STAR CLUSTERS IN M31. V. INTERNAL DYNAMICAL TRENDS: SOME TROUBLESOME, SOME REASSURING

Journal Article · Fri Jul 15 04:00:00 EDT 2011 · Astronomical Journal (New York, N.Y. Online)

DOI:https://doi.org/10.1088/0004-6256/142/1/8· OSTI ID:21583072

Strader, Jay; Caldwell, Nelson

We present internal velocity dispersions and precise radial velocities for 200 globular clusters (GCs) in M31 that are derived using new high-resolution spectra from MMT/Hectochelle. Of these, 163 also have King model structural parameters that allow us to estimate their mass-to-light ratios. This is, by far, the largest such data set available for any galaxy, including the Milky Way. These data strongly confirm earlier suggestions that the optical and near-infrared mass-to-light ratios of M31 GCs decline with increasing metallicity. This behavior is the opposite of that predicted by stellar population models for a standard initial mass function. We show that this phenomenon does not appear to be caused by standard dynamical evolution. A shallower mass function for metal-rich GCs (with dN/dM{proportional_to}M{sup -0.8}-M{sup -1.3} below 1 M{sub sun}) can explain the bulk of extant observations. We also observe a consistent, monotonic correlation between mass-to-light ratio and cluster mass. This correlation, in contrast to the correlation with metallicity, is well explained by the accepted model of dynamical evolution of GCs through mass segregation and the preferential loss of low-mass stars, and these data are among the best available to constrain this process.

• OSTI ID: 21583072
• Journal Information: Astronomical Journal (New York, N.Y. Online), Journal Name: Astronomical Journal (New York, N.Y. Online) Journal Issue: 1 Vol. 142; ISSN 1538-3881
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
EVOLUTION
GALACTIC EVOLUTION
GALAXIES
LUMINOSITY
MASS
MILKY WAY
OPTICAL PROPERTIES
PHYSICAL PROPERTIES
RADIAL VELOCITY
STAR CLUSTERS
STAR EVOLUTION
STARS
STRUCTURAL MODELS
VELOCITY