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

Rose, T.; Edge, A.C.; Combes, F.; Gaspari, M.; Hamer, S.; Nesvadba, N.; Russell, H.; Tremblay, G.R.; Baum, S.A.; O’Dea, C.; Peck, A.B.; Sarazin, C.; Vantyghem, A.; Bremer, M.; Donahue, M.; Fabian, A.C.; Ferland, G.; McNamara, B.R.; Mittal, R.; Oonk, J.B.R.; Salomé, P.; Swinbank, A.M.; Voit, M.

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


T. Rose

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. Oonk

P. Salomé

M. Voit


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. By comparing the relative strengths of the lines for the most strongly absorbing region, we are able to estimate a gas temperature of 42+25−11 K and line-of-sight column densities of NCO=2+3−1×1017cm−2 and NH2=7+10−4×1020cm−2⁠.


Rose, T., Edge, A., Combes, F., Gaspari, M., Hamer, S., Nesvadba, N., …Voit, M. (2019). Deep and narrow CO absorption revealing molecular clouds in the Hydra-A brightest cluster galaxy. Monthly Notices of the Royal Astronomical Society, 485(1), 229-238.

Journal Article Type Article
Acceptance Date Feb 5, 2019
Online Publication Date Feb 11, 2019
Publication Date May 1, 2019
Deposit Date Feb 19, 2019
Publicly Available Date Feb 19, 2019
Journal Monthly Notices of the Royal Astronomical Society
Print ISSN 0035-8711
Electronic ISSN 1365-2966
Publisher Royal Astronomical Society
Peer Reviewed Peer Reviewed
Volume 485
Issue 1
Pages 229-238
Public URL


Accepted Journal Article (1.4 Mb)

Copyright Statement
© 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society.

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