This investigator's institution has no country in the STScI database. 0 Assigned ID: 7462 ----- Attempting Submission 1 (Thu Apr 16 16:33:22 GMT 2026) ----- HST Phase I Proposal 7462 successfully submitted. Receipt: # 7462-1 ----- Attempting Submission 2 (Thu Apr 16 22:44:25 GMT 2026) ----- HST Phase I Proposal 7462 successfully submitted. Receipt: # 7462-2 Matt Hilton's database entry does not specify South Africa. He said that MyST is not picking it up correctly from ORCid. Reducing angles to improve dragon's and schedulability. Adding in POS TARG offsets to sharpen PSF and reduce chip gap overlap. 133861855 ----- Attempting Submission 1 (Tue Aug 18 13:22:59 GMT 2026) ----- HST Phase II Proposal 18366 successfully submitted. Receipt: # 18366-1 ----- Attempting Submission 2 (Fri Aug 28 03:56:47 GMT 2026) ----- An extraordinary dusty Einstein ring at z = 2.95 We propose a joint HST-JWST program to conduct a multi-wavelength analysis of ACT-S J0732.1+1709, an extraordinary 4"-radius, group-scale Einstein ring at z = 2.95. Discovered as one of the brightest high-redshift sub-mm galaxies, this "cosmic telescope" provides strong magnification (>10), allowing us to resolve the starbursting galaxy at the sub-100 pc scales typically inaccessible at cosmic noon. We will use HST/WFC3 to map unobscured rest-frame UV star formation and JWST/NIRCam to trace the mature stellar backbone in the rest-frame optical. This will reveal if the system is a coherent disk or a complex merger. High-resolution imaging is a prerequisite to identify multiply-imaged knots and the morphology of the lensing group. Combining these data with existing ALMA CO and dust continuum data, we will map star formation efficiency and gas-to-stellar mass ratios. We will also test the IRX-beta relationship at sub-kpc scales and locate intense dust obscuration. We request HST (F606W, F814W) and JWST (F150W, F444W) imaging. To mitigate a nearby bright interloper, we utilize specific dither patterns and roll angles to manage diffraction spikes and saturation. This program provides the essential high-resolution priors needed to resolve the baryon cycle in a system at z = 3. To model the source flux density, we have used a dusty CIGALE SED model (from [23] and consistent with Herschel dusty z ~ 3 galaxies) to translate the mm-wavelength flux density to the HST bands. For the total ring, in F606W we estimate an average flux density of 6.4 * 10^-7 Jy, and in F814 we estimate 2.0 * 10^-6 Jy. For the solid angle of the Einstein ring, we estimate a 4" radius and a 1" thickness, with a filling factor of f = 0.25, characteristic of a DSFG, for an effective solid angle of 6.3 arcsec^2 . Thus the typical surface brightnesses in the two HST bands are 1.0 * 10^-7 Jy arcsec^-2 and 3.2 * 10^-7 Jy arcsec^-2 . According to the WFC3 Exposure Time Calculator, under typical conditions and 50 minutes of visibility per orbit, in a typical 0.4"-radius region, six orbits with F606W will yield S/N of 11.3 and six orbits with F814W will yield S/N of 19.3. Since our SED is uncertain in the rest-frame UV, these S/N estimates give us some cushion if the brightness is lower than expected. On the other hand, if the galaxy is less dusty than our model, the rest frame UV emission will be less obscured and brighter. Here is the reasoning for the proposed observations. Nearby star--- The bright star nearby, V~16, will saturate F606W band in about ~18 s. Although exposures this short are possible, the readout overhead is severe, so we have to accept some bloom from the saturated star. A rough computation indicates that the radius of the nearby star bloom will match the radius where the diffraction spikes fall below the background, at 2"-3", at about 600s. I keep all exposures shorter than that. Roll angles--- The available roll angles are roughly 255-332 deg for this target. Unfortunately this directs the CCD columns and thus the bloom from the saturated star toward the Einstein ring. Diffraction spikes are +/- 45 deg from the bloom. We get 12 orbits, so we have chosen 12 visits, with orientation angles to cover the full range. This lets us rotate through almost but not quite 90 degrees, and will distribute the bloom and diffraction spikes differently in each visit of the telescope. Readout times--- The main decision is full frame images (the pair of the UVIS1/UVIS2 CCDs, each 2048x4096) versus sub array images. The onboard buffer can hold two full frame images. The buffer can be dumped while the telescope is exposing if nothing else is happening. Subarrays imaging has better charge transfer efficiency and long exposures have better charge transfer efficiency. Subarray images have shorter readout time, so short exposures with less saturation are more efficient. Short exposures need to be "flashed" which improves CTE at the cost of photon shot noise. The readout times are roughly: 512x512 (20"x20") subarray: 50 s 4096x4096 (160"x160") full frame: 115 s These sizes compare to the ~8"-10" diameter of the Einstein ring. Also, we don't know the redshift of the lens, but the photo-z is z=0.7 +/- 0.3. At 0.7, 10" is about 70-75 kpc, so the smallest subarray covers the Einstein ring, but not very far around the group core, so we need large frames to see the lensing group. Observing sequence per visit--- * 512x512 exposure at F606W repeated x 2 for 275 s each * 512x512 exposure at F814W repeated x 2 for 275 s each * Slight repointing * Full frame exposure at F606W for 567 s * Buffer dump #1 during that exposure * Full frame exposure at F814W for 567 s, readout during occultation * Buffer dump #2 also during Earth occultation Such a sequence gets us shorter exposures in the Einstein Ring for half the time, and the broader field half the time, which covers the lensing group. An alternative is to just do the longer full frame exposures repeatedly. This yields almost the same total time on target overall, but you sacrifice the shorter exposures in the Einstein ring area for 2x deeper coverage in the broader field. Outside the Einstein ring where we are just seeing the lensing group, so we should not need such deep coverage, and the adopted plan with the short exposures helps deal with saturation in the nearby star. The team combines expertise in millimeter survey analysis, sub-millimeter interferometry, galaxy evolution, and cluster physics to ensure the successful execution of this joint HST-JWST program. Kevin Huffenberger (PI, Texas A&M) will provide project leadership and oversight, and leads the follow-up of dusty sources identified in ACT DR6 maps. Cristian Vargas (Postdoc, TAMU) will lead the primary data reduction and source studies for the HST and JWST components. As a lead for ACT/Simons Observatory source studies, he is uniquely positioned to integrate this high-resolution imaging with existing survey data. Aaron Hughes (Graduate Student, TAMU) will perform the HST and JWST data processing, closely mentored by Huffenberger and Vargas to ensure consistency with his ongoing ALMA reductions. This work is a central component of his Ph.D. thesis. Andrew Baker (Co-I, Rutgers) brings extensive experience in dusty galaxies and interferometry; he oversaw the lensing reconstruction analysis in e.g. Rivera et al. (2019) and will provide guidance on the morphological analysis of lensed sources. John P. Hughes (Co-I, Rutgers) and Matt Hilton (Co-I, Witswatersrand) provide expertise in galaxy cluster physics and cluster-finding, ensuring the environmental context and lensing potential of the targets are accurately modeled. The team has the dedicated personnel and technical heritage required to move from raw data to published science within the standard proprietary period. Galaxies 6 false false false false false false false true PRIMARY 3 true SUPPORTED GALAXY EINSTEIN RING GRAVITATIONAL LENS HIGH REDSHIFT GALAXY YES Estimated surface brightness for F606W. Source should be quite red, and brighter in F814W. J2000 J2000 26.40 mag arcsec^-2 WFC3/UVIS Imaging No No F606W WFC3/UVIS Imaging No No F814W /tmp/OPVisit15714279920322995280.xml The scheduling data was generated by CASM 34.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 18366 :visit-id "01" :proposal-version -1 :trans-version "20260618" :date "27-Aug-2026 22:54:28.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 594976 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18366 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18366 :visit-id "01" :orbit-number 1 :pcs-time 301 :si-vis-utilization 2675 :al-overhead-at-end 121 :internal-dur-at-end 352 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2976 :pcs-gap 0 ) true 1 0 /tmp/OPVisit15927430702476838627.xml The scheduling data was generated by CASM 34.2. 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(Tic-Visit :proposal-id 18366 :visit-id "05" :proposal-version -1 :trans-version "20260618" :date "27-Aug-2026 22:54:29.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 594976 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18366 :visit-id "05" :obset-id "05" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18366 :visit-id "05" :orbit-number 1 :pcs-time 301 :si-vis-utilization 2675 :al-overhead-at-end 121 :internal-dur-at-end 352 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2976 :pcs-gap 0 ) true 1 0 /tmp/OPVisit10023136871366696323.xml The scheduling data was generated by CASM 34.2. CASM was run in Phase II mode. 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