Globular Clusters in a Cosmological N-body Simulation (1706.01938v2)

Abstract: Stellar dynamical model globular clusters are introduced into reconstituted versions of the dark matter halos of the Via-Lactea II (VL-2) simulation to follow the star cluster tidal mass loss and stellar stream formation. The clusters initially evolve within their local sub-galactic halo, later being accreted into the main halo. Stars are continually removed from the clusters, but those that emerged in the sub-galactic halos are dispersed in a wide stream when accreted into the main halo. Thin tidal streams that survive to the present can begin to form once a cluster is in the main halo. A higher redshift start places the star clusters in denser halos where they are subject to stronger tides leading to higher average mass loss rates. A z=3 start leads to a rich set of star streams with nearly all within 100 kpc having a remnant progenitor star cluster in the stream. In contrast, in a z=8 start, all star clusters that are accreted onto the main halo are completely dissolved. These results are compared to the available data on Milky-Way streams, where the majority of streams do not have clearly associated globular clusters. which, if generally true, suggests that there were at least twice as many massive globular clusters at high redshift.

• The paper finds that the starting redshift critically determines tidal mass loss and stream formation in globular clusters.
• It shows clusters initiated at z=3 experience significant mass shedding, whereas those at z=8 dissolve rapidly upon halo accretion.
• The results align with Milky Way observations and inform predictions of gravitational wave sources from binary black hole mergers.

Analyzing Globular Clusters in Cosmological N-Body Simulations

This paper explores the complex interactions of globular clusters within the cosmological framework of the Via Lactea II (VL-2) N-body simulations. The research probes the impact of dark matter halos, at various redshifts, on stellar cluster mass loss and tidal stream formations. Primarily, it seeks to elucidate the historical dynamics of these celestial bodies and their contributions to the Milky Way's halo.

Key Findings

The simulation integrates stellar dynamical model globular clusters into the reconstituted dark matter halos of the VL-2 simulation. A central discovery is that the starting redshift significantly influences tidal mass loss and stream formation. A z=3 initiation places the clusters in denser sub-galactic halos, resulting in heightened tidal forces and, consequently, increased mass shedding. Conversely, starting at z=8 results in cluster dissolution upon accretion into the main halo, emphasizing the role of evolutionary timing in cluster survival.

Numerical Results and Observations

1. Mass Loss Dynamics: In higher density halos at z=3, present a pronounced mass loss rate due to robust tidal forces, with nearly all clusters containing remnant progenitor stars within 100 kpc. In stark contrast, the earlier z=8 start sees complete dissolution of clusters after accretion.
2. Stream Characteristics: The simulations reveal that thin and extensive stellar streams, observable to the current day, predominantly emerge once clusters integrate into the main halo. Tidal streams were wider and more dispersed when formed from clusters initially within sub-galactic halos.
3. Comparison with Observational Data: The simulations align with available Milky Way data, where most streams lack associated progenitor clusters, suggesting potentially double the massive globular clusters existed at higher redshifts.

Implications and Theoretical Impacts

This paper implies a necessary revision in our understanding of globular cluster dynamics and their evolution under different cosmological histories. The pronounced mass loss at higher redshifts aligns with existing observations of galactic halos, providing a computational validation for the dynamical history of globular clusters.

Moreover, the implications of the paper extend to the understanding of gravitational wave sources, as the dense star environments within these clusters might be prolific sites for binary black hole mergers. Therefore, an increased estimated population of globular clusters at earlier cosmic times could potentially reconcile current LIGO event rates with theoretical predictions.

Future Directions

The paper highlights the necessity for further investigation into cluster dynamics using larger N-body simulations for precise mass-loss quantification and extended interrogation of the low mass sub-halos. Advanced simulation methodologies could better resolve the gravitational interactions within clusters, thereby refining mass function evolution models.

In conclusion, the paper advances our comprehension of globular cluster formation history and dynamics through detailed cosmological simulation, presenting substantial insights into their role in both historical and modern galactic architecture. The integration of more sophisticated models and higher-resolution simulations remains a promising avenue for deepening this understanding.