0 Assigned ID: 4560 ----- Attempting Submission 1 (Wed May 24 19:56:04 GMT 2023) ----- HST Phase I Proposal 4560 successfully submitted. Receipt: # 4560-1 ----- Attempting Submission 2 (Wed May 24 21:59:21 GMT 2023) ----- HST Phase I Proposal 4560 successfully submitted. Receipt: # 4560-2 ----- Attempting Submission 3 (Wed May 24 22:30:12 GMT 2023) ----- HST Phase I Proposal 4560 successfully submitted. Receipt: # 4560-3 ----- Attempting Submission 4 (Wed May 24 23:56:39 GMT 2023) ----- The pattern+subpattern combination was used to create a modified dither box for which both x and y pointings were slightly dithered --- the larger move to move the target across the chip gap, and the smaller moves to ensure that while dithering the perpendicular direction, there is also a y-offset to ensure the chip gap is sampled in at least three frames. If there are any issues with this pattern please let me know. 1700711469 ----- Attempting Submission 1 (Wed Sep 13 14:02:10 GMT 2023) ----- We have identified a relatively nearby (z~0.039) collisional ring galaxy (CRG), formed by an impulsive impactor with a massive perturber, likely in a head-on collision. This object, dubbed the "Bullseye," is a special case among CRGs: it has not one or two, but as many as seven candidate rings, three of which are confirmed; the existence of so many predominantly symmetric rings indicates we have caught this galaxy in a short (~few hundred Myr) window during its post-impact evolution. Several of the ring candidates both in the interior and at large radii require HST resolution to confirm. Beyond being the best laboratory thus far discovered to test collisional theory, the system also appears to have a low surface brightness component in the outskirts with candidates for star-forming clumps at large radii (R~60-75 kpc). Simulations have suggested that the expansion and fading of collisional rings might produce Giant Low Surface Brightness Galaxies (e.g., Malin I), but this theory has lacked the key transition object displaying strong evidence of both a collision and a low surface brightness disk. Here we propose to obtain F475W and F814W imaging of the system, leveraging the resolution of HST to definitively characterize the small (<0.5'') substructures in the galaxy, confirm whether the emission in the outskirts is a faded ring, and investigate candidates for the impactor whose collision produced the ring structure in the system. If confirmed as a transition object, this system would open the door to new investigations of an almost entirely unexplored galactic evolutionary pathway in forthcoming deep all-sky surveys. The target should be observed for 1 full orbit in F475W and 1 full orbit in F814W. We request four exposures to be obtained in each band in order to appropriately dither over the chip gap (as the galaxy nearly fills the ACS footprint, and the center needs to be well sampled), along with adequate cosmic ray and hot pixel removal. We request a standard dither pattern maintaining proper sampling and enabling redundancy in the chip gap. The galaxy will be centered near the middle of the two chips. There are no roll angle constraints. Co-PI van Dokkum is an expert in the reduction and analysis of HST data, and has led several large HST programs including 3D-HST (e.g., van Dokkum et al. 2013). Co-PI Pasha and Co-I Miller have experience analyzing HST data products (see, e.g., Pasha et al. 2021, van Dokkum et al. 2023, Miller et al. 2023). All investigators have been involved with the use of HST imaging and spectroscopy for studying galaxy formation, structure, and evolution. Galaxies Intergalactic Medium and the Circumgalactic Medium 6 false false false false false false false false SUPPORTED GALAXY DISK INTERACTING GALAXY RING STAR FORMING REGION J2000 DECAM_g 625.54 nanomaggy, DECAM_r 1550.5 nanomaggy, DECAM_z 3135.7 nanomaggy ACS/WFC Imaging No No F475W ACS/WFC Imaging No No F814W POS-TARG DITHER DITHER 2 30 LINE false false 5 2 90 POS-TARG LINE 45 1 true /Users/ipasha/Downloads/OP-cache/HST-17508-Phase-II-v01.xml 1694206927609 The scheduling data was generated by CASM 31.1. CASM was run in Phase II mode. 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