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

Abstract

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.

Authors:
; ;  [1]
  1. Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States)
Publication Date:
OSTI Identifier:
21583072
Resource Type:
Journal Article
Journal Name:
Astronomical Journal (New York, N.Y. Online)
Additional Journal Information:
Journal Volume: 142; Journal Issue: 1; Other Information: DOI: 10.1088/0004-6256/142/1/8; Journal ID: ISSN 1538-3881
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; GALACTIC EVOLUTION; LUMINOSITY; MASS; MILKY WAY; RADIAL VELOCITY; STAR CLUSTERS; STAR EVOLUTION; STARS; STRUCTURAL MODELS; EVOLUTION; GALAXIES; OPTICAL PROPERTIES; PHYSICAL PROPERTIES; VELOCITY

Citation Formats

Strader, Jay, Caldwell, Nelson, and Seth, Anil C., E-mail: jstrader@cfa.harvard.edu. STAR CLUSTERS IN M31. V. INTERNAL DYNAMICAL TRENDS: SOME TROUBLESOME, SOME REASSURING. United States: N. p., 2011. Web. doi:10.1088/0004-6256/142/1/8.
Strader, Jay, Caldwell, Nelson, & Seth, Anil C., E-mail: jstrader@cfa.harvard.edu. STAR CLUSTERS IN M31. V. INTERNAL DYNAMICAL TRENDS: SOME TROUBLESOME, SOME REASSURING. United States. doi:10.1088/0004-6256/142/1/8.
Strader, Jay, Caldwell, Nelson, and Seth, Anil C., E-mail: jstrader@cfa.harvard.edu. Fri . "STAR CLUSTERS IN M31. V. INTERNAL DYNAMICAL TRENDS: SOME TROUBLESOME, SOME REASSURING". United States. doi:10.1088/0004-6256/142/1/8.
@article{osti_21583072,
title = {STAR CLUSTERS IN M31. V. INTERNAL DYNAMICAL TRENDS: SOME TROUBLESOME, SOME REASSURING},
author = {Strader, Jay and Caldwell, Nelson and Seth, Anil C., E-mail: jstrader@cfa.harvard.edu},
abstractNote = {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.},
doi = {10.1088/0004-6256/142/1/8},
journal = {Astronomical Journal (New York, N.Y. Online)},
issn = {1538-3881},
number = 1,
volume = 142,
place = {United States},
year = {2011},
month = {7}
}