scholarly journals A Semi-Analytic Approach to Understanding the Bimodality of GCs in the Milky Way & M31

2006 ◽  
Vol 2 (S235) ◽  
pp. 132-132
Author(s):  
B. Rothberg ◽  
R. Somerville ◽  
B. Whitmore ◽  
W. Harris
Keyword(s):  
Globular Clusters ◽  
Milky Way ◽  
Spiral Galaxies ◽  
Broad Band ◽  
Physical Characteristics ◽  
Analytic Approach ◽  
The Galaxy ◽  
Analytic Models ◽  
Parent Galaxy ◽  
Centaurus A

AbstractOne of the most important results in the study of Globular Clusters (GC) has been the discovery of bimodality in the broad-band colors of many systems. Observations of the Milky Way, M31 and Centaurus A strongly suggest this is a bi-modality in metallicity. One method of constraining, and perhaps better understanding the observed bimodality of GCs is to use semi-analytic models (SAMs) to test both the galaxy and GC formation scenarios. We present the results of a study to test whether SAMs can accurately reproduce the physical characteristics of both the parent galaxy (including luminosity, mass and metallicity) and GC populations. The focus of the work is to test whether the SAMs are capable of reproducing the observed properties of spiral galaxies, in particular the Milky Way and M31, and what, if any, constraints this may place on the formation scenarios of GCs. Among the results are indications that bimodality may be directly connected with reionization at z ~ 7–8.

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 accreted nuclear clusters of the Milky Way

2020 ◽  
Vol 500 (2) ◽  
pp. 2514-2524
Author(s):  
Joel Pfeffer ◽  
Carmela Lardo ◽  
Nate Bastian ◽  
Sara Saracino ◽  
Sebastian Kamann
Keyword(s):  
Globular Clusters ◽  
Milky Way ◽  
Dwarf Galaxy ◽  
Star Clusters ◽  
Host Galaxy ◽  
The Galaxy ◽  
Nuclear Clusters ◽  
The Common ◽  
Massive Clusters ◽  
Peculiar Case

ABSTRACT A number of the massive clusters in the halo, bulge, and disc of the Galaxy are not genuine globular clusters (GCs) but instead are different beasts altogether. They are the remnant nuclear star clusters (NSCs) of ancient galaxies since accreted by the Milky Way. While some clusters are readily identifiable as NSCs and can be readily traced back to their host galaxy (e.g. M54 and the Sagittarius Dwarf galaxy), others have proven more elusive. Here, we combine a number of independent constraints, focusing on their internal abundances and overall kinematics, to find NSCs accreted by the Galaxy and trace them to their accretion event. We find that the true NSCs accreted by the Galaxy are: M54 from the Sagittarius Dwarf, ω Centari from Gaia-Enceladus/Sausage, NGC 6273 from Kraken, and (potentially) NGC 6934 from the Helmi Streams. These NSCs are prime candidates for searches of intermediate-mass black holes (BHs) within star clusters, given the common occurrence of galaxies hosting both NSCs and central massive BHs. No NSC appears to be associated with Sequoia or other minor accretion events. Other claimed NSCs are shown not to be such. We also discuss the peculiar case of Terzan 5, which may represent a unique case of a cluster–cluster merger.

scholarly journals An Overview of the Globular Cluster System of the Galaxy

1988 ◽  
Vol 126 ◽  
pp. 37-48
Author(s):  
Robert Zinn
Keyword(s):  
Globular Cluster ◽  
Globular Clusters ◽  
Milky Way ◽  
Galactic Center ◽  
Galactic Plane ◽  
Cluster System ◽  
Open Clusters ◽  
The Galaxy ◽  
Globular Cluster System ◽  
Harlow Shapley

Harlow Shapley (1918) used the positions of globular clusters in space to determine the dimensions of our Galaxy. His conclusion that the Sun does not lie near the center of the Galaxy is widely recognized as one of the most important astronomical discoveries of this century. Nearly as important, but much less publicized, was his realization that, unlike stars, open clusters, HII regions and planetary nebulae, globular clusters are not concentrated near the plane of the Milky Way. His data showed that the globular clusters are distributed over very large distances from the galactic plane and the galactic center. Ever since this discovery that the Galaxy has a vast halo containing globular clusters, it has been clear that these clusters are key objects for probing the evolution of the Galaxy. Later work, which showed that globular clusters are very old and, on average, very metal poor, underscored their importance. In the spirit of this research, which started with Shapley's, this review discusses the characteristics of the globular cluster system that have the most bearing on the evolution of the Galaxy.

scholarly journals Dynamics of Globular Cluster Systems

1983 ◽  
Vol 100 ◽  
pp. 359-364
Author(s):  
K. C. Freeman
Keyword(s):  
Globular Cluster ◽  
Globular Clusters ◽  
Milky Way ◽  
Cluster Formation ◽  
Active Phase ◽  
Chemical Abundance ◽  
Cluster Systems ◽  
Chemical Enrichment ◽  
Wide Range ◽  
The Galaxy

In the Milky Way, the globular clusters are all very old, and we are accustomed to think of them as the oldest objects in the Galaxy. The clusters cover a wide range of chemical abundance, from near solar down to about [Fe/H] ⋍ −2.3. However there are field stars with abundances significantly lower than −2.3 (eg Bond, 1980); this implies that the clusters formed during the active phase of chemical enrichment, with cluster formation beginning at a time when the enrichment processes were already well under way.

scholarly journals The Chemical Abundances of the Halo Clusters of the Galaxy

1978 ◽  
Vol 80 ◽  
pp. 177-182
Author(s):  
R. Canterna ◽  
R. A. Schommer
Keyword(s):  
Globular Clusters ◽  
Broad Band ◽  
Mean Value ◽  
Red Giants ◽  
Galactocentric Distance ◽  
Chemical Abundances ◽  
Dwarf Spheroidal Galaxies ◽  
The Galaxy ◽  
Ursa Minor ◽  
Metal Abundances

Photometric metal abundances of individual red giants in eight extremely distant halo globular clusters and the Draco and Ursa Minor dwarf spheroidal galaxies have been obtained using the Washington broad-band system, C, M, T1, T2(Canterna 1976). Observations were made at the KPNO 2.1-m and CTIO 1.5-m telescopes. In Table I we list for each system the mean value of [Fe/H], the number of stars observed in each system, n, the Galactocentric distance, RGC, the intrinsic color of the giant branch at the level of the horizontal branch (HB), (B-V)o,g, and the fraction of HB stars bluer than the RR Lyrae gap, fB. Sources for unpublished color-magnitude diagram (CMD) data are: Pal 11 (Canterna and Schommer), Pal 12 (Canterna and Harris), and Ursa Minor (Schommer, Olszewski and Kunkel).

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 &gt; 2 for the ‘low-energy’/Kraken group, adding further evidence that the Milky Way had two significant mergers in its past.

HR Diagrams of Galaxies: Ages and Stages of Evolution

1978 ◽  
Vol 80 ◽  
pp. 247-257
Author(s):  
Beatrice M. Tinsley
Keyword(s):  
Globular Clusters ◽  
Milky Way ◽  
Stellar Populations ◽  
Young Star ◽  
Red Giants ◽  
Type I ◽  
Type Ii ◽  
Hubble Sequence ◽  
The Galaxy ◽  
Bright Blue

Baade (1944) based his concept of stellar populations in galaxies on the HR diagrams that he inferred from the magnitude at which their brightest stars could be resolved. His type I population had bright blue supergiants like those in the disk of the Milky Way, while the brightest stars in type II were the red giants found in globular clusters. He postulated that the Hubble sequence of galaxy types from irregulars to ellipticals contained increasing proportions of Population II relative to Population I, and that similar differences characterized nuclear bulges of spirals relative to their disks. A very important revision of this picture came with the discovery by Morgan and Mayall (1957; Morgan, 1956, 1959) that the integrated blue light of the nuclear bulges of M31 and the Galaxy is dominated by strong-lined CN giants, not by the weak-lined type found in globular clusters. On the basis of integrated spectra of galaxies, Morgan developed a revised population scheme, in which the extreme types are a young-star rich population, like Baade's extreme Population I, and a young-star deficient population, analogous to Population II but generally metal-rich. Different proportions of these two types are still thought to represent the main differences among stellar populations in different regions of galaxies.

Dynamical evolution of globular clusters: Recent developments

2017 ◽  
Vol 26 (09) ◽  
pp. 1730017
Author(s):  
Marco Merafina
Keyword(s):  
Globular Cluster ◽  
Globular Clusters ◽  
Milky Way ◽  
Structural Parameters ◽  
Dynamical Evolution ◽  
Limit Value ◽  
Tidal Forces ◽  
The Galaxy ◽  
Recent Developments ◽  
Theoretical Results

We analyze structural parameters of the globular clusters belonging to the Milky Way system which were listed in the latest edition of the Harris Catalogue. We search for observational evidences of the effect of tidal forces induced by the Galaxy on the dynamical and thermodynamical evolution of a globular cluster. The behavior for the [Formula: see text] distribution exhibited by the globular cluster population seems to be in contrast with theoretical results in literature about gravothermal instability, and suggest a new limit value smaller than the previous one.

scholarly journals Infrared surveys of Galactic star clusters

2009 ◽  
Vol 5 (S266) ◽  
pp. 203-210 ◽  
Author(s):  
Valentin D. Ivanov ◽  
Maria Messineo ◽  
Qingfeng Zhu ◽  
Don Figer ◽  
J. Borissova ◽  
...  
Keyword(s):  
Surface Density ◽  
Globular Clusters ◽  
Visual Inspection ◽  
Milky Way ◽  
Star Clusters ◽  
Detection Algorithm ◽  
Point Sources ◽  
The Galaxy ◽  
Infrared Surveys ◽  
Selection Of

AbstractMany attempts have been made to carry out a complete observational census of Milky Way star clusters based on recent near- and mid-infrared surveys. However, more clusters are still being discovered, indicating that existing catalogs are incomplete. We attempt to estimate the total number of supermassive (SM; Mcl ≥ 104 M⊙) clusters in the Galaxy, and to improve the yield from the automated cluster searches. Assuming that the ‘local’ census of SM clusters is complete, and that their surface density accross the disk follows that of the stars, we predict that the Milky Way contains ≥81 ± 21 SM clusters. We apply a cluster-detection algorithm to the 2mass Point Source Catalog after a preliminary color and/or magnitude selection of the point sources to improves the surface-density cluster-to-field contrast. Our algorithm identified 94 new candidates, and re-identified 34 known clusters. During the visual inspection, we detected an additional 41 new candidates, and re-identified 32 known objects. Preliminary characterization suggests that the new list may contain red-supergiant, open and globular clusters.

scholarly journals The orbital evolution of UFDs and GCs in an evolving Galactic potential

2020 ◽  
Vol 500 (3) ◽  
pp. 2937-2957
Author(s):  
Benjamin M Armstrong ◽  
Kenji Bekki ◽  
Aaron D Ludlow
Keyword(s):  
Globular Clusters ◽  
Milky Way ◽  
Orbital Evolution ◽  
Orbital Parameters ◽  
Angular Momenta ◽  
Galactic Potential ◽  
The Galaxy ◽  
Galaxy Masses ◽  
The Difference ◽  
Evolving Models

ABSTRACT We use the second Gaia data release to investigate the kinematics of 17 ultra-faint dwarf galaxies (UFDs) and 154 globular clusters (GCs) in the Milky Way, focusing on the differences between static and evolving models of the Galactic potential. An evolving potential modifies a satellite’s orbit relative to its static equivalent, though the difference is small compared to existing uncertainties on orbital parameters. We find that the UFD Boötes II is likely on its first passage around the Milky Way. Depending on the assumed mass of the Milky Way, the UFDs Triangulum II, Hydrus I, Coma Berenices, Draco II, and Ursa Major II, as well as the GC Pyxis, may also be on first infall so may be useful for constraining the mass of the Galaxy. We identify a clear kinematic distinction between metal-rich ([Fe/H] &gt; −1.1) and metal-poor GCs ([Fe/H] ≤ −1.1). Although most metal-rich clusters occupy predominately prograde orbits, with low eccentricities (e ≈ 0.35) and similar specific angular momenta and orbital planes as the Galactic disc, seven show potentially retrograde orbits, the origin of which is unclear. Metal-poor clusters have more diverse orbits, higher eccentricities (e ≈ 0.65), and half of them have orbital planes offset from the disc by 60° to 120°—twice as many as the metal-poor GCs. The UFDs have similar θ and ϕ to the metal-poor GCs, suggesting a similar origin. We provide a catalogue of orbital parameters for UFDs and GCs for two different Galaxy masses and their observational uncertainties.

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