Is Lyman Alpha Emitter CR7 Powered by a Direct Collapse Black Hole?

0 Assigned ID: 28 ----- Attempting Submission 1 (Sat Mar 26 15:25:52 GMT 2016) ----- HST Phase I Proposal 28 (CR7Cycle24.apt) successfully submitted. Receipt: # 28-1 ----- Attempting Submission 2 (Sun Mar 27 13:56:18 GMT 2016) ----- HST Phase I Proposal 28 (CR7Cycle24.apt) successfully submitted. Receipt: # 28-2 ----- Attempting Submission 3 (Wed Apr 06 10:31:51 GMT 2016) ----- HST Phase I Proposal 28 (CR7Cycle24.apt) successfully submitted. Receipt: # 28-3 ----- Attempting Submission 4 (Thu Apr 07 19:42:18 GMT 2016) ----- HST Phase I Proposal 28 (CR7Cycle24.apt) successfully submitted. Receipt: # 28-4 0 ----- Attempting Submission 1 (Tue Jul 12 09:15:28 GMT 2016) ----- Is Lyman Alpha Emitter CR7 Powered by a Direct Collapse Black Hole? 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. 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 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. Massive Black Holes and their Hosts Galaxies 12 false false false false false false SUPPORTED GALAXY HIGH REDSHIFT GALAXY J2000 J2000 J=24.6 WFC3/IR Imaging No No F110W WFC3/IR Imaging No No F160W WFC3/IR Imaging No No F110W WFC3/IR Imaging No No F160W POS-TARG DITHER 4.92090 LINE 4.69606 false false 90.3118 4 7.76885 WFC3-IR-DITHER-BOX-MIN 2

false

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