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| 1 | +--- |
| 2 | +title: 'Gala: A Python package for galactic dynamics' |
| 3 | +tags: |
| 4 | + - Python |
| 5 | + - astronomy |
| 6 | + - dynamics |
| 7 | + - galactic dynamics |
| 8 | + - milky way |
| 9 | +authors: |
| 10 | + - name: Adrian M. Price-Whelan |
| 11 | + orcid: 0000-0000-0000-0000 |
| 12 | + equal-contrib: true |
| 13 | + affiliation: "1, 2" # (Multiple affiliations must be quoted) |
| 14 | + - name: Author Without ORCID |
| 15 | + equal-contrib: true # (This is how you can denote equal contributions between multiple authors) |
| 16 | + affiliation: 2 |
| 17 | + - name: Author with no affiliation |
| 18 | + corresponding: true # (This is how to denote the corresponding author) |
| 19 | + affiliation: 3 |
| 20 | + - given-names: Ludwig |
| 21 | + dropping-particle: van |
| 22 | + surname: Beethoven |
| 23 | + affiliation: 3 |
| 24 | +affiliations: |
| 25 | + - name: Lyman Spitzer, Jr. Fellow, Princeton University, United States |
| 26 | + index: 1 |
| 27 | + ror: 00hx57361 |
| 28 | + - name: Institution Name, Country |
| 29 | + index: 2 |
| 30 | + - name: Independent Researcher, Country |
| 31 | + index: 3 |
| 32 | +date: 13 August 2017 |
| 33 | +bibliography: paper.bib |
| 34 | + |
| 35 | +# Optional fields if submitting to a AAS journal too, see this blog post: |
| 36 | +# https://blog.joss.theoj.org/2018/12/a-new-collaboration-with-aas-publishing |
| 37 | +aas-doi: 10.3847/xxxxx <- update this with the DOI from AAS once you know it. |
| 38 | +aas-journal: Astrophysical Journal <- The name of the AAS journal. |
| 39 | +--- |
| 40 | + |
| 41 | +# Summary |
| 42 | + |
| 43 | +The forces on stars, galaxies, and dark matter under external gravitational |
| 44 | +fields lead to the dynamical evolution of structures in the universe. The orbits |
| 45 | +of these bodies are therefore key to understanding the formation, history, and |
| 46 | +future state of galaxies. The field of "galactic dynamics," which aims to model |
| 47 | +the gravitating components of galaxies to study their structure and evolution, |
| 48 | +is now well-established, commonly taught, and frequently used in astronomy. |
| 49 | +Aside from toy problems and demonstrations, the majority of problems require |
| 50 | +efficient numerical tools, many of which require the same base code (e.g., for |
| 51 | +performing numerical orbit integration). |
| 52 | + |
| 53 | +# Statement of need |
| 54 | + |
| 55 | +`Gala` is an Astropy-affiliated Python package for galactic dynamics. Python |
| 56 | +enables wrapping low-level languages (e.g., C) for speed without losing |
| 57 | +flexibility or ease-of-use in the user-interface. The API for `Gala` was |
| 58 | +designed to provide a class-based and user-friendly interface to fast (C or |
| 59 | +Cython-optimized) implementations of common operations such as gravitational |
| 60 | +potential and force evaluation, orbit integration, dynamical transformations, |
| 61 | +and chaos indicators for nonlinear dynamics. `Gala` also relies heavily on and |
| 62 | +interfaces well with the implementations of physical units and astronomical |
| 63 | +coordinate systems in the `Astropy` package [@astropy] (`astropy.units` and |
| 64 | +`astropy.coordinates`). |
| 65 | + |
| 66 | +`Gala` was designed to be used by both astronomical researchers and by |
| 67 | +students in courses on gravitational dynamics or astronomy. It has already been |
| 68 | +used in a number of scientific publications [@Pearson:2017] and has also been |
| 69 | +used in graduate courses on Galactic dynamics to, e.g., provide interactive |
| 70 | +visualizations of textbook material [@Binney:2008]. The combination of speed, |
| 71 | +design, and support for Astropy functionality in `Gala` will enable exciting |
| 72 | +scientific explorations of forthcoming data releases from the *Gaia* mission |
| 73 | +[@gaia] by students and experts alike. |
| 74 | + |
| 75 | +# Mathematics |
| 76 | + |
| 77 | +Single dollars ($) are required for inline mathematics e.g. $f(x) = e^{\pi/x}$ |
| 78 | + |
| 79 | +Double dollars make self-standing equations: |
| 80 | + |
| 81 | +$$\Theta(x) = \left\{\begin{array}{l} |
| 82 | +0\textrm{ if } x < 0\cr |
| 83 | +1\textrm{ else} |
| 84 | +\end{array}\right.$$ |
| 85 | + |
| 86 | +You can also use plain \LaTeX for equations |
| 87 | +\begin{equation}\label{eq:fourier} |
| 88 | +\hat f(\omega) = \int_{-\infty}^{\infty} f(x) e^{i\omega x} dx |
| 89 | +\end{equation} |
| 90 | +and refer to \autoref{eq:fourier} from text. |
| 91 | + |
| 92 | +# Citations |
| 93 | + |
| 94 | +Citations to entries in paper.bib should be in |
| 95 | +[rMarkdown](http://rmarkdown.rstudio.com/authoring_bibliographies_and_citations.html) |
| 96 | +format. |
| 97 | + |
| 98 | +If you want to cite a software repository URL (e.g. something on GitHub without a preferred |
| 99 | +citation) then you can do it with the example BibTeX entry below for @fidgit. |
| 100 | + |
| 101 | +For a quick reference, the following citation commands can be used: |
| 102 | +- `@author:2001` -> "Author et al. (2001)" |
| 103 | +- `[@author:2001]` -> "(Author et al., 2001)" |
| 104 | +- `[@author1:2001; @author2:2001]` -> "(Author1 et al., 2001; Author2 et al., 2002)" |
| 105 | + |
| 106 | +# Figures |
| 107 | + |
| 108 | +Figures can be included like this: |
| 109 | + |
| 110 | +and referenced from text using \autoref{fig:example}. |
| 111 | + |
| 112 | +Figure sizes can be customized by adding an optional second parameter: |
| 113 | +{ width=20% } |
| 114 | + |
| 115 | +# Acknowledgements |
| 116 | + |
| 117 | +We acknowledge contributions from Brigitta Sipocz, Syrtis Major, and Semyeong |
| 118 | +Oh, and support from Kathryn Johnston during the genesis of this project. |
| 119 | + |
| 120 | +# References |
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