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The contribution of dissolving star clusters to the population of ultra faint objects in the outer halo of the Milky Way

Contenta, Filippo, Gieles, Mark, Balbinot, Eduardo and Collins, Michelle (2016) The contribution of dissolving star clusters to the population of ultra faint objects in the outer halo of the Milky Way Monthly Notices of the Royal Astronomical Society, 466 (2). pp. 1741-1756.

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Abstract

In the last decade, several ultra faint objects (UFOs, MV −3.5) have been discovered in the outer halo of the Milky Way. For some of these objects, it is not clear whether they are star clusters or (ultra faint) dwarf galaxies. In this work, we quantify the contribution of star clusters to the population of UFOs. We extrapolated the mass and Galactocentric radius distribution of the globular clusters using a population model, finding that the Milky Way contains about 3.3+7.3 −1.6 star clusters with MV −3.5 and Galactocentric radius ≥20 kpc. To understand whether dissolving clusters can appear as UFOs, we run a suite of direct N-body models, varying the orbit, the Galactic potential, the binary fraction and the black hole (BH) natal kick velocities. In the analyses, we consider observational biases such as luminosity limit, field stars and line-of-sight projection. We find that star clusters contribute to both the compact and the extended population of UFOs: clusters without BHs appear compact with radii ∼5 pc, while clusters that retain their BHs after formation have radii 20 pc. The properties of the extended clusters are remarkably similar to those of dwarf galaxies: high-inferred mass-to-light ratios due to binaries, binary properties mildly affected by dynamical evolution, no observable mass segregation and flattened stellar mass function. We conclude that the slope of the stellar mass function as a function of Galactocentric radius and the presence/absence of cold streams can discriminate between dark matter-free and dark matter-dominated UFOs.

Item Type: Article
Subjects : Physics
Divisions : Faculty of Engineering and Physical Sciences > Physics
Authors :
NameEmailORCID
Contenta, Filippof.contenta@surrey.ac.ukUNSPECIFIED
Gieles, Markm.gieles@surrey.ac.ukUNSPECIFIED
Balbinot, Eduardoe.balbinot@surrey.ac.ukUNSPECIFIED
Collins, Michellem.collins@surrey.ac.ukUNSPECIFIED
Date : 10 December 2016
Funders : ERC
Identification Number : 10.1093/mnras/stw3178
Copyright Disclaimer : This is a pre-copyedited, author-produced PDF of an article accepted for publication in The contribution of dissolving star clusters to the population of ultra-faint objects in the outer halo of the Milky Way following peer review. The version of record Monthly Notices of the Royal Astronomical Society is available online at: mnras.oxfordjournals.org/content/early/2016/12/09/mnras.stw3178.abstract
Uncontrolled Keywords : methods: numerical – stars: kinematics and dynamics – globular clusters: general – Galaxy: halo – galaxies: dwarf.
Depositing User : Symplectic Elements
Date Deposited : 27 Jan 2017 15:03
Last Modified : 31 Oct 2017 19:04
URI: http://epubs.surrey.ac.uk/id/eprint/813383

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