The Two Dimensional Projected Spatial Distribution of Globular Clusters: Method and Application to NGC4261

TL;DR

This paper introduces a new method using K-Nearest Neighbor density estimation and Monte Carlo simulations to analyze the 2D spatial distribution of globular clusters in galaxies, revealing complex anisotropic features.

Contribution

The paper presents a novel approach for mapping 2D globular cluster distributions and applies it to NGC4261, uncovering significant anisotropic and spiral-like structures.

Findings

Confirmed non-isotropic 2D GC distribution in NGC4261

Detected spiral-like and shell features in GC distribution

Red and blue GCs show different spatial patterns

Abstract

We present a new method for the determination of the two-dimensional (2D) projected spatial distribution of globular clusters (GCs) in external galaxies. This method is based on the K-Nearest Neighbor density estimator of Dressler (1980), complemented by MonteCarlo simulations to establish the statistical significance of the results. We apply this method to NGC4261, a "test galaxy" where significant 2D anisotropy in the GC distribution has been reported. We confirm that the 2D distribution of GC is not azimuthally isotropic. Moreover, we demonstrate that the 2D distribution departures from the average GC radial distribution results in highly significant spiral-like or broken shell features. Overall, the same perturbations are found in "red" and "blue" GCs, but with some differences. In particular, we observe a central feature, roughly aligned with the minor axis of NGC4261, composed of red and most luminous GCs. Blue and fainter GCs are more frequent at large radial distances and follow the spiral-like features of the overall density structure. These results suggest a complex merging history for NGC4261.