D'Abrusco, Raffaele, Fabbiano, G., Strader, J., Zezas, Andreas, Mineo, S., Fragos, T., Bonfini, P., Luo, B., Kim, D. -W, and King, A. 2013. "The Two-dimensional Projected Spatial Distribution of Globular Clusters. I. Method and Application to NGC 4261." The Astrophysical Journal 773:87. https://doi.org/10.1088/0004-637X/773/2/87
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, complemented by Monte-Carlo simulations to establish the statistical significance of the results. We apply this method to NGC 4261, 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 NGC 4261, 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 NGC 4261.