One minor comment on APT, which is that I found on my laptop (os x 10.6.8) that if I changed the roll angle of visit 4 relative to visit 1, then I had to save, close, and reload before the proper roll angle would become visible in Aladin. Thanks to Linda Dressel for her excellent assistance with a wfc3/ir mosaicing question. ----- Attempting Submission 1 (Fri Jul 13 19:11:43 GMT 2012) ----- We propose ACS/WFC and WFC3/IR imaging of IDCS J1426.5+3508, which at z=1.75 is the most massive cluster yet discovered at z>1.4, and the first cluster at this epoch for which the Sunyaev-Zel'dovich effect has been observed. Our previous work also revealed a giant arc associated with this cluster, making it the most distant known strong lensing cluster. The existence of this arc revives the longstanding arc statistics problem -- theoretical calculations predict that no such arc should exist across the entire sky. The aim of this program is to constrain the total mass and concentration of the dark matter halo to understand the origin of this discrepacy. A weak lensing determination of the total mass will also provide the first direct calibration of the SZ-lensing mass relation at this epoch. This calibration is of central relevance to programs aiming to use cluster counts out to this redshift to constrain dark energy, such as eROSITA and ground-based SZ searches. Moreover, our observations are designed to also enable detection of multiply imaged sources to enable joint strong+weak lensing analysis to better constrain the mass model. This cluster is extreme in mass for the redshift, anomalous as a strong lensing system, and unique among all clusters currently known. We are requesting deep imaging for IDCS J1426.5+3508 to obtain a weak lensing mass, identify multiply-imaged, strongly lensed background galaxies, and better constrain the redshift for the recently discovered giant arc associated with this cluster. The spatial resolution, sensitivity, and stability of HST are essential for this program. The shear measurements required for this program and background source density needed for weak lensing are only achievable with HST. Technical Drivers: The weak lensing is the primary driver for our technical requirements. The goal of the weak lensing analysis is to obtain a total weak lensing mass with S/N>5 (i.e. 20% precision), which will enable a first validation of SZ-based mass estimates at this epoch and help discern the reason theoretical expectations for arc statistics are incorrect. If the resolution is associated with a higher than expected cluster mass, then the S/N will exceed this nominal threshold. The critical ingredients for the lensing analysis are (1) sufficient field-of-view that the lensing map extends out to at least r200, (2) sufficient density of background galaxies from which to reconstruct the shear field, and (3) multiband photometry to reject cluster members and foreground galaxies, which otherwise reduce the S/N. Area: The first of these requirements is satisfied by the ACS field-of-view without mosaicing. For the cluster redshift and nominal SZ mass estimate, the radius of the cluster is r200=830 kpc, or 106''. The cluster diameter is thus almost identically matched to the 202'' width of ACS. For WFC3/IR photometry (see below), we do however require a 2x2 mosaic to match this area. Depth and Filters: The requisite background density is dependent upon the desired S/N for the weak lensing mass. Previous ACS studies of galaxy clusters at z=1-1.5 have demonstrated that S/N>5 can be achieved for clusters of similar mass given a raw background galaxy density of ~80-100 per sq. arcmin, even in the presence of ~50% foreground contamination (Jee et al. 2009, 2011). We will use the F606W filter for shape measurements because it provides the most efficient means of reaching the requisite source density. This data will also constrain whether the known arc lies below or above z~4 based upon whether it is a Lyman dropout in F606W -- a key input for modeling the strong lensing (Fig. 3). To guide our expectations for background source counts, we use the Hubble Ultra Deep Field counts and photometric redshifts from Coe et al. (2006). For a cluster at z=1.75, a background source density of 100 per sq. arcmin corresponds to a limiting magnitude F606W=28 (AB). In addition to the main filter for shape measurements, we also require data in two additional filters to enable color selection of background galaxies. We employ a simple color cut, requiring F606W-F814W<0.5 for candidate background sources. This cut eliminates the majority of low-redshift foreground members, and tests with the HUDF indicate that the residual contamination from foreground galaxies is ~40%, an acceptable level for this analysis (Jee et al. 2009, 2011). Meanwhile, the F160W filter provides a band redward of the 4000 Angstrom break, enabling clean rejection of cluster members on the red sequence. For a Bruzual & Charlot (2003) model a passively evolving galaxy with formation redshift z_f=6 has F814-F160~3. The nominal depths, in AB magnitudes, for this program are F606W=28 (10 sigma), F814W=28 (5 sigma), and F160W=25.8 (5 sigma) for a 0.25'' radius aperture. In the F606W we require 10 sigma sensitivity at the depth corresponding to the target source density to enable robust shape measurements of the background galaxies. For F814W we require only 5 sigma detection for foreground rejection and coarse redshift estimation of lensed sources. Based upon both the HST exposure time calculators and our past observing programs, we calculate that the required exposure times to achieve these depths are 20ks in F606W and 12ks in F814W. For F160W, the quoted depth corresponds to 1.2ks (0.5 orbits), which is sufficiently deep for identification of galaxies that lie on the red sequence down to the F606W limit. Previous observations of the cluster include 5ks of data in F814W, which will be re-used and augmented in the current program. A sufficiently deep F160W exposure also exists for the cluster core, but does not cover the full ACS field-of-view. We therefore request a 2x2 mosaic to map this region. Using the visibility estimators in the HST Primer for Cycle 20, the require depths in F606W and F814W can be achieved with 8 orbits and 3 orbit, respectively (augmented by the previous F814W data). In F160W we require two total orbits, split equally between four mosaic pointings. In addition to providing clean rejection of cluster members out to r200, these observations will be coupled with the existing central F160W pointing to push 0.85 mag fainter in the cluster core, which is useful for extracting faint red, strongly-lensed sources as well as probing the faint end of the cluster luminosity function. We also note that all calculations assume average earthshine; LOWSKY is not requested because it only minimally improves the efficiency. My main concern is making sure that the WFC3/IR mosaic matches the ACS field-of-view, including having the proper orientation constraint. Double-checking that this is correctly entered is greatly appreciated. Related to the above note, the target coordinate is set to lie halfway between the BCG and gravitational arc, which are separated by 14". The coordinates of these two objects are (14:26:32.55,+35:08:23.6) and (12:26:32.76, +35:08:37.8). The requested orientation constraint below is designed to avoid the BCG lying in the chip gap for the ACS observations and the arc lying very close to the edge of the wfc3/ir coverage during two of the dither positions, so that we will have full exposure on both. If this orientation request significantly impacts schedulability though, it can be removed/relaxed. In this case please let me know though, as I may wish to shift the central coordinate a bit. COSMOLOGY 12 false 0.0 0.0 false false false false SUPPORTED CLUSTER OF GALAXIES GRAVITATIONAL LENS HIGH REDSHIFT CLUSTER J2000 J2000 ACS/WFC Imaging No No F606W ACS/WFC Imaging No No F814W WFC3/IR Imaging No No F160W POS-TARG DITHER DITHER 4 3.011 ACS-WFC-DITHER-BOX false 69.05 true 0.187 0.265 2 85.28 POS-TARG ACS-WFC-DITHER-LINE 20.67 1 true POS-TARG DITHER DITHER 3 3.011 LINE false true 0.17 2 85.28 POS-TARG ACS-WFC-DITHER-LINE 47.23 2 true POS-TARG DITHER 0.572 LINE 0.365 false false 74.653 4 18.528 WFC3-IR-DITHER-BOX-MIN 4 false 1341843674049 /Users/anthony/OP-cache/HST_HIGHZLENSINGCLUSTER-v01.xml Same orient constraint links visits (01 02 03) The scheduling data was generated by CASM 20.2. CASM was run in Phase II mode. The target coordinate is set to lie halfway between the BCG and gravitational arc, which are separated by 14". The coordinates of these two objects are (14:26:32.55,+35:08:23.6) and (12:26:32.76, +35:08:37.8). The requested orientation constraint below is designed to avoid the BCG lying in the chip gap for the ACS observations and the arc lying very close to the edge of the wfc3/ir coverage during two of the dither positions, so that we will have full exposure on both. If this orientation request significantly impacts schedulability though, it can be removed/relaxed. In this case please let me know though, as I may wish to shift the central coordinate a bit. (Tic-Visit :proposal-id 12994 :visit-id "01" :proposal-version -1 :trans-version "20120604" :date "09-Jul-2012 10:21:13.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 4 :saa-model "27" :si-bright-earth-limb-angle 20.0 :data-volume 2273792 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12994 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12994 :visit-id "01" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2954 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3287 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12994 :visit-id "01" :orbit-number 2 :pcs-time 222 :si-vis-utilization 3064 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3287 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12994 :visit-id "01" :orbit-number 3 :pcs-time 222 :si-vis-utilization 3064 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3287 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12994 :visit-id "01" :orbit-number 4 :pcs-time 222 :si-vis-utilization 3064 :al-overhead-at-end 0 :internal-dur-at-end 347 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3287 :pcs-gap 0 ) true 4 0 1341843676811 /Users/anthony/OP-cache/HST_HIGHZLENSINGCLUSTER-v02.xml Same orient constraint links visits (01 02 03) The scheduling data was generated by CASM 20.2. CASM was run in Phase II mode. Orientation needs to be the same as for visits 1 and 3. (Tic-Visit :proposal-id 12994 :visit-id "02" :proposal-version -1 :trans-version "20120604" :date "09-Jul-2012 10:21:16.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 4 :saa-model "27" :si-bright-earth-limb-angle 20.0 :data-volume 2273792 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12994 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12994 :visit-id "02" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2954 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3287 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12994 :visit-id "02" :orbit-number 2 :pcs-time 222 :si-vis-utilization 3064 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3287 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12994 :visit-id "02" :orbit-number 3 :pcs-time 222 :si-vis-utilization 3064 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3287 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12994 :visit-id "02" :orbit-number 4 :pcs-time 222 :si-vis-utilization 3064 :al-overhead-at-end 0 :internal-dur-at-end 347 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3287 :pcs-gap 0 ) true 4 0 1341843679226 /Users/anthony/OP-cache/HST_HIGHZLENSINGCLUSTER-v03.xml Same orient constraint links visits (01 02 03) The scheduling data was generated by CASM 20.2. CASM was run in Phase II mode. Orientation needs to be the same as visits 1 and 2. (Tic-Visit :proposal-id 12994 :visit-id "03" :proposal-version -1 :trans-version "20120604" :date "09-Jul-2012 10:21:18.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 3 :saa-model "27" :si-bright-earth-limb-angle 20.0 :data-volume 1705344 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12994 :visit-id "03" :obset-id "03" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12994 :visit-id "03" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2954 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3287 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12994 :visit-id "03" :orbit-number 2 :pcs-time 222 :si-vis-utilization 3064 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3287 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12994 :visit-id "03" :orbit-number 3 :pcs-time 222 :si-vis-utilization 3064 :al-overhead-at-end 0 :internal-dur-at-end 347 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3287 :pcs-gap 0 ) true 3 0 /Users/anthony/OP-cache/HST_HIGHZLENSINGCLUSTER-v04.xml 1341843684738 The scheduling data was generated by CASM 20.2. CASM was run in Phase II mode. Orientation needs to be 135 degrees from visit 1. If visibility is an issue, please let me know and I will tweak the program design for slightly different roll angles. (Tic-Visit :proposal-id 12994 :visit-id "04" :proposal-version -1 :trans-version "20120604" :date "09-Jul-2012 10:21:23.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "30" :si-bright-earth-limb-angle 20.0 :data-volume 3969264 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12994 :visit-id "04" :obset-id "04" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12994 :visit-id "04" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2938 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3287 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12994 :visit-id "04" :orbit-number 2 :pcs-time 222 :si-vis-utilization 3038 :al-overhead-at-end 0 :internal-dur-at-end 633 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3287 :pcs-gap 0 ) true 2 0