galpy: A python LIBRARY FOR GALACTIC DYNAMICS

Abstract

I describe the design, implementation, and usage of galpy, a Python package\nfor galactic-dynamics calculations. At its core, galpy consists of a general\nframework for representing galactic potentials both in Python and in C (for\naccelerated computations); galpy functions, objects, and methods can generally\ntake arbitrary combinations of these as arguments. Numerical orbit integration\nis supported with a variety of Runge-Kutta-type and symplectic integrators. For\nplanar orbits, integration of the phase-space volume is also possible. galpy\nsupports the calculation of action-angle coordinates and orbital frequencies\nfor a given phase-space point for general spherical potentials, using\nstate-of-the-art numerical approximations for axisymmetric potentials, and\nmaking use of a recent general approximation for any static potential. A number\nof different distribution functions (DFs) are also included in the current\nrelease; currently these consist of two-dimensional axisymmetric and\nnon-axisymmetric disk DFs, a three-dimensional disk DF, and a DF framework for\ntidal streams. I provide several examples to illustrate the use of the code. I\npresent a simple model for the Milky Way's gravitational potential consistent\nwith the latest observations. I also numerically calculate the Oort functions\nfor different tracer populations of stars and compare it to a new analytical\napproximation. Additionally, I characterize the response of a\nkinematically-warm disk to an elliptical m=2 perturbation in detail. Overall,\ngalpy consists of about 54,000 lines, including 23,000 lines of code in the\nmodule, 11,000 lines of test code, and about 20,000 lines of documentation. The\ntest suite covers 99.6% of the code.\n galpy is available at http://github.com/jobovy/galpy with extensive\ndocumentation available at http://galpy.readthedocs.org/en/latest .\n

Keywords

Affiliated Institutions

• Institute for Advanced Study US

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