Documentation

The goal of this research project is to examine the long-term stability of the Eridanus II star cluster in the presence of various mass Primordial Black Holes at different mass fractions of the Eri II dark matter halo. Eri II is an ultra-faint dwarf galaxy discovered by the Dark Energy Survey [1][2]. It is thought to be a distant (366 kpc from the Sun) Milky Way satellite, though this is uncertain [3]. Eridanus II has a half-light radius of $R_{1/2}=2.31 “$. Most importantly, Eri II has a star cluster at a projected distance of ~45 pc from the center of Eri II. The star cluster is fainter and more extended than is expected for star cluster in the Milky Way [4].

The Eri II system has long been an interesting test-case for dark matter modeling. For instance, dark matter (DM)-baryon interactions, such as by supernovae (SN), smoothing cusps [5] to cores [6]. There should be a lower mass bound under which a galaxy will have insufficient energy to affect the DM cusp-core transformation [7]. In cuspy profiles the star-cluster rapidly sinks to the center of the galaxy, while in a cored profile the star cluster maintains a long-term stable orbit [8]. This method has been applied to Eridanus II [9].

In application to primordial black holes, we are working to extend the analysis done in Contenta (2018) [9], but include, at various mass fractions of the Eri II halo, different initial mass function Primordial Black Hole (PBH) distributions. The dissolution of the star cluster in the presence of the PBHs would tightly constrain PBHs-as-DM. Studies of Eri II have been conducted previously, for example Carr (2016) [10]. These results have been claimed to be the strongest constraints on PBH DM, and are motivated by Fokker-Planck arguments of the effect of heating of the star cluster. However, even if the cluster gets unbound, it may still remain near the center of the dwarf and appear as a cluster, in which case the strong constraints would be incorrect. Full N-Body simulations are warranted to verify the Fokker-Planck analysis.

Documentation

• Eridanus_PBH Documentation
• Probing Cusp-Core with Star Clusters

Attribution

If you make use of this code, please consider citing the utilipy Zenodo DOI as a software citation:

@software{utilipy:zenodo,
  author       = {nstarman},
  title        = {utilipy},
  publisher    = {Zenodo},
  doi          = {10.5281/zenodo.3491011},
  url          = {https://doi.org/10.5281/zenodo.3491011}
}

Also consider citing the following papers galpy [11], AMUSE [12] [13] [14] [15], BHTree [16], and SeBa [17] [18]

References

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Filippo Contenta, Eduardo Balbinot, James A. Petts, Justin I. Read, Mark Gieles, Michelle L. M. Collins, Jorge Peñarrubia, Maxime Delorme, and Alessia Gualandris. Probing dark matter with star clusters: a dark matter core in the ultra-faint dwarf Eridanus II. \mnras , 476(3):3124–3136, May 2018. arXiv:1705.01820, doi:10.1093/mnras/sty424.

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