Galactic Latitude Dependence of Near-Infrared Diffuse Galactic Light :
  Thermal Emission or Scattered Light?
  Near-infrared (IR) diffuse Galactic light (DGL) consists of scattered light
and thermal emission from interstellar dust grains illuminated by interstellar
radiation field (ISRF). At 1.25 and 2.2um, recent observational study shows
that intensity ratios of the DGL to interstellar 100um dust emission steeply
decrease toward high Galactic latitudes (b). In this paper, we investigate
origin(s) of the b-dependence on the basis of models of thermal emission and
scattered light. Combining a thermal emission model with regional variation of
the polycyclic aromatic hydrocarbon abundance observed with Planck, we show
that contribution of the near-IR thermal emission component to the observed DGL
is less than ~20%. We also examine the b-dependence of the scattered light,
assuming a plane-parallel Galaxy with smooth distributions of the ISRF and dust
density along vertical direction, and assuming a scattering phase function
according to a recently developed model of interstellar dust. We normalize the
scattered light intensity to the 100um intensity corrected for deviation from
the cosecant-b law according to the Planck observation. As the result, the
present model taking all the b-dependence of dust and ISRF properties can
account for the observed b-dependence of the near-IR DGL. However, uncertainty
of the correction for the 100um emission is large and other normalizing
quantities may be appropriate for more robust analysis of the DGL.
