  Optical trapping and manipulation of microcavity exciton polaritons rely on
effective potentials induced by the interaction of polaritons with a reservoir
of high energy excitonic particles injected by an off-resonant optical pump.
Here, we experimentally investigate possible mechanisms responsible for
reshaping of these effective potentials in the low-density exciton-polariton
regime. We infer the spatial distribution of the reservoir from the spatially
resolved energy of exciton-polariton emission measured at zero momentum (zero
kinetic energy). Power-dependent shape analysis of the potential barrier
induced by a focused continuous wave laser pump shows a monotonic decrease of
the barrier width with increasing excitation power, which is attributed to the
local heating of the sample at the pump spot. In addition, we observe the
significant influence of the reservoir on the zero-momentum emission tens of
micrometers away from the laser pump spot, which is in line with the previously
reported enhanced transport of high-momentum excitonic polaritons from the
bottleneck region. Our work presents evidence for a complex spatial reshaping
of the reservoir with the pump power, contrary to the common assumption of a
static reservoir distribution fixed by the intensity profile of the pump.
