VEGAS-SSS II: Comparing the globular cluster systems in NGC3115 and NGC1399 using VEGAS and FDS survey data

Abstract

We analyze the globular cluster (GC) systems in two very different galaxies, N3115 and N1399. With the papers of this series, we aim at highlighting common and different properties in the GC systems in galaxies covering a wide range of parameter space. We compare the GCs in N3115 and N1399 as derived from the analysis of u, g, and i band images taken with the VST telescope as part of the VEGAS and FDS surveys. We selected GC candidates using as reference the morpho-photometric and color properties of confirmed GCs. The surface density of GCs in N3115 reveal a morphology similar to the profile of field stars; the same is true when blue and red GCs are taken separately. The GC maps for N1399 are richer in structure and confirm the existence of an intracluster GC component. We confirm the presence of a spatial offset in the N1399 GC centroid and find that the centroid of the GCs for N3115 coincides well with the galaxy center. Both GC systems show unambiguous color bimodality in g-i and u-i. The azimuthal average of the radial density profiles in both galaxies reveals a larger spatial extent for the total GCs population with respect to the galaxy surface brightness profile. As for the specific frequency of GCs, Sn, we find it is a factor of two higher in N1399 than for N3115. By inspecting the radial behavior of the specific frequency, Sn(<r), for the total, blue, and red GCs, we find notable similarities between the trends for red GCs in the two targets. In spite of extremely different host environments, the red GCs in both cases appear closely linked to the light distribution of field stars. Blue GCs extend to larger galactocentric scales than red GCs, marking a significant difference between the two galaxies: the blue/red GCs and field stellar components of N3115 appear well thermalized with each other and the blue GCs in N1399 appear to fade into an unrelaxed intracluster GC population.