Tracing Lyman alpha escape in the CRISTAL-02 galaxy at z~5.3

October 2026 • 2026A&A...714A.179A

Authors • Ali, Arshi • Guaita, Lucia • Aravena, Manuel • Davies, Rebecca L. • González, Jorge • Villanueva, Vicente • Oyarzún, Diego • Herrera-Camus, Rodrigo • Nanni, Ambra • Faisst, Andreas • Koekemoer, Anton M. • Fisher, Deanne B. • Inami, Hanae • Molina, Juan • Spilker, Justin • Liu, Lun-Jun • Solimano, Manuel • Ginolfi, Michele • Romano, Michael • Nezhad, Negin • Dam, Poulomi • Wang, Wuji • Li, Yuan

Abstract • Aims. We investigate the mechanisms regulating the escape of Lyman-alpha (Lyα) photons in the star-forming galaxy CRISTAL-02 at redshift z ≈ 5.3. Previous studies revealed a diffused and extended Lyα emitting gas (radius ~16.5 kpc) and a possible [C II] outflow. The galaxy has been identified with five distinct clumps, two of which have been suggested as potential active galactic nuclei (AGN) candidates (Clump A and B hereafter). We study how AGN or star formation activities influence the spatial distribution and visibility of Lyα emission. Methods. Using integral field spectroscopic Lyα data from VLT/MUSE and JWST/NIRSpec integral field unit (IFU) observations of Hα and Hβ, complemented by NIRCam UV imaging, we constructed spatially matched emission-line maps. We derived flux, emission-line ratio, and extinction maps as well as spatially resolved measurements of the Lyα escape fraction and ionizing photon production efficiency. Results. We find that the Lyα emission extends preferentially along the [C II] outflow direction, while the Hα and UV emission trace the galactic disk. Two compact regions (Clumps A and B) exhibit contrasting properties: Clump A, associated with lower dust attenuation, shows enhanced Lyα/Hα ratios and a higher Lyα escape fraction, whereas Clump B shows stronger Hα and UV emission but suppressed Lyα. The results indicate that Lyα escape can be influenced by AGN or star formation-driven outflows, dust attenuation, and local gas conditions. Conclusions. This study provides one of the first spatially resolved measurements of the Lyα escape fraction and ionizing photon production efficiency in distant systems, and it highlights the role of feedback-driven gas clearing and anisotropic outflows in shaping the observed Lyα properties. The current observational evidence is most consistent with the presence of an outflow, while the mechanism driving it remains uncertain, as the available data do not uniquely distinguish between AGN and star formation-driven feedback. Future spatially resolved multiwavelength IFU observations combining Lyα, Hα, and [C II] emission will be essential to disentangling these scenarios and establishing the dominant feedback mechanism.

Links

• POSTSCRIPT https://www.aanda.org/10.1051/0004-6361/202660326/postscript