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Lyman-alpha spectroscopy of extreme [O III] emitting galaxies at z ≃ 2-3: implications for Lyα visibility and LyC leakage at z > 6

Tang, M; Stark, D; Chevallard, J; Charlot, S; Endsley, R; Congiu, E; (2021) Lyman-alpha spectroscopy of extreme [O III] emitting galaxies at z ≃ 2-3: implications for Lyα visibility and LyC leakage at z > 6. Monthly Notices of the Royal Astronomical Society , 503 (3) pp. 4105-4117. 10.1093/mnras/stab705. Green open access

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Abstract

Spectroscopic observations of massive z > 7 galaxies selected to have extremely large [O III] + H β equivalent width (EW ∼1500 Å) have recently revealed large Ly α detection rates, in contrast to the weak emission seen in the general population. Why these systems are uniquely visible in Ly α at redshifts where the intergalactic medium (IGM) is likely significantly neutral is not clear. With the goal of better understanding these results, we have begun a campaign with MMT and Magellan to measure Ly α in galaxies with similar [O III] + H β EWs at z ≃ 2–3. At these redshifts, the IGM is highly ionized, allowing us to clearly disentangle how the Ly α properties depend on the [O III] + H β EW. Here, we present Ly α EWs of 49 galaxies at z = 2.2–3.7 with intense [O III] + H β line emission (EW = 300–3000 Å). Our results demonstrate that strong Ly α emission (EW >20 Å) becomes more common in galaxies with larger [O III] + H β EW, reflecting a combination of increasingly efficient ionizing photon production and enhanced transmission of Ly α. Among the galaxies with the most extreme [O III] + H β emission (EW ∼1500 Å), we find that strong Ly α emission is not ubiquitous, with only 50 per cent of our population showing Ly α EW >20 Å. Our data suggest that the range of Ly α strengths is related to the observed ellipticity, with those systems that appear edge-on or elongated having weaker Ly α emission. We use these results to interpret the anomalous Ly α properties seen in z > 7 galaxies with extreme [O III] + H β emission and discuss implications for the escape of ionizing radiation from these extreme line emitting galaxies.

Type: Article
Title: Lyman-alpha spectroscopy of extreme [O III] emitting galaxies at z ≃ 2-3: implications for Lyα visibility and LyC leakage at z > 6
Open access status: An open access version is available from UCL Discovery
DOI: 10.1093/mnras/stab705
Publisher version: http://dx.doi.org/10.1093/mnras/stab705
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: galaxies: evolution, galaxies: formation, galaxies: high-redshift, cosmology: observations
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/10124412
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