Dynamical Mass Measurements of Contaminated Galaxy Clusters Using Machine Learning

TL;DR

This paper demonstrates that machine learning, specifically support distribution machines, can significantly improve dynamical mass estimates of galaxy clusters contaminated by interlopers, outperforming traditional methods.

Contribution

The study introduces a machine learning approach that effectively predicts galaxy cluster masses from contaminated data, surpassing standard scaling relation methods in accuracy.

Findings

SDM achieves better than a factor-of-two improvement in mass prediction accuracy.

SDM outperforms traditional scaling relations even with contaminated cluster data.

The method more accurately reproduces the cluster mass function.

Abstract

We study dynamical mass measurements of galaxy clusters contaminated by interlopers and show that a modern machine learning (ML) algorithm can predict masses by better than a factor of two compared to a standard scaling relation approach. We create two mock catalogs from Multidark's publicly available $N$-body MDPL1 simulation, one with perfect galaxy cluster membership information and the other where a simple cylindrical cut around the cluster center allows interlopers to contaminate the clusters. In the standard approach, we use a power-law scaling relation to infer cluster mass from galaxy line-of-sight (LOS) velocity dispersion. Assuming perfect membership knowledge, this unrealistic case produces a wide fractional mass error distribution, with a width of $\Delta\epsilon\approx0.87$. Interlopers introduce additional scatter, significantly widening the error distribution further ($\Delta\epsilon\approx2.13$). We employ the support distribution machine (SDM) class of algorithms to learn from distributions of data to predict single values. Applied to distributions of galaxy observables such as LOS velocity and projected distance from the cluster center, SDM yields better than a factor-of-two improvement ($\Delta\epsilon\approx0.67$) for the contaminated case. Remarkably, SDM applied to contaminated clusters is better able to recover masses than even the scaling relation approach applied to uncontaminated clusters. We show that the SDM method more accurately reproduces the cluster mass function, making it a valuable tool for employing cluster observations to evaluate cosmological models.