0 Assigned ID: 7585 ----- Attempting Submission 1 (Thu Apr 16 19:49:09 GMT 2026) ----- Could not connect to APT Status Server The list of Investigators does not match the STScI records for this program. 0 ----- Attempting Submission 1 (Tue Aug 18 14:03:32 GMT 2026) ----- The requested Co-I change has already been approved. Stars Born in the Wind: Where and How Are Stars Formed in the M82 Outflow? Galactic outflows are a fundamental component of galaxy evolution, yet it remains unclear whether they act only as negative feedback or can also trigger star formation by compressing gas. This positive-feedback mode has been suggested by theory and by indirect nebular diagnostics, but it has never been established through direct detection and age-dating of the young stars themselves. With its proximity and prototypical bipolar superwind, M82 is the only system where this can be tested star by star. Recent HST optical-band imaging has revealed halo stellar populations plausibly linked to the starburst history of the disk, and our analysis of archival HST UV data uncovers candidate OB stars closely associated with filamentary outflow structures. These results strongly motivate deeper multi-band UV-optical imaging to securely identify young massive stars and break the age-extinction degeneracy. We therefore propose deep HST imaging of three regions in the M82 superwind, spanning 2-11 kpc from the disk, to carry out the first spatially resolved census of young massive stars born across the outflow. By combining new observations with archival data, we will directly detect and age-date the young stars in the outflows, quantify their contribution to the recent star formation in M82, and determine whether they formed within the outflow itself or instead at wind-CGM interaction sites. This programme will provide the clearest direct test yet of star formation in galactic outflows and constrain its implications for feedback physics. We will obtain WFC3/UVIS imaging of three fields in the M82 outflow to identify and age-date young massive stars potentially formed in the wind. The primary observations use F275W and F336W, combined with at least one optical band in each field, to isolate hot upper-main-sequence stars and constrain their ages and extinction. Fields 1 and 2 already have archival optical imaging, so only new UV imaging is required there. Field 3 lacks the needed optical coverage, so we also obtain F475W and F814W imaging. The program uses 24 orbits in total, organized into 10 visits. Field 1 is observed in two visits: one 3-orbit visit in F275W and one 1-orbit visit in F336W. Field 2 is observed in two visits: one 3-orbit visit in F275W and one 2-orbit visit in F336W. Field 3 is observed in six visits: one 3-orbit visit in F275W, one 2-orbit visit in F336W, one 2-orbit visit in F475W, one 2-orbit visit in F814W, and two 3-orbit visits in F656N. We use a WFC3/UVIS three-point dither pattern to improve sampling, reject cosmic rays, and cover detector artifacts. The UV and narrow-band exposures use post-flash as needed for CTE performance. Visits within each field are constrained to the same orientation so that all filters cover the same sky area and can be combined into matched photometric catalogs. The proposed programme brings together a team with complementary expertise in galactic outflows, resolved stellar populations, ultraviolet imaging, and multi-phase gas in nearby galaxies. Yucheng Guo (PI) has extensive experience studying galactic winds and the circumgalactic medium using multi-wavelength observations, particularly HST narrowband imaging. He has worked directly on the M82 outflow and will lead the analysis and scientific interpretation of the proposed data. Timothy Heckman is an expert on galactic-scale outflows, feedback, and starburst galaxies, with decades of leadership in the study of M82 and the physics of gaseous outflows across multiple phases. His experience provides essential guidance on the physical interpretation of the outflow star formation and its broader implications for galaxy evolution. Adam Smercina brings strong expertise in resolved stellar populations, stellar photometry, and colour-magnitude diagram analysis with HST, which is central to detecting young stars and deriving the star-formation history. Sanchayeeta Borthakur contributes deep expertise in the circumgalactic medium, gas flows, and the connection between galaxies and their surrounding environments, providing important context for interpreting star formation at the wind-CGM interface. Vaishnav Rao has direct expertise in resolved stellar populations in M82 with HST optical data (Rao et al. 2025). His analysis of halo stellar populations and their star-formation histories provides a strong foundation for this programme, particularly for CMD fitting, stellar photometry, and the interpretation of outflow-linked star formation. Together, this team has the observational, technical, and scientific expertise required to carry out the proposed programme and to extract robust physical constraints from the resulting dataset. Galaxies Stellar Populations and the Interstellar Medium 6 false false false false true false false false false false SUPPORTED GALAXY STARBURST WIND J2000 J2000 GALAXY STARBURST WIND J2000 J2000 GALAXY STARBURST WIND J2000 J2000 WFC3/UVIS Imaging No No F275W WFC3/UVIS Imaging No No F336W WFC3/UVIS Imaging No No F275W WFC3/UVIS Imaging No No F336W WFC3/UVIS Imaging No No F275W WFC3/UVIS Imaging No No F336W WFC3/UVIS Imaging No No F475W WFC3/UVIS Imaging No No F814W WFC3/UVIS Imaging No No F656N POS-TARG DITHER 2.98 LINE false false 3 46.84 WFC3-UVIS-DITHER-LINE-3PT 1 false /Users/guo/Dropbox/research/observations/2026B/HST_massive_stars/OP-cache/P2-v01.xml The scheduling data was generated by CASM 34.2. CASM was run in Phase II mode. 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CASM was run in Phase II mode. (Tic-Visit :proposal-id 18331 :visit-id "02" :proposal-version -1 :trans-version "20260618" :date "14-Aug-2026 13:24:05.0" :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 866240 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18331 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18331 :visit-id "02" :orbit-number 1 :pcs-time 301 :si-vis-utilization 2789 :al-overhead-at-end 126 :internal-dur-at-end 352 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3092 :pcs-gap 0 ) true 1 0 /Users/guo/Dropbox/research/observations/2026B/HST_massive_stars/OP-cache/P2-v03.xml The scheduling data was generated by CASM 34.2. CASM was run in Phase II mode. 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CASM was run in Phase II mode. 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CASM was run in Phase II mode. 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CASM was run in Phase II mode. 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CASM was run in Phase II mode. 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CASM was run in Phase II mode. 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CASM was run in Phase II mode. 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