Is the distant globular cluster Pal 14 in a deep-freeze?

Abstract

We investigate the velocity dispersion of Pal 14, an outer Milky-Way globular cluster at Galactocentric distance of 71 kpc with a very low stellar density (central density 0.1-0.2 Msun/pc^3). Due to this low stellar density the binary population of Pal 14 is likely to be close to the primordial binary population. Artificial clusters are generated with the observed properties of Pal 14 and the velocity dispersion within these clusters is measured as Jordi et al. (2009) have done with 17 observed stars of Pal 14. We discuss the effect of the binary population on these measurements and find that the small velocity dispersion of 0.38 km/s which has been found by Jordi et al. (2009) would imply a binary fraction of less than 0.1, even though from the stellar density of Pal 14 we would expect a binary fraction of more than 0.5. We also discuss the effect of mass segregation on the velocity dispersion as possible explanation for this discrepancy, but find that it would increase the velocity dispersion further. Thus, either Pal 14 has a very unusual stellar population and its birth process was significantly different than we see in today's star forming regions, or the binary population is regular and we would have to correct the observed 0.38 km/s for binarity. In this case the true velocity dispersion of Pal 14 would be much smaller than this value and the cluster would have to be considered as "kinematically frigid", thereby possibly posing a challenge for Newtonian dynamics but in the opposite sense to MOND.

8 pages, 4 figures, accepted for publication in ApJ

References in corpus (9)

• A top-heavy stellar initial mass function in starbursts as an explanation for the high mass-to-light ratios of ultra compact dwarf galaxies
• Binary Stars in the Orion Nebula Cluster
• Testing Fundamental Physics with Distant Star Clusters: Analysis of Observational Data on Palomar 14
• On the velocity dispersion of young star clusters: super-virial or binaries?
• The effect of binaries on the dynamical mass determination of star clusters
• The influence of gas expulsion and initial mass-segregation on the stellar mass-function of globular star clusters
• Probable member stars of the gravitational theory-testing globular clusters AM 1, Pal 3 and Pal 14
• A new method to create initially mass segregated star clusters in virial equilibrium
• Current data on the globular cluster Palomar 14 are not inconsistent with MOND

Cited by in corpus (10)

• Peculiarities in Velocity Dispersion and Surface Density Profiles of Star Clusters
• Discovery of tidal tails around the distant globular cluster Palomar 14
• Direct N-body simulations of globular clusters: (I) Palomar 14
• The non-segregated population of blue straggler stars in the remote globular cluster Palomar 14
• The velocity dispersion and mass function of the outer halo globular cluster Palomar 4
• Distant star clusters of the Milky Way in MOND
• Mass segregation in the outer halo globular cluster Palomar 14
• The Curious Case of Palomar 13: The Influence of the Orbital Phase on the Appearance of Galactic Satellites
• A Monte Carlo analysis of the velocity dispersion of the globular cluster Palomar 14
• The tidal features of the classical Milky Way satellites: Expected in MOND but inconsistent with cold dark matter models