17508( 2) - 13-Sep-2023 14:07:51 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 17508 Version: 2 Check-in Time: 13-Sep-2023 14:07:51 STScI Edit Number: 0 Title HST imaging of a newly discovered many-ringed galaxy ------------------------------------------------------------------------------------ Type Cycle GO 31 ------------------------------------------------------------------------------------ Investigators Contact? PI: Imad Pasha Yale University Y CoI: Prof. Pieter van Dokkum Yale University Y CoI: Mr. Tim Blake Miller Yale University N ------------------------------------------------------------------------------------ Abstract 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. ------------------------------------------------------------------------------------ Observations Description ------------------------ 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. ------------------------------------------------------------------------------------ 17508( 2) - 13-Sep-2023 14:07:51 - [ 2] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 LEDA1313424 GALAXY, DISK, RA=00H09M39.3466S +/- 0.25", J2000 Z = V = 15.3 +/- 1 DECAM_g 625.54 INTERACTING GALAXY, DEC=+07D04'49.26" +/- 0.25" 0.03941 nanomaggy, DECAM_r 1550.5 nanomaggy, RING, STAR FORMING DECAM_z 3135.7 nanomaggy REGION Reference Frame: Other: SIMBAD Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 2000 0.0 0.0 0.0 ------------------------------------------------------------------------------------------------------------------------------------ 17508( 2) - 13-Sep-2023 14:07:51 - [ 3] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type LINE LINE Pattern_Purpose DITHER DITHER Number_Of_Points 2 2 Point_Spacing 30 5 Line_Spacing Coordinate_Frame POS-TARG POS-TARG Pattern_Orient 90 45 Angle_Between_Sides Center_Pattern NO NO ------------------------------------------------------------------------------------------------------------------------------------ 17508( 2) - 13-Sep-2023 14:07:51 - [ 4] Visit: 01 Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 LEDA1313424 ACS/WFC ACCUM WFC F475W 1 600 S POS TARG -5, -27; see below PATTERN 1 1 (2025 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 LEDA1313424 ACS/WFC ACCUM WFC F814W 1 600 S POS TARG -5, -27; see below PATTERN 1 2 (2061 S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ LEDA1313424 1 ACS/WFC ACCUM WFC F475W 1 1 none none 1 506.0 S LEDA1313424 1 ACS/WFC ACCUM WFC F475W 1 2 none none 1 506.0 S LEDA1313424 1 ACS/WFC ACCUM WFC F475W 2 1 none none 1 506.0 S LEDA1313424 1 ACS/WFC ACCUM WFC F475W 2 2 none none 1 507.0 S LEDA1313424 2 ACS/WFC ACCUM WFC F814W 1 1 none none 2 506.0 S LEDA1313424 2 ACS/WFC ACCUM WFC F814W 1 2 none none 2 506.0 S LEDA1313424 2 ACS/WFC ACCUM WFC F814W 2 1 none none 2 506.0 S LEDA1313424 2 ACS/WFC ACCUM WFC F814W 2 2 none none 2 543.0 S 17508( 2) - 13-Sep-2023 14:07:51 - [ 5] Summary Form for Proposal 17508 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures WFC ------------------------------------------------------------------------------------------------------------------------------------ Configurations ACS/WFC ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PATTERN 1 1, PATTERN 1 2, POS TARG -5, -27 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F475W, F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names LEDA1313424 ------------------------------------------------------------------------------------------------------------------------------------