18423( 2) - 14-Aug-2026 20:16:47 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 18423 Version: 2 Check-in Time: 14-Aug-2026 20:16:47 STScI Edit Number: 0 Title Probing the Origin of the UV Continuum in Local LRD Analogs with HST Polarimetry ------------------------------------------------------------------------------------ Type Cycle GO 34 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Shu Wang University of Southampton Y CoI: Prof. Sebastian F Hoenig University of Southampton N CoI: Dr. Shenli Tang University of Southampton N CoI: Prof. Christian Knigge University of Southampton N CoI: Dr. Mengtao Tang Shanghai Jiao Tong University N CoI: Dr. Jianwei Lyu University of Arizona N CoI: Prof. Manda Banerji University of Southampton N ------------------------------------------------------------------------------------ Abstract Little Red Dots (LRDs) discovered by JWST may represent a key phase of early black hole and galaxy growth, yet their physical nature remains uncertain. A promising framework invokes an accreting black hole embedded in a dense gas envelope, which can explain many of the key observed properties of LRDs from the optical to the infrared. However, the origin of the rest-UV continuum remains unresolved: it may arise from a compact nuclear stellar population, or from AGN radiation escaping through a clumpy envelope after multiple scatterings. We propose HST/ACS imaging polarimetry for three recently identified local LRD analogs at redshifts of 0.1--0.2. Using F475W, F606W and F775W, we will measure the nuclear polarization on the blue and red sides of the Balmer break while minimizing the extended host-galaxy dilution through HST's high spatial resolution. A significant polarization excess in the blue continuum would provide strong evidence for scattered AGN light and support a role for electron scattering in shaping LRD spectra. This program will provide the first direct polarimetric constraint on the origin of the UV continuum in LRD analogs and help assess how reliably the physical properties of high-redshift LRDs can be inferred. ------------------------------------------------------------------------------------ Observations Description ------------------------ Polarimetric observation using ACS/WFC ------------------------------------------------------------------------------------ 18423( 2) - 14-Aug-2026 20:16:47 - [ 2] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 SDSS-J102208 GALAXY, QSO RA=10H22M8.5288S, J2000 V = 20.73 .52+084156.1 DEC=+08D41'56.20" Reference Frame: ICRS 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 ------------------------------------------------------------------------------------------------------------------------------------ 2 2MASS-J10253 GALAXY, QSO RA=10H25M30.2924S, J2000 V = 19.77 030+1402078 DEC=+14D02'7.39" Reference Frame: ICRS 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 ------------------------------------------------------------------------------------------------------------------------------------ 3 SDSS-J104755 GALAXY, QSO RA=10H47M55.9248S, J2000 V = 19.81 .92+073951.2 DEC=+07D39'51.23" Reference Frame: ICRS Comments: The PM is within error = 0 Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 2000 4.453114548853402E-5 8.400000000000001E-5 2.907E-4 ------------------------------------------------------------------------------------------------------------------------------------ 18423( 2) - 14-Aug-2026 20:16:47 - [ 3] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 2 Primary_Pattern Secondary_Pattern Pattern_Type LINE Pattern_Purpose DITHER Number_Of_Points 2 Point_Spacing 1 Line_Spacing Coordinate_Frame POS-TARG Pattern_Orient 0 Angle_Between_Sides Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ 18423( 2) - 14-Aug-2026 20:16:47 - [ 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 SDSS-J10220 ACS/WFC ACCUM WFC F475W, 1 342 S (684 PATTERN 2 1-3 8.52+084156 POL0V S) .1 ------------------------------------------------------------------------------------------------------------------------------------ 2 SDSS-J10220 ACS/WFC ACCUM WFC F606W, 1 273 S (546 8.52+084156 POL0V S) .1 ------------------------------------------------------------------------------------------------------------------------------------ 3 SDSS-J10220 ACS/WFC ACCUM WFC F775W, 1 168 S (336 8.52+084156 POL0V S) .1 ------------------------------------------------------------------------------------------------------------------------------------ 4 SDSS-J10220 ACS/WFC ACCUM WFC F475W, 1 342 S (684 PATTERN 2 4-6 8.52+084156 POL60V S) .1 ------------------------------------------------------------------------------------------------------------------------------------ 5 SDSS-J10220 ACS/WFC ACCUM WFC F606W, 1 273 S (546 8.52+084156 POL60V S) .1 ------------------------------------------------------------------------------------------------------------------------------------ 6 SDSS-J10220 ACS/WFC ACCUM WFC F775W, 1 168 S (336 8.52+084156 POL60V S) .1 ------------------------------------------------------------------------------------------------------------------------------------ 7 SDSS-J10220 ACS/WFC ACCUM WFC F475W, 1 342 S (684 PATTERN 2 7-9 8.52+084156 POL120V S) .1 ------------------------------------------------------------------------------------------------------------------------------------ 8 SDSS-J10220 ACS/WFC ACCUM WFC F606W, 1 273 S (546 8.52+084156 POL120V S) .1 ------------------------------------------------------------------------------------------------------------------------------------ 9 SDSS-J10220 ACS/WFC ACCUM WFC F775W, 1 168 S (336 8.52+084156 POL120V S) .1 ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ 18423( 2) - 14-Aug-2026 20:16:47 - [ 5] 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 | ------------------------------------------------------------------------------------------------------------------------------------ SDSS-J102208.52+084 1 ACS/WFC ACCUM WFC F475W, 1 none none none 1 N/A 156.1 POL0V SDSS-J102208.52+084 1 ACS/WFC ACCUM WFC F475W, 2 none none none 1 N/A 156.1 POL0V SDSS-J102208.52+084 2 ACS/WFC ACCUM WFC F606W, 1 none none none 1 N/A 156.1 POL0V SDSS-J102208.52+084 2 ACS/WFC ACCUM WFC F606W, 2 none none none 1 N/A 156.1 POL0V SDSS-J102208.52+084 3 ACS/WFC ACCUM WFC F775W, 1 none none none 1 N/A 156.1 POL0V SDSS-J102208.52+084 3 ACS/WFC ACCUM WFC F775W, 2 none none none 1 N/A 156.1 POL0V SDSS-J102208.52+084 4 ACS/WFC ACCUM WFC F475W, 1 none none none 2 N/A 156.1 POL60V SDSS-J102208.52+084 4 ACS/WFC ACCUM WFC F475W, 2 none none none 2 N/A 156.1 POL60V SDSS-J102208.52+084 5 ACS/WFC ACCUM WFC F606W, 1 none none none 2 N/A 156.1 POL60V SDSS-J102208.52+084 5 ACS/WFC ACCUM WFC F606W, 2 none none none 2 N/A 156.1 POL60V SDSS-J102208.52+084 6 ACS/WFC ACCUM WFC F775W, 1 none none none 2 N/A 156.1 POL60V SDSS-J102208.52+084 6 ACS/WFC ACCUM WFC F775W, 2 none none none 2 N/A 156.1 POL60V SDSS-J102208.52+084 7 ACS/WFC ACCUM WFC F475W, 1 none none none 3 N/A 156.1 POL120V SDSS-J102208.52+084 7 ACS/WFC ACCUM WFC F475W, 2 none none none 3 N/A 156.1 POL120V SDSS-J102208.52+084 8 ACS/WFC ACCUM WFC F606W, 1 none none none 3 N/A 156.1 POL120V SDSS-J102208.52+084 8 ACS/WFC ACCUM WFC F606W, 2 none none none 3 N/A 156.1 POL120V SDSS-J102208.52+084 9 ACS/WFC ACCUM WFC F775W, 1 none none none 3 N/A 156.1 POL120V SDSS-J102208.52+084 9 ACS/WFC ACCUM WFC F775W, 2 none none none 3 N/A 156.1 POL120V 18423( 2) - 14-Aug-2026 20:16:47 - [ 6] Visit: 02 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 2MASS-J1025 ACS/WFC ACCUM WFC F475W, 1 342 S (684 PATTERN 2 1-3 3030+140207 POL0V S) 8 ------------------------------------------------------------------------------------------------------------------------------------ 2 2MASS-J1025 ACS/WFC ACCUM WFC F606W, 1 273 S (546 3030+140207 POL0V S) 8 ------------------------------------------------------------------------------------------------------------------------------------ 3 2MASS-J1025 ACS/WFC ACCUM WFC F775W, 1 168 S (336 3030+140207 POL0V S) 8 ------------------------------------------------------------------------------------------------------------------------------------ 4 2MASS-J1025 ACS/WFC ACCUM WFC F475W, 1 342 S (684 PATTERN 2 4-6 3030+140207 POL60V S) 8 ------------------------------------------------------------------------------------------------------------------------------------ 5 2MASS-J1025 ACS/WFC ACCUM WFC F606W, 1 273 S (546 3030+140207 POL60V S) 8 ------------------------------------------------------------------------------------------------------------------------------------ 6 2MASS-J1025 ACS/WFC ACCUM WFC F775W, 1 168 S (336 3030+140207 POL60V S) 8 ------------------------------------------------------------------------------------------------------------------------------------ 7 2MASS-J1025 ACS/WFC ACCUM WFC F475W, 1 342 S (684 PATTERN 2 7-9 3030+140207 POL120V S) 8 ------------------------------------------------------------------------------------------------------------------------------------ 8 2MASS-J1025 ACS/WFC ACCUM WFC F606W, 1 273 S (546 3030+140207 POL120V S) 8 ------------------------------------------------------------------------------------------------------------------------------------ 9 2MASS-J1025 ACS/WFC ACCUM WFC F775W, 1 168 S (336 3030+140207 POL120V S) 8 ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ 18423( 2) - 14-Aug-2026 20:16:47 - [ 7] 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 | ------------------------------------------------------------------------------------------------------------------------------------ 2MASS-J10253030+140 1 ACS/WFC ACCUM WFC F475W, 1 none none none 1 N/A 2078 POL0V 2MASS-J10253030+140 1 ACS/WFC ACCUM WFC F475W, 2 none none none 1 N/A 2078 POL0V 2MASS-J10253030+140 2 ACS/WFC ACCUM WFC F606W, 1 none none none 1 N/A 2078 POL0V 2MASS-J10253030+140 2 ACS/WFC ACCUM WFC F606W, 2 none none none 1 N/A 2078 POL0V 2MASS-J10253030+140 3 ACS/WFC ACCUM WFC F775W, 1 none none none 1 N/A 2078 POL0V 2MASS-J10253030+140 3 ACS/WFC ACCUM WFC F775W, 2 none none none 1 N/A 2078 POL0V 2MASS-J10253030+140 4 ACS/WFC ACCUM WFC F475W, 1 none none none 2 N/A 2078 POL60V 2MASS-J10253030+140 4 ACS/WFC ACCUM WFC F475W, 2 none none none 2 N/A 2078 POL60V 2MASS-J10253030+140 5 ACS/WFC ACCUM WFC F606W, 1 none none none 2 N/A 2078 POL60V 2MASS-J10253030+140 5 ACS/WFC ACCUM WFC F606W, 2 none none none 2 N/A 2078 POL60V 2MASS-J10253030+140 6 ACS/WFC ACCUM WFC F775W, 1 none none none 2 N/A 2078 POL60V 2MASS-J10253030+140 6 ACS/WFC ACCUM WFC F775W, 2 none none none 2 N/A 2078 POL60V 2MASS-J10253030+140 7 ACS/WFC ACCUM WFC F475W, 1 none none none 3 N/A 2078 POL120V 2MASS-J10253030+140 7 ACS/WFC ACCUM WFC F475W, 2 none none none 3 N/A 2078 POL120V 2MASS-J10253030+140 8 ACS/WFC ACCUM WFC F606W, 1 none none none 3 N/A 2078 POL120V 2MASS-J10253030+140 8 ACS/WFC ACCUM WFC F606W, 2 none none none 3 N/A 2078 POL120V 2MASS-J10253030+140 9 ACS/WFC ACCUM WFC F775W, 1 none none none 3 N/A 2078 POL120V 2MASS-J10253030+140 9 ACS/WFC ACCUM WFC F775W, 2 none none none 3 N/A 2078 POL120V 18423( 2) - 14-Aug-2026 20:16:47 - [ 8] Visit: 03 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 SDSS-J10475 ACS/WFC ACCUM WFC F475W, 1 342 S (684 PATTERN 2 1-3 5.92+073951 POL0V S) .2 ------------------------------------------------------------------------------------------------------------------------------------ 2 SDSS-J10475 ACS/WFC ACCUM WFC F606W, 1 273 S (546 5.92+073951 POL0V S) .2 ------------------------------------------------------------------------------------------------------------------------------------ 3 SDSS-J10475 ACS/WFC ACCUM WFC F775W, 1 168 S (336 5.92+073951 POL0V S) .2 ------------------------------------------------------------------------------------------------------------------------------------ 4 SDSS-J10475 ACS/WFC ACCUM WFC F475W, 1 342 S (684 PATTERN 2 4-6 5.92+073951 POL60V S) .2 ------------------------------------------------------------------------------------------------------------------------------------ 5 SDSS-J10475 ACS/WFC ACCUM WFC F606W, 1 273 S (546 5.92+073951 POL60V S) .2 ------------------------------------------------------------------------------------------------------------------------------------ 6 SDSS-J10475 ACS/WFC ACCUM WFC F775W, 1 168 S (336 5.92+073951 POL60V S) .2 ------------------------------------------------------------------------------------------------------------------------------------ 7 SDSS-J10475 ACS/WFC ACCUM WFC F475W, 1 342 S (684 PATTERN 2 7-9 5.92+073951 POL120V S) .2 ------------------------------------------------------------------------------------------------------------------------------------ 8 SDSS-J10475 ACS/WFC ACCUM WFC F606W, 1 273 S (546 5.92+073951 POL120V S) .2 ------------------------------------------------------------------------------------------------------------------------------------ 9 SDSS-J10475 ACS/WFC ACCUM WFC F775W, 1 168 S (336 5.92+073951 POL120V S) .2 ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ 18423( 2) - 14-Aug-2026 20:16:47 - [ 9] 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 | ------------------------------------------------------------------------------------------------------------------------------------ SDSS-J104755.92+073 1 ACS/WFC ACCUM WFC F475W, 1 none none none 1 N/A 951.2 POL0V SDSS-J104755.92+073 1 ACS/WFC ACCUM WFC F475W, 2 none none none 1 N/A 951.2 POL0V SDSS-J104755.92+073 2 ACS/WFC ACCUM WFC F606W, 1 none none none 1 N/A 951.2 POL0V SDSS-J104755.92+073 2 ACS/WFC ACCUM WFC F606W, 2 none none none 1 N/A 951.2 POL0V SDSS-J104755.92+073 3 ACS/WFC ACCUM WFC F775W, 1 none none none 1 N/A 951.2 POL0V SDSS-J104755.92+073 3 ACS/WFC ACCUM WFC F775W, 2 none none none 1 N/A 951.2 POL0V SDSS-J104755.92+073 4 ACS/WFC ACCUM WFC F475W, 1 none none none 2 N/A 951.2 POL60V SDSS-J104755.92+073 4 ACS/WFC ACCUM WFC F475W, 2 none none none 2 N/A 951.2 POL60V SDSS-J104755.92+073 5 ACS/WFC ACCUM WFC F606W, 1 none none none 2 N/A 951.2 POL60V SDSS-J104755.92+073 5 ACS/WFC ACCUM WFC F606W, 2 none none none 2 N/A 951.2 POL60V SDSS-J104755.92+073 6 ACS/WFC ACCUM WFC F775W, 1 none none none 2 N/A 951.2 POL60V SDSS-J104755.92+073 6 ACS/WFC ACCUM WFC F775W, 2 none none none 2 N/A 951.2 POL60V SDSS-J104755.92+073 7 ACS/WFC ACCUM WFC F475W, 1 none none none 3 N/A 951.2 POL120V SDSS-J104755.92+073 7 ACS/WFC ACCUM WFC F475W, 2 none none none 3 N/A 951.2 POL120V SDSS-J104755.92+073 8 ACS/WFC ACCUM WFC F606W, 1 none none none 3 N/A 951.2 POL120V SDSS-J104755.92+073 8 ACS/WFC ACCUM WFC F606W, 2 none none none 3 N/A 951.2 POL120V SDSS-J104755.92+073 9 ACS/WFC ACCUM WFC F775W, 1 none none none 3 N/A 951.2 POL120V SDSS-J104755.92+073 9 ACS/WFC ACCUM WFC F775W, 2 none none none 3 N/A 951.2 POL120V 18423( 2) - 14-Aug-2026 20:16:47 - [ 10] Summary Form for Proposal 18423 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures WFC ------------------------------------------------------------------------------------------------------------------------------------ Configurations ACS/WFC ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PATTERN 2 1-3, PATTERN 2 4-6, PATTERN 2 7-9 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F475W, F606W, F775W, POL0V, POL120V, POL60V ------------------------------------------------------------------------------------------------------------------------------------ Target Names 2MASS-J10253030+1402078, SDSS-J102208.52+084156.1, SDSS-J104755.92+073951.2 ------------------------------------------------------------------------------------------------------------------------------------