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

Authors :
Endsley, Ryan
Stark, Daniel P
Bouwens, Rychard J
Schouws, Sander
Smit, Renske
Stefanon, Mauro
Inami, Hanae
Bowler, Rebecca A A
Oesch, Pascal
Gonzalez, Valentino
Aravena, Manuel
da Cunha, Elisabete
Dayal, Pratika
Ferrara, Andrea
Graziani, Luca
Nanayakkara, Themiya
Pallottini, Andrea
Schneider, Raffaella
Sommovigo, Laura
Topping, Michael
Source :
Monthly Notices of the Royal Astronomical Society; Dec2022, Vol. 517 Issue 4, p5642-5659, 18p
Publication Year :
2022

Abstract

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 (M<subscript>UV</subscript> ∼ −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<superscript>–1</superscript>) and broad (FWHM ≈ 300–650 km s<superscript>−1</superscript>), with two sources showing emission extending to ≈750 km s<superscript>−1</superscript>. 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. [ABSTRACT FROM AUTHOR]

Details

Language :
English
ISSN :
00358711
Volume :
517
Issue :
4
Database :
Complementary Index
Journal :
Monthly Notices of the Royal Astronomical Society
Publication Type :
Academic Journal
Accession number :
160354296
Full Text :
https://doi.org/10.1093/mnras/stac3064