N/A MACSJ0553.4-3342 2 ACS/WFC ACCUM WFC F814W 2 2 none none 4 N/A MACSJ0553.4-3342 2 ACS/WFC ACCUM WFC F814W 2 3 none none 4 N/A MACSJ0553.4-3342 3 ACS/WFC ACCUM WFC F606W 1 1 none none 5 N/A MACSJ0553.4-3342 3 ACS/WFC ACCUM WFC F606W 1 2 none none 5 N/A MACSJ0553.4-3342 3 ACS/WFC ACCUM WFC F606W 2 1 none none 5 N/A MACSJ0553.4-3342 3 ACS/WFC ACCUM WFC F606W 2 2 none none 5 N/A 12362( 2) - 20-Sep-2010 11:21:05 - [ 6] Summary Form for Proposal 12362 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures WFC ------------------------------------------------------------------------------------------------------------------------------------ Configurations ACS/WFC ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements LOW-SKY, PATTERN 1 1, PATTERN 1 2, PATTERN 2 3 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F435W, F606W, F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names MACSJ0553.4-3342 ------------------------------------------------------------------------------------------------------------------------------------