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.
The REBELS ALMA Survey: efficient Ly????? transmission of UV-bright z ??? 7 galaxies from large velocity offsets and broad line widths / Endsley, Ryan; P Stark, Daniel; J Bouwens, Rychard; Schouws, Sander; Smit, Renske; Stefanon, Mauro; Inami, Hanae; A Bowler, Rebecca A; Oesch, PASCAL ANDREAS; Gonzalez, Valentino; Aravena, Manuel; Da??cunha, Elisabete; Dayal, Pratika; Ferrara, Andrea; Graziani, Luca; Nanayakkara, Themiya; Pallottini, Andrea; Schneider, Raffaella; Sommovigo, Laura; Topping, Michael; Van??der??werf, Paul; Hutter, Anne. - In: MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY. - ISSN 0035-8711. - 517:4(2022), pp. 5642-5659. [10.1093/mnras/stac3064]
The REBELS ALMA Survey: efficient Ly????? transmission of UV-bright z ??? 7 galaxies from large velocity offsets and broad line widths
Pascal Oesch;Pratika Dayal;Luca Graziani;Raffaella Schneider;
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 (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.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.