  Azimuthal anisotropy in heavy-ion collisions is studied by taking into
account the ridges generated by semi-hard scattering of intermediate-momentum
partons, which can be sensitive to the initial spatial configuration of the
medium in non-central collisions. In a simple treatment of the problem where
the recombination of only thermal partons is considered, analytical formulas
can be derived that yield results in accord with the data on v_2 for p_T <1-2
GeV/c. Centrality dependence is described by a geometrical factor. Ridge
phenomenology is used to determine the initial slopes of v_2 at low p_T for
both pion and proton. For higher p_T, shower partons from high-p_T jets must be
included, but they are not considered here.
