@@ -46,53 +46,57 @@ because galaxies exhibit complex morphologies, which cannot be described by trad
4646there are so many sources, they routinely overlap with each other, either due to physical interactions or due to their
4747close alignment along the line of sight. To extract all information of interest and avoid biases from incorrect modeling
4848assumptions, it is therefore necessary to simultaneously model full scenes comprising many sources instead of analyzing
49- each source separately, and each of the source models may itself need to be composed of multiple, morphological complex
49+ each source separately, and each of the source models may itself need to be composed of multiple,
50+ morphologically complex
5051components.
5152
5253# Statement of need
5354
5455` scarlet2 ` is a Python package for full-scene modeling in observational astronomy. It inherits modeling assumptions from
5556` scarlet ` [ @scarlet ] , namely that a scene comprises multiple sources, each source comprises multiple
56- components, and
57- each component is determined by a spectrum model and a morphology model, whose outer product represents the light
57+ components, and each component is determined by a spectrum model and a morphology model, whose outer product
58+ represents the light
5859emission in a sky region as a hyperspectral data cube (wavelength $\times$ height $\times$ width). ` scarlet2 ` retains
5960the object-oriented paradigm and many classes and functions from ` scarlet ` , but augments standard Python with the ` jax `
6061library [ @jax2018github ] for automatic differentiation and just-in-time compilation.
6162
6263` scarlet2 ` acts as a flexible, modular, and extendable modeling language for celestial sources that combines parametric
6364and non-parametric models to describe complex scenarios such as multi-source blending, strong-lensing systems,
6465supernovae and their host galaxies, etc. As a modeling language, ` scarlet2 ` is agnostic about the optimization or
65- inference method the user wants to employ, but it provides methods to optimize the likelihood function or sample from
66+ inference method the user wants to employ, but it also provides methods to optimize the likelihood function or
67+ sample from
6668the posterior, which utilize the ` optax ` package [ @deepmind2020jax ] or the ` numpyro ` inference framework
6769[ @pyro-2019 ; @phan-2019 ] , respectively. The likelihood of multiple
68- observations (at different resolutions, wavelengths, or observing epochs) times can be combined for a joint model of
70+ observations (at different resolutions, wavelengths, or observing epochs) can be combined for a joint model of
6971static and transient sources. To match the coordinates from different observations, ` scarlet2 ` utilizes the ` Astropy `
7072package [ @astropy ] . ` scarlet2 ` can also interface with deep learning methods. Besides being natively portable
71- to GPUs,
72- parameters can be specified with neural networks as data-driven priors, which helps break the degeneracies that arise
73+ to GPUs, parameters can be specified with neural networks as data-driven priors, which helps break the
74+ degeneracies that arise
7375when multiple components are fit simultaneously [ @sampson-2024 ] .
7476
7577![ Scene with seven detected sources in multi-band images from the Hyper Suprime-Cam Subaru Strategic Program.
7678Each source is modelled with a non-parametric spectrum and morphology (1st panel), the entire scene is then convolved
7779with the telescope's point spread function (2nd panel) and compared to the observations (3rd panel).
78- The residuals (4th panel) reveal the presence of undetected sources and source components (e.g. in the center of source
80+ The residuals (4th panel) reveal the presence of previously undetected sources and source components (e.g. in the center of source
7981#1 ).] ( scarlet2_model.png )
8082
8183To support the wide range of scientific studies that will be made with large sky surveys, ` scarlet2 ` was designed with
82- flexibility and ease of use in mind. Several publications have developed and demonstrated new capabilities, including
83- modeling of interstellar dust embedded in distant galaxies
84- [ @siegel-2025 ] and of transient sources such as active galactic nuclei [ @ward-2025 ] and tidal disruption
85- events
86- [ @yao-2025 ] .
87- Future developments will integrate into cloud-based science platforms, provide support for users to make effective
84+ flexibility and ease of use in mind. Several publications have developed and demonstrated its capabilities,
85+ including
86+ modeling of interstellar dust embedded in distant galaxies [ @siegel-2025 ] and of transient sources such as
87+ active galactic
88+ nuclei [ @ward-2025 ] and tidal disruption events [ @yao-2025 ] .
89+ Future developments will integrate ` scarlet2 ` into cloud-based science platforms, provide support for users to
90+ make effective
8891modeling choices and to validate their inference results, and create a robust processing pipeline for joint pixel-level
8992analyses of surveys from the Vera C. Rubin Observatory, the Euclid mission, the Nancy Grace Roman Space Telescope, and
9093the La Silla Schmidt Southern Survey.
9194
9295# Acknowledgements
9396
9497We acknowledge contributions from
95- the [ LINCC Frameworks Incubator Program] ( https://lsstdiscoveryalliance.org/programs/lincc-frameworks/incubators/ ) , in
98+ the [ LINCC Frameworks Incubator Program] ( https://lsstdiscoveryalliance.org/programs/lincc-frameworks/incubators/ ) ,
99+ in
96100particular from software engineers Max West, Drew Oldag, and Sean McGuire, in adopting comprehensive software workflows
97101through the Python Project Template [ @oldag-2024 ] and creating a user-focused recommendation and validation
98102suite.
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