Hi everyone, I think there is a small error in the angular momentum calculation. Below, L is calculated as: L = velocity x radius def _SpecificAngularMomentumX(field, data): xv, yv, zv = obtain_velocities(data) rv = obtain_rvec(data) return yv*rv[2,:] - zv*rv[1,:] def _SpecificAngularMomentumY(field, data): xv, yv, zv = obtain_velocities(data) rv = obtain_rvec(data) return -(xv*rv[2,:] - zv*rv[0,:]) def _SpecificAngularMomentumZ(field, data): xv, yv, zv = obtain_velocities(data) rv = obtain_rvec(data) return xv*rv[1,:] - yv*rv[0,:] but it should be: L = radius x velocity This leads to a sign error (and gives me a whole load of retrograde GMCs!) def _SpecificAngularMomentumX(field, data): xv, yv, zv = obtain_velocities(data) rv = obtain_rvec(data) return zv*rv[1,:] - yv*rv[2,:] def _SpecificAngularMomentumY(field, data): xv, yv, zv = obtain_velocities(data) rv = obtain_rvec(data) return -(zv*rv[0,:] - xv*rv[2,:]) def _SpecificAngularMomentumZ(field, data): xv, yv, zv = obtain_velocities(data) rv = obtain_rvec(data) return yv*rv[0,:] - xv*rv[1,:] Does that look right? Elizabeth ------------------------------------------------------ Elizabeth TASKER Assistant Professor Physics Department, Faculty of Science Hokkaido University Sapporo, Japan tasker@astro1.sci.hokudai.ac.jp http://astro3.sci.hokudai.ac.jp/~tasker/ ------------------------------------------------------