Probing dark matter with star clusters: a dark matter core in the ultra-faint dwarf Eridanus II

(2) Institute for Astronomy; Alessia Gualandris (1) ((1) Department of Physics; Blackford Hill); Eduardo Balbinot (1); Filippo Contenta (1); James A. Petts (1); Jorge Pe\~narrubia (2); Justin I. Read (1); Mark Gieles (1); Maxime Delorme (1)

Probing dark matter with star clusters: a dark matter core in the ultra-faint dwarf Eridanus II

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arxiv 1705.01820 v3 pith:NGMBIQAE submitted 2017-05-04 astro-ph.GA

Probing dark matter with star clusters: a dark matter core in the ultra-faint dwarf Eridanus II

Filippo Contenta (1) , Eduardo Balbinot (1) , James A. Petts (1) , Justin I. Read (1) , Mark Gieles (1) , Michelle L. M. Collins (1) , Jorge Pe\~narrubia (2) , Maxime Delorme (1)

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Alessia Gualandris (1) ((1) Department of Physics University of Surrey (2) Institute for Astronomy University of Edinburgh Royal Observatory Blackford Hill)

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We present a new technique to probe the central dark matter (DM) density profile of galaxies that harnesses both the survival and observed properties of star clusters. As a first application, we apply our method to the `ultra-faint' dwarf Eridanus II (Eri II) that has a lone star cluster ~45 pc from its centre. Using a grid of collisional $N$-body simulations, incorporating the effects of stellar evolution, external tides and dynamical friction, we show that a DM core for Eri II naturally reproduces the size and the projected position of its star cluster. By contrast, a dense cusped galaxy requires the cluster to lie implausibly far from the centre of Eri II (>1 kpc), with a high inclination orbit that must be observed at a particular orbital phase. Our results, therefore, favour a dark matter core. This implies that either a cold DM cusp was `heated up' at the centre of Eri II by bursty star formation, or we are seeing an evidence for physics beyond cold DM.

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