An application of machine learning techniques to galaxy cluster mass estimation using the MACSIS simulations

TL;DR

This paper demonstrates that machine learning models trained on simulated galaxy clusters can significantly improve mass estimation accuracy, reducing scatter by a factor of four compared to traditional methods, with implications for cosmology.

Contribution

The study shows that ML techniques trained on hydrodynamical simulations can accurately predict galaxy cluster masses, outperforming traditional methods and remaining robust across different simulation types.

Findings

ML reduces mass prediction scatter from 35% to 7%.

Omitting galaxy velocities does not affect mass prediction within r200c.

ML models recover weak lensing masses with similar accuracy to true masses.

Abstract

Machine learning (ML) techniques, in particular supervised regression algorithms, are a promising new way to use multiple observables to predict a cluster's mass or other key features. To investigate this approach we use the \textsc{MACSIS} sample of simulated hydrodynamical galaxy clusters to train a variety of ML models, mimicking different datasets. We find that compared to predicting the cluster mass from the $\sigma -M$ relation, the scatter in the predicted-to-true mass ratio is reduced by a factor of 4, from $0.130\pm0.004$ dex (${\simeq} 35$ per cent) to $0.031 \pm 0.001$ dex (${\simeq} 7$ per cent) when using the same, interloper contaminated, spectroscopic galaxy sample. Interestingly, omitting line-of-sight galaxy velocities from the training set has no effect on the scatter when the galaxies are taken from within $r_{200c}$. We also train ML models to reproduce estimated masses derived from mock X-ray and weak lensing analyses. While the weak lensing masses can be recovered with a similar scatter to that when training on the true mass, the hydrostatic mass suffers from significantly higher scatter of ${\simeq} 0.13$ dex (${\simeq} 35$ per cent). Training models using dark matter only simulations does not significantly increase the scatter in predicted cluster mass compared to training on simulated clusters with hydrodynamics. In summary, we find ML techniques to offer a powerful method to predict masses for large samples of clusters, a vital requirement for cosmological analysis with future surveys.