15414( 3) - 08-Dec-2017 18:36:37 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 15414 Version: 3 Check-in Time: 08-Dec-2017 18:36:37 STScI Edit Number: 0 Title Confirming Extreme Lyman Continuum Emission in a z=3.27 Star-Forming Galaxy ------------------------------------------------------------------------------------ Type Cycle GO 25 ------------------------------------------------------------------------------------ Investigators Contact? PI: Mr. Rohan Naidu Harvard University Y CoI: Prof. Pascal Oesch Observatoire de Geneve N CoI: Dr. Joel Leja Harvard University N CoI: Prof. Charlie Conroy Harvard University N CoI: Dr. Benjamin D. Johnson Harvard University N CoI: Ms. Josephine Kerutt Leibniz-Institut fur Astrophysik Potsdam N (AIP) CoI: Prof. Lutz Wisotzki Leibniz-Institut fur Astrophysik Potsdam N (AIP) CoI: Dr. Anne Verhamme Observatoire de Geneve N CoI: Dr. Naveen A. Reddy University of California - Riverside N CoI: Prof. Garth D. Illingworth University of California - Santa Cruz N CoI: Dr. Mireia Montes Yale University N ------------------------------------------------------------------------------------ Abstract Identifying the drivers of cosmic reionization ("Lyman Continuum (LyC)" leakers) is an open frontier in observational cosmology. Star-forming galaxies are leading candidates, provided their critical parameter "f_esc" (the fraction of ionizing photons escaping to the IGM) is found to exceed 10-20%. Since the opaque IGM precludes direct observations of f_esc at z>6, extensive searches for low-z LyC leakers have been mounted. These sources, however, have proven notoriously elusive--only three have been found at z>0.5. We propose to confirm LyC emission from a new, promising candidate (GS15601) at z_spec=3.2705+/-0.0007, which would be the highest redshift and most extreme LyC leaker so far. GS15601 was detected in deep F336W WFC3/UVIS imaging in our HDUV survey which directly probes LyC emission at z>3. Detailed simulations show that its high F336W LyC flux implies an extreme LyC output, a very high f_esc>50%, and an almost transparent IGM line of sight. Unfortunately, GS15601 was imaged by a detector region with poor charge transfer efficiency (CTE)--its flux is robustly recovered but S/N is lost. Given the potentially extraordinary physical situation in GS15601, and the systematic uncertainties introduced by CTE loss correction and cosmic ray cleaning, we seek independent confirmation of this high LyC flux measurement with a small amount of additional F336W data. If confirmed, GS15601 will give us the rare chance to study the physics of LyC escape and calibrate indirect methods of inferring f_esc from UV and optical lines--these indirect methods are our only hope of measuring f_esc at z>6 with JWST and solving the puzzle of cosmic reionization. ------------------------------------------------------------------------------------ Observations Description ------------------------ This program aims to obtain a robust F336W flux measurement for a z=3.27 galaxy. The current flux we measure is significantly affected by charge 15414( 3) - 08-Dec-2017 18:36:37 - [ 2] transfer inefficiency. In this program we will place GS15601 close to the edge of the detector (15" from the UVIS2 pointing position), hence minimizing charge transfer and providing an independent, clean measurement. Additionally, we will flash the detector to the required 12 electron/pixel level before every exposure in order to produce a uniform image that can be appropriately CTE corrected over the full WFC3/UVIS field-of-view. Pointing: we use the UVIS2 pointing position with an additional y=-15" POSTARG offset in order to put the primary target close to the readout and minimize the CTE losses. Orbit Structure: We propose the following structure: three visits, the first two have two orbits each (4 exposures) and the final visit has a single orbit (2 exposures). Dithering: The two orbit visits use the standard 4point UVIS dither box, while the 1 orbit visit uses a two point linear dither. Between each visit, we apply a small POSTARG offset to step across the UVIS chip gap and improve the data quality. Post-Flash: We use an 8 electron post-flash background to reach the 12e- level at each readout to improve the CTE. ACS Parallels: In parallel to our WFC3/UVIS exposures, we will take ACS/WFC3 parallel imaging in F435W. Orients: No constraints are set on the orients of these observations, but ideally the visit should be scheduled close enough in time to have a similar orient for each. ------------------------------------------------------------------------------------ 15414( 3) - 08-Dec-2017 18:36:37 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 GS-MUSE-LYC GALAXY, STARBURST RA=03H32M23.8000S, J2000 V = 26 DEC=-27D50'21.10" Reference Frame: ICRS ------------------------------------------------------------------------------------------------------------------------------------ 15414( 3) - 08-Dec-2017 18:36:37 - [ 4] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type WFC3-UVIS-DITHER-BOX Pattern_Purpose DITHER Number_Of_Points 4 Point_Spacing 0.173 Line_Spacing 0.112 Coordinate_Frame POS-TARG Pattern_Orient 23.884 Angle_Between_Sides 81.785 Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 2 Primary_Pattern Secondary_Pattern Pattern_Type WFC3-UVIS-DITHER-LINE Pattern_Purpose DITHER Number_Of_Points 2 Point_Spacing 0.145 Line_Spacing Coordinate_Frame POS-TARG Pattern_Orient 46.84 Angle_Between_Sides Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ 15414( 3) - 08-Dec-2017 18:36:37 - [ 5] Visit: 01 (V1-4pt) Visit Requirements: ORIENT 5D TO 345 D 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 GS-MUSE-LYC WFC3/UVI ACCUM UVIS2-C1K F336W FLASH=8 1 1338 S POS TARG 0, 0; PATTERN 1 S 1C-CTE (5532 S) 1-2; PAR 2 WITH 1 ------------------------------------------------------------------------------------------------------------------------------------ 2 ANY ACS/WFC ACCUM WFC F435W 1 1250 S see below (5200 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 | ------------------------------------------------------------------------------------------------------------------------------------ GS-MUSE-LYC 1 WFC3/UVI ACCUM UVIS2-C1 F336W 1 none none none 1 N/A S K1C-CTE GS-MUSE-LYC 1 WFC3/UVI ACCUM UVIS2-C1 F336W 2 none none none 1 N/A S K1C-CTE GS-MUSE-LYC 1 WFC3/UVI ACCUM UVIS2-C1 F336W 3 none none none 2 1428.0 S S K1C-CTE GS-MUSE-LYC 1 WFC3/UVI ACCUM UVIS2-C1 F336W 4 none none none 2 1428.0 S S K1C-CTE ANY 2 ACS/WFC ACCUM WFC F435W 1 none none none 1 1260.0 S ANY 2 ACS/WFC ACCUM WFC F435W 2 none none none 1 N/A ANY 2 ACS/WFC ACCUM WFC F435W 3 none none none 2 1400.0 S ANY 2 ACS/WFC ACCUM WFC F435W 4 none none none 2 1290.0 S 15414( 3) - 08-Dec-2017 18:36:37 - [ 6] Visit: 02 (V2-4pt) Visit Requirements: SAME ORIENT AS 01 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 GS-MUSE-LYC WFC3/UVI ACCUM UVIS2-C1K F336W FLASH=8 1 1300 S POS TARG -0.42, -2.02; S 1C-CTE see below PATTERN 1 1-2; PAR 2 (5528 S) WITH 1 ------------------------------------------------------------------------------------------------------------------------------------ 2 ANY ACS/WFC ACCUM WFC F435W 1 1250 S see below (5196 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 | ------------------------------------------------------------------------------------------------------------------------------------ GS-MUSE-LYC 1 WFC3/UVI ACCUM UVIS2-C1 F336W 1 none none none 1 1336.0 S S K1C-CTE GS-MUSE-LYC 1 WFC3/UVI ACCUM UVIS2-C1 F336W 2 none none none 1 1336.0 S S K1C-CTE GS-MUSE-LYC 1 WFC3/UVI ACCUM UVIS2-C1 F336W 3 none none none 2 1428.0 S S K1C-CTE GS-MUSE-LYC 1 WFC3/UVI ACCUM UVIS2-C1 F336W 4 none none none 2 1428.0 S S K1C-CTE ANY 2 ACS/WFC ACCUM WFC F435W 1 none none none 1 1256.0 S ANY 2 ACS/WFC ACCUM WFC F435W 2 none none none 1 N/A ANY 2 ACS/WFC ACCUM WFC F435W 3 none none none 2 1400.0 S ANY 2 ACS/WFC ACCUM WFC F435W 4 none none none 2 1290.0 S 15414( 3) - 08-Dec-2017 18:36:37 - [ 7] Visit: 03 (V3-2pt) Visit Requirements: SAME ORIENT AS 01 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 GS-MUSE-LYC WFC3/UVI ACCUM UVIS2-C1K F336W FLASH=8 1 1300 S POS TARG -0.21, -1.01; S 1C-CTE see below PATTERN 2 1-2; PAR 2 (2672 S) WITH 1 ------------------------------------------------------------------------------------------------------------------------------------ 2 ANY ACS/WFC ACCUM WFC F435W 1 1250 S see below (2506 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 | ------------------------------------------------------------------------------------------------------------------------------------ GS-MUSE-LYC 1 WFC3/UVI ACCUM UVIS2-C1 F336W 1 none none none 1 1336.0 S S K1C-CTE GS-MUSE-LYC 1 WFC3/UVI ACCUM UVIS2-C1 F336W 2 none none none 1 1336.0 S S K1C-CTE ANY 2 ACS/WFC ACCUM WFC F435W 1 none none none 1 1256.0 S ANY 2 ACS/WFC ACCUM WFC F435W 2 none none none 1 N/A 15414( 3) - 08-Dec-2017 18:36:37 - [ 8] Summary Form for Proposal 15414 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures UVIS2-C1K1C-CTE, WFC ------------------------------------------------------------------------------------------------------------------------------------ Configurations ACS/WFC, WFC3/UVIS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters FLASH=8 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENT 5D TO 345 D, PAR 2 WITH 1, PATTERN 1 1-2, PATTERN 2 1-2, POS TARG -0.21, -1.01, POS TARG -0.42, -2.02, POS TARG 0, 0, SAME ORIENT AS 01 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F336W, F435W ------------------------------------------------------------------------------------------------------------------------------------ Target Names ANY, GS-MUSE-LYC ------------------------------------------------------------------------------------------------------------------------------------