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SUMMARY:Helium Mixing in Quasi-global Simulations of the Intracluster Medi
 um - Thomas Berlok (Niels Bohr Institute\, Copenhagen)
DTSTART:20161114T160000Z
DTEND:20161114T170000Z
UID:TALK67399@talks.cam.ac.uk
CONTACT:Jean Teyssandier
DESCRIPTION:The assumption of a spatially uniform helium distribution in t
 he intracluster medium (ICM) can lead to biases in the estimates of key cl
 uster parameters if composition gradients are present. The helium concentr
 ation profile in galaxy clusters is unfortunately not directly observable.
  Current models addressing sedimentation are one-dimensional and parametri
 ze the presence of magnetic fields in a crude way\, ignoring the weakly co
 llisional\, magnetized nature of the medium. When these effects are consid
 ered\, a wide variety of instabilities can play an important role in the p
 lasma dynamics. In a series of recent papers\, we have developed the local
 \, linear theory of these instabilities and addressed their non-linear dev
 elopment with a modified version of Athena. For this Astrophysics Seminar 
 I will present a quasi-global approach that we use to simulate the mixing 
 of helium as induced by a generalization of the heat-flux-driven buoyancy 
 instability (HBI)\, which feeds off thermal and composition gradients. In 
 the inner region of the ICM\, mixing can occur on a time scale of a few Gy
 rs\, which suggests that composition gradients in cluster cores might be s
 hallower than one-dimensional models predict.
LOCATION:MR14\,  Centre for Mathematical Sciences\, Wilberforce Road\, Cam
 bridge
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