A Dynamically Driven, Universal Thermal Profile of Galaxy Groups and
  Clusters
  Large scale structures such as groups and clusters of galaxies show a
universal, nearly linear entropy radial profile $K(r)$. Using deprojected 16
clusters and 12 groups from the literature, we find that $K\propto
r^{0.96\pm0.01}$, consistent with the mean power-law index $(0.9\mbox{--}1.1)$
of previous studies. A similarly good fit is given by a $\tau\propto
r^{0.72\pm0.01}$ ratio between cooling and free-fall times. Both profiles
slightly flatten at small radii, as $\tau$ becomes of order unity. The entropy
profile is usually attributed to self-similar shock accretion (shown to be
inconsistent with the data), to non-standard heat conduction, or to turbulent
heating. We argue that a dynamical mechanism is needed to sustain such a
universal profile, oblivious to the temperature peak at the edge of the core
and to the virial shock at the outskirts, and robust to the presence of ongoing
cooling, merger, and active galactic nucleus (AGN) activity. In particular, we
show that such a profile can be naturally obtained in a spiral flow, which is
likely to underlie most galaxy aggregates according to the ubiquitous spiral
patterns and cold fronts observed. Generalizing a two-phase spiral flow model
out to the virial radius surprisingly reproduces the thermal profile. A
generalized Schwarzschild criterion indicates that observed spiral patterns
must involve a convective layer, which may regulate the thermal profile.
