12313( 2) - 29-Jun-2010 10:29:32 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 12313 Version: 2 Check-in Time: 29-Jun-2010 10:29:32 STScI Edit Number: 0 Title An in-depth study of dark matter in the massive cluster merger MACSJ0358.8-2955 ------------------------------------------------------------------------------------ Type Cycle GO 18 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Harald Ebeling University of Hawaii CoI: Dr. Johan Richard University of Durham N CoI: Prof. Marusa Bradac University of California - Davis N CoI: Dr. Marceau Limousin Laboratoire d'Astrophysique de Marseille N CoI: Prof. Priyamvada Natarajan Yale University N CoI: Prof. Jean-Paul Kneib Laboratoire d'Astrophysique de Marseille N CoI: Dr. Alastair C. Edge University of Durham N CoI: Mr. Cheng-Jiun Ma University of Hawaii N ------------------------------------------------------------------------------------ Abstract We propose multi-passband observations with HST/ACS (F435W, F606W, and F814W) and moderately deep X-ray observations with Chandra/ACIS-I of the massive cluster merger MACSJ0358.8-2955 at z=0.434. The combination of existing HST/ACS and Chandra/ACIS-I snapshots shows strong evidence for a segregation of luminous and dark matter in a linear cluster merger, making this system a prime candidate for a quantitative study of the properties of dark matter. We have already identified and spectroscopically confirmed two sets of strongly lensed multiple-image systems. The resulting tentative model of the mass distribution shows a highly elongated critical line and further supports a linear, post-collision geometry that may enable a third, independent measurement of the self-interaction cross section of dark matter from cluster mergers. The colour and morphological information provided by the proposed HST/ACS observations will allow us to unambiguously identify additional multiple-image systems to refine our mass model, and to obtain further independent constraints on the mass profile from a weak-lensing analysis. The proposed Chandra/ACIS-I will provide complementary information on the intra-cluster gas, most importantly an accurate mapping of its distribution, but also spatially resolved gas temperatures. In combination with groundbased spectroscopy (underway), these observations will permit us to reconstruct the three-dimensional geometry and dynamics of this merger and to perform an independent test of the results on the existence and properties of dark matter obtained for the Bullet Cluster and MACSJ0025.4-1222. ------------------------------------------------------------------------------------ Observations Description ------------------------ We propose moderately deep ACS observations in three passbands (two orbits in each of F435W and F814W, one in F606W) of the massive merger MACSJ0358.8?2955. 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 12313( 2) - 29-Jun-2010 10:29:32 - [ 2] galaxies in the cluster and the foreground, which cause a dilution of the measured shear. Resolved colours are also crucial for our science bonus, the study of the cluster galaxy population (colours and morphology) and its evolution as a function of static and dynamic environment. Our strategy follows closely the one used successfully by us before (GO-11100; PI Brada ?c) for the analysis of MACSJ0025.4?1222 but goes deeper in F435W, accounting for the narrower width of the filter compared to F606W and F814W, the spectral sensitivity of ACS, and the SED of typical galaxies. We will make use of the existing ACS/F606W data which add about 0.5 orbits to the depth in this passband. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 12313( 2) - 29-Jun-2010 10:29:32 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 MACSJ0358.8- CLUSTER OF GALAXIES, RA=03H58M53.0800S +/- 5", J2000 V = 20 2955 GRAVITATIONAL LENS, DEC=-29D55'51.60" +/- 5" RICH CLUSTER Reference Frame: ICRS Comments: ------------------------------------------------------------------------------------------------------------------------------------ 12313( 2) - 29-Jun-2010 10:29:32 - [ 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 ------------------------------------------------------------------------------------------------------------------------------------ 12313( 2) - 29-Jun-2010 10:29:32 - [ 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 MACSJ0358.8 ACS/WFC ACCUM WFC F435W CR-SPLIT=NO 1 750 S LOW-SKY; PATTERN 1 1 -2955 ------------------------------------------------------------------------------------------------------------------------------------ 2 MACSJ0358.8 ACS/WFC ACCUM WFC F814W CR-SPLIT=NO 1 770 S LOW-SKY; PATTERN 1 2 -2955 ------------------------------------------------------------------------------------------------------------------------------------ 3 MACSJ0358.8 ACS/WFC ACCUM WFC F606W CR-SPLIT=NO 1 530 S LOW-SKY; PATTERN 2 3 -2955 ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ MACSJ0358.8-2955 1 ACS/WFC ACCUM WFC F435W 1 1 none none 1 N/A MACSJ0358.8-2955 1 ACS/WFC ACCUM WFC F435W 1 2 none none 1 N/A MACSJ0358.8-2955 1 ACS/WFC ACCUM WFC F435W 1 3 none none 1 N/A MACSJ0358.8-2955 1 ACS/WFC ACCUM WFC F435W 2 1 none none 2 N/A MACSJ0358.8-2955 1 ACS/WFC ACCUM WFC F435W 2 2 none none 2 N/A MACSJ0358.8-2955 1 ACS/WFC ACCUM WFC F435W 2 3 none none 2 N/A MACSJ0358.8-2955 2 ACS/WFC ACCUM WFC F814W 1 1 none none 3 N/A MACSJ0358.8-2955 2 ACS/WFC ACCUM WFC F814W 1 2 none none 3 N/A MACSJ0358.8-2955 2 ACS/WFC ACCUM WFC F814W 1 3 none none 3 N/A MACSJ0358.8-2955 2 ACS/WFC ACCUM WFC F814W 2 1 none none 4 N/A MACSJ0358.8-2955 2 ACS/WFC ACCUM WFC F814W 2 2 none none 4 N/A MACSJ0358.8-2955 2 ACS/WFC ACCUM WFC F814W 2 3 none none 4 N/A MACSJ0358.8-2955 3 ACS/WFC ACCUM WFC F606W 1 1 none none 5 N/A MACSJ0358.8-2955 3 ACS/WFC ACCUM WFC F606W 1 2 none none 5 N/A MACSJ0358.8-2955 3 ACS/WFC ACCUM WFC F606W 2 1 none none 5 N/A MACSJ0358.8-2955 3 ACS/WFC ACCUM WFC F606W 2 2 none none 5 N/A 12313( 2) - 29-Jun-2010 10:29:32 - [ 6] Summary Form for Proposal 12313 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 MACSJ0358.8-2955 ------------------------------------------------------------------------------------------------------------------------------------