The velocity dispersion and mass-to-light ratio of the remote halo globular cluster NGC 2419

Understand

Precise radial velocity measurements from HIRES on the Keck I telescope are presented for 40 stars in the outer halo globular cluster NGC 2419.

• These data are used to probe the cluster's stellar mass function and search for the presence of dark matter in this cluster.
• NGC 2419 is one of the best Galactic globular clusters for such a study due to its long relaxation time (T_{r0} ~ 10^{10} yr) and large Galactocentric distance (R_{GC} ~ 90 kpc) -- properties that make significant evolutionary changes in the low-mass end of the cluster mass function unlikely.
• We find a mean cluster velocity of <v_r>=-20.3 +- 0.7 km/sec and an internal velocity dispersion of \sigma = 4.14 +- 0.48 km/sec, leading to a total mass of (9.0 +- 2.2) * 10^5 Msun and a global mass-to-light ratio of M/L_V = 2.05 +- 0.50 in solar units.