Caught in the act: diffuse stellar and Lyα emission around a halo-less quasar in the assembling cluster CARLA J0800+4029 at z = 2
A quasar at the heart of a forming galaxy cluster shows almost no glowing gas around it. The gas lights up a little further away, along a tidal stream of stars and galaxies caught in the middle of merging.
What was found
- No clear extended Lyα halo surrounds the radio-loud quasar. The brightest Lyα emission sits away from it, tied to a disturbed group of galaxies with tidal features and diffuse starlight.
- The limit at the position of the quasar is about 3.4 times fainter than the offset emission, among the tightest constraints of this kind at similar redshift.
- The Lyα glow and the diffuse stellar light line up, which suggests that gas and stars were moved together while the cluster assembled.
- Close to the quasar the gas may be ionised, depleted or suppressed, while the offset region appears better suited to emit Lyα.
This summary is written for a general audience. The paper has the full details.
Cite this paper
Gallego, S. G., Mei, S., Daddi, E., Noirot, G., Wylezalek, D., & Rich, R. M. 2026, Astronomy & Astrophysics (submitted), arXiv:2609.37445
@article{gallego2026,
author = {Gallego, Sofia G. and Mei, Simona and Daddi, Emanuele and Noirot, Gaël and Wylezalek, Dominika and Rich, R. M.},
title = {{Caught in the act: diffuse stellar and Lyα emission around a halo-less quasar in the assembling cluster CARLA J0800+4029 at z = 2}},
journal = {arXiv e-prints},
year = {2026},
eprint = {2609.37445},
archivePrefix = {arXiv}
}Topics Clusters and protoclusters Quasars and AGN Circumgalactic and intergalactic gas