Learning the Universe: Cosmological and Astrophysical Parameter Inference with Galaxy Luminosity Functions and Colours

TL;DR

This study introduces a novel simulation-based inference method using galaxy luminosity functions and colours to constrain cosmological and astrophysical parameters, leveraging a large synthetic dataset from hydrodynamic simulations.

Contribution

It is the first to combine galaxy luminosity functions and colours with simulation-based inference for cosmological parameter estimation.

Findings

Constraints obtained on $oldsymbol{ m extit{ extbf{ extOmega}}}_m$, $oldsymbol{ m extit{ extbf{ extsigma}}}_8$, and feedback parameters.

Demonstrated that galaxy colours encode information about star formation and metallicity history.

Identified limitations in model generalization across different galaxy formation simulations.

Abstract

We perform the first direct cosmological and astrophysical parameter inference from the combination of galaxy luminosity functions and colours using a simulation based inference approach. Using the Synthesizer code we simulate the dust attenuated ultraviolet-near infrared stellar emission from galaxies in thousands of cosmological hydrodynamic simulations from the CAMELS suite, including the Swift-EAGLE, IllustrisTNG, Simba & Astrid galaxy formation models. For each galaxy we calculate the rest-frame luminosity in a number of photometric bands, including the SDSS $\textit{ugriz}$ and GALEX FUV & NUV filters; this dataset represents the largest catalogue of synthetic photometry based on hydrodynamic galaxy formation simulations produced to date, totalling >200 million sources. From these we compile luminosity functions and colour distributions, and find clear dependencies on both cosmology and feedback. We then perform simulation based (likelihood-free) inference using these distributions to constrain $\Omega_m$, $\sigma_8$, and four parameters controlling the strength of stellar and AGN feedback. Both colour distributions and luminosity functions provide complementary information on certain parameters when performing inference. We achieve constraints on the stellar feedback parameters, as well as $\Omega_m$ and $\sigma_8$. The latter is attributable to the fact that the photometry encodes the star formation-metal enrichment history of each galaxy; galaxies in a universe with a higher $\sigma_8$ tend to form earlier and have higher metallicities, which leads to redder colours. We find that a model trained on one galaxy formation simulation generalises poorly when applied to another, and attribute this to differences in the subgrid prescriptions, and lack of flexibility in our emission modelling. The photometric catalogues are publicly available at: https://camels.readthedocs.io/