  The Sunyaev-Zel'dovich effect (SZE) observable-mass (Y-M) scaling relation is
a promising technique for obtaining mass estimates for large samples of galaxy
clusters and holds a key to studying the nature of dark matter and dark energy.
However, cosmological inference based on SZE cluster surveys is limited by our
incomplete knowledge of bias, scatter, and evolution in the Y-M relation. In
this work, we investigate the effects of galaxy cluster mergers on the scaling
relation using the Omega500 high-resolution cosmological hydrodynamic
simulation. We show that the non-thermal pressure associated with
merger-induced gas motions contributes significantly to the bias, scatter, and
evolution of the scaling relation. After the merger, the kinetic energy of
merging systems is slowly converted into thermal energy through dissipation of
turbulent gas motions, which causes the thermal SZE signal to increase steadily
with time. This post-merger evolution is one of the primary source of bias and
scatter in the Y-M relation. However, we show that when the missing non-thermal
energy is accounted for, the resulting relation exhibits little to no redshift
evolution and the scatter around the scaling relation is ~20-30 % smaller than
that of the thermal SZE signal alone. Our work opens up a possibility to
further improve the current robust mass proxy, Y, by accounting for the missing
non-thermal pressure component. We discuss future prospect of measuring
internal gas motions in galaxy clusters and its implication for cluster-based
cosmological tests.
