scholarly journals The likelihood of undiscovered globular clusters in the outskirts of the Milky Way

2021 ◽  
Vol 502 (3) ◽  
pp. 4547-4557
Author(s):  
Jeremy J Webb ◽  
Raymond G Carlberg
Keyword(s):  
Equilibrium State ◽  
Globular Cluster ◽  
Globular Clusters ◽  
Milky Way ◽  
Expected Number ◽  
Galactocentric Distance ◽  
Deep Imaging ◽  
Low Metallicity ◽  
Globular Cluster System ◽  
Kinematic Properties

ABSTRACT The currently known Galactic globular cluster population extends out to a maximum galactocentric distance of ∼145 kpc, with the peculiarity that the outermost clusters predominantly have an inward velocity. Orbit averaging finds that this configuration occurs by chance about $6{{\ \rm per\ cent}}$ of the time, suggesting that several globular clusters with positive radial velocities remain undiscovered. We evaluate the expected number of undiscovered clusters at large distances under the assumption that the cluster population has a smooth radial distribution and is in equilibrium within the Milky Way’s virial radius. By comparing the present day kinematic properties of outer clusters to random orbital configurations of the Galactic globular cluster system through orbit averaging, we estimate a likelihood of $73{{\ \rm per\ cent}}$ of there being at least one undiscovered globular cluster within the Milky Way. This estimate assumes the current population is complete out to 50 kpc, and increases to $91{{\ \rm per\ cent}}$ if the population is complete out to 150 kpc. The likelihood of there being two undiscovered clusters is between $60$ and $70{{\ \rm per\ cent}}$, with the likelihood of there being three undiscovered clusters being on the order of $50{{\ \rm per\ cent}}$. The most likely scenario is that the undiscovered clusters are moving outwards, which results in the outer cluster population being consistent with an equilibrium state. Searches for distant and possibly quite low concentration and very low metallicity globular clusters will be enabled with upcoming deep imaging surveys.

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 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.

scholarly journals An outer shade of Pal: Abundance analysis of the outer halo globular cluster Palomar 13

2019 ◽  
Vol 632 ◽  
pp. A55 ◽  
Author(s):  
Andreas Koch ◽  
Patrick Côté
Keyword(s):  
Globular Cluster ◽  
Neutron Capture ◽  
Milky Way ◽  
Signal To Noise Ratio ◽  
Light Element ◽  
Chemical Abundance ◽  
Galactocentric Distance ◽  
The Mean ◽  
Remote System ◽  
Kinematic Properties

At a Galactocentric distance of 27 kpc, Palomar 13 is an old globular cluster (GC) belonging to the outer halo. We present a chemical abundance analysis of this remote system from high-resolution spectra obtained with the Keck/HIRES spectrograph. Owing to the low signal-to-noise ratio of the data, our analysis is based on a coaddition of the spectra of 18 member stars. We are able to determine integrated abundance ratios for 16 species of 14 elements, of α-elements (Mg, Si, Ca, and Ti), Fe-peak (Sc, Mn, Cr, Ni, Cu, and Zn), and neutron-capture elements (Y and Ba). While the mean Na abundance is found to be slightly enhanced and halo-like, our method does not allow us to probe an abundance spread that would be expected in this light element if multiple populations are present in Pal 13. We find a metal-poor mean metallicity of −1.91 ± 0.05 (statistical) ±0.22 (systematic), confirming that Pal 13 is a typical metal-poor representative of the outer halo. While there are some differences between individual α-elements, such as halo-like Mg and Si versus the mildly lower Ca and Ti abundances, the mean [α/Fe] of 0.34 ± 0.06 is consistent with the marginally lower α component of the halo field and GC stars at similar metallicity. We discuss our results in the context of other objects in the outer halo and consider which of these objects were likely accreted. We also discuss the properties of their progenitors. While chemically, Pal 13 is similar to Gaia-Enceladus and some of its GCs, this is not supported by its kinematic properties within the Milky Way system. Moreover, its chemodynamical similarity with NGC 5466, a purported progeny of the Sequoia accretion event, might indicate a common origin in this progenitor. However, the ambiguities in the full abundance space of this comparison emphasize the difficulties in unequivocally labeling a single GC as an accreted object, let alone assigning it to a single progenitor.

scholarly journals The Globular Cluster System of NGC 5128: Ages, Metallicities, Kinematics and Structural Parameters

2010 ◽  
Vol 27 (4) ◽  
pp. 379-389 ◽  
Author(s):  
K. A. Woodley ◽  
M. Gómez
Keyword(s):  
Globular Cluster ◽  
Globular Clusters ◽  
Structural Parameters ◽  
Cluster System ◽  
High Signal ◽  
Galactocentric Distance ◽  
Noise Spectroscopy ◽  
Formation And Evolution ◽  
Globular Cluster System ◽  
Cluster Age

AbstractWe review our recent studies of the globular cluster system of NGC 5128. First, we have obtained low-resolution, high signal-to-noise spectroscopy of 72 globular clusters using Gemini-S/GMOS to obtain the ages, metallicities, and the level of alpha enrichment of the metal-poor and metal-rich globular cluster subpopulations. Second, we have explored the rotational signature and velocity dispersion of the galaxy's halo using over 560 globular clusters with radial velocity measurements. We have also compared the dependence of these properties on galactocentric distance and globular cluster age and metallicity. Using globular clusters as tracer objects, we have analyzed the mass, and mass-to-light ratio of NGC 5128. Last, we have measured the structural parameters, such as half-light radii, of over 570 globular clusters from a superb 1.2-square-degree Magellan/IMACS image. We will present the findings of these studies and discuss the connection to the formation and evolution of NGC 5128.

The GOTHAM survey: chemical evolution of Milky Way globular clusters

2017 ◽  
Vol 13 (S334) ◽  
pp. 25-28
Author(s):  
Bruno Dias ◽  
Beatriz Barbuy ◽  
Ivo Saviane ◽  
Enrico V. Held ◽  
Gary Da Costa ◽  
...  
Keyword(s):  
Chemical Evolution ◽  
Globular Cluster ◽  
Globular Clusters ◽  
Stellar Population ◽  
Milky Way ◽  
Open Clusters ◽  
Giant Stars ◽  
Globular Cluster System ◽  
Galactic Globular Clusters ◽  
Red Giant

AbstractMilky Way globular clusters are excellent laboratories for stellar population detailed analysis that can be applied to extragalactic environments with the advent of the 40m-class telescopes like the ELT. The globular cluster population traces the early evolution of the Milky Way which is the field of Galactic archaeology. We present our GlObular clusTer Homogeneous Abundance Measurement (GOTHAM) survey. We derived radial velocities, Teff, log(g), [Fe/H], [Mg/Fe] for red giant stars in one third of all Galactic globular clusters that represent well the Milky Way globular cluster system in terms of metallicity, mass, reddening, and distance. Our method is based on low-resolution spectroscopy and is intrinsically reddening free and efficient even for faint stars. Our [Fe/H] determinations agree with high-resolution results to within 0.08 dex. The GOTHAM survey provides a new metallicity scale for Galactic globular clusters with a significant update of metallicities higher than [Fe/H] > -0.7. We show that the trend of [Mg/Fe] with metallicity is not constant as previously found, because now we have more metal-rich clusters. Moreover, peculiar clusters whose [Mg/Fe] does not match Galactic stars for a given metallicity are discussed. We also measured the CaII triplet index for all stars and we show that the different chemical evolution of Milky Way open clusters, field stars, and globular clusters implies different calibrations of calcium triplet to metallicity.

scholarly journals Kinematics of the Galactic Globular Cluster System

1988 ◽  
Vol 126 ◽  
pp. 49-60 ◽  
Author(s):  
R. F. Webbink
Keyword(s):  
Angular Momentum ◽  
Velocity Distribution ◽  
Radial Velocity ◽  
Globular Cluster ◽  
Velocity Dispersion ◽  
Proper Motions ◽  
Galactocentric Distance ◽  
Residual Velocity ◽  
Globular Cluster System ◽  
Kinematic Properties

Constraints on cluster kinematics proper motions, radial velocities and tidal radii are reviewed. Analysis of the cluster radial velocity distribution suggests a rotation law for the system in which the specific angular momentum is nearby independent of galactocentric distance, and the residual velocity dispersion is isotropic. However, the absence of severely tidally truncated clusters indicates that nearly radial orbits are absent from this distribution. The kinematic properties of the remote halo clusters remain largely indeterminate. Absolute proper motions measured directly with respect to background galaxies and quasars are needed to determine the kinematics of these objects, and also to elucidate the process of tidal stripping.

scholarly journals The globular cluster system of the Auriga simulations

2020 ◽  
Vol 496 (1) ◽  
pp. 638-648 ◽  
Author(s):  
Timo L R Halbesma ◽  
Robert J J Grand ◽  
Facundo A Gómez ◽  
Federico Marinacci ◽  
Rüdiger Pakmor ◽  
...  
Keyword(s):  
Globular Cluster ◽  
Milky Way ◽  
Cluster Formation ◽  
Solar Radius ◽  
High Mass ◽  
Formation Model ◽  
The Galaxy ◽  
High Mass Loss ◽  
Globular Cluster System ◽  
Varying Mass

ABSTRACT We investigate whether the galaxy and star formation model used for the Auriga simulations can produce a realistic globular cluster (GC) population. We compare statistics of GC candidate star particles in the Auriga haloes with catalogues of the Milky Way (MW) and Andromeda (M31) GC populations. We find that the Auriga simulations do produce sufficient stellar mass for GC candidates at radii and metallicities that are typical for the MW GC system (GCS). We also find varying mass ratios of the simulated GC candidates relative to the observed mass in the MW and M31 GCSs for different bins of galactocentric radius metallicity (rgal–[Fe/H]). Overall, the Auriga simulations produce GC candidates with higher metallicities than the MW and M31 GCS and they are found at larger radii than observed. The Auriga simulations would require bound cluster formation efficiencies higher than 10 per cent for the metal-poor GC candidates, and those within the Solar radius should experience negligible destruction rates to be consistent with observations. GC candidates in the outer halo, on the other hand, should either have low formation efficiencies, or experience high mass-loss for the Auriga simulations to produce a GCS that is consistent with that of the MW or M31. Finally, the scatter in the metallicity as well as in the radial distribution between different Auriga runs is considerably smaller than the differences between that of the MW and M31 GCSs. The Auriga model is unlikely to give rise to a GCS that can be consistent with both galaxies.

Globular cluster tidal interactions and mergers in the Galactic disc

2019 ◽  
Vol 14 (S351) ◽  
pp. 442-446
Author(s):  
Alessandra Mastrobuono-Battisti ◽  
Sergey Khoperskov ◽  
Paola Di Matteo ◽  
Misha Haywood
Keyword(s):  
Globular Cluster ◽  
Iron Content ◽  
Globular Clusters ◽  
Dynamical Evolution ◽  
Stellar Populations ◽  
Cluster System ◽  
Galactic Disc ◽  
Tidal Interactions ◽  
Globular Cluster System ◽  
Shed Light

AbstractThe Galactic globular cluster system went and is still going through dynamical processes that require to be explored in detail. Here we illustrate how primordial massive globular clusters born in the Milky Way’s disc evolved by stripping material from each other or even merging very early during their lives. These processes might explain the puzzling presence of star-by-star spreads in iron content observed in massive globular clusters and should be taken into account when studying globular cluster stellar populations. In this context, we show how the direct comparison between the predictions provided by our direct N-body simulations and observations can shed light on the origin and chemo-dynamical evolution of globular clusters.

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.

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