Flexible Simulation Based Inference for Galaxy Photometric Fitting with Synthesizer

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Main Authors: Harvey, Thomas, Lovell, Christopher C., Newman, Sophie, Conselice, Christopher J., Austin, Duncan, Roper, William J., Vijayan, Aswin P., Wilkins, Stephen M., Iglesias-Navarro, Patricia, Rusakov, Vadim, Li, Qiong, Adams, Nathan, Magdwick, Kai, Goolsby, Caio M., Huertas-Company, Marc, Ho, Matthew
Format: Preprint
Published: 2025
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author Harvey, Thomas
Lovell, Christopher C.
Newman, Sophie
Conselice, Christopher J.
Austin, Duncan
Roper, William J.
Vijayan, Aswin P.
Wilkins, Stephen M.
Iglesias-Navarro, Patricia
Rusakov, Vadim
Li, Qiong
Adams, Nathan
Magdwick, Kai
Goolsby, Caio M.
Huertas-Company, Marc
Ho, Matthew
author_facet Harvey, Thomas
Lovell, Christopher C.
Newman, Sophie
Conselice, Christopher J.
Austin, Duncan
Roper, William J.
Vijayan, Aswin P.
Wilkins, Stephen M.
Iglesias-Navarro, Patricia
Rusakov, Vadim
Li, Qiong
Adams, Nathan
Magdwick, Kai
Goolsby, Caio M.
Huertas-Company, Marc
Ho, Matthew
contents We introduce Synference, a new, flexible Python framework for galaxy SED fitting using simulation-based inference (SBI). Synference leverages the Synthesizer package for flexible forward-modelling of galaxy SEDs and integrates the LtU-ILI package to ensure best practices in model training and validation. In this work we demonstrate Synference by training a neural posterior estimator on $10^6$ simulated galaxies, based on a flexible 8-parameter physical model, to infer galaxy properties from 14-band HST and JWST photometry. We validate this model, demonstrating excellent parameter recovery (e.g. R$^2>$0.99 for M$_\star$) and accurate posterior calibration against nested sampling results. We apply our trained model to 3,088 spectroscopically-confirmed galaxies in the JADES GOODS-South field. The amortized inference is exceptionally fast, having nearly fixed cost per posterior evaluation and processing the entire sample in $\sim$3 minutes on a single CPU (18 galaxies/CPU/sec), a $\sim$1700$\times$ speedup over traditional nested sampling or MCMC techniques. We demonstrate Synference's ability to simultaneously infer photometric redshifts and physical parameters, and highlight its utility for rapid Bayesian model comparison by demonstrating systematic stellar mass differences between two commonly used stellar population synthesis models. Synference is a powerful, scalable tool poised to maximise the scientific return of next-generation galaxy surveys.
format Preprint
id arxiv_https___arxiv_org_abs_2511_10640
institution arXiv
publishDate 2025
record_format arxiv
spellingShingle Flexible Simulation Based Inference for Galaxy Photometric Fitting with Synthesizer
Harvey, Thomas
Lovell, Christopher C.
Newman, Sophie
Conselice, Christopher J.
Austin, Duncan
Roper, William J.
Vijayan, Aswin P.
Wilkins, Stephen M.
Iglesias-Navarro, Patricia
Rusakov, Vadim
Li, Qiong
Adams, Nathan
Magdwick, Kai
Goolsby, Caio M.
Huertas-Company, Marc
Ho, Matthew
Astrophysics of Galaxies
Cosmology and Nongalactic Astrophysics
Instrumentation and Methods for Astrophysics
We introduce Synference, a new, flexible Python framework for galaxy SED fitting using simulation-based inference (SBI). Synference leverages the Synthesizer package for flexible forward-modelling of galaxy SEDs and integrates the LtU-ILI package to ensure best practices in model training and validation. In this work we demonstrate Synference by training a neural posterior estimator on $10^6$ simulated galaxies, based on a flexible 8-parameter physical model, to infer galaxy properties from 14-band HST and JWST photometry. We validate this model, demonstrating excellent parameter recovery (e.g. R$^2>$0.99 for M$_\star$) and accurate posterior calibration against nested sampling results. We apply our trained model to 3,088 spectroscopically-confirmed galaxies in the JADES GOODS-South field. The amortized inference is exceptionally fast, having nearly fixed cost per posterior evaluation and processing the entire sample in $\sim$3 minutes on a single CPU (18 galaxies/CPU/sec), a $\sim$1700$\times$ speedup over traditional nested sampling or MCMC techniques. We demonstrate Synference's ability to simultaneously infer photometric redshifts and physical parameters, and highlight its utility for rapid Bayesian model comparison by demonstrating systematic stellar mass differences between two commonly used stellar population synthesis models. Synference is a powerful, scalable tool poised to maximise the scientific return of next-generation galaxy surveys.
title Flexible Simulation Based Inference for Galaxy Photometric Fitting with Synthesizer
topic Astrophysics of Galaxies
Cosmology and Nongalactic Astrophysics
Instrumentation and Methods for Astrophysics
url https://arxiv.org/abs/2511.10640