11587( 3) - 01-Jul-2008 18:57:50 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 11587 Version: 3 Check-in Time: 01-Jul-2008 18:57:50 STScI Edit Number: 1 Title Probing Population III Star Formation in a z=7 Galaxy ------------------------------------------------------------------------------------ Type Cycle GO 17 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Xiaohui Fan University of Arizona CoI: Mr. Yujin Yang University of Arizona N CoI: Dr. Siang Peng Oh University of California - Santa Barbara N CoI: Prof. Romeel Dave University of Arizona N CoI: Dr. Ann Zabludoff University of Arizona N ------------------------------------------------------------------------------------ Abstract Population III (Pop III) stars, the first generation, metal-free stars in the Universe, have been a main focus of the studies of early galaxy formation and reionization. HeII 1640 emission originates from energetic ionizing photons beyond 54.4eV, and is an ideal tracer of massive Pop III star formation with strong far-UV radiation. HeII has not yet been detected directly in individual galaxies at z<6.3, indicating a small contribution of Pop III star formation at those redshifts. We propose to use WFC3 narrow-band imaging to measure the flux of HeII emission in galaxy IOK-1 (z=6.96), the highest redshift spectroscopically confirmed galaxy to date. At this redshift, the HeII line is perfectly located in the WFC3 F130N filter passband. Our deep narrow-band imaging will detect a HeII flux down to 4x10^-18 erg/s/cm^2 at the 5-sigma level, corresponding to a star formation rate from massive Pop III stars of ~1 M_sun per year, a factor of ~5 improvement to the best ground-based results at lower redshift. Strong HeII emission, if detected, will provide the first direct evidence of significant Pop III formation in early galaxies at the end of the reionization epoch. We will also carry out short F125W broad-band observations to measure the rest-frame UV flux of this galaxy in order to constrain its total star formation rate and to provide continuum subtraction for narrow-band imaging. ------------------------------------------------------------------------------------ Observations Description ------------------------ We will image in two filters with WFC3/IR: (1) 8-orbit exposure in F130N. (2) 2-orbit exposure in F125W. We will divide the program into two visits. In each visit, we will observe: (1) Four orbits in F130N. We will carry out a 4-point dither sequence with orbit-long (~2600) exposures in the narrow F130N band. This will bring the images to being background-limited. (2) One orbit in F125W. We will do the same 4-point dither sequence with ~650sec exposures to populate one orbit. We will do a small POS-TARG offset for the second visit and repeat the same sequence. Real Time Justification 11587( 3) - 01-Jul-2008 18:57:50 - [ 2] ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 11587( 3) - 01-Jul-2008 18:57:50 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 IOK-1 GALAXY, HIGH REDSHIFT RA=13H23M59.8000S +/- 0.1", J2000 Z = 6.96 NB973 = 24.60; z_AB >27.05 GALAXY DEC=+27D24'55.80" +/- 0.1" Reference Frame: ICRS Comments: ------------------------------------------------------------------------------------------------------------------------------------ 11587( 3) - 01-Jul-2008 18:57:50 - [ 4] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 4 Primary_Pattern Secondary_Pattern Pattern_Type WFC3-IR-DITHER-BOX-MIN Pattern_Purpose DITHER Number_Of_Points 4 Point_Spacing 0.572 Line_Spacing 0.365 Coordinate_Frame POS-TARG Pattern_Orient 18.528 Angle_Between_Sides 74.653 Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ 11587( 3) - 01-Jul-2008 18:57:50 - [ 5] Visit: 01 Visit Requirements: On Hold Comments: Additional Comments: IOK-1 4-point dither in F130N (4 orbits) and F125W (1 orbit) Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 IOK-1 WFC3/IR MULTIAC IR F130N SAMP-SEQ=SPARS200, NSAMP=15 1 DEF GS ACQ SCENARIO ONEB1B3; CUM PATTERN 4 1 ------------------------------------------------------------------------------------------------------------------------------------ 2 IOK-1 WFC3/IR MULTIAC IR F125W SAMP-SEQ=SPARS50, NSAMP=14 1 DEF PATTERN 4 2 CUM ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ IOK-1 1 WFC3/IR MULTIAC IR F130N 1 none none none 1 N/A CUM IOK-1 1 WFC3/IR MULTIAC IR F130N 2 none none none 2 N/A CUM IOK-1 1 WFC3/IR MULTIAC IR F130N 3 none none none 3 N/A CUM IOK-1 1 WFC3/IR MULTIAC IR F130N 4 none none none 4 N/A CUM IOK-1 2 WFC3/IR MULTIAC IR F125W 1 none none none 5 N/A CUM IOK-1 2 WFC3/IR MULTIAC IR F125W 2 none none none 5 N/A CUM IOK-1 2 WFC3/IR MULTIAC IR F125W 3 none none none 5 N/A CUM IOK-1 2 WFC3/IR MULTIAC IR F125W 4 none none none 5 N/A CUM 11587( 3) - 01-Jul-2008 18:57:50 - [ 6] Visit: 02 Visit Requirements: On Hold Comments: Additional Comments: IOK-1 4-point dither: F130N (4 orbits) and F125W (1 orbit), shifted by 17.25 pixels in X and Y from visit 1 for better flat-fielding Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 IOK-1 WFC3/IR MULTIAC IR F130N SAMP-SEQ=SPARS200, NSAMP=15 1 DEF POS TARG 2.3374, 2.0890; CUM GS ACQ SCENARIO ONEB1B3; PATTERN 4 1 ------------------------------------------------------------------------------------------------------------------------------------ 2 IOK-1 WFC3/IR MULTIAC IR F125W SAMP-SEQ=SPARS50, NSAMP=14 1 DEF POS TARG 2.3374, 2.0890; CUM PATTERN 4 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 | ------------------------------------------------------------------------------------------------------------------------------------ IOK-1 1 WFC3/IR MULTIAC IR F130N 1 none none none 1 N/A CUM IOK-1 1 WFC3/IR MULTIAC IR F130N 2 none none none 2 N/A CUM IOK-1 1 WFC3/IR MULTIAC IR F130N 3 none none none 3 N/A CUM IOK-1 1 WFC3/IR MULTIAC IR F130N 4 none none none 4 N/A CUM IOK-1 2 WFC3/IR MULTIAC IR F125W 1 none none none 5 N/A CUM IOK-1 2 WFC3/IR MULTIAC IR F125W 2 none none none 5 N/A CUM IOK-1 2 WFC3/IR MULTIAC IR F125W 3 none none none 5 N/A CUM IOK-1 2 WFC3/IR MULTIAC IR F125W 4 none none none 5 N/A CUM 11587( 3) - 01-Jul-2008 18:57:50 - [ 7] Summary Form for Proposal 11587 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures IR ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFC3/IR ------------------------------------------------------------------------------------------------------------------------------------ Opmodes MULTIACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters NSAMP=14, NSAMP=15, SAMP-SEQ=SPARS200, SAMP-SEQ=SPARS50 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements GS ACQ SCENARIO ONEB1B3, PATTERN 4 1, PATTERN 4 2, POS TARG 2.3374, 2.0890 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F125W, F130N ------------------------------------------------------------------------------------------------------------------------------------ Target Names IOK-1 ------------------------------------------------------------------------------------------------------------------------------------