0 Assigned ID: 6774 ----- Attempting Submission 1 (Thu Apr 10 22:19:44 GMT 2025) ----- The ORIENT range and target position for Visit 9 has been changed. (2/13/2026)) 1568236949 ----- Attempting Submission 1 (Thu Aug 14 19:12:47 GMT 2025) ----- HST Phase II Proposal 18086 successfully submitted. Receipt: # 18086-1 ----- Attempting Submission 4 (Fri Nov 14 15:05:15 GMT 2025) ----- HST Phase II Proposal 18086 successfully submitted. Receipt: # 18086-4 ----- Attempting Submission 6 (Tue Feb 10 23:11:47 GMT 2026) ----- HST Phase II Proposal 18086 successfully submitted. Receipt: # 18086-6 ----- Attempting Submission 7 (Fri Feb 13 19:51:31 GMT 2026) ----- The impact of stellar feedback as revealed by thousands of resolved HII regions in NGC 253 We propose for full-disk narrowband H-alpha imaging of NGC253, the nearest southern massive, star-forming spiral galaxy. This imaging is critical to resolve the inner structure of 2,500 HII regions known from full-disk VLT/MUSE spectral mapping and JWST/MIRI imaging. The proposed mapping would also complement awarded HST broadband imaging that captures the stellar populations powering these regions. HII regions are the critical locations of pre-supernova stellar feedback. However, even at the 3.5 Mpc distance to NGC253, ground-based observations cannot resolve the size or morphology of the inner cores where this feedback plays out. Only HST can reach the required ~1 pc resolution. Combining these new HST data with the VLT/MUSE, JWST, and broadband HST mapping, we will (1) measure the size and morphology of each region, (2) relate these to the mass, location, and age of the powering stellar population, and (3) compare the distribution of ionized gas to the observed PAH and dust emission from JWST, linking the feedback to the surrounding ISM and testing models of PAH destruction in ionized gas. This proposal will be the first-ever data set that combines full optical spectral mapping, JWST IR imaging, pc-resolution ionized gas mapping, and resolved UV-optical mapping of the stellar population. This unprecedented data set is crucial for expanding our understanding of HII region physics and stellar feedback, along with the countless possible applications to resolved sources, ISM, stellar, and galactic wind studies. We have designed a full-disk survey of NGC 253 to observe the F657N band of WFC3/UVIS. This wavelength probes the H-alpha emission across the galaxy, tracing areas of active star formation on the smallest scales of individual HII regions. In combination with the full-galaxy MUSE and JWST imaging, HST H-alpha imaging will reveal the inner structure and chemical composition of HII regions, providing crucial information on the impacts of stellar feedback. This program has been designed to match the orientation and coverage of the previously awarded observations of NUV-visbile filters (GO 17809). The mosaic is organized in a 2x8 tile layout with 10% overlap. We require the orientation angle to be 272.0-272.4 deg in order to match the in progress HST observations and existing JWST/MIRI imaging. The matching mosaic layout is crucial for continuum subtraction in the proposed bands. Each exposure will be 430 seconds, allowing us to detect HII regions powered by single massive stars within the disk. We will reach S/N of 10 for luminosities 10^35 erg/s. This proposal is being submitted as part of the PHANGS collaboration, with world experts in nearby galaxy observations and simulations. Team expertise spans vast knowledge of the interstellar medium, stellar populations and clusters, and HII regions, and dust emission. There is also extensive experience performing cutting-edge science with data from JWST, HST, and VLT/MUSE, including both data reduction and analyis. The team is well equipped to carry out the scientific goals laid out in this proposal. PI R. McClain is experienced in multiwavelength observations of the ISM and HII regions. McClain has spent significant time studying HII region structure in NGC 253 with MUSE and JWST/MIRI. Co-I Leroy is a world-leader in nearby galaxy dust and ISM observations and is experienced with leading large collaborations of scientists. Thilker is an expert in multiwavelength observations of star formation and stellar clusters and associations, SED fitting and HST observing. Thilker is the PI of the complementary awarded HST broadband observations (GO 17809) and currently spearheads the PHANGS-HST collaboration. Barnes is an expert in HII regions and stellar feedback estimations and leads the PHANGS-HST H-alpha observation survey. Chandar, together with Barnes, developed HST H-alpha data reduction pipeline, which will be used in the reduction of the proposed data. Williams, Gerasimov, Oakes, and Tian provide extensive experience with data reduction, multiwavelength stellar feedback, dust, and stellar populations observations. Their help will be crucial in the analysis of these data. Lopez is a world expert in multiwavelength stellar feedback observations including ISM, star formation, HII regions, and galactic winds. Bolatto provides extensive experience with the galaxy NGC253 and is a world expert in galactic winds, galaxy evolution, stellar feedback, and galactic centers. Stellar Populations and the Interstellar Medium Galaxies 6 false false false false false false SUPPORTED GALAXY SPIRAL ARM This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 GALAXY SPIRAL ARM This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 GALAXY SPIRAL ARM This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 GALAXY SPIRAL ARM This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 GALAXY SPIRAL ARM This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 GALAXY SPIRAL ARM This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 GALAXY SPIRAL ARM This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 GALAXY SPIRAL ARM This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 GALAXY SPIRAL ARM This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 GALAXY SPIRAL ARM This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 GALAXY SPIRAL ARM This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 GALAXY SPIRAL ARM This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 WFC3/UVIS Imaging No No F657N WFC3/UVIS Imaging No No F657N WFC3/UVIS Imaging No No F657N WFC3/UVIS Imaging No No F657N POS-TARG DITHER 0.135 LINE false false 4 46.84 WFC3-UVIS-DITHER-LINE-3PT 1 false POS-TARG DITHER 0.145 LINE false false 2 46.84 WFC3-UVIS-DITHER-LINE 2 false The scheduling data was generated by CASM 33.1. CASM was run in Phase II mode. /private/var/folders/n2/qh_mfynj4f39g_6xc17ydv6r0000gp/T/OPVisit5147168149679551831.xml (Tic-Visit :proposal-id 18086 :visit-id "01" :proposal-version -1 :trans-version "20250624" :date "13-Feb-2026 14:49:57.0" :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 1154992 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18086 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18086 :visit-id "01" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2601 :al-overhead-at-end 127 :internal-dur-at-end 668 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2983 :pcs-gap 0 ) true 1 0 The scheduling data was generated by CASM 33.1. CASM was run in Phase II mode. /private/var/folders/n2/qh_mfynj4f39g_6xc17ydv6r0000gp/T/OPVisit17809109245150757154.xml (Tic-Visit :proposal-id 18086 :visit-id "02" :proposal-version -1 :trans-version "20250624" :date "13-Feb-2026 14:49:57.0" :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 1154992 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18086 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18086 :visit-id "02" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2601 :al-overhead-at-end 127 :internal-dur-at-end 668 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2983 :pcs-gap 0 ) true 1 0 The scheduling data was generated by CASM 33.1. CASM was run in Phase II mode. /private/var/folders/n2/qh_mfynj4f39g_6xc17ydv6r0000gp/T/OPVisit4608767597981755699.xml (Tic-Visit :proposal-id 18086 :visit-id "03" :proposal-version -1 :trans-version "20250624" :date "13-Feb-2026 14:49:58.0" :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 1154992 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18086 :visit-id "03" :obset-id "03" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18086 :visit-id "03" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2601 :al-overhead-at-end 127 :internal-dur-at-end 668 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2983 :pcs-gap 0 ) true 1 0 The scheduling data was generated by CASM 33.1. CASM was run in Phase II mode. /private/var/folders/n2/qh_mfynj4f39g_6xc17ydv6r0000gp/T/OPVisit14087947719304561101.xml (Tic-Visit :proposal-id 18086 :visit-id "04" :proposal-version -1 :trans-version "20250624" :date "13-Feb-2026 14:49:58.0" :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 1154992 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18086 :visit-id "04" :obset-id "04" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18086 :visit-id "04" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2601 :al-overhead-at-end 127 :internal-dur-at-end 668 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2983 :pcs-gap 0 ) true 1 0 The scheduling data was generated by CASM 33.1. CASM was run in Phase II mode. /private/var/folders/n2/qh_mfynj4f39g_6xc17ydv6r0000gp/T/OPVisit6199639764260402748.xml (Tic-Visit :proposal-id 18086 :visit-id "05" :proposal-version -1 :trans-version "20250624" :date "13-Feb-2026 14:49:58.0" :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 1154992 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18086 :visit-id "05" :obset-id "05" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18086 :visit-id "05" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2601 :al-overhead-at-end 127 :internal-dur-at-end 668 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2983 :pcs-gap 0 ) true 1 0 The scheduling data was generated by CASM 33.1. CASM was run in Phase II mode. /private/var/folders/n2/qh_mfynj4f39g_6xc17ydv6r0000gp/T/OPVisit1434647535169556179.xml (Tic-Visit :proposal-id 18086 :visit-id "06" :proposal-version -1 :trans-version "20250624" :date "13-Feb-2026 14:49:58.0" :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 1154992 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18086 :visit-id "06" :obset-id "06" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18086 :visit-id "06" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2601 :al-overhead-at-end 127 :internal-dur-at-end 668 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2983 :pcs-gap 0 ) true 1 0 The scheduling data was generated by CASM 33.1. CASM was run in Phase II mode. /private/var/folders/n2/qh_mfynj4f39g_6xc17ydv6r0000gp/T/OPVisit2184994264635620117.xml (Tic-Visit :proposal-id 18086 :visit-id "07" :proposal-version -1 :trans-version "20250624" :date "13-Feb-2026 14:49:58.0" :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 1154992 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18086 :visit-id "07" :obset-id "07" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18086 :visit-id "07" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2601 :al-overhead-at-end 127 :internal-dur-at-end 668 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2983 :pcs-gap 0 ) true 1 0 The scheduling data was generated by CASM 33.1. CASM was run in Phase II mode. /private/var/folders/n2/qh_mfynj4f39g_6xc17ydv6r0000gp/T/OPVisit15274205423902414751.xml (Tic-Visit :proposal-id 18086 :visit-id "08" :proposal-version -1 :trans-version "20250624" :date "13-Feb-2026 14:49:59.0" :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 1154992 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18086 :visit-id "08" :obset-id "08" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18086 :visit-id "08" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2601 :al-overhead-at-end 127 :internal-dur-at-end 668 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2983 :pcs-gap 0 ) true 1 0 The scheduling data was generated by CASM 33.1. CASM was run in Phase II mode. /private/var/folders/n2/qh_mfynj4f39g_6xc17ydv6r0000gp/T/OPVisit9608102330635021212.xml (Tic-Visit :proposal-id 18086 :visit-id "09" :proposal-version -1 :trans-version "20250624" :date "13-Feb-2026 14:49:59.0" :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 1154992 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18086 :visit-id "09" :obset-id "09" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18086 :visit-id "09" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2601 :al-overhead-at-end 127 :internal-dur-at-end 668 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2983 :pcs-gap 0 ) true 1 0 The scheduling data was generated by CASM 33.1. CASM was run in Phase II mode. /private/var/folders/n2/qh_mfynj4f39g_6xc17ydv6r0000gp/T/OPVisit6579511914107495231.xml (Tic-Visit :proposal-id 18086 :visit-id "10" :proposal-version -1 :trans-version "20250624" :date "13-Feb-2026 14:49:59.0" :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 1154992 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18086 :visit-id "10" :obset-id "10" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18086 :visit-id "10" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2601 :al-overhead-at-end 127 :internal-dur-at-end 668 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2983 :pcs-gap 0 ) true 1 0 The scheduling data was generated by CASM 33.1. CASM was run in Phase II mode. /private/var/folders/n2/qh_mfynj4f39g_6xc17ydv6r0000gp/T/OPVisit2673555194304594263.xml (Tic-Visit :proposal-id 18086 :visit-id "11" :proposal-version -1 :trans-version "20250624" :date "13-Feb-2026 14:49:59.0" :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 1154992 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18086 :visit-id "11" :obset-id "11" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18086 :visit-id "11" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2601 :al-overhead-at-end 127 :internal-dur-at-end 668 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2983 :pcs-gap 0 ) true 1 0 The scheduling data was generated by CASM 33.1. CASM was run in Phase II mode. /private/var/folders/n2/qh_mfynj4f39g_6xc17ydv6r0000gp/T/OPVisit9652514509941812452.xml (Tic-Visit :proposal-id 18086 :visit-id "12" :proposal-version -1 :trans-version "20250624" :date "13-Feb-2026 14:50:00.0" :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 1154992 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18086 :visit-id "12" :obset-id "12" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18086 :visit-id "12" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2601 :al-overhead-at-end 127 :internal-dur-at-end 668 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2983 :pcs-gap 0 ) true 1 0