Beams from a Starburst Galaxy Nucleus

A twin-exhaust beam model is applied to the outflow from starburst galaxies. The beam flow is assumed to be embedded in the external envelope bound by the central star cluster. The velocity field and the cross-sectional area of the beam flow are obtained analytically as a function of the distance from the center. The terminal speed v_∞ is about v_∞ ~ sqrt {2(f - 1)GM/b}, where f is the ratio of the temperature of the beam gas to that of the external gas, M the mass of the central star cluster, and b the effective radius of the central star cluster. For typical values of the parameters, this terminal speed becomes of the order of 900 km s(-1) , that is consistent with the observation. During the early stage of starburst winds, the flow is collimated by external pressure and the beam model may be established.