Kavli Affiliate: Kohei Inayoshi
| First 5 Authors: Haojie Hu, Yu Qiu, Marie-Lou Gendron-Marsolais, Tamara Bogdanovic, Julie Hlavacek-Larrondo
| Summary:
The hot intracluster medium (ICM) is thought to be quiescent with low
observed velocity dispersions. Surface brightness fluctuations of the ICM also
suggest that its turbulence is subsonic with a Kolmogorov scaling relation,
indicating that the viscosity is suppressed and the kinetic energy cascades
down the length scales unscathed. However, recent observations of the cold gas
filaments in galaxy clusters find that the scaling relations are steeper than
that of the hot plasma, signaling kinetic energy losses and the presence of
supersonic flows. In this work we use high-resolution simulations to explore
the turbulent velocity structure of the cold filaments at the cores of galaxy
clusters. Our results indicate that supersonic turbulent structures can be
"frozen" in the cold gas that cools and fragments out of a fast outflow driven
by the central active galactic nucleus (AGN), when the cooling time is shorter
than the dynamical sound-crossing time. After the cold gas formation, however,
the slope of the velocity structure function (VSF) flattens significantly over
short, 10-Myr timescales. The lack of flattened VSF in observations of
H$alpha$ filaments indicates that the H$alpha$-emitting phase is short-lived
for the cold gas in galaxy clusters. On the other hand, the ubiquity of
supersonic structures in the cold filaments strongly suggests that supersonic
outflows are an integral part of AGN-ICM interaction, and that AGN activity
plays a crucial role at driving turbulence in galaxy clusters.
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