A Hydrodynamical Thermal Irradiated Wind from the Outer Thin Accretion Disk in Low-luminosity Active Galactic Nuclei

Abstract

Evidently, low-luminosity active galactic nuclei (LLAGNs) are comprised of an inner advective disk and an outer geometrically thin disk. Wind is inevitable in LLAGNs, mainly interpreted in an indirect way, also the evidence is growing for the presence of wind in the outer thin disk. We present a hydrodynamics (HD) model for wind from the outer thin disk, where the main driver is the inner disk irradiation (which is parameterized by a number $x$ in hydrostatic equilibrium equation) and the heating mechanism is photoionization. The model works for low-intensity irradiation or from a height $z_s$ in the optically thin medium. We solve the model equations in cylindrical coordinates along the $z$-axis for a given radius $r$ with assuming a tiny vertical speed $v_z$ ($\ll c_s$ sound speed). The sonic point conditions assure an isobaric regime above the sonic height ($z^{max}$); in addition to the height $z_f (\ll z^{max}$), the radial pressure gradient also supports the fluid rotation, and both jointly assure a wind ejection from the $z^{max}$ with fluid speed. The $z^{max}$ increases with $x$, and beyond a large $z^{max}$ (say $z^{max}_t$ corresponding to maximum $x$), there is no physical solution. We start the computation from the outer radius $r_o^{thin}$ to the inner $r_{in}^{thin}$ with a Bondi mass accretion rate $\dot{M}_{Bondi}$, to explore the $r$ dependency of the mass inflow rate $\dot{M}$ and wind properties. We constrain the model by fixing $\dot{M}$ at $r_{in}^{thin}$ from the observations of NGC 1097 and check the feasibility of the model by comparing the energetics with the observed bolometric luminosity. The wind is an equatorial with a viewing angle $i>85$ degrees and capable to generate red/blueshifted lines, which would be a general characteristics for LLAGNs.