Assigned ID: 848 ----- Attempting Submission 1 (Sat Feb 27 00:04:11 GMT 2010) ----- HST Phase I Proposal 848 (cycle18-0358.apt) successfully submitted. ----- Attempting Submission 2 (Sat Feb 27 00:39:49 GMT 2010) ----- HST Phase I Proposal 848 (cycle18-0358.apt) successfully submitted. ----- Attempting Submission 1 (Mon Jun 28 21:34:37 GMT 2010) ----- 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.

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 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 ˇc) 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. COSMOLOGY 12 false 50 0.0 false false false false false false SUPPORTED CLUSTER OF GALAXIES GRAVITATIONAL LENS RICH CLUSTER J2000 03 58 53.0800 -29 55 51.60 J2000 ACS/WFC Imaging No No F435W ACS/WFC Imaging No No F606W ACS/WFC Imaging No No F814W POS-TARG DITHER DITHER 3 3.011 6-position dither ACS-WFC-DITHER-LINE true true 0.138 2 85.28 POS-TARG ACS-WFC-DITHER-LINE 32.99 1 true POS-TARG DITHER DITHER 2 3.011 4-position dither ACS-WFC-DITHER-LINE true true 0.138 2 85.28 POS-TARG ACS-WFC-DITHER-LINE 32.99 2 true 1277760537137 /private/tmp/OPVisit1294167643725057276.xml The scheduling data was generated by CASM 18.3.1. CASM was run in Phase II mode. (Tic-Visit :proposal-id 12313 :visit-id "01" :proposal-version -1 :trans-version "20100505" :date "28-Jun-2010 11:28:56.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 5 :saa-model "27" :si-bright-earth-limb-angle 40.0 :data-volume 4547584 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12313 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12313 :visit-id "01" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2786 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "Y" :pcs-visibility 3191 :pcs-gap 399 ) (Tic-Orbit :proposal-id 12313 :visit-id "01" :orbit-number 2 :pcs-time 222 :si-vis-utilization 2704 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "Y" :pcs-visibility 3191 :pcs-gap 399 ) (Tic-Orbit :proposal-id 12313 :visit-id "01" :orbit-number 3 :pcs-time 222 :si-vis-utilization 2786 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "Y" :pcs-visibility 3191 :pcs-gap 399 ) (Tic-Orbit :proposal-id 12313 :visit-id "01" :orbit-number 4 :pcs-time 222 :si-vis-utilization 2764 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "Y" :pcs-visibility 3191 :pcs-gap 399 ) (Tic-Orbit :proposal-id 12313 :visit-id "01" :orbit-number 5 :pcs-time 222 :si-vis-utilization 2791 :al-overhead-at-end 0 :internal-dur-at-end 349 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "Y" :pcs-visibility 3191 :pcs-gap 399 ) true 5 0