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Ubiquitous cold and massive filaments in cool core clusters.

Olivares, V. and Salome, P. and Combes, F. and Hamer, S. and Guillard, P. and Lehnert, M. D. and Polles, F. L. and Beckmann, R. S. and Dubois, Y. and Donahue, M. and Edge, A. and Fabian, A. C. and McNamara, B. and Rose, T. and Russell, H. R. and Tremblay, G. and Vantyghem, A. and Canning, R. E. A. and Ferland, G. and Godard, B. and Peirani, S. and Pineau des Forets, G. (2019) 'Ubiquitous cold and massive filaments in cool core clusters.', Astronomy & astrophysics., 631 . A22.


Multi-phase filamentary structures around brightest cluster galaxies (BCG) are likely a key step of AGN-feedback. We observed molecular gas in three cool cluster cores, namely Centaurus, Abell S1101, and RXJ1539.5, and gathered ALMA (Atacama Large Millimeter/submillimeter Array) and MUSE (Multi Unit Spectroscopic Explorer) data for 12 other clusters. Those observations show clumpy, massive, and long (3−25 kpc) molecular filaments, preferentially located around the radio bubbles inflated by the AGN. Two objects show nuclear molecular disks. The optical nebula is certainly tracing the warm envelopes of cold molecular filaments. Surprisingly, the radial profile of the Hα/CO flux ratio is roughly constant for most of the objects, suggesting that (i) between 1.2 and 6 times more cold gas could be present and (ii) local processes must be responsible for the excitation. Projected velocities are between 100 and 400 km s−1, with disturbed kinematics and sometimes coherent gradients. This is likely due to the mixing in projection of several thin (and as yet) unresolved filaments. The velocity fields may be stirred by turbulence induced by bubbles, jets, or merger-induced sloshing. Velocity and dispersions are low, below the escape velocity. Cold clouds should eventually fall back and fuel the AGN. We compare the radial extent of the filaments, rfil, with the region where the X-ray gas can become thermally unstable. The filaments are always inside the low-entropy and short-cooling-time region, where tcool/tff <  20 (9 of 13 sources). The range of tcool/tff of 8−23 at rfil, is likely due to (i) a more complex gravitational potential affecting the free-fall time tff (sloshing, mergers, etc.) and (ii) the presence of inhomogeneities or uplifted gas in the ICM, affecting the cooling time tcool. For some of the sources, rfil lies where the ratio of the cooling time to the eddy-turnover time, tcool/teddy, is approximately unity.

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Publisher statement:Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Date accepted:22 July 2019
Date deposited:07 November 2019
Date of first online publication:15 October 2019
Date first made open access:07 November 2019

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