scholarly journals Kinematics of Star Clusters in M33: Distinct Populations

2002 ◽  
Vol 207 ◽  
pp. 160-162 ◽  
Author(s):  
Rupali Chandar ◽  
Luciana Bianchi ◽  
Holland C. Ford ◽  
Ata Sarajedini
Keyword(s):  
Globular Clusters ◽  
Milky Way ◽  
Velocity Dispersion ◽  
Star Cluster ◽  
Substantial Portion ◽  
Metal Abundance ◽  
Cluster Properties ◽  
Best Fit ◽  
Composite Disk

We analyse star cluster properties in the nearby spiral galaxy M33, combining our extensive HST WFPC2 photometry and ground-based follow up spectroscopy. These data show that cluster velocity dispersion increases with age. Simulations comparing synthetic disk and halo populations with observations indicate a composite disk/halo system for the old M33 clusters. The best fit fraction of 85 ± 5% halo plus 15 ± 5% disk differs from that found in the Milky Way, where ∼ 30% of the globular clusters are metal rich objects associated with the bulge and/or thick disk. Spectroscopic line indices for a halo subsample (17 objects) reveal an age spread of ∼ 5 — 7 Gyr, and little progression in metal abundance with age. This is consistent with a chaotic formation for a substantial portion of the M33 halo, and also consistent with an accretion origin for a large number of the halo clusters.

scholarly journals Using Gaia for studying Milky Way star clusters

2019 ◽  
Vol 14 (S351) ◽  
pp. 536-539
Author(s):  
Eugene Vasiliev
Keyword(s):  
Globular Clusters ◽  
Milky Way ◽  
Velocity Dispersion ◽  
Systematic Errors ◽  
Space Distribution ◽  
Proper Motions ◽  
Integrals Of Motion ◽  
Spatially Correlated ◽  
Dimensional Phase Space ◽  
Best Fit

AbstractWe review the implications of the Gaia Data Release 2 catalogue for studying the dynamics of Milky Way globular clusters, focusing on two separate topics.The first one is the analysis of the full 6-dimensional phase-space distribution of the entire population of Milky Way globular clusters: their mean proper motions (PM) can be measured with an exquisite precision (down to 0.05 mas yr−1, including systematic errors). Using these data, and a suitable ansatz for the steady-state distribution function (DF) of the cluster population, we then determine simultaneously the best-fit parameters of this DF and the total Milky Way potential. We also discuss possible correlated structures in the space of integrals of motion.The second topic addresses the internal dynamics of a few dozen of the closest and richest globular clusters, again using the Gaia PM to measure the velocity dispersion and internal rotation, with a proper treatment of spatially correlated systematic errors. Clear rotation signatures are detected in 10 clusters, and a few more show weaker signatures at a level ∼0.05 mas yr−1. PM dispersion profiles can be reliably measured down to 0.1 mas yr−1, and agree well with the line-of-sight velocity dispersion profiles from the literature.

scholarly journals IC 4499 revised: Spectro-photometric evidence of small light-element variations

2018 ◽  
Vol 618 ◽  
pp. A131 ◽  
Author(s):  
E. Dalessandro ◽  
C. Lardo ◽  
M. Cadelano ◽  
S. Saracino ◽  
N. Bastian ◽  
...  
Keyword(s):  
Globular Clusters ◽  
Milky Way ◽  
Dwarf Galaxy ◽  
Light Element ◽  
High Resolution Spectroscopy ◽  
Multiple Populations ◽  
Number Ratio ◽  
Red Giant ◽  
Good Agreement

It has been suggested that IC 4499 is one of the very few old globulars to not host multiple populations with light-element variations. To follow-up on this very interesting result, here we have made use of accurate HST photometry and FLAMES at VLT high-resolution spectroscopy to investigate in more detail the stellar population properties of this system. We find that the red giant branch of the cluster is clearly bimodal in near-UV-optical colour-magnitude diagrams, thus suggesting that IC 4499 is actually composed by two sub-populations of stars with different nitrogen abundances. This represents the first detection of multiple populations in IC 4499. Consistently, we also find that one star out of six is Na-rich to some extent, while we do not detect any evidence of intrinsic spread in both Mg and O. The number ratio between stars with normal and enriched nitrogen is in good agreement with the number ratio – mass trend observed in Galactic globular clusters. Also, as typically found in other systems, nitrogen rich stars are more centrally concentrated than normal stars, although this result cannot be considered conclusive because of the limited field of view covered by our observations (∼1rh). On the contrary, we observe that both the RGB UV colour spread, which is a proxy of N variations, and Na abundance variations, are significantly smaller than those observed in Milky Way globular clusters with mass and metallicity comparable to IC 4499. The modest N and Na spreads observed in this system can be tentatively connected to the fact that IC 4499 likely formed in a disrupted dwarf galaxy orbiting the Milky Way, as previously proposed based on its orbit.

scholarly journals Predicting accreted satellite galaxy masses and accretion redshifts based on globular cluster orbits in the E-MOSAICS simulations

2020 ◽  
Vol 499 (4) ◽  
pp. 4863-4875
Author(s):  
Joel L Pfeffer ◽  
Sebastian Trujillo-Gomez ◽  
J M D Kruijssen ◽  
Robert A Crain ◽  
Meghan E Hughes ◽  
...  
Keyword(s):  
Globular Clusters ◽  
Milky Way ◽  
Star Cluster ◽  
Low Energy ◽  
Orbital Energy ◽  
High Energies ◽  
Satellite Galaxy ◽  
The Galaxy ◽  
Galaxy Masses

ABSTRACT The ages and metallicities of globular clusters (GCs) are known to be powerful tracers of the properties of their progenitor galaxies, enabling their use in determining the merger histories of galaxies. However, while useful in separating GCs into individual accretion events, the orbits of GC groups themselves have received less attention as probes of their progenitor galaxy properties. In this work, we use simulations of galaxies and their GC systems from the MOdelling Star cluster population Assembly In Cosmological Simulations within EAGLE project to explore how the present-day orbital properties of GCs are related to the properties of their progenitor galaxies. We find that the orbits of GCs deposited by accretion events are sensitive to the mass and merger redshift of the satellite galaxy. Earlier mergers and larger galaxy masses deposit GCs at smaller median apocentres and lower total orbital energy. The orbital properties of accreted groups of GCs can therefore be used to infer the properties of their progenitor galaxy, though there exists a degeneracy between galaxy mass and accretion time. Combining GC orbits with other tracers (GC ages, metallicities) will help to break the galaxy mass/accretion time degeneracy, enabling stronger constraints on the properties of their progenitor galaxy. In situ GCs generally orbit at lower energies (small apocentres) than accreted GCs, however they exhibit a large tail to high energies and even retrograde orbits (relative to the present-day disc), showing significant overlap with accreted GCs. Applying the results to Milky Way GCs groups suggests a merger redshift z ∼ 1.5 for the Gaia Sausage/Enceladus and z > 2 for the ‘low-energy’/Kraken group, adding further evidence that the Milky Way had two significant mergers in its past.

scholarly journals Improved dynamical modelling of the Arches cluster

2013 ◽  
Vol 9 (S303) ◽  
pp. 59-60
Author(s):  
Joowon Lee ◽  
Sungsoo S. Kim
Keyword(s):  
Surface Brightness ◽  
Massive Star ◽  
Velocity Dispersion ◽  
Galactic Center ◽  
Dynamical Evolution ◽  
Star Cluster ◽  
Initial Mass ◽  
Data Set ◽  
Cluster A ◽  
Best Fit

AbstractRecently, Clarkson et al. (2012) measured the intrinsic velocity dispersion of the Arches cluster, a young and massive star cluster in the Galactic center. Using the observed velocity dispersion profile and the surface brightness profile of Espinoza et al. (2009), they estimate the cluster's present-day mass to be ∼ 1.5×104 M⊙ by fitting an isothermal King model. In this study, we trace the best-fit initial mass for the Arches cluster using the same observed data set and also the anisotropic Fokker-Planck calculations for the dynamical evolution.

scholarly journals The Influence of Gas Expulsion on the Evolution of Star Clusters

2007 ◽  
Vol 3 (S246) ◽  
pp. 36-40
Author(s):  
H. Baumgardt ◽  
P. Kroupa
Keyword(s):  
Globular Clusters ◽  
Milky Way ◽  
Three Dimensional ◽  
Star Clusters ◽  
Dynamical Evolution ◽  
Mass Function ◽  
Star Cluster ◽  
Dissolution Mechanism ◽  
Large Set ◽  
Cluster Systems

AbstractWe present new results on the dynamical evolution and dissolution of star clusters due to residual gas expulsion and the effect this has on the mass function and other properties of star cluster systems. To this end, we have carried out a large set of N-body simulations, varying the star formation efficiency, gas expulsion time scale and strength of the external tidal field, obtaining a three-dimensional grid of models which can be used to predict the evolution of individual star clusters or whole star cluster systems by interpolating between our runs. When applied to the Milky Way globular cluster system, we find that gas expulsion is the main dissolution mechanism for star clusters, destroying about 80% of all clusters within a few 10s of Myers. Together with later dynamical evolution, it seems possible to turn an initial power-law mass function into a log-normal one with properties similar to what has been observed for the Milky Way globular clusters.

scholarly journals Results from HST Observations of Six LMC Globular Cluster Fields

1999 ◽  
Vol 190 ◽  
pp. 448-449 ◽  
Author(s):  
K. A. G. Olsen ◽  
P. W. Hodge ◽  
M. Mateo ◽  
E. W. Olszewski ◽  
R. A. Schommer ◽  
...  
Keyword(s):  
Star Formation ◽  
Globular Clusters ◽  
Milky Way ◽  
Evolutionary Models ◽  
First Stars ◽  
Field Star ◽  
Star Studies ◽  
Red Giant ◽  
Star Formation Histories ◽  
Best Fit

We present deep HST color-magnitude diagrams of fields centered on the six old LMC globular clusters NGC 1754, NGC 1835, NGC 1898, NGC 1916, NGC 2005, and NGC 2019. Separate cluster and field star CMDs are shown. The time of formation of the LMC is studied from an analysis of the cluster CMDs. Based on a comparison of the CMDs with sequences of the Milky Way clusters M3, M5, and M55, we suggest that the LMC formed its first stars at the same time as the Milky Way to within 1 Gyr. We find additional evidence that these LMC globular clusters are as old as the oldest Milky Way clusters through a comparison of our data with the horizontal branch evolutionary models of Lee, Demarque, & Zinn (1994).The evolution of the LMC following its formation is studied through an analysis of the field star CMDs. Through an automated comparison with stellar evolution models, we extract the star formation histories implied by the CMDs. Our best-fit star formation histories imply that the LMC has been actively forming stars over the last 4 Gyr, in agreement with previous field star studies. The four fields that lie in the Bar also contain significant numbers of stars with ages of 4–8 Gyr in the best-fit cases. The most notable disagreement between the best-fit models and observed CMDs is in the color of the red giant branch.

scholarly journals The Formation Chronology of Local Group Spiral Galaxies

2002 ◽  
Vol 207 ◽  
pp. 73-82
Author(s):  
Ata Sarajedini
Keyword(s):  
Globular Clusters ◽  
Milky Way ◽  
Local Group ◽  
Spiral Galaxies ◽  
Dwarf Galaxy ◽  
Additional Parameter ◽  
Horizontal Branch ◽  
The Galaxy ◽  
Metal Abundance ◽  
Cluster Age

The ‘Second Parameter Effect’ (2ndPE) has long been recognized as an important probe into the formation of spiral galaxies. The concept that the horizontal branch morphologies of globular clusters are primarily affected by metal abundance in the inner halo (RGC<8 kpc) of the Galaxy but require an additional parameter (probably cluster age) to explain their behavior in the outer halo (RGC > 8 kpc), suggests that the former experienced a rapid monotonic collapse while the latter underwent a slower chaotic formation scenario. As such, in the Milky Way, the so-called second parameter boundary is located at 8 kpc. We find that, in the other Local Group spirals — M31 and M33 — this boundary lies at ∼40 kpc and ∼0 kpc, respectively. We therefore speculate that the boundary delimiting rapid monotonic halo collapse from the chaotic accretion of dwarf galaxy fragments is inversely related to the mass of the spiral galaxy.

scholarly journals The Dynamical Mass of the Young Cluster W3 in NGC 7252: Heavy-Weight Globular Cluster or Ultra-Compact Dwarf Galaxy?

2005 ◽  
Vol 13 ◽  
pp. 169-170
Author(s):  
Claudia Maraston ◽  
N. Bastian ◽  
R. P. Saglia ◽  
Markus Kissler-Patig ◽  
François Schweizer ◽  
...  
Keyword(s):  
Globular Clusters ◽  
Stellar Population ◽  
Milky Way ◽  
Dwarf Galaxy ◽  
Elliptical Galaxies ◽  
Star Cluster ◽  
Dynamical Mass ◽  
Fundamental Plane ◽  
Dwarf Elliptical Galaxies ◽  
First Time

AbstractWe have measured the dynamical mass of the highly luminous star cluster W3 in the young merger remnant galaxy NGC 7252. The value is Mdyn = (8 ± 2) × 107M⊙, and represents the highest dynamically-confirmed mass for an extra-galactic star cluster so far. The dynamical mass is in excellent agreement with the luminous mass (Maraston et al. 2001). This results from the use of stellar population models that include correctly the brightest AGB stellar phase, dominant in young stellar populations. To classify W3, we employ the fundamental plane of stellar systems (Bender, Burstein & Faber 1992), for the first time in these kinds of studies. We find that W3 lies far from typical Milky Way globular clusters, but it is also far from the heavyweights ωCen in the Milky Way and G1 in M31, because it is too extended for its mass, and from dwarf elliptical galaxies because it is much more compact for its mass. Instead W3 lies close to the ultra-compact Fornax objects (Drinkwater et al. 2003) and to the compact elliptical M32, possibly shedding light on the still mysterious nature of these objects. A previously deserted region of the fundamental plane starts to be populated.

scholarly journals Spectroscopy of the Globular Clusters in M87

1987 ◽  
Vol 127 ◽  
pp. 451-452
Author(s):  
J.R. Mould ◽  
J.B. Oke ◽  
J.M. Nemec
Keyword(s):  
Density Distribution ◽  
Globular Cluster ◽  
Globular Clusters ◽  
Milky Way ◽  
Velocity Dispersion ◽  
Cluster System ◽  
Hot Gas ◽  
The Mean ◽  
Globular Cluster System ◽  
Young Clusters

With a velocity dispersion of 370 ± 50 km/sec the globular cluster system of M87 is kinematically hotter than the stars in the giant elliptical itself. This is consistent with the clusters' shallower density distribution for isotropic orbits. the mean metallicity of the 27 clusters in the sample analyzed here is no more than a factor of 2 more metal rich than the cluster system of the Milky Way, but considerably more metal poor than the integrated starlight in the field at a radius of 1' from the center of M87. There is no evidence for the existence of young clusters in the system. the mass-radius relation between 1' and 5' required to contain the globular clusters joins on to that required to contain the hot gas around M87.

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