ON THE TEMPORAL EVOLUTION OF THE STELLAR MASS FUNCTION IN GALACTIC CLUSTERS
- European Space Agency, Space Science Department, Keplerlaan 1, 2200 AG Noordwijk (Netherlands)
- Istituto di Astrofisica Spaziale e Fisica Cosmica, Via Gobetti 101, 40129 Bologna (Italy)
We show that we can obtain a good fit to the present-day stellar mass functions (MFs) of a large sample of young and old Galactic clusters in the range 0.1-10 M{sub sun} with a tapered power-law distribution function with an exponential truncation of the form dN/dm{proportional_to}m{sup {alpha}} [1 -e{sup -}(m/m{sub c}){sup {beta}}]. The average value of the power-law index {alpha} is {approx}-2, that of {beta} is {approx}2.5, whereas the characteristic mass m{sub c} is in the range 0.1-0.8 M {sub sun} and does not seem to vary in any systematic way with the present cluster parameters such as metal abundance, total cluster mass, or central concentration. However, m{sub c} shows a remarkable correlation with the dynamical age of the cluster, namely, m{sub c} /M {sub sun} {approx_equal} 0.15 + 0.5 x {tau}{sup 3/4}{sub dyn}, where {tau}{sub dyn} is the dynamical age taken as the ratio of cluster age and dissolution time. The small scatter seen around this correlation is consistent with the uncertainties in the estimated value of {tau}{sub dyn}. We attribute the observed trend to the onset of mass segregation via two-body relaxation in a tidal environment, causing the preferential loss of low-mass stars from the cluster and hence a drift of the characteristic mass m{sub c} toward higher values. If dynamical evolution is indeed at the origin of the observed trend, it would seem plausible that high-concentration globular clusters, now with median m{sub c} {approx_equal} 0.33 M{sub sun}, were born with a stellar MF very similar to that measured today in the youngest Galactic clusters and with a value of m{sub c} {approx_equal} 0.15 M{sub sun}. This hypothesis is consistent with the absence of a turnover in the MF of the Galactic bulge down to the observational limit at {approx}0.2 M{sub sun} and, if correct, it would carry the implication that the characteristic mass is not set by the thermal Jeans mass of the cloud.
- OSTI ID:
- 21455158
- Journal Information:
- Astrophysical Journal, Vol. 718, Issue 1; Other Information: DOI: 10.1088/0004-637X/718/1/105; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
Similar Records
THE LUMINOSITY, MASS, AND AGE DISTRIBUTIONS OF COMPACT STAR CLUSTERS IN M83 BASED ON HUBBLE SPACE TELESCOPE/WIDE FIELD CAMERA 3 OBSERVATIONS
THE ANTENNAE GALAXIES (NGC 4038/4039) REVISITED: ADVANCED CAMERA FOR SURVEYS AND NICMOS OBSERVATIONS OF A PROTOTYPICAL MERGER