Mass segregation

About: Mass segregation is a research topic. Over the lifetime, 1024 publications have been published within this topic receiving 57729 citations.

Clusters of galaxies

Abstract: Observational properties of clusters of galaxies and some theoretical interpretations are reviewed. The major subjects of the review include catalogs of clusters, the static properties of rich clusters, cluster dynamics, X-ray emission from clusters of galaxies, and cluster radio emission. Observed static properties discussed are: richness, classification schemes, galactic content, cD galaxies, density profiles, sizes, and the optical luminosity function. Several characteristic time scales of clusters of galaxies are examined along with mass segregation, the dynamical evolution of clusters, cluster masses, mass-to-light ratios, the missing-mass problem, and the mean galactic and cluster mass densities in the universe. The main characteristics of clusters that contain X-ray emission are summarized, emphasizing the relation of the X-ray emission to optical properties. The most important properties of cluster radio emission are outlined, the relation of this emission to the other cluster properties studied is indicated, and evidence suggesting the influence of an intracluster gas on the radio galaxies and their relativistic electrons is noted.

Constraints on the Stellar/Sub-stellar Mass Function in the Inner Orion Nebula Cluster

Abstract: We present the results of a 0.5-0.9" FWHM imaging survey at K (2.2 micron) and H (1.6 micron) covering 5.1' x 5.1' centered on Theta 1C Ori, the most massive star in the Orion Nebula Cluster (ONC). At the age and distance of this cluster, and in the absence of extinction, the hydrogen burning limit (0.08 Mo) occurs at K~13.5 mag while an object of mass 0.02 Mo has K~16.2 mag. Our photometry is complete for source detection at the 7 sigma level to K~17.5 mag and thus is sensitive to objects as low-mass as 0.02 Mo seen through visual extinction values as high as 10 magnitudes. We use the observed magnitudes, colors, and star counts to constrain the shape of the inner ONC stellar mass function across the hydrogen burning limit. After determining the stellar age and near-infrared excess properties of the optically visible stars in this same inner ONC region, we present a new technique that incorporates these distributions when extracting the mass function from the observed density of stars in the K-(H-K) diagram. We find that our data are inconsistent with a mass function that rises across the stellar/sub-stellar boundary. Instead, we find that the most likely form of the inner ONC mass function is one that rises to a peak around 0.15 Mo, and then declines across the hydrogen-burning limit with slope N(log M) ~ M^(0.57+/-0.05). We emphasize that our conclusions apply to the inner 0.71 pc x 0.71 pc of the ONC only; they may not apply to the ONC as a whole where some evidence for general mass segregation has been found.

Relaxation and tidal stripping in rich clusters of galaxies. II. Evolution of the luminosity distribution.

Abstract: A set of differential equations is derived which describes the evolution of a rich cluster of galaxies over relaxation time scales. Two physical processes are included. Exchange of orbital kinetic energy between galaxies of different masses, due to gravitational two-body encounters, is computed from the isotropic, orbit-averaged Fokker-Planck equation. Tidal stripping of galaxies with massive halos is approximated by the corss sections of Richstone. The fraction of cluster mass in the ''background'' is allowed to increase with time as the galaxies are stripped; the energy of the background also increases due to dynamical interaction with the galaxies. The equations are integrated numerically, starting from a Schechter distribution of galaxy masses. Unless most of the virial mass in initially in the background, tidal stripping tends to obscure the effects of mass segregation (though not, presumably, luminosity segregation) by rapidly depleting the cluster core of massive galaxies. The background so produced dominates the core and is strongly concentrated to the center, falling off as r/sup -4/ at large radii. Putting most of the mass initially in the background increases the importance of mass segregation relative to stripping; in this case the galaxy distribution develops a significantly smaller core radius than the background.more » The final core mass distribution is qualitatively similar in both cases to that of a cD galaxy, in that it contains a central mass of low velocity dispersion surrounded by a high velocity dispersion envelope. However, the mass in the cluster core tends to decrease with time. Tidal strippings greatly increases dynamical friction time scales by reducing galaxy masses, and these results suggest that the small amounts of luminosity segregation observed in rich clusters might be consistent with all of the cluster mass having been originally tied to galaxies.« less

Mass segregation in young stellar clusters

Abstract: We investigate the evolutionary effect of dynamical mass segregation in young stellar clusters. Dynamical mass segregation acts on a time-scale of order the relaxation time of a cluster. Although some degree of mass segregation occurs earlier, the position of massive stars in rich young clusters generally reflects the cluster's initial conditions. In particular, the positions of the massive stars in the Trapezium cluster in Orion cannot be due to dynamical mass segregation, but indicate that they formed in, or near, the centre of the cluster. Implications of this for cluster formation and for the formation of high-mass stars are discussed.

The structure of the nuclear stellar cluster of the Milky Way

Abstract: Aims. The centre of the Milky Way is the nearest nucleus of a galaxy and offers a unique possibility to study the structure and dynamics of a dense stellar cluster around a super-massive black hole. Methods. We present high-resolution seeing limited and AO NIR imaging observations of the stellar cluster within about one parsec of Sgr A*, the massive black hole at the centre of the Milky Way. Stellar number counts and the diffuse background light density were extracted from these observations in order to examine the structure of the nuclear stellar cluster. A detailed map of the variation of interstellar extinction in the central ∼0.5 pc of the Milky Way is presented and used to correct the stellar number counts and diffuse light density. Results. Our findings are as follows: (a) a broken-power law provides an excellent fit to the overall structure of the GC nuclear cluster. The power-law slope of the cusp is Γ = 0.19 ±0.05, the break radius is R break = 6.0" ± 1.0" or 0.22 + 0.04 pc, and the cluster density decreases with a power-law index of Γ = 0.75 ± 0.1 outside of R break . (b) Using the best velocity dispersion measurements from the literature, we derive higher mass estimates for the central parsec than assumed until now. The inferred density of the cluster at the break radius is 2.8 ± 1.3 x 10 6 M ⊙ pc -3 . This high density agrees well with the small extent and flat slope of the cusp. Possibly, the mass of the stars makes up only about 50% of the total cluster mass. (c) Possible indications of mass segregation in the cusp are found (d) The cluster appears not entirely homogeneous. Several density clumps are detected that are concentrated at projected distances of R = 3" and R = 7" from Sgr A*. (e) There appears to exist an under-density of horizontal branch/red clump stars near R = 5", or an over-density of stars of similar brightness at R = 3" and R = 7". (f) The extinction map in combination with cometary-like features in an L'-band image may provide support for the assumption of an outflow from Sgr A*.