18047( 2) - 14-Aug-2025 11:07:12 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 18047 Version: 2 Check-in Time: 14-Aug-2025 11:07:12 STScI Edit Number: 0 Title Disentangling the True Nature of Three Broadline-Offset & VLBA/Gaia-Offset Quasars with HST ------------------------------------------------------------------------------------ Type Cycle GO 33 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Peter Breiding State University of New York Binghamton Y ------------------------------------------------------------------------------------ Abstract In a sample of 15, 900 SDSS quasars, Eracleous et al. (2012) found 88 objects exhibiting broad emission lines with >1000 km/s velocity offsets with respect to the host galaxy rest frame. One leading hypothesis for the origin of these velocity-offset broad lines is the dynamics of a binary supermassive black hole (SMBH), with competing hypotheses of recoiling SMBH and a broad line region (BLR) gas outflow due to entrainment by a relativistic jet. Three of these quasars were also shown to have signficiant VLBI/Gaia offsets in follow-up VLBA observations, where recoiling SMBHs, binary SMBHs, and optical synchrotron jets are all potential causes of these offsets. We propose HST observations to test the various competing physical models for both the observed spectroscopic and astrometric offsets, requiring a total of 3 ACS/WFC + F606W orbits to achieve our science goals. ------------------------------------------------------------------------------------ Observations Description ------------------------ These observations are focused on three quasars (all z~0.2-0.3), where we allocate one orbit per target with ACS/WFC + F606W. The F606W filter is required for our science goals as it matches the Gaia filter used to measure the quasar radio-optical astrometric offsets. These observations require long exposures in order to maximize sensitivity to low surface brightness indicators of a previous major galaxy merger in the host galaxy of our quasar targets (this is essential to our science goals). We will use 4x438s science exposures in order to achieve 1752s of total integration time on each target. According to the online ACS Exposure Time Calculator, this will allow for 5-sigma surface brightness sensitivity limits of ~ 26 AB magnitudes per square arcsec (which should be sufficient for faint host galaxy structural analysis). The WFC1-FIX aperture and POS TARG offset of X=40 arcsec and Y=5 arcsec (moving towards the B amplifier of the WFC1 chip) was chosen to improve charge transfer efficiency performance and lower amplifier readnoise -- allowing us the best sensitivity to faint host galaxy componenets which are relevant to our science goals (e.g., imaging faint tidal structures or possible faint jet structures). This strategy will also keep our quasar position far away from the chip gap during the dithers. We will use the standard ACS/WFC 4-point box dither pattern (4x438s exposures) in order to allow for a good sampling of the PSF for PSF modeling and subtraction. These exposure times may lead to saturation of a few central core PSF pixels for our quasars (note that the AB V-band magnitudes for our quasars range from ~ 18.3-19.2). Therefore, we also employ a short 30s exposure at the start of each orbit, allowing us to obtain a good model of the 18047( 2) - 14-Aug-2025 11:07:12 - [ 2] central core and inner wings of the PSF. We can use the unsaturated core pixels from the short 30s exposures to reconstruct the saturated pixels in the PSF cores of the longer dithered exposures. The short 30s exposure and the longer dithered 4x438s exposures are in "non-interruptible sequences" with the same WFC1-FIX position offsets. This will ensure that the short exposures occur at the same chip position as the first dither point (and without much time separation), allowing us to construct a PSF model for the central pixels which is very close to the PSF core sampled by the subsequent dithered exposures. ------------------------------------------------------------------------------------ 18047( 2) - 14-Aug-2025 11:07:12 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 2MASS-J09503 GALAXY, QSO RA=09H50M36.7566S, J2000 Z = V = 18.34 674+5128382 DEC=+51D28'38.07" 0.214 Reference Frame: Other: SIMBAD Comments: This object was generated by the targetselector and retrieved from the SIMBAD database. Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 2015.5 -4.388602477941542E-6 8.39E-4 0.0 ------------------------------------------------------------------------------------------------------------------------------------ 2 2MASS-J12111 GALAXY, QSO RA=12H11M13.9824S, J2000 Z = V = 19.02 399+4647120 DEC=+46D47'11.98" 0.295 Reference Frame: Other: SIMBAD Extended: YES Comments: This object was generated by the targetselector and retrieved from the SIMBAD database. Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 2015.5 -1.8499131969291317E-6 1.21E-4 0.0 ------------------------------------------------------------------------------------------------------------------------------------ 3 2MASS-J12281 GALAXY, QSO RA=12H28M11.8876S, J2000 Z = V = 19.15 188+5146232 DEC=+51D46'22.78" 0.321 Reference Frame: Other: SIMBAD Extended: YES Comments: This object was generated by the targetselector and retrieved from the SIMBAD database. Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 2015.5 -3.361460077475965E-5 6.850000000000001E-4 0.0 ------------------------------------------------------------------------------------------------------------------------------------ 18047( 2) - 14-Aug-2025 11:07:12 - [ 4] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type ACS-WFC-DITHER-BOX Pattern_Purpose DITHER Number_Of_Points 4 Point_Spacing 0.2637 Line_Spacing 0.1856 Coordinate_Frame POS-TARG Pattern_Orient 20.7 Angle_Between_Sides 69.02 Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ 18047( 2) - 14-Aug-2025 11:07:12 - [ 5] 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 2MASS-J0950 ACS/WFC ACCUM WFC1-FIX F606W 1 30 S (30 POS TARG 40, 5; SEQ 1-2 3674+512838 S) NON-INT 2 ------------------------------------------------------------------------------------------------------------------------------------ 2 2MASS-J0950 ACS/WFC ACCUM WFC1-FIX F606W 1 438 S POS TARG 40, 5; PATTERN 3674+512838 (1752 S) 1 2 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 | ------------------------------------------------------------------------------------------------------------------------------------ 2MASS-J09503674+512 1 ACS/WFC ACCUM WFC1-FIX F606W none none none none 1 N/A 8382 2MASS-J09503674+512 2 ACS/WFC ACCUM WFC1-FIX F606W 1 none none none 1 N/A 8382 2MASS-J09503674+512 2 ACS/WFC ACCUM WFC1-FIX F606W 2 none none none 1 N/A 8382 2MASS-J09503674+512 2 ACS/WFC ACCUM WFC1-FIX F606W 3 none none none 1 N/A 8382 2MASS-J09503674+512 2 ACS/WFC ACCUM WFC1-FIX F606W 4 none none none 1 N/A 8382 18047( 2) - 14-Aug-2025 11:07:12 - [ 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-J1211 ACS/WFC ACCUM WFC1-FIX F606W 1 30 S (30 POS TARG 40, 5; SEQ 1-2 1399+464712 S) NON-INT 0 ------------------------------------------------------------------------------------------------------------------------------------ 2 2MASS-J1211 ACS/WFC ACCUM WFC1-FIX F606W 1 438 S POS TARG 40, 5; PATTERN 1399+464712 (1752 S) 1 2 0 ------------------------------------------------------------------------------------------------------------------------------------ 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-J12111399+464 1 ACS/WFC ACCUM WFC1-FIX F606W none none none none 1 N/A 7120 2MASS-J12111399+464 2 ACS/WFC ACCUM WFC1-FIX F606W 1 none none none 1 N/A 7120 2MASS-J12111399+464 2 ACS/WFC ACCUM WFC1-FIX F606W 2 none none none 1 N/A 7120 2MASS-J12111399+464 2 ACS/WFC ACCUM WFC1-FIX F606W 3 none none none 1 N/A 7120 2MASS-J12111399+464 2 ACS/WFC ACCUM WFC1-FIX F606W 4 none none none 1 N/A 7120 18047( 2) - 14-Aug-2025 11:07:12 - [ 7] 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 2MASS-J1228 ACS/WFC ACCUM WFC1-FIX F606W 1 30 S (30 POS TARG 40, 5; SEQ 1-2 1188+514623 S) NON-INT 2 ------------------------------------------------------------------------------------------------------------------------------------ 2 2MASS-J1228 ACS/WFC ACCUM WFC1-FIX F606W 1 438 S POS TARG 40, 5; PATTERN 1188+514623 (1752 S) 1 2 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 | ------------------------------------------------------------------------------------------------------------------------------------ 2MASS-J12281188+514 1 ACS/WFC ACCUM WFC1-FIX F606W none none none none 1 N/A 6232 2MASS-J12281188+514 2 ACS/WFC ACCUM WFC1-FIX F606W 1 none none none 1 N/A 6232 2MASS-J12281188+514 2 ACS/WFC ACCUM WFC1-FIX F606W 2 none none none 1 N/A 6232 2MASS-J12281188+514 2 ACS/WFC ACCUM WFC1-FIX F606W 3 none none none 1 N/A 6232 2MASS-J12281188+514 2 ACS/WFC ACCUM WFC1-FIX F606W 4 none none none 1 N/A 6232 18047( 2) - 14-Aug-2025 11:07:12 - [ 8] Summary Form for Proposal 18047 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures WFC1-FIX ------------------------------------------------------------------------------------------------------------------------------------ Configurations ACS/WFC ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PATTERN 1 2, POS TARG 40, 5, SEQ 1-2 NON-INT ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F606W ------------------------------------------------------------------------------------------------------------------------------------ Target Names 2MASS-J09503674+5128382, 2MASS-J12111399+4647120, 2MASS-J12281188+5146232 ------------------------------------------------------------------------------------------------------------------------------------