Deep and narrow CO absorption revealing molecular clouds in the Hydra-A brightest cluster galaxy

Tom Rose, A. C. Edge, F. Combes, M. Gaspari, S. Hamer, N. Nesvadba, H. Russell, G. R. Tremblay, S. A. Baum, C. O'Dea, A. B. Peck, C. Sarazin, A. Vantyghem, M. Bremer, M. Donahue, A. C. Fabian, G. Ferland, B. R. McNamara, R. Mittal, J. B.R. OonkP. Salomé, A. M. Swinbank, M. Voit

Research output: Contribution to journalArticlepeer-review

31 Scopus citations


Active galactic nuclei play a crucial role in the accretion and ejection of gas in galaxies. Although their outflows are well studied, finding direct evidence of accretion has proved very difficult and has so far been done for very few sources. A promising way to study the significance of cold accretion is by observing the absorption of an active galactic nucleus's extremely bright radio emission by the cold gas lying along the line of sight. As such, we present ALMA CO(1-0) and CO(2-1) observations of the Hydra-A brightest cluster galaxy (z = 0.054) which reveal the existence of cold, molecular gas clouds along the line of sight to the galaxy's extremely bright and compact mm-continuum source. They have apparent motions relative to the central supermassive black hole of between-43 and-4 km s-1 and are most likely moving along stable, low ellipticity orbits. The identified clouds form part of a ∼109 M, approximately edge-on disc of cold molecular gas. With peak CO(2-1) optical depths of τ = 0.88 +0.06-0.06, they include the narrowest and by far the deepest absorption of this type which has been observed to date in a brightest cluster galaxy.

Original languageEnglish
Pages (from-to)229-238
Number of pages10
JournalMonthly Notices of the Royal Astronomical Society
Issue number1
StatePublished - May 1 2019

Bibliographical note

Publisher Copyright:
© 2019 Oxford University Press. All rights reserved.


  • galaxies: ISM
  • galaxies: clusters: individual: Hydra-A
  • radio lines: galaxies

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


Dive into the research topics of 'Deep and narrow CO absorption revealing molecular clouds in the Hydra-A brightest cluster galaxy'. Together they form a unique fingerprint.

Cite this