The principal objective of this proposal is to study the physical nature of dark matter by using two, massive, newly-identified merging clusters of galaxies. As shown by the pioneering example of the ``bullet cluster'' (1E0657-56), such systems are ideal laboratories for detecting dark matter and distinguishing between cold dark matter (CDM) and other scenarios (e.g. self-interacting dark matter). Our limit on the self-interaction cross-section of dark matter relies on the assumption of a normal pre-merger mass-to-light ratios, and a small impact parameter during the collision of the two clusters. In order to mitigate any possible systematic effects, it is vital to extend this work to other, similar systems. With detailed observations of new systems, the systematic uncertainties in the dark matter cross section calculations can be improved substantially, allowing us to move from rough order of magnitude estimates to measurements with quantifiable uncertainties that can be compared usefully with the predictions from numerical simulations. Our targets are two extraordinary, high-redshift, merging galaxy clusters recently discovered by the Massive Cluster Survey (MACS). This survey is by far the best matched to this study, since it selects medium redshift (optimal for gravitational lensing studies) and X-ray luminous (hence massive) objects. We have selected the best candidates with clear evidence for considerable offsets between the hot X-ray emitting gas and optically luminous stellar material. The two most striking examples are the targets of this proposal. To pin down the position of the dark matter component we require high resolution, absolutely calibrated mass maps. The combination of weak and strong lensing measurements is needed to attain this goal. This can only be achieved with the excellent resolving power of the HST (in combination with wide-field, multicolor Subaru data already in hand). We therefore request multicolor HST/WFPC2 observations of the two merging clusters. The combination of constraints from multiply lensed images (identified via morphology and color information) and high-resolution weak lensing data will allow us to construct, self-consistently, their mass distribution from the very centers to the outskirts. Gravitational lensing thus provides a unique tool transforming these clusters into dark matter laboratories. They will supply us with answers as to the nature and properties of dark matter, and how it shapes galaxies and galaxy clusters and their evolution through cosmic time.

The goal of this program is to identify strongly lensed sources, and measure distortions of background sources due to weak lensing by these two massive, intermediate redshift merging clusters. The resolution of HST is critical to this program for two reasons: (1) the search for and identification of multiply imaged sources; and (2) shape measurements of background galaxies. The exquisite resolution will allow the morphological and color classification of multiple images, as well providing a high number-density of sources that can be used for weak lensing. Together, these will enable us to derive a high-fidelity strong+weak lensing mass map accurate on the small scales (angular separations ~45arcsec needed to unambiguously separate the contribution from baryons (derived from X-ray mass maps) and dark matter. Required Area: This program requires one pointing per cluster. Due to the WF4 CCD anomaly, we prefer to use WF2 and WF3 for the purpose of weak lensing, therefore we request observations at a specific roll-angle (see special requirements). We still plan to use information from WF4 to study mass distribution on larger scale, we do not, however rely on those observations. Required Filters: The main purpose of this program is to identify the strongly lensed sources, which requires color information. This will not only help us to identify the multiple images, but will also aid in determining photometric redshift estimates for the sources. To this end, we plan to perform careful point spread function (PSF) matched photometry using both ground- and space-based data. The color information is also needed for the weak lensing data, both for efficient subtraction of the cluster members from the catalogs, as well as for the estimate of the redshift distribution of the background population; knowledge of at least the average redshift for the ensemble of weak lensing sources is needed for the absolute calibration of the cluster mass reconstruction. To obtain this calibration we plan to match colors these sources to auxiliary data like the HDF-S photometric redshift catalog of Fontana et al 99. The main filter requirements are therefore broad wavelength coverage and high depth, achieved in relatively short exposure time. We therefore request observations in the following filters. - For MACSJ2243.3-0935 we request complementary observations in WFPC2/F450W, WFPC2/F606W, and WFPC2/F814W. - For MACSJ0025.4-1222 we request WFPC2/F450W data to allow the unambiguous determination of strong lensing systems. Dither Pattern: For all observations we will use 2 exposures per orbit. We are using standard WFPC2 dither pattern (17) to cover the chip gap and remove artifacts. Each time 4 point dither is completed we shift the pattern by (2+1/4pix,2+1/4pix) first and (4+1/4pix,0pix) next and repeat the pattern. COSMOLOGY 12 false 0.0 false false false false false false SUPPORTED CLUSTER OF GALAXIES GRAVITATIONAL LENS RICH CLUSTER J2000 00 25 30.1900 -12 22 44.49 J2000 CLUSTER OF GALAXIES GRAVITATIONAL LENS RICH CLUSTER J2000 00 25 30.1900 -12 22 44.49 J2000 CLUSTER OF GALAXIES GRAVITATIONAL LENS RICH CLUSTER J2000 22 43 20.4000 -09 35 25.57 J2000 CALIBRATION POINT SPREAD FUNCTION This object was generated by the targetselector and retrieved from the NED database. J2000 21 33 27.0000 -00 49 24.00 J2000 WFPC2 Imaging No F450W WFPC2 Imaging No F450W WFPC2 Imaging No F555W WFPC2 Imaging No F702W WFPC2 Imaging No F450W WFPC2 Imaging No F555W WFPC2 Imaging No F702W POS-TARG DITHER 2.349 Big diamond, pattern 17 LINE 2.349 false false 154.009995 4 32.009998 BOX 1 false POS-TARG DITHER 2.349 Half of big diamond LINE false false 2 32.009998 LINE 2 false (Tic-Visit :proposal-id 11100 :visit-id "01" :proposal-version -1 :trans-version "20070325" :date "29-Jun-2007 12:03:02.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 5 :saa-model "26" :si-bright-earth-limb-angle 20.0 :data-volume 448160 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 11100 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 11100 :visit-id "01" :orbit-number 1 :pcs-time 355 :si-vis-utilization 2723 :al-overhead-at-end 157 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3137 :pcs-gap 0 ) (Tic-Orbit :proposal-id 11100 :visit-id "01" :orbit-number 2 :pcs-time 355 :si-vis-utilization 2722 :al-overhead-at-end 158 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3137 :pcs-gap 0 ) (Tic-Orbit :proposal-id 11100 :visit-id "01" :orbit-number 3 :pcs-time 355 :si-vis-utilization 2723 :al-overhead-at-end 157 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3137 :pcs-gap 0 ) (Tic-Orbit :proposal-id 11100 :visit-id "01" :orbit-number 4 :pcs-time 355 :si-vis-utilization 2723 :al-overhead-at-end 157 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3137 :pcs-gap 0 ) (Tic-Orbit :proposal-id 11100 :visit-id "01" :orbit-number 5 :pcs-time 355 :si-vis-utilization 2700 :al-overhead-at-end 180 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3137 :pcs-gap 0 ) false 5 0 (Tic-Visit :proposal-id 11100 :visit-id "01" :proposal-version -1 :trans-version "20070325" :date "29-Jun-2007 12:03:02.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 5 :saa-model "26" :si-bright-earth-limb-angle 20.0 :data-volume 448160 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 11100 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 11100 :visit-id "01" :orbit-number 1 :pcs-time 355 :si-vis-utilization 2723 :al-overhead-at-end 157 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3137 :pcs-gap 0 ) (Tic-Orbit :proposal-id 11100 :visit-id "01" :orbit-number 2 :pcs-time 355 :si-vis-utilization 2722 :al-overhead-at-end 158 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3137 :pcs-gap 0 ) (Tic-Orbit :proposal-id 11100 :visit-id "01" :orbit-number 3 :pcs-time 355 :si-vis-utilization 2723 :al-overhead-at-end 157 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3137 :pcs-gap 0 ) (Tic-Orbit :proposal-id 11100 :visit-id "01" :orbit-number 4 :pcs-time 355 :si-vis-utilization 2723 :al-overhead-at-end 157 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3137 :pcs-gap 0 ) (Tic-Orbit :proposal-id 11100 :visit-id "01" :orbit-number 5 :pcs-time 355 :si-vis-utilization 2700 :al-overhead-at-end 180 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3137 :pcs-gap 0 ) false 5 0 (Tic-Visit :proposal-id 11100 :visit-id "02" :proposal-version -1 :trans-version "20070325" :date "01-Aug-2007 16:17:42.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 5 :saa-model "26" :si-bright-earth-limb-angle 20.0 :data-volume 448160 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 11100 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 11100 :visit-id "02" :orbit-number 1 :pcs-time 355 :si-vis-utilization 2723 :al-overhead-at-end 157 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3132 :pcs-gap 0 ) (Tic-Orbit :proposal-id 11100 :visit-id "02" :orbit-number 2 :pcs-time 355 :si-vis-utilization 2722 :al-overhead-at-end 158 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3132 :pcs-gap 0 ) (Tic-Orbit :proposal-id 11100 :visit-id "02" :orbit-number 3 :pcs-time 355 :si-vis-utilization 2723 :al-overhead-at-end 157 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3132 :pcs-gap 0 ) (Tic-Orbit :proposal-id 11100 :visit-id "02" :orbit-number 4 :pcs-time 355 :si-vis-utilization 2723 :al-overhead-at-end 157 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3132 :pcs-gap 0 ) (Tic-Orbit :proposal-id 11100 :visit-id "02" :orbit-number 5 :pcs-time 355 :si-vis-utilization 2700 :al-overhead-at-end 180 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3132 :pcs-gap 0 ) false 5 0 (Tic-Visit :proposal-id 11100 :visit-id "03" :proposal-version -1 :trans-version "20070325" :date "01-Aug-2007 16:18:02.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 6 :saa-model "26" :si-bright-earth-limb-angle 20.0 :data-volume 537792 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 11100 :visit-id "03" :obset-id "03" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 11100 :visit-id "03" :orbit-number 1 :pcs-time 355 :si-vis-utilization 2723 :al-overhead-at-end 157 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3132 :pcs-gap 0 ) (Tic-Orbit :proposal-id 11100 :visit-id "03" :orbit-number 2 :pcs-time 355 :si-vis-utilization 2722 :al-overhead-at-end 158 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3132 :pcs-gap 0 ) (Tic-Orbit :proposal-id 11100 :visit-id "03" :orbit-number 3 :pcs-time 355 :si-vis-utilization 2723 :al-overhead-at-end 157 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3132 :pcs-gap 0 ) (Tic-Orbit :proposal-id 11100 :visit-id "03" :orbit-number 4 :pcs-time 355 :si-vis-utilization 2723 :al-overhead-at-end 157 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3132 :pcs-gap 0 ) (Tic-Orbit :proposal-id 11100 :visit-id "03" :orbit-number 5 :pcs-time 355 :si-vis-utilization 2723 :al-overhead-at-end 157 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3132 :pcs-gap 0 ) (Tic-Orbit :proposal-id 11100 :visit-id "03" :orbit-number 6 :pcs-time 355 :si-vis-utilization 2700 :al-overhead-at-end 180 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3132 :pcs-gap 0 ) false 6 0 (Tic-Visit :proposal-id 11100 :visit-id "04" :proposal-version -1 :trans-version "20070325" :date "29-Jun-2007 11:56:15.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 6 :saa-model "26" :si-bright-earth-limb-angle 20.0 :data-volume 537792 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 11100 :visit-id "04" :obset-id "04" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 11100 :visit-id "04" :orbit-number 1 :pcs-time 355 :si-vis-utilization 2723 :al-overhead-at-end 157 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3132 :pcs-gap 0 ) (Tic-Orbit :proposal-id 11100 :visit-id "04" :orbit-number 2 :pcs-time 355 :si-vis-utilization 2722 :al-overhead-at-end 158 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3132 :pcs-gap 0 ) (Tic-Orbit :proposal-id 11100 :visit-id "04" :orbit-number 3 :pcs-time 355 :si-vis-utilization 2723 :al-overhead-at-end 157 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3132 :pcs-gap 0 ) (Tic-Orbit :proposal-id 11100 :visit-id "04" :orbit-number 4 :pcs-time 355 :si-vis-utilization 2723 :al-overhead-at-end 157 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3132 :pcs-gap 0 ) (Tic-Orbit :proposal-id 11100 :visit-id "04" :orbit-number 5 :pcs-time 355 :si-vis-utilization 2723 :al-overhead-at-end 157 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3132 :pcs-gap 0 ) (Tic-Orbit :proposal-id 11100 :visit-id "04" :orbit-number 6 :pcs-time 355 :si-vis-utilization 2700 :al-overhead-at-end 180 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3132 :pcs-gap 0 ) false 6 0 (Tic-Visit :proposal-id 11100 :visit-id "05" :proposal-version -1 :trans-version "20070325" :date "29-Jun-2007 11:56:19.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "26" :si-bright-earth-limb-angle 20.0 :data-volume 537792 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 11100 :visit-id "05" :obset-id "05" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 11100 :visit-id "05" :orbit-number 1 :pcs-time 355 :si-vis-utilization 2760 :al-overhead-at-end 120 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3132 :pcs-gap 0 ) false 1 0