Origin and evolution of dust-obscured galaxies in galaxy mergers
  Dust Obscured Galaxies (DOGs), which are observationally characterized as
faint in the optical and bright in the infrared, are the final stage of galaxy
mergers and are essential objects in the evolution of galaxies and active
galactic nuclei (AGNs). However, the relationship between torus-scale gas
dynamics around AGNs and DOGs lifetime remain unclear. We obtained evolution of
the spectral energy distributions (SEDs) of a galaxy merger system with AGN
feedback, from post-processed pseudo-observations based on an N-body/Smoothed
Particle Hydrodynamics (SPH) simulation. We focused on a late stage merger of
two identical galaxies with a supermassive black hole (SMBH) of 10$^8$
M$_\odot$. We found that the infrared luminosity of the system reaches ultra-
and hyper-luminous infrared galaxy classes (10$^{12}$ and 10$^{13}$ L$_\odot$,
respectively). The DOGs phase corresponds to a state in which the AGNs are
buried in dense gas and dust, with the infrared luminosity exceeding 3.3
$\times$ 10$^{12}$ L$_\odot$. We also identified the sub-categories of DOGs,
namely bump and power-law DOGs from the SEDs and their evolution. The bump DOGs
tend to evolve to power-law DOGs on several Myrs. We found that contribution
from the hot dust around the nucleus in the infrared radiation is essential for
identifying the system as a power-law DOG; the gas and dust distribute
non-spherically around the nucleus, therefore, the observed properties of DOGs
depend on the viewing angle. In our model, the lifetime of merger-driven DOGs
is less than 4 Myrs, suggesting that the observed DOGs phase is a brief aspect
of galaxy mergers.
