Lyα and C iii] emission in z = 7–9 Galaxies: accelerated reionization around luminous star-forming systems?
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.
Additional Information
© 2017 Oxford University Press. Received: 03 June 2016. Revision Received: 01 September 2016. Accepted: 06 September 2016. Published: 07 September 2016. We thank Mark Dijkstra, Dawn Erb, Martin Haehnelt, Guido Roberts-Borsani for enlightening conversations. We are grateful to Dawn Erb for providing data on z ≃ 2–3 Lyα velocity offsets. DPS acknowledges support from the National Science Foundation through the grant AST-1410155. RSE acknowledges support from the European Research Council through an Advanced Grant FP7/669253. SC, JG and AVG acknowledge support from the ERC via an Advanced Grant under grant agreement no. 321323– NEOGAL AZ is supported by NASA through Hubble Fellowship grant #HST-HF2-51334.001-A awarded by STScI, which is operated by the Association of Universities for Research in Astronomy, Inc. under NASA contract NAS 5-26555. This work was partially supported by a NASA Keck PI Data Award, administered by the NASA Exoplanet Science Institute. Data presented herein were obtained at the W. M. Keck Observatory from telescope time allocated to the National Aeronautics and Space Administration through the agency's scientific partnership with the California Institute of Technology and the University of California. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors acknowledge the very significant cultural role that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.Attached Files
Published - stw2233.pdf
Submitted - 1606.01304.pdf
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Additional details
- Eprint ID
- 75367
- Resolver ID
- CaltechAUTHORS:20170324-063600391
- AST-1410155
- NSF
- FP7/669253
- European Research Council (ERC)
- 321323-NEOGAL
- European Research Council (ERC)
- HST-HF2-51334.001-A
- NASA Hubble Fellowship
- NAS 5-26555
- NASA
- W. M. Keck Foundation
- Created
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2017-03-24Created from EPrint's datestamp field
- Updated
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2021-11-15Created from EPrint's last_modified field