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No evidence for Population III stars or a direct collapse black hole in the z = 6.6 Lyman α emitter ‘CR7’

Bowler, R. A. A. and McLure, R. J. and Dunlop, J. S. and McLeod, D. J. and Stanway, E. R. and Eldridge, J. J. and Jarvis, M. J. (2017) No evidence for Population III stars or a direct collapse black hole in the z = 6.6 Lyman α emitter ‘CR7’. Monthly Notices of the Royal Astronomical Society, 469 (1). pp. 448-458. ISSN 0035-8711.

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The z = 6.6 Lyman α emitter ‘CR7’ has been claimed to have a Population III (Pop III) like stellar population, or alternatively, be a candidate direct collapse black hole (DCBH). In this paper, we investigate the evidence for these exotic scenarios using recently available, deeper, optical, near-infrared and mid-infrared imaging. We find strong Spitzer/Infrared Array Camera detections for the main component of CR7 at 3.6 and 4.5 μm, and show that it has a blue colour ([3.6] − [4.5] = −1.2 ± 0.3). This colour cannot be reproduced by current Pop III or pristine DCBH models. Instead, the results suggest that the [3.6] band is contaminated by the [O III]λλ 4959, 5007 emission line with an implied rest-frame equivalent width of EW0(H β + [O III]) ≳ 2000 Å. Furthermore, we find that new near-infrared data from the UltraVISTA survey supports a weaker He II λ1640 emission line than previously measured, with EW0 = 40 ± 30 Å. For the fainter components of CR7 visible in Hubble Space Telescope imaging, we find no evidence that they are particularly red as previously claimed, and show that the derived masses and ages are considerably uncertain. In light of the likely detection of strong [O III] emission in CR7, we discuss other more standard interpretations of the system that are consistent with the data. We find that a low-mass, narrow-line active galactic nucleus can reproduce the observed features of CR7, including the lack of radio and X-ray detections. Alternatively, a young, low-metallicity (∼1/200 Z⊙) starburst, modelled including binary stellar pathways, can reproduce the inferred strength of the He II line and simultaneously the strength of the observed [O III] emission, but only if the gas shows supersolar α-element abundances (O/Fe ≃ 5 (O/Fe)⊙).

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Additional Information:C 2017 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. Accepted 2017 April 3. Received 2017 March 14; in original form 2016 September 5. This work was supported by the Oxford Centre for Astrophysical Surveys, which is funded through generous support from the Hintze Family Charitable Foundation. JSD acknowledges the support of the European Research Council via the award of an Advanced Grant (PI: J. Dunlop), and the contribution of the EC FP7 SPACE project ASTRODEEP (Ref.No: 312725). RJM and DJM acknowledge the support from the European Research Council via the award of a Consolidator Grant (PI: R. McLure). ERS acknowledges support from UK Science and Technology Facilities Council (STFC) consolidated grant ST/L000733/1. MJJ acknowledges support from the UK STFC [ST/N000919/1]. This publication arises from research partly funded by the John Fell Oxford University Press (OUP) Research Fund. ERS and JJE wish to acknowledge the contribution of the high-performance computing facilities and the staff at the Centre for eResearch at the University of Auckland. New Zealand’s national facilities are provided by the New Zealand eScience Infrastructure (NeSI) and funded jointly by NeSI’s collaborator institutions and through the Ministry of Business, Innovation and Employment Infrastructure programme ( This work is based in part on observations made with the NASA/ESA HST, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. This work is based on data products from observations made with ESO telescopes at the La Silla Paranal Observatories under ESO programme ID 179.A-2005 and on data products produced by TERAPIX and the Cambridge Astronomy survey Unit on behalf of the UltraVISTA consortium. This work is based in part on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a NASA contract.
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ID Code:78645
Deposited By: Joy Painter
Deposited On:28 Jun 2017 20:24
Last Modified:28 Jun 2017 20:24

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