The Effects of Thermal Conduction on Radiatively Inefficient Accretion Flows

We quantify the effects of electron thermal conduction on the properties ofhot accretion flows, under the assumption of spherical symmetry. Electron heatconduction is important for low accretion rate systems where the electroncooling time is longer than the conduction time of the plasma, such as Sgr A*in the Galactic Center. For accretion flows with density profiles similar tothe Bondi solution (n[r] ~ r^[-3/2]), we show that heat conduction leads tosuper-virial temperatures, implying that conduction significantly modifies thedynamics of the accretion flow. We then self-consistently solve for thedynamics of spherical accretion in the presence of saturated conduction andelectron heating. We find that the accretion rate onto the central object canbe reduced by ~1-3 orders of magnitude relative to the canonical Bondi rate.Electron conduction may thus be an important ingredient in explaining the lowradiative efficiencies and low accretion rates inferred from observations oflow-luminosity galactic nuclei. The solutions presented in this paper may alsodescribe the nonlinear saturation of the magnetothermal instability in hotaccretion flows.Comment: 17 pages, 9 figures, accepted for publication in The Astrophysical Journal. Changes: additional order-of-magnitude estimates of the importance of conductive heating, discussion of pre-heating instabilities, estimate of magnetothermal instability growth rate in a hot accretion flo