18243( 2) - 22-Apr-2026 18:11:51 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 18243 Version: 2 Check-in Time: 22-Apr-2026 18:11:51 STScI Edit Number: 0 Title Spatially Resolving A HMXB Stellar Population at Cosmic Noon With Strong Lensing ------------------------------------------------------------------------------------ Type Cycle GO 33 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Matthew Bayliss University of Cincinnati Main Campus Y CoI: Dr. Joshua Aaron Roberson University of Cincinnati Main Campus N CoI: Dr. Taylor Alexandra Hutchison NASA Goddard Space Flight Center N CoI: Prof. Keren Sharon University of Michigan N CoI: Dr. Jane R. Rigby NASA Goddard Space Flight Center N CoI: Prof. Michael A. McDonald Massachusetts Institute of Technology N CoI: M. Riley Owens University of California - Berkeley N CoI: Dr. Gourav Khullar University of Washington N CoI: Dr. Michael Florian Eureka Scientific Inc. N CoI: Dr. Haakon Dahle University of Oslo N CoI: Prof. Michael D. Gladders University of Chicago N CoI: Dr. Keunho J. Kim California Institute of Technology N CoI: Dr. Guillaume Mahler Universite de Liege N CoI: Dr. Catherine Cerny University of Michigan N CoI: Erik Solhaug University of Chicago N CoI: Ms. Aleena Ebey University of Cincinnati Main Campus N CoI: Cole Panzer University of Cincinnati Main Campus N ------------------------------------------------------------------------------------ Abstract High Mass X-ray Binaries (HMXBs) trace some of the youngest, most extreme, stellar populations. They produce large amounts of high energy emission and feedback in galaxies that are dominated by young stellar populations, a stage that describes all galaxies at some point in their evolutionary history. Furthermore, these extreme but short-lived X-ray sources can clear out the interstellar medium (mechanically), and ionize gas - both important processes for driving cosmic re-ionization. However, HMXBs and their associated stellar populations are not well-understood, especially in the distant universe. Characterizing these sources and the stellar populations that host them is crucial for a wide range of problems in observational astrophysics, from high-mass stars to galaxy evolution to re-ionization. We propose a unique study of the only highly magnified X-ray emitting dwarf starburst galaxy known. Hubble imaging and ground based spectroscopy reveal that the lensed dwarf (logM/MSun<8) galaxy hosts an X-ray bright HMXB population. The strong lensing magnification enables a zoomed-in, spatially resolved study of the HMXB-hosting region within the lensed galaxy. These data will measure the isolated emission from the HMXB population, undiluted by other regions of the galaxy, enabling a study that connects star-formation, nebular gas in the ISM, stellar populations, and HMXBs on the star cluster scale during the epoch of peak star-formation in the Universe. Joint HST UV imaging and archival MIRI imaging will multiply the science value of the JWST observations, constraining the gas and stellar populations. This HST program was awarded jointly with JWST program JWST-GO-10329. ------------------------------------------------------------------------------------ 18243( 2) - 22-Apr-2026 18:11:51 - [ 2] Observations Description ------------------------ This is a program awarded jointly with a cycle 5 JWST program that is targeting a highly magnified, strongly lensed dwarf galaxy with confirmed low-luminosity X-ray emission, believed to originate from a high mass X-ray binary population in the lensed galaxy. The goal of the observations is to measure the spatially resolved properties of the stellar populations and nebular gas across the lensed galaxy, and in particular to zero in on the properties of the region of the galaxy that produces the X-ray emission. The JWST data will deliver rest-frame optical through-NIR imaging and spectroscopy of the lensed galaxy, which will be combined with HST imaging spanning the rest-frame UV. Three archival HST imaging bands for this field cover ~4800-8000 angstroms, immediately blueward of the JWST data. This HST program will obtain new imaging in two blue WFC3/UVIS filters (F336W and F390W) that provide complementary coverage of the lensed galaxy's spectral energy distribution extending to the far rest-frame UV, where the hottest, most massive stars dominate the continuum emission. ------------------------------------------------------------------------------------ 18243( 2) - 22-Apr-2026 18:11:51 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 PHOENIX-XRAY GALAXY, STARBURST RA=23H44M46.4507S, J2000 V = 24.0 +/- 0.05 -ARC DEC=-42D43'5.43" Reference Frame: ICRS ------------------------------------------------------------------------------------------------------------------------------------ 18243( 2) - 22-Apr-2026 18:11:51 - [ 4] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type WFC3-UVIS-GAP-LINE WFC3-UVIS-DITHER-LINE-3PT Pattern_Purpose MOSAIC DITHER Number_Of_Points 2 3 Point_Spacing 2.414 0.135 Line_Spacing Coordinate_Frame POS-TARG POS-TARG Pattern_Orient 85.759 46.84 Angle_Between_Sides Center_Pattern YES NO ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 2 Primary_Pattern Secondary_Pattern Pattern_Type WFC3-UVIS-GAP-LINE WFC3-UVIS-DITHER-LINE Pattern_Purpose MOSAIC DITHER Number_Of_Points 2 2 Point_Spacing 2.414 0.145 Line_Spacing Coordinate_Frame POS-TARG POS-TARG Pattern_Orient 85.759 46.84 Angle_Between_Sides Center_Pattern YES NO ------------------------------------------------------------------------------------------------------------------------------------ 18243( 2) - 22-Apr-2026 18:11:51 - [ 5] Visit: 01 (F336W imaging) 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 PHOENIX-XRA WFC3/UVI ACCUM UVIS2-C1K F336W FLASH=15 1 1100 S PATTERN 1 1 Y-ARC S 1C-CTE see below (7388 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 | ------------------------------------------------------------------------------------------------------------------------------------ PHOENIX-XRAY-ARC 1 WFC3/UVI ACCUM UVIS2-C1 F336W 1 1 none none 1 1238.0 S S K1C-CTE PHOENIX-XRAY-ARC 1 WFC3/UVI ACCUM UVIS2-C1 F336W 1 2 none none 1 1238.0 S S K1C-CTE PHOENIX-XRAY-ARC 1 WFC3/UVI ACCUM UVIS2-C1 F336W 1 3 none none 2 1228.0 S S K1C-CTE PHOENIX-XRAY-ARC 1 WFC3/UVI ACCUM UVIS2-C1 F336W 2 1 none none 2 1228.0 S S K1C-CTE PHOENIX-XRAY-ARC 1 WFC3/UVI ACCUM UVIS2-C1 F336W 2 2 none none 3 1228.0 S S K1C-CTE PHOENIX-XRAY-ARC 1 WFC3/UVI ACCUM UVIS2-C1 F336W 2 3 none none 3 1228.0 S S K1C-CTE 18243( 2) - 22-Apr-2026 18:11:51 - [ 6] Visit: 02 (F390W imaging) 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 PHOENIX-XRA WFC3/UVI ACCUM UVIS2-C1K F390W FLASH=12 1 1200 S PATTERN 2 1 Y-ARC S 1C-CTE see below (4932 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 | ------------------------------------------------------------------------------------------------------------------------------------ PHOENIX-XRAY-ARC 1 WFC3/UVI ACCUM UVIS2-C1 F390W 1 1 none none 1 1239.0 S S K1C-CTE PHOENIX-XRAY-ARC 1 WFC3/UVI ACCUM UVIS2-C1 F390W 1 2 none none 1 1239.0 S S K1C-CTE PHOENIX-XRAY-ARC 1 WFC3/UVI ACCUM UVIS2-C1 F390W 2 1 none none 2 1227.0 S S K1C-CTE PHOENIX-XRAY-ARC 1 WFC3/UVI ACCUM UVIS2-C1 F390W 2 2 none none 2 1227.0 S S K1C-CTE 18243( 2) - 22-Apr-2026 18:11:51 - [ 7] Summary Form for Proposal 18243 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures UVIS2-C1K1C-CTE ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFC3/UVIS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters FLASH=12, FLASH=15 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PATTERN 1 1, PATTERN 2 1 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F336W, F390W ------------------------------------------------------------------------------------------------------------------------------------ Target Names PHOENIX-XRAY-ARC ------------------------------------------------------------------------------------------------------------------------------------