The formation of dusty cold gas filaments from galaxy cluster simulations


Galaxy clusters are the most massive collapsed structures in the Universe, with potential wells filled with hot, X-ray-emitting intracluster medium (ICM). Observations, however, show that a substantial number of clusters (the so-called cool-core clusters) also contain large amounts of cold gas in their centres, some of which is in the form of spatially extended filaments spanning scales of tens of kiloparsecs1,2. These findings have raised questions about the origin of the cold gas, as well as its relationship with the central active galactic nucleus (AGN), whose feedback has been established as a ubiquitous feature in such galaxy clusters3,4,5. Here, we report a radiation-hydrodynamic simulation of AGN feedback in a galaxy cluster, in which cold filaments form from the warm, AGN-driven outflows with temperatures between 104 and 107 K as they rise in the cluster core. Our analysis reveals a new mechanism that, through the combination of radiative cooling and ram pressure, naturally promotes outflows whose cooling times are shorter than their rising times, giving birth to spatially extended cold gas filaments. Our results strongly suggest that the formation of cold gas and AGN feedback in galaxy clusters are inextricably linked and shed light on how AGN feedback couples to the ICM.

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

Fig. 1: Formation of cold gas filaments from warm galactic outflows.
Fig. 2: Evolution of AGN-driven outflows for gases of different temperatures.
Fig. 3: Comparison of properties of the simulated X-ray-emitting plasma with observations.

Data availability

The data that support the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request.

Code availability

The simulations presented here were performed using an adapted version of the Enzo code. The main repository is available at, and the customizations made for this work are available from the corresponding author upon request.


  1. 1.

    Hu, E. M., Cowie, L. L. & Wang, Z. Long-slit spectroscopy of gas in the cores of X-ray luminous clusters. Astrophys. J. Suppl. Ser. 59, 447–498 (1985).

    ADS  Article  Google Scholar 

  2. 2.

    Edge, A. C. The detection of molecular gas in the central galaxies of cooling flow clusters. Mon. Not. R. Astron. Soc. 328, 762–782 (2001).

    ADS  Article  Google Scholar 

  3. 3.

    Fabian, A. Observational evidence of active galactic nuclei feedback. Annu. Rev. Astron. Astrophys. 50, 455–489 (2012).

    ADS  Article  Google Scholar 

  4. 4.

    Voit, G. M., Donahue, M., Bryan, G. L. & McDonald, M. Regulation of star formation in giant galaxies by precipitation, feedback and conduction. Nature 519, 203–206 (2015).

    ADS  Article  Google Scholar 

  5. 5.

    McNamara, B. R. et al. A mechanism for stimulating AGN feedback by lifting gas in massive galaxies. Astrophys. J. 830, 79 (2016).

    ADS  Article  Google Scholar 

  6. 6.

    Gaspari, M., Ruszkowski, M. & Sharma, P. Cause and effect of feedback: multiphase gas in cluster cores heated by AGN jets. Astrophys. J. 746, 94 (2012).

    ADS  Article  Google Scholar 

  7. 7.

    Li, Y. et al. Cooling, AGN feedback, and star formation in simulated cool-core galaxy clusters. Astrophys. J. 811, 73 (2015).

    ADS  Article  Google Scholar 

  8. 8.

    Prasad, D., Sharma, P. & Babul, A. Cool core cycles: cold gas and AGN jet feedback in cluster cores. Astrophys. J. 811, 108 (2015).

    ADS  Article  Google Scholar 

  9. 9.

    Hogan, M. T. et al. The onset of thermally unstable cooling from the hot atmospheres of giant galaxies in clusters: constraints on feedback models. Astrophys. J. 851, 66 (2017).

    ADS  Article  Google Scholar 

  10. 10.

    Sparks, W. B., Macchetto, F. & Golombek, D. Imaging observations of gas and dust in NGC 4696 and implications for cooling flow models. Astrophys. J. 345, 153–162 (1989).

    ADS  Article  Google Scholar 

  11. 11.

    Goudfrooij, P., Hansen, L., Jorgensen, H. E. & Norgaard-Nielsen, H. U. Interstellar matter in Shapley-Ames elliptical galaxies. II. The distribution of dust and ionized gas. Astron. Astrophys. Suppl. Ser. 105, 341–383 (1994).

    ADS  Google Scholar 

  12. 12.

    Donahue, M. et al. Polycyclic aromatic hydrocarbons, ionized gas, and molecular hydrogen in brightest cluster galaxies of cool-core clusters of galaxies. Astrophys. J. 732, 40 (2011).

    ADS  Article  Google Scholar 

  13. 13.

    Conselice, C. J., Gallagher, J. S. & Wyse, R. F. G. On the nature of the NGC 1275 system. Astron. J. 122, 2281–2300 (2001).

    ADS  Article  Google Scholar 

  14. 14.

    Fabian, A. C. et al. Magnetic support of the optical emission line filaments in NGC 1275. Nature 454, 968–970 (2008).

    ADS  Article  Google Scholar 

  15. 15.

    McDonald, M., Veilleux, S., Rupke, D. S. N. & Mushotzky, R. On the origin of the extended Hα filaments in cooling flow clusters. Astrophys. J. 721, 1262–1283 (2010).

    ADS  Article  Google Scholar 

  16. 16.

    Gendron-Marsolais, M. et al. Revealing the velocity structure of the filamentary nebula in NGC 1275 in its entirety. Mon. Not. R. Astron. Soc. Lett. 479, L28–L33 (2018).

    ADS  Google Scholar 

  17. 17.

    Qiu, Y., Bogdanović, T., Li, Y. & McDonald, M. Using Hα filaments to probe active galactic nuclei feedback in galaxy clusters. Astrophys. J. Lett. 872, L11 (2019).

    ADS  Article  Google Scholar 

  18. 18.

    Babyk, I. V. et al. A universal entropy profile for the hot atmospheres of galaxies and clusters within R2500. Astrophys. J. 862, 39 (2018).

    ADS  Article  Google Scholar 

  19. 19.

    Bryan, G. L. et al. Enzo: an adaptive mesh refinement code for astrophysics. Astrophys. J. Suppl. Ser. 211, 19 (2014).

    ADS  Article  Google Scholar 

  20. 20.

    Qiu, Y., Bogdanović, T., Li, Y., Park, K. & Wise, J. H. The interplay of kinetic and radiative feedback in galaxy clusters. Astrophys. J. 877, 47 (2019).

    ADS  Article  Google Scholar 

  21. 21.

    Bîrzan, L., Rafferty, D. A., McNamara, B. R., Wise, M. W. & Nulsen, P. E. J. A systematic study of radio-induced X-ray cavities in clusters, groups, and galaxies. Astrophys. J. 607, 800–809 (2004).

    ADS  Article  Google Scholar 

  22. 22.

    McNamara, B. R. et al. The heating of gas in a galaxy cluster by X-ray cavities and large-scale shock fronts. Nature 433, 45–47 (2005).

    ADS  Article  Google Scholar 

  23. 23.

    Russell, H. R. et al. ALMA observations of massive molecular gas filaments encasing radio bubbles in the Phoenix cluster. Astrophys. J. 836, 130 (2017).

    ADS  Article  Google Scholar 

  24. 24.

    McDonald, M. et al. Anatomy of a cooling flow: the feedback response to pure cooling in the core of the Phoenix cluster. Astrophys. J. 885, 63 (2019).

    ADS  Article  Google Scholar 

  25. 25.

    McDonald, M., Veilleux, S. & Rupke, D. S. N. Optical spectroscopy of Hα filaments in cool core clusters: kinematics, reddening, and sources of ionization. Astrophys. J. 746, 153 (2012).

    ADS  Article  Google Scholar 

  26. 26.

    Zhang, D., Thompson, T. A., Quataert, E. & Murray, N. Entrainment in trouble: cool cloud acceleration and destruction in hot supernova-driven galactic winds. Mon. Not. R. Astron. Soc. 468, 4801–4814 (2017).

    ADS  Article  Google Scholar 

  27. 27.

    Beckmann, R. S. et al. Dense gas formation and destruction in a simulated Perseus-like galaxy cluster with spin-driven black hole feedback. Astron. Astrophys. 631, A60 (2019).

    Article  Google Scholar 

  28. 28.

    McDonald, M. et al. A massive, cooling-flow-induced starburst in the core of a luminous cluster of galaxies. Nature 488, 349–352 (2012).

    ADS  Article  Google Scholar 

  29. 29.

    Voit, G. M., Kay, S. T. & Bryan, G. L. The baseline intracluster entropy profile from gravitational structure formation. Mon. Not. R. Astron. Soc. 364, 909–916 (2005).

    ADS  Article  Google Scholar 

  30. 30.

    Panagoulia, E. K., Fabian, A. C. & Sanders, J. S. A volume-limited sample of X-ray galaxy groups and clusters – I. Radial entropy and cooling time profiles. Mon. Not. R. Astron. Soc. 438, 2341–2354 (2014).

    ADS  Article  Google Scholar 

  31. 31.

    Wise, J. H. & Abel, T. ENZO+MORAY: radiation hydrodynamics adaptive mesh refinement simulations with adaptive ray tracing. Mon. Not. R. Astron. Soc. 414, 3458–3491 (2011).

    ADS  Article  Google Scholar 

  32. 32.

    Wilman, R. J., Edge, A. C. & Johnstone, R. M. The nature of the molecular gas system in the core of NGC 1275. Mon. Not. R. Astron. Soc. 359, 755–764 (2005).

    ADS  Article  Google Scholar 

  33. 33.

    Mathews, W. G., Faltenbacher, A. & Brighenti, F. Heating cooling flows with weak shock waves. Astrophys. J. 638, 659–667 (2006).

    ADS  Article  Google Scholar 

  34. 34.

    Navarro, J. F., Frenk, C. S. & White, S. D. M. The structure of cold dark matter halos. Astrophys. J. 462, 563 (1996).

    ADS  Article  Google Scholar 

  35. 35.

    Churazov, E., Forman, W., Jones, C., Sunyaev, R. & Böhringer, H. XMM—Newton observations of the Perseus cluster — II. Evidence for gas motions in the core. Mon. Not. R. Astron. Soc. 347, 29–35 (2004).

    ADS  Article  Google Scholar 

  36. 36.

    Tremblay, G. R. et al. Cold, clumpy accretion onto an active supermassive black hole. Nature 534, 218–221 (2016).

    ADS  Article  Google Scholar 

  37. 37.

    Johnstone, R. M., Fabian, A. C. & Nulsen, P. E. J. The optical spectra of central galaxies in southern clusters: evidence for star formation. Mon. Not. R. Astron. Soc. 224, 75–91 (1987).

    ADS  Article  Google Scholar 

  38. 38.

    Heckman, T. M., Baum, S. A., van Breugel, W. J. M. & McCarthy, P. Dynamical, physical, and chemical properties of emission-line nebulae in cooling flows. Astrophys. J. 338, 48 (1989).

    ADS  Article  Google Scholar 

  39. 39.

    Crawford, C. S., Allen, S. W., Ebeling, H., Edge, A. C. & Fabian, A. C. The ROSAT brightest cluster sample — III. Optical spectra of the central cluster galaxies. Mon. Not. R. Astron. Soc. 306, 857–896 (1999).

    ADS  Article  Google Scholar 

  40. 40.

    Jaffe, W., Bremer, M. N. & van der Werf, P. P. Infrared spectra of cooling flow galaxies. Mon. Not. R. Astron. Soc. 324, 443–449 (2001).

    ADS  Article  Google Scholar 

  41. 41.

    Edge, A. C. & Frayer, D. T. Resolving molecular gas in the central galaxies of cooling flow clusters. Astrophys. J. 594, L13–L17 (2003).

    ADS  Article  Google Scholar 

  42. 42.

    Salomé, P. & Combes, F. Cold molecular gas in cooling flow clusters of galaxies. Astron. Astrophys. 412, 657–667 (2003).

    ADS  Article  Google Scholar 

  43. 43.

    Jaffe, W., Bremer, M. N. & Baker, K. H ii and H2 in the envelopes of cooling flow central galaxies. Mon. Not. R. Astron. Soc. 360, 748–762 (2005).

    ADS  Article  Google Scholar 

  44. 44.

    Johnstone, R. M. et al. Discovery of atomic and molecular mid-infrared emission lines in off-nuclear regions of NGC 1275 and NGC 4696 with the Spitzer Space Telescope. Mon. Not. R. Astron. Soc. 382, 1246–1260 (2007).

    ADS  Article  Google Scholar 

  45. 45.

    Edwards, L. O. V., Hudson, M. J., Balogh, M. L. & Smith, R. J. Line emission in the brightest cluster galaxies of the NOAO Fundamental Plane and Sloan Digital Sky Surveys. Mon. Not. R. Astron. Soc. 379, 100–110 (2007).

    ADS  Article  Google Scholar 

  46. 46.

    Hatch, N. A., Crawford, C. S. & Fabian, A. C. Ionized nebulae surrounding brightest cluster galaxies. Mon. Not. R. Astron. Soc. 380, 33–43 (2007).

    ADS  Article  Google Scholar 

  47. 47.

    Oonk, J. B. R., Jaffe, W., Bremer, M. N. & Van Weeren, R. J. The distribution and condition of the warm molecular gas in Abell 2597 and Sersic 159-03. Mon. Not. R. Astron. Soc. 405, 898–932 (2010).

    ADS  Google Scholar 

  48. 48.

    Russell, H. R. et al. Driving massive molecular gas flows in central cluster galaxies with AGN feedback. Mon. Not. R. Astron. Soc. 490, 3025–3045 (2019).

    ADS  Article  Google Scholar 

  49. 49.

    McDonald, M. et al. Deep Chandra, HST-COS, and MegaCam observations of the Phoenix cluster: extreme star formation and AGN feedback on hundred kiloparsec scales. Astrophys. J. 811, 111 (2015).

    ADS  Article  Google Scholar 

  50. 50.

    Fabian, A. C., Walker, S. A., Pinto, C., Russell, H. R. & Edge, A. C. Effects of the variability of the nucleus of NGC 1275 on X-ray observations of the surrounding intracluster medium. Mon. Not. R. Astron. Soc. 451, 3061–3067 (2015).

    ADS  Article  Google Scholar 

  51. 51.

    Sarazin, C. L. & White, R. E. III Steady state cooling flow models for normal elliptical galaxies. Astrophys. J. 320, 32–48 (1987).

    ADS  Article  Google Scholar 

  52. 52.

    Kirkpatrick, C. C. & McNamara, B. R. Hot outflows in galaxy clusters. Mon. Not. R. Astron. Soc. 452, 4361–4376 (2015).

    ADS  Article  Google Scholar 

  53. 53.

    Draine, B. T. & Salpeter, E. E. On the physics of dust grains in hot gas. Astrophys. J. 231, 77–94 (1979).

    ADS  Article  Google Scholar 

  54. 54.

    Li, Y., Bryan, G. L. & Quataert, E. The fate of asymptotic giant branch winds in massive galaxies and the intracluster medium. Astrophys. J. 887, 41 (2019).

    ADS  Article  Google Scholar 

  55. 55.

    Draine, B. T. Physics of the Interstellar and Intergalactic Medium (Princeton Univ. Press, 2011).

  56. 56.

    Mittal, R. et al. Herschel observations of extended atomic gas in the core of the Perseus cluster. Mon. Not. R. Astron. Soc. 426, 2957–2977 (2012).

    ADS  Article  Google Scholar 

  57. 57.

    Fabian, A. C. et al. The energy source of the filaments around the giant galaxy NGC 1275. Mon. Not. R. Astron. Soc. 417, 172–177 (2011).

    ADS  Article  Google Scholar 

  58. 58.

    Fabian, A. C. et al. HST imaging of the dusty filaments and nucleus swirl in NGC4696 at the centre of the Centaurus Cluster. Mon. Not. R. Astron. Soc. 461, 922–928 (2016).

    ADS  Article  Google Scholar 

  59. 59.

    Mittal, R. et al. Herschel observations of the Centaurus cluster – the dynamics of cold gas in a cool core. Mon. Not. R. Astron. Soc. 418, 2386–2402 (2011).

    ADS  Article  Google Scholar 

  60. 60.

    Sarangi, A., Dwek, E. & Kazanas, D. Dust formation in AGN winds. Astrophys. J. 885, 126 (2019).

    ADS  Article  Google Scholar 

Download references


Y.Q. thanks L. C. Ho and S. M. Faber for useful discussions. Y.Q. acknowledges support from the National Key R&D Program of China (2016YFA0400702), the National Science Foundation of China (11721303, 11991052), and the High-Performance Computing Platform of Peking University. T.B. thanks the Kavli Institute for Theoretical Physics, where one portion of this work was completed, for its hospitality. Support for this work was in part provided by the National Aeronautics and Space Administration through Chandra Award Number TM7-18008X issued by the Chandra X-ray Center, which is operated by the Smithsonian Astrophysical Observatory for and on behalf of the National Aeronautics Space Administration under contract NAS803060. This research was supported in part by the National Science Foundation under grant number NSF PHY-1748958, and in part through research cyberinfrastructure resources and services provided by the Partnership for an Advanced Computing Environment (PACE) at the Georgia Institute of Technology, Atlanta, Georgia, USA.

Author information




Y.Q. performed the simulation and analysed the data. Y.Q. and T.B. wrote the manuscript. Y.L., M.M. and B.R.M. commented on the manuscript and data analysis, and made suggestions for comparisons with observation. M.M. and B.R.M. provided the observational data in Fig. 3a.

Corresponding author

Correspondence to Yu Qiu.

Ethics declarations

Competing interests

The authors declare no competing interests.

Additional information

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Extended data

Extended Data Fig. 1 Evolution of AGN feedback luminosity in the zoom-in simulation.

The total AGN luminosity is allocated to kinetic (blue) and radiative (orange) luminosity as a function of SMBH accretion rate. Lighter coloured bands correspond to the instantaneous AGN luminosities and darker lines show luminosities smoothed over 0.2 Myr. Dotted vertical lines mark the instances in time corresponding to the panels in Fig. 1a–c. Inset shows the evolution of the AGN luminosity over 10 Gyr in the parent simulation, smoothed over ~0.1 Gyr. The grey vertical strip marks the duration of the high-cadence re-simulation.

Extended Data Fig. 2 Instantaneous radial velocity distribution for outflows in the high-cadence simulation.

Outflow speed as a function of radius, colour-coded in terms of the mass-weighted temperature (a) and neutral hydrogen mass (b). The bulk of the cold gas is traveling with speeds below 1,000 km s−1, in agreement with observations and with predictions of the analytic model. The time of this snapshot corresponds to Fig. 1b.

Extended Data Fig. 3 Velocity dispersion of different temperature phases of the gas in simulated cluster core.

The resulting velocity dispersion is calculated as the average of the x, y, and z components, each weighted by the X-ray emissivity (for hot and warm gas) and Hα emissivity (for cold gas), at radii between 3 and 20 kpc (see Supplementary Information). While warm and cold gas share similar values, the velocity dispersion of the hot gas shows stronger, uncorrelated variability, indicating a separate kinematic origin from the cold gas filaments.

Extended Data Fig. 4 Origin of the cold filaments.

a–c, Projected gas density showing the spatial reach of the AGN-driven material, traced by a passive fluid injected from the central 1 kpc, corresponding in time to Fig. 1a–c. A movie showing the evolution in the high-cadence simulation is provided in Supplementary Video 1.

Extended Data Fig. 5 Dust erosion in warm outflows.

a, The size of the smallest dust grain that can survive in the warm outflows as a function of their initial temperature. For a characteristic dust grain size of 1 μm or less, most dust content is eliminated in outflows with initial temperature higher than 4 × 106 K. b, Radial temperature distribution of the tracer fluid, colour-coded with the thermal dust sputtering rate, weighted by cell mass. For dust size a ~ 0.1 μm, blue colour corresponds to a sputtering timescale of tsp 1 Myr. This is longer than the cooling time of the warm outflows, indicating that dust can be preserved in the outflowing gas.

Supplementary information

Supplementary Information

Supplementary discussion and references.

Supplementary Video 1

Formation of cold gas filaments from warm galactic outflows driven by AGN feedback. Left: 20-Myr evolution of the warm and cold outflows, projected along the line of sight. Orange (grey) colour intensity represents the column density of ionized (neutral) hydrogen for warm (cold) gas, same as in Fig. 1a–c. Right: spatial expansion of the tracer fluid injected from the central 1 kpc at the start of the simulation. Colour intensity shows the projected gas mass density of computation cells that contain the tracer fluid. Visual comparison with the left movie indicates that cold filaments contain gas launched from the centre of the cluster.

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Qiu, Y., Bogdanović, T., Li, Y. et al. The formation of dusty cold gas filaments from galaxy cluster simulations. Nat Astron (2020).

Download citation