CONSTRAINTS ON MACHO DARK MATTER FROM COMPACT STELLAR SYSTEMS IN ULTRA-FAINT DWARF GALAXIES

• Published in: Astrophysical journal. Letters Vol. 824; no. 2; p. L31
• Main Author: Brandt, Timothy D.
• Format: Journal Article
• Language: English
• Published: United States The American Astronomical Society 20.06.2016
• Subjects: ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; Clusters; Dark matter; Disks; DISPERSIONS; Dwarf galaxies; GALAXIES; galaxies: dwarf; galaxies: kinematics and dynamics; HEATING; LIMITING VALUES; MASS; NONLUMINOUS MATTER; STAR CLUSTERS; STARS; stars: kinematics and dynamics; VELOCITY; VISIBLE RADIATION
• ISSN: 2041-8205; 2041-8213
• DOI: 10.3847/2041-8205/824/2/L31

ABSTRACT I show that a recently discovered star cluster near the center of the ultra-faint dwarf galaxy Eridanus II provides strong constraints on massive compact halo objects (MACHOs) of 5 M as the main component of dark matter. MACHO dark matter will dynamically heat the cluster, driving it to larger sizes and higher velocity dispersions until it dissolves into its host galaxy. The stars in compact ultra-faint dwarf galaxies themselves will be subject to the same dynamical heating; the survival of at least 10 such galaxies places independent limits on MACHO dark matter of masses 10 M . Both Eri II's cluster and the compact ultra-faint dwarfs are characterized by stellar masses of just a few thousand M and half-light radii of 13 pc (for the cluster) and ∼30 pc (for the ultra-faint dwarfs). These systems close the ∼20-100 M window of allowed MACHO dark matter and combine with existing constraints from microlensing, wide binaries, and disk kinematics to rule out dark matter composed entirely of MACHOs from ∼10−7M up to arbitrarily high masses.