14596( 2) - 18-Jul-2016 16:03:22 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 14596 Version: 2 Check-in Time: 18-Jul-2016 16:03:22 STScI Edit Number: 0 Title Is Lyman Alpha Emitter CR7 Powered by a Direct Collapse Black Hole? ------------------------------------------------------------------------------------ Type Cycle GO 24 ------------------------------------------------------------------------------------ Investigators Contact? PI: Prof. Xiaohui Fan University of Arizona Y CoI: Prof. Andrea Ferrara Scuola Normale Superiore, Pisa N CoI: Dr. Fabio Pacucci Yale University N CoI: Dr. Andrea Pallottini University of Cambridge N ------------------------------------------------------------------------------------ Abstract Discoveries of luminous quasars powered by supermassive black holes (BH) with masses up to 10 billion solar masses challenge theories of early BH formation and growth, and suggests the existence of direct collapse black holes (DCBHs) with masses >10^4 solar masses as their initial seeds. CR7 (z=6.6) is the brightest Ly alpha emitter ever discovered, with strong HeII emission line and no metal lines, suggesting that it could be the first Population III galaxy formed in a metal-free environment. Alternatively, its properties can also be explained by an AGN powered by a DCBH in the last stage of its accretion at 10^(6-7) solar masses. If it is a DCBH-powered AGN, CR7 is expected to vary at >0.1 mag level in month to year timescales. We propose to carry out new HST/WFC3 F110W and F125W observations in two separate visits. This, combined with archival observations in 2012, will measure the variability of CR7 with rest-frame time lags ranging from 50 days to 300 days. If any significant variability is detected, this will conclusively show that CR7 is a AGN, and is highly likely powered by a DCBH. Its variability property will put a first constraint on models of DCBH accretion; a lack of variability, on the other hand, would strongly suggest CR7 to be powered by Pop-III stars. This modest 4-orbit HST program could help identify either the first DCBH or the first Pop-III galaxy in the early universe, an exciting prospect for future investigations in the JWST era. ------------------------------------------------------------------------------------ Observations Description ------------------------ PROGRAM GOALS: Our goal is to measure the photometric variability of bright Ly alpha emitter CR7 at z=6.6 in order to test if it is a Pop-III galaxy or a direct collapse black hole powered AGN. If it is powered by a million solar mass BH and has similar variability properties as low-luminosity local AGNs, we expect it to show variability with rms amplitude of ~0.15 - 0.2 mag in the rest-frame UV at longer than a month timescale in the rest-frame. Theoretical model also suggests longer term variability on the feedback timescale of order a year or longer. We aim at measuring variability at both month and year timescales. We will obtain deep F110W and F160W exposures of CR7 in two new epochs (two visits) in Cycle 24, separately by ~300 days (~40 days in the rest-frame). In each visit, we will obtain exposure for one orbit in each of the F110W and 14596( 2) - 18-Jul-2016 16:03:22 - [ 2] F160W filters. This, combined with archival data of the same field observed in 2012, we give us three epochs and test CR7 variability in both month and year timescales. DITHERING AND EXPOSURE: The CR7 field was observed in program 12578 (PI: Forster-Schreiber) by HST/WFC3 in F110W and F160W bands in 2012. In our program, we will adopt the same exposure and dithering part used in program 12578 (visit 3, orbits 2 and 3). For each orbit, we will have four sub-exposures. We will use customized WFC3-IR-DITHER-BOX-MIN dither pattern with the same box size (~5") as used in program 12758. The sub-integer pixel offsets ensure sampling by 1/2 pixel in each of the x and y directions. Similarly, we will use the MULTIACCUM readout mode with SPARS50 and NSAMP = 14. This choice maximizes the use of the visibility period during each orbit, allows parallel buffer dumps, and provides a sufficient number of non-destructive reads to further mitigate the impact of cosmic rays. TIME CONSTRAINTS: This is a monitor program. We request the first visit to be in the early part of the window, before May 15, 2017, and the second visit to be separated by no less than 250 days (~one month in the rest frame at z=6.6). In total, the program will have four orbits, with two visits of two orbits each. ------------------------------------------------------------------------------------ 14596( 2) - 18-Jul-2016 16:03:22 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 CR7 GALAXY, HIGH REDSHIFT RA=10H00M58.0050S +/- 0.1", J2000 J=24.6 GALAXY DEC=+01D48'15.25" +/- 0.1" Reference Frame: ICRS ------------------------------------------------------------------------------------------------------------------------------------ 14596( 2) - 18-Jul-2016 16:03:22 - [ 4] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 2 Primary_Pattern Secondary_Pattern Pattern_Type WFC3-IR-DITHER-BOX-MIN Pattern_Purpose DITHER Number_Of_Points 4 Point_Spacing 4.92090 Line_Spacing 4.69606 Coordinate_Frame POS-TARG Pattern_Orient 7.76885 Angle_Between_Sides 90.3118 Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ 14596( 2) - 18-Jul-2016 16:03:22 - [ 5] Visit: 01 (CR7-epoch1) Visit Requirements: BEFORE 15-MAY-2017:00:00:00 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 CR7 WFC3/IR MULTIAC IR-FIX F160W NSAMP=14, SAMP-SEQ=SPARS50 1 DEF PATTERN 2 1 CUM (2611.753 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 CR7 WFC3/IR MULTIAC IR-FIX F110W NSAMP=14, SAMP-SEQ=SPARS50 1 DEF PATTERN 2 2 CUM (2611.753 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 | ------------------------------------------------------------------------------------------------------------------------------------ CR7 1 WFC3/IR MULTIAC IR-FIX F160W 1 none none none 1 N/A CUM CR7 1 WFC3/IR MULTIAC IR-FIX F160W 2 none none none 1 N/A CUM CR7 1 WFC3/IR MULTIAC IR-FIX F160W 3 none none none 1 N/A CUM CR7 1 WFC3/IR MULTIAC IR-FIX F160W 4 none none none 1 N/A CUM CR7 2 WFC3/IR MULTIAC IR-FIX F110W 1 none none none 2 N/A CUM CR7 2 WFC3/IR MULTIAC IR-FIX F110W 2 none none none 2 N/A CUM CR7 2 WFC3/IR MULTIAC IR-FIX F110W 3 none none none 2 N/A CUM CR7 2 WFC3/IR MULTIAC IR-FIX F110W 4 none none none 2 N/A CUM 14596( 2) - 18-Jul-2016 16:03:22 - [ 6] Visit: 02 (CR7-epoch2) Visit Requirements: AFTER 01 BY 250 D TO 400 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 CR7 WFC3/IR MULTIAC IR-FIX F160W NSAMP=14, SAMP-SEQ=SPARS50 1 DEF PATTERN 2 1 CUM (2611.753 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 CR7 WFC3/IR MULTIAC IR-FIX F110W NSAMP=14, SAMP-SEQ=SPARS50 1 DEF PATTERN 2 2 CUM (2611.753 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 | ------------------------------------------------------------------------------------------------------------------------------------ CR7 1 WFC3/IR MULTIAC IR-FIX F160W 1 none none none 1 N/A CUM CR7 1 WFC3/IR MULTIAC IR-FIX F160W 2 none none none 1 N/A CUM CR7 1 WFC3/IR MULTIAC IR-FIX F160W 3 none none none 1 N/A CUM CR7 1 WFC3/IR MULTIAC IR-FIX F160W 4 none none none 1 N/A CUM CR7 2 WFC3/IR MULTIAC IR-FIX F110W 1 none none none 2 N/A CUM CR7 2 WFC3/IR MULTIAC IR-FIX F110W 2 none none none 2 N/A CUM CR7 2 WFC3/IR MULTIAC IR-FIX F110W 3 none none none 2 N/A CUM CR7 2 WFC3/IR MULTIAC IR-FIX F110W 4 none none none 2 N/A CUM 14596( 2) - 18-Jul-2016 16:03:22 - [ 7] Summary Form for Proposal 14596 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures IR-FIX ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFC3/IR ------------------------------------------------------------------------------------------------------------------------------------ Opmodes MULTIACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters NSAMP=14, SAMP-SEQ=SPARS50 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements AFTER 01 BY 250 D TO 400 D, BEFORE 15-MAY-2017:00:00:00, PATTERN 2 1, PATTERN 2 2 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F110W, F160W ------------------------------------------------------------------------------------------------------------------------------------ Target Names CR7 ------------------------------------------------------------------------------------------------------------------------------------