Interpretable machine learning of halo gas density profiles: a sensitivity analysis of cosmological hydrodynamical simulations

TL;DR

This study uses machine learning and sensitivity analysis on cosmological simulations to understand how galaxy and halo properties influence the distribution of gas in dark matter haloes across different feedback models and redshifts.

Contribution

It introduces a random forest model to predict halo gas density profiles from galaxy properties and applies Sobol sensitivity analysis to quantify feature importance across simulations.

Findings

Halo mass and gas mass of the central galaxy are key determinants of gas distribution.

The importance of features varies with feedback scenario and redshift.

The framework can be integrated into semi-analytic models and used to interpret future observations.

Abstract

Stellar and AGN-driven feedback processes affect the distribution of gas on a wide range of scales, from within galaxies well into the intergalactic medium. Yet, it remains unclear how feedback, through its connection to key galaxy properties, shapes the radial gas density profile in the host halo. We tackle this question using suites of the EAGLE, IllustrisTNG, and Simba cosmological hydrodynamical simulations, which span a variety of feedback models. We develop a random forest algorithm that predicts the radial gas density profile within haloes from the total halo mass and five global properties of the central galaxy: gas and stellar mass; star formation rate; mass and accretion rate of the central black hole (BH). The algorithm reproduces the simulated gas density profiles with an average accuracy of $\sim$80-90% over the halo mass range $10^{9.5} \, \mathrm{M}_{\odot} < M_{\rm 200c} < 10^{15} \, \mathrm{M}_{\odot}$ and redshift interval $0<z<4$. For the first time, we apply Sobol statistical sensitivity analysis to full cosmological hydrodynamical simulations, quantifying how each feature affects the gas density as a function of distance from the halo centre. Across all simulations and redshifts, the total halo mass and the gas mass of the central galaxy are the most strongly tied to the halo gas distribution, while stellar and BH properties are generally less informative. The exact relative importance of the different features depends on the feedback scenario and redshift. Our framework can be readily embedded in semi-analytic models of galaxy formation to incorporate halo gas density profiles consistent with different hydrodynamical simulations. Our work also provides a proof of concept for constraining feedback models with future observations of galaxy properties and of the surrounding gas distribution.