Mass segregation

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

Galaxy and mass assembly (GAMA): the clustering of galaxy groups

Abstract: We explore the clustering of galaxy groups in the Galaxy and Mass Assembly (GAMA) survey to investigate the dependence of group bias and profile on separation scale and group mass. Due to the inherent uncertainty in estimating the group selection function, and hence the group autocorrelation function, we instead measure the projected galaxy–group cross-correlation function. We find that the group profile has a strong dependence on scale and group mass on scales r⊥≲1h−1⁠. We also find evidence that the most massive groups live in extended, overdense, structures. In the first application of marked clustering statistics to groups, we find that group-mass marked clustering peaks on scales comparable to the typical group radius of r⊥ ≈ 0.5 h−1. While massive galaxies are associated with massive groups, the marked statistics show no indication of galaxy mass segregation within groups. We show similar results from the IllustrisTNG simulations and the L-GALAXIES model, although L-GALAXIES shows an enhanced bias and galaxy mass dependence on small scales.

Characterizing the dynamical state of star clusters from snapshots of their spatial distributions

Abstract: We determine the distribution of stellar surface densities, \Sigma, from models of static and dynamically evolving star clusters with different morphologies, including both radially smooth and substructured clusters. We find that the \Sigma distribution is degenerate, in the sense that many different cluster morphologies (smooth or substructured) produce similar cumulative distributions. However, when used in tandem with a measure of structure, such as the Q-parameter, the current spatial and dynamical state of a star cluster can be inferred. The effect of cluster dynamics on the \Sigma distribution and the Q-parameter is investigated using N-body simulations and we find that, depending on the assumed initial conditions, the \Sigma distribution can rapidly evolve from high to low densities in less than 5Myr. This suggests that the \Sigma distribution can only be used to assess the current density of a star forming region, and provides little information on its initial density. However, if the \Sigma distribution is used together with the Q-parameter, then information on the amount of substructure can be used as a proxy to infer the amount of dynamical evolution that has taken place. Substructure is erased quickly through dynamics, which can disrupt binary star systems and planets, as well as facilitate dynamical mass segregation. Therefore, dynamical processing in young star forming regions could still be significant, even without currently observed high densities.

Dynamical Evolution of Two-Component Star Clusters

Abstract: The dynamical evolution of two-component star clusters, each of which is enclosed within a perfectly reflecting sphere, is investigated by numerically solving moment equations derived from the Boltzmann equation. One of the two adopted model clusters evolves, starting from a state of no mass segregation, toward an equilibrium state at a quite slow rate. The other one evolves away from an equilibrium state and its central density increases without limit. The different evolutionary behaviors of the two model clusters are explained by the fact that there exists no equilibrium state for such clusters if the total energy is less than a certain critical value. The critical value increases with increasing total mass fraction of the heavier stars. This is qualitatively the same as Spitzer's theorem (1969) expressed in another way.

A MAD view of Trumpler 14

Abstract: We present adaptive optics (AO) near-infrared observations of the core of the Tr 14 cluster in the Carina region obtained with the ESO multi-conjugate AO demonstrator, MAD. Our campaign yields AO-corrected observations with an image quality of about 0.2 arcsec across the 2 arcmin field of view, which is the widest AO mosaic ever obtained. We detected almost 2000 sources spanning a dynamic range of 10 mag. The pre-main sequence (PMS) locus in the colour-magnitude diagram is well reproduced by Palla & Stahler isochrones with an age of 3 to 5 1E+05 yr, confirming the very young age of the cluster. We derive a very high (deprojected) central density n0~4.5(+/-0.5) \times 10^4 pc^-3 and estimate the total mass of the cluster to be about ~4.3^{+3.3}_{-1.5} \times 10^3 Msun, although contamination of the field of view might have a significant impact on the derived mass. We show that the pairing process is largely dominated by chance alignment so that physical pairs are difficult to disentangle from spurious ones based on our single epoch observation. Yet, we identify 150 likely bound pairs, 30% of these with a separation smaller than 0.5 arcsec (~1300AU). We further show that at the 2-sigma level massive stars have more companions than lower-mass stars and that those companions are respectively brighter on average, thus more massive. Finally, we find some hints of mass segregation for stars heavier than about 10 Msun. If confirmed, the observed degree of mass segregation could be explained by dynamical evolution, despite the young age of the cluster.

Is the young star cluster ngc 376 dissolving in the field of the small magellanic cloud

Abstract: We use deep images acquired with the Advanced Camera for Surveys (ACS) on board the Hubble Space Telescope in the filters F555W and F814W to characterize the properties of NGC 376, a young star cluster located in the wing of the Small Magellanic Cloud. Using isochrone fitting we derive for NGC 376 an age of 28 {+-} 7 Myr, in good agreement with previous studies. The high spatial resolution ACS data allow us to determine the center of gravity of the cluster and to construct extended surface brightness and radial density profiles. Neither of these profiles can be fitted with a theoretical model, suggesting that the cluster is not in virial equilibrium. Considering the young age of the cluster, we speculate that the distortion of the radial profiles may be the result of the rapid gas dispersal that follows the initial phase of star formation (SF). The cluster shows clear evidence of dynamical mass segregation. From the properties of the radial profiles and the present-day mass function we conclude that NGC 376 appears to have already lost nearly 90% of its initial stellar mass, probably as a consequence of the sudden gas dispersal that follows the early phase of SF.