In this paper, using 2MASS photometry, we study the mass functions $ϕ(M) = dN/dM \propto M^{-α}$ of a sample of nine clusters of ages varying from 4 Myr--1.2 Gyr and Galactocentric distances from 6--12 kpc. We look for evidence of mass segregation in these clusters by tracing the variation in the value of $α$ in different regions of the cluster as a function of the parameter $τ= t_{age}/t_{relax}$ (where $t_{age}$ is the age of the cluster and $t_{relax}$ is the relaxation time of the cluster), Galactocentric distance, age and size of the cluster. The value of $α$ value increases with age and $τ$ and fits straight lines with slopes $m$ and y-intercepts $c$ given by $m=0.40\pm0.03$, $c=-1.86\pm0.27$ and $m=0.01\pm0.001$, $c=-0.85\pm0.02$, respectively and is a clear indicator of the dynamical processes involved. The confidence level of the Pearson's product-moment correlation of $α$ with age is 0.76 with p=0.002 and with $τ$ is 0.71 with p=0.007. The value of $α$ also increases with Galactocentric distance, indicating the presence of a larger relative number of low mass stars in clusters at larger Galactocentric distances. We find two clusters, viz. IC 1805 and NGC 1893, with evidence of primordial or early dynamical mass segregation. Implications of primordial mass segregation on the formation of massive stars and recent results supporting early dynamical mass segregation are discussed.
It has been shown that galaxy properties depend strongly on their host environment. In order to understand the relevant physical processes driving galaxy evolution it is important to study the observed properties of galaxies in different environments. Mass segregation in bound galaxy structures is an important indicator of evolutionary history and dynamical friction timescales. Using group catalogues derived from the Sloan Digital Sky Survey Data Release 7 (SDSS DR7) we investigate mass segregation trends in galaxy groups at low redshift. We investigate average galaxy stellar mass as a functio…
We investigate mass segregation in group and cluster environments by identifying galaxy analogues in high-resolution dark matter simulations. Subhalos identified by the AHF and ROCKSTAR halo finders have similar mass functions, independent of resolution, but different radial distributions due to significantly different subhalo hierarchies. We propose a simple way to classify subhalos as galaxy analogues. The radial distributions of galaxy analogues agree well at large halo-centric radii for both AHF and ROCKSTAR but disagree near parent halo centres where the phase-space information used by RO…
Supermassive black holes dominate the gravitational potential in galactic nuclei. In these dense environments, stars follow nearly Keplerian orbits and see their orbital planes relax through the potential fluctuations generated by the stellar cluster itself. For typical astrophysical galactic nuclei, the most likely outcome of this vector resonant relaxation (VRR) is that the orbital planes of the most massive stars spontaneously self-align within a narrow disc. We present a maximum entropy method to systematically determine this long-term distribution of orientations and use it for a wide ran…
Gas expulsion or gas retention is a central issue in most of the models for multiple stellar populations and light element anti-correlations in globular clusters. The success of the residual matter expulsion or its retention within young stellar clusters has also a fundamental importance in order to understand how star formation proceeds in present-day and ancient star-forming galaxies and if proto-globular clusters with multiple stellar populations are formed in the present epoch. It is usually suggested that either the residual gas is rapidly ejected from star-forming clouds by stellar winds…
We perform a series of direct $N$-body calculations to investigate the effect of residual gas expulsion from the gas-embedded progenitors of present-day globular clusters (GCs) on the stellar mass function (MF). Our models start either tidally filling or underfilling, and either with or without primordial mass segregation. We cover 100 Myr of the evolution of modeled clusters and show that the expulsion of residual gas from initially mass-segregated clusters leads to a significantly shallower slope of the stellar MF in the low- ($m\leq 0.50 M_\odot$) and intermediate-mass ($\simeq 0.50-0.85 M_…
We investigate the mass loss of galaxies in groups and clusters with high-resolution DM simulations. We detect weak mass segregation in the inner regions of group/cluster haloes, consistent with observational findings. This applies to samples of galaxy analogues selected using either their present-day mass or past maximum (peak) mass. We find a strong radial trend in the fractional mass lost by the galaxies since peak, independent of their mass. This suggests that segregation is due to massive galaxies having formed closer to the halo centres and not the preferential destruction of smaller gal…
We examine the spatial distribution and mass segregation of dense molecular cloud cores in a number of nearby star forming regions that span about four orders of magnitude in star formation activity. We use an approach based on the calculation of the minimum spanning tree, and for each region, we calculate the structure parameter Q and the mass segregation ratio measured for various numbers of the most massive cores. Our results indicate that the distribution of dense cores in young star forming regions is very substructured and that it is likely that this substructure will be imprinted onto t…
We investigate the contentious issue of the presence, or lack thereof, of satellites mass segregation in galaxy groups using the Galaxy And Mass Assembly (GAMA) survey, the GALFORM semi-analytic and the EAGLE cosmological hydrodynamical simulation catalogues of galaxy groups. We select groups with halo mass $12 \leqslant \log(M_{\text{halo}}/h^{-1}M_\odot) <14.5$ and redshift $z \leqslant 0.32$ and probe the radial distribution of stellar mass out to twice the group virial radius. All the samples are carefully constructed to be complete in stellar mass at each redshift range and efforts are ma…
Context: Star clusters form within giant molecular clouds that are strongly altered by the feedback action of the massive stars, but the cluster still remains embedded in a dense, highly turbulent medium and interactions with ambient structures may modify its dynamical evolution from that expected if it were isolated. Aims: We aim to study coupling mechanisms between the dynamical evolution of the cluster, accelerated by the mass segregation process, with harassment effects caused by the gaseous environment. Methods: We simulated the cluster dynamical evolution combining $N$-body and hydrodyna…
The young star clusters we observe today are the building blocks of a new generation of stars and planets in our Galaxy and beyond. Despite their fundamental role we still lack knowledge about the conditions under which star clusters form and the impact of these often harsh environments on the evolution of their stellar and substellar members. We demonstrate the vital role numerical simulations play to uncover both key issues. Using dynamical models of different star cluster environments we show the variety of effects stellar interactions potentially have. Moreover, our significantly improved …
Stars form in dense, clustered environments, where feedback from newly formed stars eventually ejects the gas, terminating star formation and leaving behind one or more star clusters. Using the STARFORGE simulations, it is possible to simulate this process in its entirety within a molecular cloud, while explicitly evolving the gas radiation and magnetic fields and following the formation of individual, low-mass stars. We find that individual star-formation sites merge to form ever larger structures, while still accreting gas. Thus clusters are assembled through a series of mergers. During the …
Dynamical evolution of massless particles in star clusters with NBODY6++GPU-MASSLESS: II. The long-term evolution of free-floating comets
New York University Abu Dhabi（阿布扎比纽约大学）；Zentrum für Astronomie der Universität Heidelberg（海德堡大学天文学中心）；Sapienza, Universitá di Roma（罗马智慧大学）；Xi’an Jiaotong-Liverpool University（西交利物浦大学）；Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg（海德堡大学天文学中心天文计算研究所）；Nicolaus Copernicus Astronomical Centre Polish Academy of Sciences（波兰科学院尼古拉·哥白尼天文学中心）；Szechenyi Istvan University（伊什特万·塞切尼大学）；Main Astronomical Observatory, National Academy of Sciences of Ukraine（乌克兰国家科学院主天文台）
Background: low-mass stars are the dominant product of the star formation process, and they trace star formation over the full range of environments, from isolated globules to clusters in the central molecular zone. In the past two decades, our understanding of the spatial distribution and properties of young low-mass stars and protostars has been revolutionized by sensitive space-based observations at X-ray and IR wavelengths. By surveying spatial scales from clusters to molecular clouds, these data provide robust measurements of key star formation properties. Goal: with their large numbers a…
