Constraints on jet - driven disk accretion in Sagittarius A ⋆

We revisit theoretical and observational constraints on geometrically-thin disk accretion in SagittariusA (SgrA ). We show that the combined effects of mass outflows and electron energization in the hot part of the accretion flow can deflate the inflowing gas from a geometrically-thick structure. This allows the gas to cool and even thermalize on an inflow timescale. As a result, a compact, relatively cool disk may form at small radii. We show that magnetic coupling between the relativistic disk and a steady-state jet results in a disk that is less luminous than a standard relativistic disk accreting at the same rate. This relaxes the observational constraints on thin-disk accretion in SgrA (and by implication, other Low-Luminosity Active Galactic Nulcei, LLAGN). We find typical cold gas accretion rates of a few×10M⊙ yr . We also find that the predicted modified disk emission is compatible with existing near-infrared (NIR) observations of SgrA in its quiescent state provided that the disk inclination angle is ∼ 87 ◦ and that the jet extracts more than 75% of the accretion power. Subject headings: Galaxy: nucleus accretion black hole physics galaxies: jets MHD