  We present holographic descriptions of thermalization in conformal field
theories using probe D-branes in AdS X S space-times. We find that the induced
metrics on Dp-brane worldvolumes which are rotating in an internal sphere
direction have horizons with characteristic Hawking temperatures even if there
is no black hole in the bulk AdS. The AdS/CFT correspondence applied to such
systems indeed reveals thermal properties such as Brownian motions and AC
conductivities in the dual conformal field theories. We also use this framework
to holographically analyze time-dependent systems undergoing a quantum quench,
where parameters in quantum field theories, such as a mass or a coupling
constant, are suddenly changed. We confirm that this leads to thermal behavior
by demonstrating the formation of apparent horizons in the induced metric after
a certain time.
