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, similar to 10(9) M-circle dot) is not understood, but the mass accretion must have played an important role. We performed 2D 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 similar to 0.4-0.6 times the mass supply rate to the disc for the BH mass of M-BH greater than or similar to 10(5) M-circle dot in high-metallicity environments of Z greater than or similar to Z(circle dot), while the wind mass-loss is negligible when the metallicity is subsolar (similar to 0.1Z(circle dot)). 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 (proportional to Z(2/3)) and BH mass dependencies (proportional to M-BH(4/3) for M-BH <= 10(6) M-circle dot and proportional to M-BH for M-BH >= 10(6) M-circle dot) of the mass-loss rate. Our model suggests that the growth of BHs by the gas accretion effectively slows down in the regime greater than or similar to 10(5) M-circle dot in metal-enriched environments greater than or similar to Z(circle dot). This means that the line-driven disc winds may have an impact on late evolution of SMBHs.

Automated summary

The study reveals that in high metallicity and large BH mass environments, more dense and fast disc winds appear, which suppress the mass accretion rate. Through simulations and modeling, it is found that the metallicity dependence of the line force and the BH mass dependence of the wind launch region's surface area are the reasons for the metallicity dependence and BH mass dependencies of the mass-loss rate.