0 Assigned ID: 6624 ----- Attempting Submission 1 (Thu Apr 10 19:21:46 GMT 2025) ----- HST Phase I Proposal 6624 successfully submitted. Receipt: # 6624-1 0 ----- Attempting Submission 1 (Thu Aug 14 01:43:31 GMT 2025) ----- HST Phase II Proposal 18075 successfully submitted. Receipt: # 18075-1 ----- Attempting Submission 2 (Thu Aug 14 21:58:08 GMT 2025) ----- HST Phase II Proposal 18075 successfully submitted. Receipt: # 18075-2 ----- Attempting Submission 3 (Tue Sep 23 18:27:26 GMT 2025) ----- Multiple intermediate-mass black holes in the local dwarf galaxy UGCA320 Identifying and studying intermediate-mass black holes (IMBHs; BH mass < 10^5 solar mass) in local dwarf galaxies offers crucial insights into the formation and growth of supermassive black holes (SMBHs), as IMBHs are believed to represent an early evolutionary stage. Determining their abundance and accretion properties is key to understanding how SMBHs assemble, and the UV emission is crucial in identifying IMBH and constraining the accretion disk properties. However, only a few IMBHs have been identified so far, and no more than one IMBH has been confirmed in any single dwarf galaxy, leaving their demographics and properties uncertain. In the dwarf galaxy UGCA 320, we identified two off-disk IMBH candidates with multiple evidence, and an off-center candidate in the disk but with inconclusive evidence. Although they have previous UV detection by Galex and Swift, large uncertainties prevent constraining the intrinsic UV slopes of the two off-disk candidates, and the broad PSF prevents resolving the candidate located in the disk. We propose HST observations using SBC/F140LP, UVIS/F225W, and UVIS/F300X to obtain cleaner AGN UV emission and construct high spatial resolution SEDs at three parsecs. These data will allow us to study IMBH accretion disk properties and provide robust evidence for them as IMBHs. 1. Visit01: ACS/SBC F140LP observation for SBC-1. The pointing can cover two targets of interest simultaneously, regardless of orientation. The four-step dithering pattern is used to improve photometric accuracy, considering flat-field variation and PSF sampling. Each exposure lasting 500s, balancing the orbits' utilization and visibility. 2. Visit02: ACS/SBC F140LP observation for SBC-2. The pointing covers the target of interest and its surrounding environment. The "DITHER-BOX" main pattern is to improve photometric accuracy, and the "DITHERC-LINE" subpattern offsets the pointing by 3" to slightly increase FOV. We also set a pointing named SBC2-BACKGROUND to obtain one dedicated background observation. Considering the orbit utilization and the visibity, the first orbit without background observation with 450s per exposure, and the second orbit with 360s per exposure. The background observation will carried out at end of source exposure, with 360s observing time. Thus, this observation needs two consecutive orbits. 3. Vist03 and Vist04: WFC3/UVIS F225W and F300X observations for UVIS-HOST. The pointing covers all three targets of interest at the same time, regardless of orientation. The "UVIS2-C1K2C-CTE" aperture and a "FLASH=15" are used to migrate the CTE effects for the three targets. The "DITHER-BOX" pattern is to improve the accuracy of photometry. Each exposure lasting 450s considering the required S/N, orbit utilization, and visibility. For UVIS observation, while the orientation is unconstrained to avoid decreasing visibility, it would be better if the aperture covers as much of the host galaxy as possible. PI--Xin Li, a PhD student, studying low luminosity AGN and dwarf galaxies. The proposed study is part of her PhD thesis. CoI--Fuyan Bian, an expert in studies of high-z galaxies and active galactic nuclei. He will give the scientific guidance and help to configure the instruments. CoI--Yong Shi, an expert in nearby galaxies and active galactic nuclei. He has extensive studies of AGN and their host galaxies with multi-wavelength data. He will give the scientific guidance and help to configure the instruments. CoI--Jialai Kang, a PhD student, studying luminous AGN and SEDs. He will help to analysis the SED with models. CoI--Yanina, a master student, studying AGN in higher redshift. She will help to analysis the SED with models. Supermassive Black Holes and Active Galaxies Galaxies 6 false true false false false false SUPPORTED ISM NUCLEUS J2000 J2000 ISM NUCLEUS J2000 J2000 CALIBRATION SKY BACKGROUND YES J2000 J2000 GALAXY MULTIPLE NUCLEI J2000 J2000 ACS/SBC Imaging No No F140LP ACS/SBC Imaging No No F140LP WFC3/UVIS Imaging No No F225W WFC3/UVIS Imaging No No F300X POS-TARG DITHER 0.179 LINE 0.116 false false 63.65 4 20.02 ACS-SBC-DITHER-BOX 1 false POS-TARG DITHER DITHER 2 0.179 ACS-SBC-DITHER-LINE 0.116 false false 63.65 3 4 20.02 POS-TARG ACS-SBC-DITHER-BOX 44.4 4 true POS-TARG DITHER 0.173 LINE 0.112 false false 81.785 4 23.884 WFC3-UVIS-DITHER-BOX 3 false /Volumes/Lily/UGCA320/proposal/HST(cycle33)/phaseII/OP-cache/APT_v3-v01.xml The scheduling data was generated by CASM 33.1. CASM was run in Phase II mode. 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CASM was run in Phase II mode. (Tic-Visit :proposal-id 18075 :visit-id "03" :proposal-version -1 :trans-version "20250624" :date "23-Sep-2025 15:20:02.0" :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 18075 :visit-id "03" :obset-id "03" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18075 :visit-id "03" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2225 :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 2976 :pcs-gap 0 ) true 1 0 /Volumes/Lily/UGCA320/proposal/HST(cycle33)/phaseII/OP-cache/APT_v3-v04.xml The scheduling data was generated by CASM 33.1. CASM was run in Phase II mode. 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