Merging of Globular Clusters in Inner Galactic Regions. I. Do They Survive the Tidal Interaction?

Abstract

The main topic of this paper is the investigation of the modes of interaction of globular clusters (GCs) moving in the inner part of a galaxy. This is tackled by means of high-resolution N -body simulations, whose first results are presented in this article. Our simulations dealt with primordial very massive (order of 10 7 M ⊙ ) GCs that were able to decay, because of dynamical friction, into the inner regions of triaxial galaxies on a time much shorter than their internal relaxation time. To check the disruptive roles of both tidal forces and GC-GC collisions, their effects were maximised by considering clusters on quasi-radial orbits and choosing the initial conditions so as to give head-on collisions at each passage through the center.The available CPU resources allowed us to simulate clusters with different structural parameters and to follow them on quasi-radial orbits during 8 passages across the center. The main findings are: i) clusters with an initial high enough King concentration parameter (c ≥ 1.2), preserve up to 50% of their initial mass; ii) the inner density distribution of the survived clusters keep a King model profile; iii) GC-GC collisions have a negligible effect with respect to that caused by the passage through the galactic center; iv) the orbital energy dissipation due to the tidal interaction is of the same order of that caused by dynamical friction; v) complex sub-structures like "ripples" and "clumps" formed, as observed around real clusters. These findings support the validity of the hypothesis of merging of GCs in the galactic central region, with modes that deserve further careful investigations.

Merging of Globular Clusters in Inner Galactic Regions. II. Nuclear Star Cluster Formation

“…), makes interesting the investigation started in the first paper of this series (Miocchi et al 2006, hereafter Paper I) of the fate of massive GCs moving in the parent galaxy field that are subjected to dynamical friction braking and tidal interaction. In Paper I, we studied the dynamical evolution of two GCs with masses %10 7 M moving in quasi-radial orbits in a triaxial galactic potential for eight passages across the galactic center.…”

Galactic nuclei formation and activity induced by globular cluster merging

“…Point (i) has been carefully studied in [26] and [14] in self consistent models of triaxial core-galaxies, and presently under study in triaxial cuspy-galaxies with dark matter haloes [10]. The validity of point (ii) has been demonstrated by first results of [4], while the resistance to galactic tidal forces of sufficiently compact GCs confirmed by [23] and the actual formation of an SSC via orbitally decayed cluster merger has been proved by detailed N-body simulations [15], [24]. Points (iii) and (iv) deserve a deeper investigation by mean of accurate modeling, even if they seem reasonably well supported by previous studies [4], [7].…”

Young star clusters in circumnuclear starburst rings

“…The high-density environments in these rings make them ideal locations to harbour large numbers of YMCs, much more so than in galaxy centres (e.g., Miocchi et al 2006). In turn, this might make these environments conducive to significant cluster-to-cluster interactions.…”

“…Two scenarios have been proposed to explain their formation: (i) as a consequence of bar-driven gas inflow and dynamical resonances in the bar, inflowing gas as well as stars accumulate in a ring which connects the two inner Lindblad resonances at the ends of the bars (e.g., Romero-Gómez et al 2006;Athanassoula et al 2010;Athanassoula 2012); or (ii) they may have formed owing to the centrifugal barrier encountered by gas migrating to the inner regions of the galaxy (Kim et al 2012). The high-density environments in these rings make them ideal locations to harbour large numbers of YMCs, much more so than in galaxy centres (e.g., Miocchi et al 2006). Indeed, based on high-resolution HST images, numerous young (a few ×10 7 yr-old) and intermediate-age (a few Gyr-old) star clusters have been uncovered in these structures (e.g., Barth et al 1995;Maoz et al 1996Maoz et al , 2001Ho 1997;Buta et al 2000;de Grijs et al 2003a,b;Mazzuca et al 2008;de Grijs & Anders 2012;Hsieh et al 2012;van der Laan et al 2013, henceforth vdL13).…”