Disentangling the formation mechanisms of nuclear star clusters

Abstract The formation of nuclear star clusters (NSCs) remains an open question. In this work, we use spatially-resolved HST/STIS spectroscopic observations of three nearby NSCs (hosted by NGC 5102, NGC 5206, and NGC 205) to constrain their formation histories by exploring radial variations of the stellar populations within each cluster. Utilizing full-spectrum fitting, we find substantial age and metallicity gradients within the central 0.″9 (16 pc) of the NSC in NGC 5102 where populations near the center are young/metal-rich (age ∼400 Myr and [M/H] ∼ −0.4) and become older/metal-poor at larger radii (mean age ∼1 Gyr and mean [M/H] ∼ −1.6 in the radial range [0.″3, 0.″9]). This behavior suggests that the young/metal-rich population at the center was formed from a period of in situ formation, while the older/metal-poor populations were likely formed by inspiraled globular clusters. The two broad populations observed in the NGC 5102 NSC (young/metal-rich and old/metal-poor) appear to be linked to the transition between the two morphological components of the NSC derived from the surface-brightness profile in Nguyen et al. (2018). The radial ranges explored in NGC 5206 and NGC 205 were much smaller due to poor data quality; in NGC 5206 we find a similar metallicity gradient to NGC 5102 (but with much lower significance), while the data for NGC 205 is too poor to reach any conclusions. Overall, this data highlights the links between the morphological and stellar population complexity of NSCs and their formation mechanisms.

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Nuclear Star Clusters

Proceedings of the International Astronomical Union ◽

10.1017/s1743921316007018 ◽

2015 ◽

Vol 12 (S316) ◽

pp. 84-90 ◽

Cited By ~ 3

Author(s):

Nadine Neumayer

Keyword(s):

Star Clusters ◽

Elliptical Galaxies ◽

Formation Mechanisms ◽

Strong Function ◽

Massive Black Holes ◽

Nearby Galaxies ◽

Dwarf Elliptical Galaxies ◽

Galaxy Masses ◽

The Universe

AbstractThe centers of galaxies host two distinct, compact components: massive black holes and nuclear star clusters. Nuclear star clusters are the densest stellar systems in the universe, with masses of ~ 107M⊙and sizes of ~ 5pc. They are almost ubiquitous at the centres of nearby galaxies with masses similar to, or lower than the Milky Way. Their occurrence both in spirals and dwarf elliptical galaxies appears to be a strong function of total galaxy light or mass. Nucleation fractions are up to 100% for total galaxy magnitudes of MB= −19mag or total galaxy luminosities of about LB= 1010L⊙and falling nucleation fractions for both smaller and higher galaxy masses. Although nuclear star clusters are so common, their formation mechanisms are still under debate. The two main formation scenarios proposed are the infall and subsequent merging of star clusters and the in-situ formation of stars at the center of a galaxy. Here, I review the state-of-the-art of nuclear star cluster observations concerning their structure, stellar populations and kinematics. These observations are used to constrain the proposed formation scenarios for nuclear star clusters. Constraints from observations show, that likely both cluster infall and in-situ star formation are at work. The relative importance of these two mechanisms is still subject of investigation.

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Blue stragglers in star clusters and the conventional SSP models

Proceedings of the International Astronomical Union ◽

10.1017/s1743921309992079 ◽

2009 ◽

Vol 5 (S266) ◽

pp. 556-556

Author(s):

Yu Xin ◽

Richard de Grijs ◽

Licai Deng ◽

Pavel Kroupa

Keyword(s):

Stellar Evolution ◽

Stellar Population ◽

Broad Band ◽

Star Clusters ◽

Open Clusters ◽

Formation Mechanisms ◽

Evolution Theory ◽

Blue Stragglers ◽

Blue Straggler ◽

Conventional Picture

AbstractThe presence of blue straggler stars (BSs) as secure members of star clusters poses a major challenge to the conventional picture of simple stellar population (SSP) models. The models are based on the stellar evolution theory of single stars, while the major formation mechanisms of BSs are all correlated with stellar interactions. Based on a sufficient working sample including 100 Galactic open clusters, one Galactic globular cluster, and seven Magellanic Cloud star clusters, we discuss the modifications of the properties of broad-band colors and Lick indices of the standard SSP models due to BS populations.

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The properties of nuclear star clusters and their host galaxies

Proceedings of the International Astronomical Union ◽

10.1017/s1743921319007117 ◽

2019 ◽

Vol 14 (S351) ◽

pp. 13-18

Author(s):

Anil C. Seth ◽

Nadine Neumayer ◽

Torsten Böker

Keyword(s):

Star Clusters ◽

Stellar Dynamics ◽

Formation Mechanisms ◽

Stellar Systems ◽

Host Galaxies ◽

The Universe

AbstractNuclear star clusters are found at the centers of most galaxies. They are the densest stellar systems in the Universe, and thus have unique and interesting stellar dynamics. We review how common nuclear star clusters are in galaxies of different masses and types, and then discuss the typical properties of NSCs. We close by discussing the formation of NSCs, and how a picture is emerging of different formation mechanisms being dominant in lower and higher mass galaxies.

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The dislocation structure of a 10° [110] tilt boundary in silicon

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100074446 ◽

1983 ◽

Vol 41 ◽

pp. 114-115

Author(s):

B. Cunningham ◽

D.G. Ast

Keyword(s):

Dislocation Structure ◽

Tilt Angle ◽

Imaging Technique ◽

Diamond Lattice ◽

Tilt Boundary ◽

Formation Mechanisms ◽

Diffraction Contrast ◽

Lattice Fringe ◽

Tilt Boundaries ◽

Chemically Vapor Deposited

There have Been a number of studies of low-angle, θ < 4°, [10] tilt boundaries in the diamond lattice. Dislocations with Burgers vectors a/2<110>, a/2<112>, a<111> and a<001> have been reported in melt-grown bicrystals of germanium, and dislocations with Burgers vectors a<001> and a/2<112> have been reported in hot-pressed bicrystals of silicon. Most of the dislocations were found to be dissociated, the dissociation widths being dependent on the tilt angle. Possible dissociation schemes and formation mechanisms for the a<001> and a<111> dislocations from the interaction of lattice dislocations have recently been given.The present study reports on the dislocation structure of a 10° [10] tilt boundary in chemically vapor deposited silicon. The dislocations in the boundary were spaced about 1-3nm apart, making them difficult to resolve by conventional diffraction contrast techniques. The dislocation structure was therefore studied by the lattice-fringe imaging technique.

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Formation Mechanisms for Multiply Twinned Particles During Nucleation in the Au/MICA System

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100114049 ◽

1975 ◽

Vol 33 ◽

pp. 84-85

Author(s):

Eal H. Lee ◽

Helmut Poppa

Keyword(s):

Deposition Time ◽

High Vacuum ◽

Dark Field ◽

Ultra High Vacuum ◽

Formation Mechanisms ◽

Heat Treated ◽

Cluster Density ◽

Diffraction Patterns ◽

Crystal Particle ◽

Multiply Twinned Particles

The formation of thin films of gold on mica has been studied in ultra-high vacuum (5xl0-10 torr) . The mica substrates were heat-treated for 24 hours at 375°C, cleaved, and annealed for 15 minutes at the deposition temperature of 300°C prior to deposition. An impingement flux of 3x1013 atoms cm-2 sec-1 was used. These conditions were found to give high number densities of multiple twin particles and are based on a systematic series of nucleation experiments described elsewhere. Individual deposits of varying deposition time were made and examined by bright and dark field TEM after "cleavage preparation" of highly transparent specimens. In the early stages of growth, the films generally consist of small particles which are either single crystals or multiply twinned; a strong preference for multiply twinned particles was found whenever the particle number densities were high. Fig. 1 shows the stable cluster density ns and the variation with deposition time of multiple twin particle and single crystal particle densities, respectively. Corresponding micrographs and diffraction patterns are shown in Fig. 2.

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