2022A&A...658L...2D

We present the detection of [CII] 158 µm emission from the Spiderweb galaxy at z = 2.1612 using the Atacama Pathfinder EXperiment (APEX). The line profile splits into an active galactic nucleus (AGN) and circumgalactic medium (CGM) component previously identified in CO and [CI]. We find that these individual [CII] components are consistent in terms of CO and far-IR luminosity ratios with the populations of other z ≥ 1 AGN and dusty star-forming galaxies. The CGM component dominates the [CII] emission in the 10'' APEX beam. Although we do not have spatially resolved data, the close correspondence of the velocity profile with the CO(1-0) detected only on scales of tens of kiloparsecs in CO(1-0) suggests that the [CII] emission is similarly extended, reminiscent of [CII] halos recently found around z > 5 galaxies. Comparing the first four ionization states of carbon, we find that the atomic [CI] emission is dominant, which increases its reliability as a molecular mass tracer. Our [CII] detection at 601.8 GHz also demonstrates the feasibility to extend the frequency range of ALMA Band 9 beyond the original specifications.