Capture of field stars by dark substructures

Jorge Peñarrubia*, Raphaël Errani, Matthew G. Walker, Mark Gieles, Tjarda C. N. Boekholt

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract / Description of output

We use analytical and 𝑁-body methods to study the capture of field stars by gravitating substructures moving across a galactic environment. The majority of stars captured by a substructure move on temporarily-bound orbits that are lost to galactic tides after a few orbital revolutions. In numerical experiments where a substructure model is immersed into a sea of field particles on a circular orbit, we find a population of particles that remain bound to the substructure potential for indefinitely-long times. This population is absent from substructure models initially placed outside the galaxy on an eccentric orbit. We show that
gravitational capture is most efficient in dwarf spheroidal galaxies (dSphs) on account of their low velocity dispersions and high stellar phase-space densities. In these galaxies ‘dark’ sub-subhaloes which do not experience in-situ star formation may capture field stars and become visible as stellar overdensities with unusual properties: (i) they would have a large size for their luminosity, (ii) contain stellar populations indistinguishable from the host galaxy, and (iii) exhibit dark matter (DM)-dominated mass-to-light ratios. We discuss the nature of several ‘anomalous’ stellar systems reported as star clusters in the Fornax and Eridanus II dSphs which exhibit some of these characteristics. DM sub-subhaloes with a mass function d𝑁/d𝑀• ∼ 𝑀−𝛼• are expected to generate stellar systems with a luminosity function, d𝑁/d𝑀★ ∼ 𝑀
−𝛽★ , where 𝛽 = (2𝛼 + 1)/3 = 1.6 for 𝛼 = 1.9. Detecting and characterizing these objects in dSphs would provide unprecedented constraints on the particle mass and cross section of a large range of DM particle candidates.
Original languageEnglish
Pages (from-to)3263-3282
Number of pages20
JournalMonthly Notices of the Royal Astronomical Society
Volume533
Issue number3
Early online date13 Aug 2024
DOIs
Publication statusPublished - 1 Sept 2024

Keywords / Materials (for Non-textual outputs)

  • Galaxy: kinematics and dynamics
  • galaxies: evolution
  • Cosmology: dark matter

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