Wide-field imaging of NGC 4365’s globular cluster system: The third subpopulation revisited

Analysis of the globular cluster (GC) system of the giant elliptical (E3) galaxy NGC 4365, from eight Hubble Space Telescope/Advanced Camera for Surveys (ACS) point-ings and a wide-field Subaru/SuprimeCam (S-Cam) image, is presented. Using magni-tude, colour and size criteria we obtain a catalogue of GC candidates. We also measure the photometric properties of the galaxy starlight, including a new measure of the ef-fective radius.We determine the lower limit on the number of GCs to be 6450 ± 110 and show that the GC system extends beyond 134 kpc (9.5 galaxy effective radii). We revisit the question of whether NGC 4365 has a bimodal or trimodal GC colour distri-bution and find support for three distinct GC colour subpopulations (i.e. blue, green and red). Sérsic profile fits to the radial surface density of each subpopulation reveal that the blue GCs are more extended than either red or green GCs. The median half light radii for GCs in the blue, green and red subpopulations are 4.1±0.30.2, 3.0±0.20.1 and 2.8±0.10.1 parsec respectively. The estimated subpopulation ellipticities are 0.66 ± 0.06, 0.55 ± 0.07 and 0.16 ± 0.25 for the blue, green and red GCs, where alignment with th