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The REBELS ALMA Survey: efficient Ly α transmission of UV-bright z ≃ 7 galaxies from large velocity offsets and broad line widths

Endsley, R, Stark, DP, Bouwens, RJ, Schouws, S, Smit, R, Stefanon, M, Inami, H, Bowler, RAA, Oesch, P, Gonzalez, V, Aravena, M, Da Cunha, E, Dayal, P, Ferrara, A, Graziani, L, Nanayakkara, T, Pallottini, A, Schneider, R, Sommovigo, L, Topping, M , Van Der Werf, P and Hutter, A (2022) The REBELS ALMA Survey: efficient Ly α transmission of UV-bright z ≃ 7 galaxies from large velocity offsets and broad line widths. Monthly Notices of the Royal Astronomical Society, 517 (4). pp. 5642-5659. ISSN 0035-8711

The REBELS ALMA Survey efficient Ly α transmission of UV-bright z ≃ 7 galaxies from large velocity offsets and broad line widths.pdf - Published Version

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Recent work has shown that UV-luminous reionization-era galaxies often exhibit strong Lyman-alpha emission despite being situated at redshifts where the IGM is thought to be substantially neutral. It has been argued that this enhanced Ly α transmission reflects the presence of massive galaxies in overdense regions which power large ionized bubbles. An alternative explanation is that massive galaxies shift more of their Ly α profile to large velocities (relative to the systemic redshift) where the IGM damping wing absorption is reduced. Such a mass-dependent trend is seen at lower redshifts, but whether one exists at z ∼7 remains unclear owing to the small number of existing systemic redshift measurements in the reionization era. This is now changing with the emergence of [C ii]-based redshifts from ALMA. Here, we report MMT/Binospec Ly α spectroscopy of eight UV-bright (MUV ∼-22) galaxies at z ≃ 7 selected from the ALMA REBELS survey. We detect Ly α in four of eight galaxies and use the [C ii] systemic redshifts to investigate the Ly α velocity profiles. The Ly α lines are significantly redshifted from systemic (average velocity offset = 223 km s-1) and broad (FWHM ≈ 300-650 km s-1), with two sources showing emission extending to ≈750 km s-1. We find that the broadest Ly α profiles are associated with the largest [C ii] line widths, suggesting a potential link between the Ly α FWHM and the dynamical mass. Since Ly α photons at high velocities transmit efficiently through the z = 7 IGM, our data suggest that velocity profiles play a significant role in boosting the Ly α visibility of the most UV-luminous reionization-era galaxies.

Item Type: Article
Additional Information: This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2022 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Uncontrolled Keywords: 0201 Astronomical and Space Sciences; Astronomy & Astrophysics
Subjects: Q Science > QB Astronomy
Q Science > QC Physics
Divisions: Astrophysics Research Institute
Publisher: Oxford University Press (OUP)
SWORD Depositor: A Symplectic
Date Deposited: 09 Jan 2023 12:44
Last Modified: 09 Jan 2023 12:45
DOI or Identification number: 10.1093/mnras/stac3064
URI: https://researchonline.ljmu.ac.uk/id/eprint/18565

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