Radiation hydrodynamics simulations of line-driven AGN disc winds: metallicity dependence and black hole growth

Abstract

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 $M_{\mathrm{BH}}\gtrsim 10^5{M}_{\odot }$ 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 ($\propto M_{\mathrm{BH}}^{4/3}$ for $M_{\mathrm{BH}}\le 10^6{M}_{\odot }$ and $\propto M_{\mathrm{BH}}$ for $M_{\mathrm{BH}}\ge 10^6{M}_{\odot }$) 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.

11 pages, 7 figures, accepted for publication in MNRAS

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Cited by in corpus (2)

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