Near-horizon limit of the charged BTZ black hole and AdS2 quantum gravity

We show that the 3D charged Banados-Teitelboim-Zanelli (BTZ) black hole solution interpolates between two different 2D AdS spacetimes: a near-extremal, near-horizon AdS(2) geometry with constant dilaton and U(1) field and an asymptotic AdS(2) geometry with a linear dilaton. Thus, the charged BTZ black hole can be considered as interpolating between the two different formulations proposed until now for AdS(2) quantum gravity. In both cases the theory is the chiral half of a 2D CFT and describes, respectively, Brown-Hennaux-like boundary deformations and near-horizon excitations. The central charge c a s of the asymptotic CFT is determined by 3D Newton constant G and the AdS length l, c(as) = 3l/G, whereas that of the near-horizon CFT also depends on the U(1) charge Q, c(nh) alpha lQ/root G.