  HESS J1825-137 is one of the most powerful and luminous TeV gamma-ray pulsar
wind nebulae (PWN). To the south of HESS J1825-137, Fermi-LAT observation
revealed a new region of GeV gamma-ray emission with three apparent peaks
(termed here, GeV-ABC). This study presents interstellar medium (ISM) data and
spectral energy distribution (SED) modelling towards the GeV emission to
understand the underlying particle acceleration. We considered several particle
accelerator scenarios - the PWN associated with HESS J1825-137, the progenitor
SNR also associated with HESS J1825-137, plus the gamma-ray binary system
LS\,5039. It was found that the progenitor SNR of HESS J1825-137 has
insufficient energetics to account for all GeV emission. GeV-ABC may be a
reflection of an earlier epoch in the history of the PWN associated with
HESS\,1825-137, assuming fast diffusion perhaps including advection. LS\,5039
cannot meet the required energetics to be the source of particle acceleration.
A combination of HESS J1825-137 and LS 5039 could be plausible sources.
