Radiation hydrodynamics simulations of line-driven AGN disc winds:
  metallicity dependence and black hole growth
  Growth of the black holes (BHs) from the seeds to supermassive BHs (SMBHs,
$\sim\!10^9\,M_\odot$) is not understood, but the mass accretion must have
played an important role. We performed two-dimensional radiation hydrodynamics
simulations of line-driven disc winds considering the metallicity dependence in
a wide range of the BH mass, and investigated the reduction of the mass
accretion rate due to the wind mass loss. Our results show that denser and
faster disc winds appear at higher metallicities and larger BH masses. The
accretion rate is suppressed to $\sim\! 0.4$--$0.6$ times the mass supply rate
to the disc for the BH mass of $M_{\rm BH}\gtrsim 10^5\,M_{\odot}$ in
high-metallicity environments of $Z\gtrsim Z_\odot$, while the wind mass loss
is negligible when the metallicity is sub-solar ($\sim 0.1Z_\odot$). By
developing a semi-analytical model, we found that the metallicity dependence of
the line force and the BH mass dependence of the surface area of the wind
launch region are the cause of the metallicity dependence ($\propto\! Z^{2/3}$)
and BH mass dependencies ($\propto\! M_{\rm BH}^{4/3}$ for $M_{\rm BH}\leq
10^6\,M_\odot$ and $\propto\! M_{\rm BH}$ for $M_{\rm BH}\geq 10^6\,M_\odot$)
of the mass-loss rate. Our model suggests that the growth of BHs by the gas
accretion effectively slows down in the regime $\gtrsim 10^{5}M_\odot$ in
metal-enriched environments $\gtrsim Z_\odot$. This means that the line-driven
disc winds may have an impact on late evolution of SMBHs.
