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+---
+title: 'Gala: A Python package for galactic dynamics'
+tags:
+  - Python
+  - astronomy
+  - dynamics
+  - galactic dynamics
+  - milky way
+authors:
+  - name: Adrian M. Price-Whelan
+    orcid: 0000-0000-0000-0000
+    equal-contrib: true
+    affiliation: "1, 2" # (Multiple affiliations must be quoted)
+  - name: Author Without ORCID
+    equal-contrib: true # (This is how you can denote equal contributions between multiple authors)
+    affiliation: 2
+  - name: Author with no affiliation
+    corresponding: true # (This is how to denote the corresponding author)
+    affiliation: 3
+  - given-names: Ludwig
+    dropping-particle: van
+    surname: Beethoven
+    affiliation: 3
+affiliations:
+ - name: Lyman Spitzer, Jr. Fellow, Princeton University, USA
+   index: 1
+ - name: Institution Name, Country
+   index: 2
+ - name: Independent Researcher, Country
+   index: 3
+date: 13 August 2017
+bibliography: paper.bib
+
+# Optional fields if submitting to a AAS journal too, see this blog post:
+# https://blog.joss.theoj.org/2018/12/a-new-collaboration-with-aas-publishing
+aas-doi: 10.3847/xxxxx <- update this with the DOI from AAS once you know it.
+aas-journal: Astrophysical Journal <- The name of the AAS journal.
+---
+
+# Summary
+
+The forces on stars, galaxies, and dark matter under external gravitational
+fields lead to the dynamical evolution of structures in the universe. The orbits
+of these bodies are therefore key to understanding the formation, history, and
+future state of galaxies. The field of "galactic dynamics," which aims to model
+the gravitating components of galaxies to study their structure and evolution,
+is now well-established, commonly taught, and frequently used in astronomy.
+Aside from toy problems and demonstrations, the majority of problems require
+efficient numerical tools, many of which require the same base code (e.g., for
+performing numerical orbit integration).
+
+# Statement of need
+
+`Gala` is an Astropy-affiliated Python package for galactic dynamics. Python
+enables wrapping low-level languages (e.g., C) for speed without losing
+flexibility or ease-of-use in the user-interface. The API for `Gala` was
+designed to provide a class-based and user-friendly interface to fast (C or
+Cython-optimized) implementations of common operations such as gravitational
+potential and force evaluation, orbit integration, dynamical transformations,
+and chaos indicators for nonlinear dynamics. `Gala` also relies heavily on and
+interfaces well with the implementations of physical units and astronomical
+coordinate systems in the `Astropy` package [@astropy] (`astropy.units` and
+`astropy.coordinates`).
+
+`Gala` was designed to be used by both astronomical researchers and by
+students in courses on gravitational dynamics or astronomy. It has already been
+used in a number of scientific publications [@Pearson:2017] and has also been
+used in graduate courses on Galactic dynamics to, e.g., provide interactive
+visualizations of textbook material [@Binney:2008]. The combination of speed,
+design, and support for Astropy functionality in `Gala` will enable exciting
+scientific explorations of forthcoming data releases from the *Gaia* mission
+[@gaia] by students and experts alike.
+
+# Mathematics
+
+Single dollars ($) are required for inline mathematics e.g. $f(x) = e^{\pi/x}$
+
+Double dollars make self-standing equations:
+
+$$\Theta(x) = \left\{\begin{array}{l}
+0\textrm{ if } x < 0\cr
+1\textrm{ else}
+\end{array}\right.$$
+
+You can also use plain \LaTeX for equations
+\begin{equation}\label{eq:fourier}
+\hat f(\omega) = \int_{-\infty}^{\infty} f(x) e^{i\omega x} dx
+\end{equation}
+and refer to \autoref{eq:fourier} from text.
+
+# Citations
+
+Citations to entries in paper.bib should be in
+[rMarkdown](http://rmarkdown.rstudio.com/authoring_bibliographies_and_citations.html)
+format.
+
+If you want to cite a software repository URL (e.g. something on GitHub without a preferred
+citation) then you can do it with the example BibTeX entry below for @fidgit.
+
+For a quick reference, the following citation commands can be used:
+- `@author:2001`  ->  "Author et al. (2001)"
+- `[@author:2001]` -> "(Author et al., 2001)"
+- `[@author1:2001; @author2:2001]` -> "(Author1 et al., 2001; Author2 et al., 2002)"
+
+# Figures
+
+Figures can be included like this:
+![Caption for example figure.\label{fig:example}](figure.png)
+and referenced from text using \autoref{fig:example}.
+
+Figure sizes can be customized by adding an optional second parameter:
+![Caption for example figure.](figure.png){ width=20% }
+
+# Acknowledgements
+
+We acknowledge contributions from Brigitta Sipocz, Syrtis Major, and Semyeong
+Oh, and support from Kathryn Johnston during the genesis of this project.
+
+# References