  In this study, we examine photoionization outflows during the late stages of
galaxy mergers, with a specific focus on the relation between observed velocity
of outflowing gas and the apparent effects of dust extinction. We used the
N-body/smoothed particle hydrodynamics (SPH) code ASURA for galaxy merger
simulations. These simulations concentrated on identical galaxy mergers
featuring supermassive black holes (SMBHs) of 10$^8$ M$_\odot$ and gas
fractions of 30\% and 10 \%. From the simulation data, we derived velocity and
velocity dispersion diagrams for the AGN-driven ionized outflowing gas. Our
findings show that high-velocity outflows with velocity dispersions of 500 km
s$^{-1}$ or greater can be observed in the late stages of galactic mergers.
Particularly, in buried AGNs, both the luminosity-weighted outflow velocity and
velocity dispersion increase owing to the apparent effects of dust extinction.
Owing to these effects, the velocity--velocity dispersion diagrams display a
noticeable blue-shifted tilt in models with higher gas fractions. Crucially,
this tilt is not influenced by the AGN luminosity but emerges from the
observational impacts of dust extinction. Our results imply that the observed
high-velocity \OIII outflow exceeding 1000 km s$^{-1}$ in buried AGNs may be
linked to the dust extinction that occurs during the late stages of gas-rich
galaxy mergers.
