A massive, cooling-flow-induced starburst in the core of a luminous cluster of galaxies

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In the cores of some clusters of galaxies the hot intracluster plasma is dense enough that it should cool radiatively in the cluster’s lifetime1,2,3, leading to continuous ‘cooling flows’ of gas sinking towards the cluster centre, yet no such cooling flow has been observed. The low observed star-formation rates4,5 and cool gas masses6 for these ‘cool-core’ clusters suggest that much of the cooling must be offset by feedback to prevent the formation of a runaway cooling flow7,8,9,10. Here we report X-ray, optical and infrared observations of the galaxy cluster SPT-CLJ2344-4243 (ref. 11) at redshift z = 0.596. These observations reveal an exceptionally luminous (8.2 × 1045 erg s−1) galaxy cluster that hosts an extremely strong cooling flow (around 3,820 solar masses a year). Further, the central galaxy in this cluster appears to be experiencing a massive starburst (formation of around 740 solar masses a year), which suggests that the feedback source responsible for preventing runaway cooling in nearby cool-core clusters may not yet be fully established in SPT-CLJ2344-4243. This large star-formation rate implies that a significant fraction of the stars in the central galaxy of this cluster may form through accretion of the intracluster medium, rather than (as is currently thought) assembling entirely via mergers.

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Figure 1: False-colour images of the galaxies and intracluster plasma in the galaxy cluster SPT-CLJ2344-4243.
Figure 2: Optical and near-infrared emission-line spectra of the central galaxy in SPT-CLJ2344-4243.
Figure 3: Spectral energy distribution of the central galaxy in SPT-CLJ2344-4243 from the far-ultraviolet to the far-infrared.


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M.McD. was supported at MIT by NASA through the Chandra X-ray Observatory. The South Pole Telescope is supported by the National Science Foundation, with partial support provided by the Kavli Foundation, and the Moore Foundation. Support for X-ray analysis was provided by NASA. Work at McGill University is supported by NSERC, the CRC programme, and CIfAR, and at Harvard University by the NSF. S.V. acknowledges a Senior NPP Award held at the NASA Goddard Space Flight Center. R.K. acknowledges a NASA Hubble Fellowship, B.A.B. acknowledges a KICP Fellowship, M.A.D. acknowledges an Alfred P. Sloan Research Fellowship, and O.Z. acknowledges a BCCP fellowship.

Author information

M.McD. reduced the X-ray and optical long slit spectroscopic data, performed the main analysis, and wrote the paper, with significant assistance from B.A.B., R.J.F. and S.V., and comments from all other authors. M.B. and J.R. reduced multi-slit observations of SPT-CLJ2344-4243 and performed the velocity dispersion analysis. P.S. and R.S. obtained the infrared spectroscopy, and P.S. reduced these data. All other authors (listed alphabetically) have contributed as part of the South Pole Telescope collaboration, by either their involvement with the initial cluster discovery with the South Pole Telescope and/or multi-wavelength follow-up.

Correspondence to M. McDonald.

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