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Lyα and C III] emission in z = 7–9 Galaxies: accelerated reionization around luminous star-forming systems?

Stark, D; Ellis, R; Charlot, S; Chevallard, J; Tang, M; Belli, S; Zitrin, A; ... Oesch, P; + view all (2017) Lyα and C III] emission in z = 7–9 Galaxies: accelerated reionization around luminous star-forming systems? Monthly Notices of the Royal Astronomical Society , 464 (1) pp. 469-479. 10.1093/mnras/stw2233. Green open access

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Abstract

We discuss new Keck/MOSFIRE spectroscopic observations of four luminous galaxies at z ≃ 7–9 selected to have intense optical line emission by Roberts-Borsani et al. Previous follow-up has revealed Lyα in two of the four galaxies. Our new MOSFIRE observations confirm that Lyα is present in the entire sample. We detect Lyα emission in the galaxy COS-zs7-1, confirming its redshift as zLyα = 7.154, and we detect Lyα in EGS-zs8-2 at zLyα = 7.477, verifying an earlier tentative detection. The ubiquity of Lyα in this sample is puzzling given that the IGM is expected to be significantly neutral over 7 < z < 9. To investigate this result in more detail, we have initiated a campaign to target UV metal lines in the four Lyα emitters as a probe of both the ionizing field and the Lyα velocity offset at early times. Here we present the detection of C III] emission in the z = 7.73 galaxy EGS-zs8-1, requiring an intense radiation field and moderately low metallicity. We argue that the radiation field is likely to affect the local environment, increasing the transmission of Lyα through the galaxy. Moreover, the centroid of C III] indicates that Lyα is redshifted by 340 km s−1. This velocity offset is larger than that seen in less luminous systems, providing an explanation for the transmission of Lyα emission through the IGM. Since the transmission is further enhanced by the likelihood that such systems are also situated in large ionized bubbles, the visibility of Lyα at z > 7 is expected to be strongly luminosity-dependent, with transmission accelerated in systems with intense star formation.

Type: Article
Title: Lyα and C III] emission in z = 7–9 Galaxies: accelerated reionization around luminous star-forming systems?
Open access status: An open access version is available from UCL Discovery
DOI: 10.1093/mnras/stw2233
Publisher version: http://dx.doi.org/10.1093/mnras/stw2233
Language: English
Additional information: This version is the version of record. For information on re-use, please refer to the publisher’s terms and conditions.
Keywords: Cosmology: observations; galaxies: evolution; galaxies: formation; galaxies: high-redshift
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Physics and Astronomy
URI: https://discovery.ucl.ac.uk/id/eprint/1505728
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