  Unresolved near-infrared background anisotropies are expected to have
contributions from the earliest galaxies during reionization and faint, dwarf
galaxies at intermediate redshifts. Previous measurements were unable to
conclusively pinpoint the dominant origin because they did not sample spatial
scales that were sufficiently large to distinguish between these two
possibilities. Here we report a measurement of the anisotropy power spectrum
from sub-arcminute to one degree angular scales and find the clustering
amplitude to be larger than the model predictions involving the two existing
explanations. As the shot-noise level of the power spectrum is consistent with
that expected from faint galaxies, a new source population on the sky is not
necessary to explain the observations. A physical mechanism that increases the
clustering amplitude, however, is needed. Motivated by recent results related
to the extended stellar light profile in dark matter halos, we consider the
possibility that the fluctuations originate from diffuse intrahalo stars of all
galaxies. We find that the measured power spectrum can be explained by an
intrahalo light fraction of 0.07 to 0.2 % relative to the total luminosity in
dark matter halos of masses log(M/M_Sun) ~ 9 to 12 at redshifts of ~ 1 to 4.
