Letter to the Editor

Feeding the spider with carbon

[CII] emission from the circumgalactic medium and active galactic nucleus^⋆

¹ European Southern Observatory, Karl Schwarzschild Straße 2, 85748 Garching, Germany
e-mail: cdebreuc@eso.org
² National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903, USA
³ Inter-University Institute for Data Intensive Astronomy, Department of Astronomy, University of Cape Town, Rondebosch 7701, South Africa
⁴ Physics Department, University of Johannesburg, 5 Kingsway Ave, Rossmore, Johannesburg 2092, South Africa
⁵ Instituto de Astrofísica de Canarias (IAC), 38205 La Laguna, Tenerife, Spain
⁶ Universidad de La Laguna, Dpto. Astrofísica, 38206 La Laguna, Tenerife, Spain
⁷ Université Lyon1, ENS-Lyon, CNRS, Centre de Recherche Astrophysique de Lyon UMR5574, 69230 Saint-Genis-Laval, France

Received: 23 July 2021
Accepted: 22 December 2021

Abstract

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.