18039( 3) - 14-Jan-2026 19:29:40 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 18039 Version: 3 Check-in Time: 14-Jan-2026 19:29:40 STScI Edit Number: 0 Title Confirming and Characterizing a Fast, Cool Inflow Toward a Luminous Quasar at z = 0.78 ------------------------------------------------------------------------------------ Type Cycle GO 33 ------------------------------------------------------------------------------------ Investigators Contact? PI: Will Liu University of Michigan Y CoI: Prof. Sean Johnson University of Michigan Y CoI: Dr. Mandy Chen Carnegie Institution of Washington N CoI: Dr. Gwen C. Rudie Carnegie Institution of Washington N CoI: Mr. Nishant Mishra University of Michigan N CoI: Dr. Zhijie Qu Tsinghua University N CoI: Prof. Joop Schaye Universiteit Leiden N CoI: Prof. Fakhri S Zahedy University of North Texas N CoI: Ms. Elise Kesler University of Michigan N CoI: Dr. Sowgat Muzahid Inter-University Centre for Astronomy and N Astrophysics CoI: Dr. Jennifer I. Li University of Illinois at Urbana - N Champaign CoI: Dr. Erin Boettcher University of Maryland N CoI: Prof. Hsiao-Wen Chen University of Chicago N CoI: Dr. Feige Wang University of Michigan N ------------------------------------------------------------------------------------ Abstract We propose HST COS+STIS observations of J0233-0455, a z=0.78 quasar exhibiting redshifted, inflowing Mg II absorption at +800 km/s, to study the elusive process of gas accretion onto supermassive black holes (SMBHs). While AGN outflows are well-documented, direct observations of gas inflows that fuel SMBHs remain extremely rare. Our target was identified through a systematic search for quasars with redshifted absorption, similar to a recent inflow discovered along with a filamentary nebula. As the brightest of the ten quasars found exhibiting the redshifted Mg II absorption, J0233-0455 is singularly suitable as a pilot target for the detailed UV spectroscopy we propose. The proposed UV spectroscopy will target key transitions including Ly-alpha, Ly-beta, the Lyman limit, C II, C IV, and O VI, allowing us to characterize the physical properties, ionization state, and chemical composition of the inflowing gas. The spectral diagnostics will enable measurements of the total mass and inflow rate of the accreting material. This study potentially offers a unique opportunity to quantitatively probe the mechanisms of black hole fueling, addressing a fundamental gap in our understanding of AGN physics and galaxy evolution. ------------------------------------------------------------------------------------ Observations Description ------------------------ Summary of Program Goals: This program aims to obtain UV spectra of J0233-0455, a z=0.78 quasar exhibiting redshifted, inflowing Mg II absorption at +800 km/s, to study the 18039( 3) - 14-Jan-2026 19:29:40 - [ 2] elusive process of gas accretion onto supermassive black holes (SMBHs). The UV spectroscopy will target key transitions including Ly-alpha, Ly-beta, the Lyman limit, C II, C IV, and O VI, allowing us to characterize the physical properties, ionization state, and chemical composition of the inflowing gas. The spectral diagnostics will enable measurements of the total mass and inflow rate of the accreting material. STIS Configuration and visit schedules: The program will use the E230M grating with a central wavelength of 2415 Ang and the 0.2"x0.2" aperture. The central wavelength provides coverage from 2000-2800 Ang, necessary to capture the Ly-alpha and C IV at 2170 and 2770 Ang for the target at redshift z=0.78. The total STIS exposure time for J0233-0455 is 5 orbits, divided into two visits of 3 and 2 orbits, in accordance with the scheduling efficiency guidelines in the STIS instrument handbook. STIS Target Acquisition: The coordinate of J0233-0455 is known to better than 0.1". An ACQ sequence is sufficient to center the quasar in the 0.2"x0.2" aperture at the start of each visit. The GALEX NUV magnitude of the quasar is (NUV)=17.4. Using the STIS Target Acquisition ETC, we find that a S/N >~ 40 can be achieved with an acquisition exposure time of 7 seconds. COS Configuration: We aim to cover Ly-beta (1832 Ang), O VI (1843 Ang), C II (1851 Ang) between 1826 and 1859 Ang using the G185M grating with central wavelength c1941, and the Lyman limit (1629 Ang) using G160M with central wavelength c1600. We will employ FP-POS offsets 2, 3, and 4 for G185M, and 1, 2, 3, 4 for G160M to ensure that each wavelength window is observed at least three times with different grating positions. The total COS exposure time for J0233-0455 is 4 orbits within one single visit. COS Target Acquisition: We will obtain an NUV image in ACQ/IMAGE mode, as the 2.5" COS entrance aperture is sufficient to center the quasar. No ACQ/SEARCH is required since the quasar coordinates are known to better than 0.1". The GALEX FUV magnitude of the quasar is (NUV) = 17.4. Using the COS Target Acquisition ETC, we find that MIRROR B must be used to avoid exceeding the bright limit, and that a S/N greater than 40 can be achieved with a 20-second exposure. ------------------------------------------------------------------------------------ 18039( 3) - 14-Jan-2026 19:29:40 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 J0233-0455 GALAXY, HALO, LYMAN RA=02H33M22.1601S +/- 0.01", J2000 V = 17.12 AB=17.4 in NUV ALPHA CLOUD, QSO, DEC=-04D55'6.92" +/- 0.01" QUASAR Reference Frame: ICRS Extended: NO ------------------------------------------------------------------------------------------------------------------------------------ 18039( 3) - 14-Jan-2026 19:29:40 - [ 4] Visit: 01 (J0233-STIS-SCI) 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 J0233-0455 STIS/CCD ACQ F28X50LP MIRROR ACQTYPE=POINT 1 7 S (7 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 J0233-0455 STIS/NUV TIME-TA 0.2X0.2 E230M 2415 BUFFER-TIME=1000 1 2000 S -MAMA G see below (2060 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 J0233-0455 STIS/NUV TIME-TA 0.2X0.2 E230M 2415 BUFFER-TIME=1000 1 2000 S -MAMA G see below (2569 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 J0233-0455 STIS/NUV TIME-TA 0.2X0.2 E230M 2415 BUFFER-TIME=1000 1 2000 S -MAMA G see below (2569 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 | ------------------------------------------------------------------------------------------------------------------------------------ J0233-0455 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A J0233-0455 2 STIS/NUV TIME-TA 0.2X0.2 E230M 2415 none none none none 1 2060.0 S -MAMA G J0233-0455 3 STIS/NUV TIME-TA 0.2X0.2 E230M 2415 none none none none 2 2569.0 S -MAMA G J0233-0455 4 STIS/NUV TIME-TA 0.2X0.2 E230M 2415 none none none none 3 2569.0 S -MAMA G 18039( 3) - 14-Jan-2026 19:29:40 - [ 5] Visit: 02 (J0233-STIS-SCI) 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 J0233-0455 STIS/CCD ACQ F28X50LP MIRROR ACQTYPE=POINT 1 7 S (7 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 J0233-0455 STIS/NUV TIME-TA 0.2X0.2 E230M 2415 BUFFER-TIME=1000 1 2000 S -MAMA G see below (2060 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 J0233-0455 STIS/NUV TIME-TA 0.2X0.2 E230M 2415 BUFFER-TIME=1000 1 2000 S -MAMA G see below (2569 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 | ------------------------------------------------------------------------------------------------------------------------------------ J0233-0455 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A J0233-0455 2 STIS/NUV TIME-TA 0.2X0.2 E230M 2415 none none none none 1 2060.0 S -MAMA G J0233-0455 3 STIS/NUV TIME-TA 0.2X0.2 E230M 2415 none none none none 2 2569.0 S -MAMA G 18039( 3) - 14-Jan-2026 19:29:40 - [ 6] Visit: 03 (J0233-COS-SCI) 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 J0233-0455 COS/NUV ACQ/IMA PSA MIRRORB 1 20 S (20 GE S) ------------------------------------------------------------------------------------------------------------------------------------ 2 J0233-0455 COS/NUV TIME-TA PSA G185M 1941 FP-POS=2, BUFFER-TIME=1257 1 2000 S G see below (2221 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 J0233-0455 COS/NUV TIME-TA PSA G185M 1941 FP-POS=3, BUFFER-TIME=1257 1 2000 S G see below (2572 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 J0233-0455 COS/NUV TIME-TA PSA G185M 1941 FP-POS=4, BUFFER-TIME=1257 1 2000 S G see below (2572 S) ------------------------------------------------------------------------------------------------------------------------------------ 5 J0233-0455 COS/FUV TIME-TA PSA G160M 1600 FP-POS=1, BUFFER-TIME=9075 1 500 S G see below (547 S) ------------------------------------------------------------------------------------------------------------------------------------ 6 J0233-0455 COS/FUV TIME-TA PSA G160M 1600 FP-POS=2, BUFFER-TIME=9075 1 500 S G see below (547 S) ------------------------------------------------------------------------------------------------------------------------------------ 7 J0233-0455 COS/FUV TIME-TA PSA G160M 1600 FP-POS=3, BUFFER-TIME=9075 1 500 S G see below (547 S) ------------------------------------------------------------------------------------------------------------------------------------ 8 J0233-0455 COS/FUV TIME-TA PSA G160M 1600 FP-POS=4, BUFFER-TIME=9075 1 500 S G see below (547 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 | ------------------------------------------------------------------------------------------------------------------------------------ J0233-0455 1 COS/NUV ACQ/IMA PSA MIRRORB none none none none 1 N/A GE J0233-0455 2 COS/NUV TIME-TA PSA G185M 1941 none none none none 1 2221.0 S G 18039( 3) - 14-Jan-2026 19:29:40 - [ 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 | ------------------------------------------------------------------------------------------------------------------------------------ J0233-0455 3 COS/NUV TIME-TA PSA G185M 1941 none none none none 2 2572.0 S G J0233-0455 4 COS/NUV TIME-TA PSA G185M 1941 none none none none 3 2572.0 S G J0233-0455 5 COS/FUV TIME-TA PSA G160M 1600 none none none none 4 547.0 S G J0233-0455 6 COS/FUV TIME-TA PSA G160M 1600 none none none none 4 547.0 S G J0233-0455 7 COS/FUV TIME-TA PSA G160M 1600 none none none none 4 547.0 S G J0233-0455 8 COS/FUV TIME-TA PSA G160M 1600 none none none none 4 547.0 S G 18039( 3) - 14-Jan-2026 19:29:40 - [ 8] Summary Form for Proposal 18039 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures 0.2X0.2, F28X50LP, PSA ------------------------------------------------------------------------------------------------------------------------------------ Configurations COS/FUV, COS/NUV, STIS/CCD, STIS/NUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ, ACQ/IMAGE, TIME-TAG ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ACQTYPE=POINT, BUFFER-TIME=1000, BUFFER-TIME=1257, BUFFER-TIME=9075, FP-POS=1, FP-POS=2, FP-POS=3, FP-POS=4 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements E230M, G160M, G185M, MIRROR, MIRRORB ------------------------------------------------------------------------------------------------------------------------------------ Target Names J0233-0455 ------------------------------------------------------------------------------------------------------------------------------------