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

Abstract

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 $\sim$$10^9$ ${\text{M}}_{\odot }$, approximately edge-on disc of cold molecular gas. With peak CO(2-1) optical depths of $\tau$=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 $42_{-11}^{+25}$ K and line-of-sight column densities of $N_{CO}=2_{-1}^{+3}\times 10^{17}c{m}^{-2}$ and $N_{H_2}=7_{-4}^{+10}\times 10^{20}c{m}^{-2}$.

11 pages, 8 figures, accepted to MNRAS

References in corpus (6)

• Molecular line emission in NGC1068 imaged with ALMA. I An AGN-driven outflow in the dense molecular gas
• Raining on black holes and massive galaxies: the top-down multiphase condensation model
• Chaotic cold accretion on to black holes in rotating atmospheres
• Molecular Gas in the X-ray Bright Group NGC 5044 as Revealed by ALMA
• A Large Mass of H2 in the Brightest Cluster Galaxy in Zwicky 3146
• Constraining star formation rates in cool-core brightest cluster galaxies

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• A molecular absorption line survey toward the AGN of Hydra-A
• Molecular Flows in Contemporary Active Galaxies and the Efficacy of Radio-Mechanical Feedback
• Does absorption against AGN reveal supermassive black hole accretion?
• A Massive, Clumpy Molecular Gas Distribution and Displaced AGN in Zw 3146
• The correlation between the 500 pc scale molecular gas masses and AGN powers for massive elliptical galaxies
• Circumnuclear Medium around the Central AGN in a Cool-Core Cluster, Abell 1644-South
• A 4~Kpc Molecular Gas Lane in Cygnus A
• Chasing ICM cooling and AGN feedback from the macro to the meso scales in the galaxy cluster ZwCl 235