Studying the asymmetry of the GC population of NGC 4261

TL;DR

This study analyzes the spatial and color distribution of globular clusters in NGC 4261, revealing a significant azimuthal asymmetry possibly caused by galaxy interaction or merger.

Contribution

It provides the first detailed analysis of the GC population's asymmetry and bimodal color distribution in NGC 4261 using HST data.

Findings

Asymmetry in GC azimuthal distribution about NE-SW axis

Bimodal color distribution of GCs with distinct blue and red populations

Red GCs have a steeper radial profile than blue GCs

Abstract

We present an analysis of the Globular Cluster (GC) population of the elliptical galaxy NGC 4261 based on HST WFPC2 data in the B, V and I bands. We study the spatial distribution of the GCs in order to probe the anisotropy in the azimuthal distribution of the discrete X-ray sources in the galaxy revealed by Chandra images (Zezas et al. 2003). The luminosity function of our GC sample (complete at the 90% level for V_mag = 23.8 mag) peaks at V_mag = 25.1 (-0.6)(+1.0) mag, which corresponds to a distance consistent with previous measurements. The colour distribution can be interpreted as being the superposition of a blue and red GC component with average colours V-I = 1.01 (-0.06)(+0.06) mag and 1.27 (-0.08)(+0.06) mag, respectively. This is consistent with a bimodal colour distribution typical of elliptical galaxies. The red GC's radial profile is steeper than that of the galaxy surface brightness, while the profile of the blue subpopulation looks more consistent with it. The most striking finding is the significant asymmetry in the azimuthal distribution of the GC population about a NE-SW direction. The lack of any obvious feature in the morphology of the galaxy suggests that the asymmetry could be the result of an interaction or a merger.