The Size Difference Between Red And Blue Globular Clusters Is NOT Due To Projection Effects

TL;DR

This study investigates whether projection effects explain the size difference between red and blue globular clusters, concluding that spatial distribution differences are not the primary cause, implying formation or evolutionary factors are responsible.

Contribution

The paper demonstrates that spatial distribution differences do not account for the size disparity, highlighting the need to consider formation or evolutionary processes.

Findings

Spatial distribution differences do not produce size differences.

Size disparity is likely due to formation or evolution.

Results challenge projection effect explanations.

Abstract

Metal-rich (red) globular clusters in massive galaxies are, on average, smaller than metal-poor (blue) globular clusters. One of the possible explanations for this phenomenon is that the two populations of clusters have different spatial distributions. We test this idea by comparing clusters observed in unusually deep, high signal-to-noise images of M87 with a simulated globular cluster population in which the red and blue clusters have different spatial distributions, matching the observations. We compare the overall distribution of cluster effective radii as well as the relationship between effective radius and galactocentric distance for both the observed and simulated red and blue subpopulations. We find that the different spatial distributions does not produce a significant size difference between the red and blue subpopulations as a whole, or at a given galactocentric distance. These results suggest that the size difference between red and blue globular clusters is likely due to differences during formation or later evolution