First Detection of Galactic Latitude Dependence of Near-Infrared Diffuse
  Galactic Light from DIRBE Reanalysis
  Observational study on near-infrared (IR) scattering properties of
interstellar dust grains has been limited due to its faintness. Using all-sky
maps obtained from Diffuse Infrared Background Experiment (DIRBE), we
investigate the scattering property from diffuse Galactic light (DGL)
measurements at 1.25, 2.2, and 3.5 {\mu}m in addition to our recent analyses of
diffuse near-IR emission (Sano et al. 2015; Sano et al. 2016). As a result, we
first find that the intensity ratios of near-IR DGL to 100 {\mu}m emission
increase toward low Galactic latitudes at 1.25 and 2.2 {\mu}m. The derived
latitude dependence can be reproduced by a scattered light model of
interstellar dust with a large scattering asymmetry factor g = <cos{\theta}> of
$0.8^{+0.2}_{-0.3}$ at 1.25 and 2.2 {\mu}m, assuming an infinite Galaxy disk as
an illuminating source. The derived asymmetry factor is comparable to the
values obtained in the optical, but several times larger than that expected
from a recent dust model. Since possible latitude dependence of
ultraviolet-excited dust emission at 1.25 and 2.2 {\mu}m would reduce the large
asymmetry factor to the reasonable value, our result may indicate the first
detection of such an additional emission component in the diffuse interstellar
medium.
