Has the Palomar 14 globular cluster been captured by the Milky Way?

TL;DR

This study models the evolution of the Palomar 14 globular cluster, suggesting it was originally formed in a dwarf galaxy and later captured by the Milky Way, with simulations matching observed properties after 11.5 billion years.

Contribution

It introduces a new scenario where Pal 14 formed in a dwarf galaxy and was captured by the Milky Way, supported by detailed N-body simulations.

Findings

Pal 14 likely formed in a dwarf galaxy with specific initial conditions.

The cluster's properties can be explained by a capture scenario after 2-3 Gyr.

Simulations reproduce observed size and mass after 11.5 Gyr.

Abstract

We examine a new scenario to model the outer halo globular cluster (GC) Pal 14 over its lifetime by performing a comprehensive set of direct N-body calculations. We assume Pal 14 was born in a now detached/disrupted dwarf galaxy with a strong tidal field. Pal 14 evolved there until the slope of the stellar mass function (MF) became close to the measured value which is observed to be significantly shallower than in most GCs. After about 2-3 Gyr, Pal 14 was then captured by the Milky Way (MW). Although the physical size of such a cluster is indistinguishable from a cluster that has lived its entire life in the MW, other parameters like its mass and the MF-slope, strongly depend on the time the cluster is taken from the dwarf galaxy. After being captured by the MW on a new orbit, the cluster expands and eventually reaches the appropriate mass and size of Pal 14 after 11.5 Gyr while reproducing the observed MF. These simulations thus suggest that Pal 14 may have formed in a dwarf galaxy with a post-gas-expulsion initial half-mass radius and mass of $r_h=7$ pc and $8<M/10^4<10 $ M$_{\odot}$, respectively, with a high degree of primordial mass segregation.