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On the nature and physical conditions of the luminous Ly α emitter CR7 and its rest-frame UV components

Sobral, David and Matthee, Jorryt and Brammer, Gabriel and Ferrara, Andrea and Alegre, Lara and Röttgering, Huub and Schaerer, Daniel and Mobasher, Bahram and Darvish, Behnam (2019) On the nature and physical conditions of the luminous Ly α emitter CR7 and its rest-frame UV components. Monthly Notices of the Royal Astronomical Society, 482 (2). pp. 2422-2441. ISSN 0035-8711.

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We present new Hubble Space Telescope (HST)/WFC3 observations and re-analyse VLT data to unveil the continuum, variability, and rest-frame ultraviolet (UV) lines of the multiple UV clumps of the most luminous Lyα emitter at z = 6.6, CR7 (COSMOS Redshift 7). Our re-reduced, flux-calibrated X-SHOOTER spectra of CR7 reveal an He II emission line in observations obtained along the major axis of Lyα emission with the best seeing conditions. He II is spatially offset by ≈+0.8 arcsec from the peak of Lyα emission, and it is found towards clump B. Our WFC3 grism spectra detects the UV continuum of CR7’s clump A, yielding a power law with β=−2.5^(+0.6)_(−0.7) and M_(UV) = −21.87^(+0.25)_(−0.20)⁠. No significant variability is found for any of the UV clumps on their own, but there is tentative (≈2.2 σ) brightening of CR7 in F110W as a whole from 2012 to 2017. HST grism data fail to robustly detect rest-frame UV lines in any of the clumps, implying fluxes ≲2×10^(−17) erg s^(−1) cm^(−2) (3σ). We perform CLOUDY modelling to constrain the metallicity and the ionizing nature of CR7. CR7 seems to be actively forming stars without any clear active galactic nucleus activity in clump A, consistent with a metallicity of ∼0.05–0.2 Z⊙. Component C or an interclump component between B and C may host a high ionization source. Our results highlight the need for spatially resolved information to study the formation and assembly of early galaxies.

Item Type:Article
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URLURL TypeDescription Paper
Sobral, David0000-0001-8823-4845
Brammer, Gabriel0000-0003-2680-005X
Darvish, Behnam0000-0003-4919-9017
Additional Information:© 2018 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model ( Accepted 2018 October 10. Received 2018 October 3; in original form 2017 October 21. Published: 24 October 2018. We thank the anonymous reviewer for the numerous detailed comments that led us to greatly improve the quality, extent, and statistical robustness of this work. DS acknowledges financial support from the Netherlands Organisation for Scientific research through a Veni fellowship. JM acknowledges the support of a Huygens PhD fellowship from Leiden University. AF acknowledges support from the ERC Advanced Grant INTERSTELLAR H2020/740120. BD acknowledges financial support from NASA through the Astrophysics Data Analysis Program, grant number NNX12AE20G and the National Science Foundation, grant number 1716907. We are thankful for several discussions and constructive comments from Johannes Zabl, Eros Vanzella, Bo Milvang-Jensen, Henry McCracken, Max Gronke, Mark Dijkstra, Richard Ellis, and Nicolas Laporte. We also thank Umar Burhanudin and Izzy Garland for taking part in the XGAL internship in Lancaster and for exploring the HST grism data independently. Based on observations obtained with HST/WFC3 programs 12578, 14495, and 14596. Based on observations of the National Japanese Observatory with the Suprime-Cam on the Subaru telescope (S14A-086) on the big island of Hawaii. This work is based in part on data products produced at TERAPIX available at the Canadian Astronomy Data Centre as part of the Canada–France–Hawaii Telescope Legacy Survey, a collaborative project of NRC and CNRS. Based on data products from observations made with ESO Telescopes at the La Silla Paranal Observatory under ESO programme IDs 294.A-5018, 294.A-5039, 092.A-0786, 093.A-0561, 097.A-0043, 097.A-0943, 098.A-0819, 298.A-5012, and 179.A-2005, and on data products produced by TERAPIX and the Cambridge Astronomy Survey Unit on behalf of the UltraVISTA consortium. The authors acknowledge the award of service time (SW2014b20) on the William Herschel Telescope (WHT). WHT and its service programme are operated on the island of La Palma by the Isaac Newton Group in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias. This research was supported by the Munich Institute for Astro- and Particle Physics of the DFG cluster of excellence ‘Origin and Structure of the Universe’. We have benefitted immensely from the public available programming language PYTHON, including NUMPY and SCIPY (Jones et al. 2001; Van Der Walt, Colbert & Varoquaux 2011), MATPLOTLIB (Hunter 2007), ASTROPY (Astropy Collaboration et al. 2013), and the TOPCAT analysis program (Taylor 2013). This research has made use of the VizieR catalogue access tool, CDS, Strasbourg, France. All data used for this paper are publicly available, and we make all reduced data available with the refereed paper.
Funding AgencyGrant Number
Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO)UNSPECIFIED
Leiden UniversityUNSPECIFIED
European Research Council (ERC)740120
Deutsche Forschungsgemeinschaft (DFG)UNSPECIFIED
Subject Keywords:galaxies: evolution – galaxies: high-redshift – galaxies: ISM– cosmology: observations – dark ages, reionization, first stars – early Universe
Record Number:CaltechAUTHORS:20190117-091515335
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Official Citation:David Sobral, Jorryt Matthee, Gabriel Brammer, Andrea Ferrara, Lara Alegre, Huub Röttgering, Daniel Schaerer, Bahram Mobasher, Behnam Darvish; On the nature and physical conditions of the luminous Ly α emitter CR7 and its rest-frame UV components, Monthly Notices of the Royal Astronomical Society, Volume 482, Issue 2, 11 January 2019, Pages 2422–2441,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:92337
Deposited By: Tony Diaz
Deposited On:22 Jan 2019 22:07
Last Modified:22 Jan 2019 22:07

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