A New Formation Scenario for the Milky Way Cluster NGC2419

TL;DR

This paper proposes that NGC2419, a distant and luminous globular cluster, formed from the merger of a star cluster complex during a galaxy interaction, supported by numerical simulations matching observed properties.

Contribution

It introduces a novel formation scenario for NGC2419 involving merged star cluster complexes, validated through extensive numerical modeling.

Findings

Simulations produce stable merger objects matching NGC2419's properties.

Effective radii are constrained despite varying initial conditions.

Degenerate states allow different initial conditions to result in similar structures.

Abstract

We present a new formation scenario for NGC2419, which is one of the most luminous,one of the most distant, and as well one of the most extended globular clusters of the Milky Way. We propose that NGC2419 is the remnant of a merged star cluster complex, which was possibly formed during an interaction between a gas-rich galaxy and the Milky Way. To test this hypothesis, we performed numerical simulations of 27 different models of star cluster complexes (CCs) moving on a highly eccentric orbit in the Galactic halo. We vary the CC mass, the CC size, and the initial distribution of star clusters in the CC to analyze the influence of these parameters on the resulting objects. In all cases, the vast majority of star clusters merged into a stable object. The derived parameters mass, absolute V-band magnitude, effective radius, velocity dispersion and the surface brightness profile are, for a number of models, in good agreement with those observed for NGC2419. Despite the large range of CC sizes, the effective radii of the merger objects are constrained to a relatively small interval. A turnover in the r_eff vs. M_encl space leads to degenerate states, i.e. relatively compact CCs can produce an object with the same structural parameters as a more massive and larger CC. In consequence, a range of initial conditions can form a merger object comparable to NGC2419 preventing us to pinpoint the exact parameters of the original CC, which formed NGC2419. We conclude that NGC2419 can be well explained by the merged cluster complex scenario. Some of the recently discovered stellar streams in the Galactic halo might be related to the parent galaxy, which produced the cluster complex in our scenario. Measurements of the proper motion of NGC2419 are necessary to prove an association with one of the stellar streams.