Poisson Cluster Process Models for Detecting Ultra-Diffuse Galaxies

TL;DR

This paper introduces novel Poisson Cluster Process models for detecting ultra-diffuse galaxies by modeling star cluster distributions, and develops new assessment tools and algorithms that outperform existing methods, revealing potential new dark galaxies.

Contribution

The paper presents new PCP models for UDG detection, a novel assessment framework for spatial predictions, and an adaptive MCMC algorithm, advancing astrophysical detection techniques.

Findings

Models outperform Log-Gaussian Cox Process in detection accuracy.

Marked PCP improves detection over unmarked models.

Potential new dark galaxy identified.

Abstract

We propose a novel set of Poisson Cluster Process (PCP) models to detect Ultra-Diffuse Galaxies (UDGs), a class of extremely faint, enigmatic galaxies of substantial interest in modern astrophysics. We model the unobserved UDG locations as parent points in a PCP, and infer their positions based on the observed spatial point patterns of their old star cluster systems. Many UDGs have somewhere from a few to hundreds of these old star clusters, which we treat as offspring points in our models. We also present a new framework to construct a marked PCP model using the marks of star clusters. The marked PCP model may enhance the detection of UDGs and offers broad applicability to problems in other disciplines. To assess the overall model performance, we design an innovative assessment tool for spatial prediction problems where only point-referenced ground truth is available, overcoming the limitation of standard ROC analyses where spatial Boolean reference maps are required. We construct a bespoke blocked Gibbs adaptive spatial birth-death-move MCMC algorithm to infer the locations of UDGs using real data from a \textit{Hubble Space Telescope} imaging survey. Based on our performance assessment tool, our novel models significantly outperform existing approaches using the Log-Gaussian Cox Process. We also obtained preliminary evidence that the marked PCP model improves UDG detection performance compared to the model without marks. Furthermore, we find evidence of a potential new ``dark galaxy'' that was not detected by previous methods.