Lyα and CIII] emission in z = 7-9 Galaxies: Accelerated reionization around luminous star-forming systems?

Daniel P. Stark, Richard S. Ellis, Stéphane Charlot, Jacopo Chevallard, Mengtao Tang, Sirio Belli, Adi Zitrin, Ramesh Mainali, Julia Gutkin, Alba Vidal-García, Rychard Bouwens, Pascal Oesch

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120 Scopus citations

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 followup 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 CIII] 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.

Original languageEnglish (US)
Pages (from-to)469-479
Number of pages11
JournalMonthly Notices of the Royal Astronomical Society
Volume464
Issue number1
DOIs
StatePublished - Jan 1 2017

Keywords

  • Cosmology: observations
  • Galaxies: evolution
  • Galaxies: formation
  • Galaxies: high-redshift

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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    Stark, D. P., Ellis, R. S., Charlot, S., Chevallard, J., Tang, M., Belli, S., Zitrin, A., Mainali, R., Gutkin, J., Vidal-García, A., Bouwens, R., & Oesch, P. (2017). Lyα and CIII] emission in z = 7-9 Galaxies: Accelerated reionization around luminous star-forming systems? Monthly Notices of the Royal Astronomical Society, 464(1), 469-479. https://doi.org/10.1093/mnras/stw2233