scholarly journals Stellar population properties of the most massive globular clusters and ultra-compact dwarf galaxies of the Fornax cluster

2015 ◽  
Vol 12 (S316) ◽  
pp. 99-104
Author(s):  
Michael Hilker
Keyword(s):  
Globular Clusters ◽  
Dwarf Galaxies ◽  
Mass Function ◽  
Nearby Galaxy ◽  
Stellar Content ◽  
Medium Resolution ◽  
Low Surface Brightness ◽  
Show Evidence ◽  
Internal Properties ◽  
Fornax Cluster

AbstractMost ultra-compact dwarf galaxies (UCDs) and very massive globular clusters reside in nearby galaxy clusters or around nearby giant galaxies. Due to their distance (> 4 Mpc) and compactness (reff < 100 pc) they are barely resolved, and thus it is difficult to obtain their internal properties. Here I present our most recent attempts to constrain the mass function, stellar content and dynamical state of UCDs in the Fornax cluster. Thanks to radial velocity membership assignment of ~ 950 globular clusters (GCs) and UCDs in the core of Fornax, the shape of their mass function is well constrained. It is consistent with the ‘standard’ Gaussian mass function of GCs. Our recent simulations on the disruption process of nucleated dwarf galaxies in cluster environments showed that ~ 40% of the most massive UCDs should originate from nuclear star clusters. Some Fornax UCDs actually show evidence for this scenario, as revealed by extended low surface brightness disks around them and onsets of tidal tails. Multi-band UV to optical imaging as well as low to medium resolution spectroscopy revealed that there exist UCDs with youngish ages, (sub-)solar [α/Fe] abundances, and probably He-enriched populations.

scholarly journals X-Raying the Dynamics of Globular Clusters

1985 ◽  
Vol 113 ◽  
pp. 43-61 ◽  
Author(s):  
Jonathan E. Grindlay
Keyword(s):  
Globular Clusters ◽  
Mass Function ◽  
Initial Mass Function ◽  
Giant Molecular Clouds ◽  
Stellar Content ◽  
X Ray ◽  
Triple Systems ◽  
Compact Binary ◽  
The Galaxy ◽  
Show Evidence

Recent studies of the x-ray sources in globular clusters have provided important new clues for both the dynamical processes in clusters and the stellar content and evolution of globular clusters. Very deep x-ray images of several globular clusters show evidence for diffuse x-ray emission from hot gas which may be related by a simple shock model to properties of both the cluster, such as its orbit in the Galaxy, and the interstellar medium in the halo of the Galaxy. The x-ray surveys conducted with the Einstein Observatory are reviewed and the results derived for the luminosity function, masses and nature of the compact x-ray sources are discussed. The evidence for the compact binary nature of the sources is now overwhelming, but long-term x-ray variability studies previously reported may suggest that some of the systems are in fact triple systems with distant companions. Possible relationships between the initial mass function, stellar density and cluster evolution are discussed, and our arguments that the ostensibly similar compact x-ray sources in the galactic bulge are remnants of a population of globular clusters disrupted by giant molecular clouds are updated.

scholarly journals A Search for Globular Clusters in the Surroundings of Dwarf Galaxies in Fornax: Intracluster Globulars?

2002 ◽  
Vol 207 ◽  
pp. 345-347
Author(s):  
Lilia P. Bassino ◽  
Sergio A. Cellone ◽  
Juan C. Forte
Keyword(s):  
Density Distribution ◽  
Globular Cluster ◽  
Surface Density ◽  
Globular Clusters ◽  
Surface Brightness ◽  
Dwarf Galaxies ◽  
Color Distribution ◽  
Low Surface Brightness ◽  
Fornax Cluster

We present the results of a search for globular clusters in the surroundings of 15 low surface brightness dwarf galaxies in the Fornax cluster, on CCD images in the C and T1 bands. Globular cluster candidates show a clear bimodal color distribution. Their surface density distribution shows no concentration towards the respective dwarf galaxies but it does show concentration towards the center of the Fornax cluster. We suggest that the potential globular clusters might not be bound to the dwarf galaxies, but might instead belong to the intra-cluster medium.

scholarly journals Globular clusters as tracers of the halo assembly of nearby central cluster galaxies

2015 ◽  
Vol 11 (S317) ◽  
pp. 128-133
Author(s):  
Michael Hilker ◽  
Tom Richtler
Keyword(s):  
Globular Clusters ◽  
Dwarf Galaxies ◽  
Nearby Galaxy ◽  
Lower Mass ◽  
Cluster Galaxies ◽  
Central Cluster ◽  
Stellar Halo ◽  
Correlation Space ◽  
Fornax Cluster ◽  
Analytical Approaches

AbstractThe properties of globular cluster systems (GCSs) in the core of the nearby galaxy clusters Fornax and Hydra I are presented. In the Fornax cluster we have gathered the largest radial velocity sample of a GCS system so far, which enables us to identify photometric and kinematic sub-populations around the central galaxy NGC 1399. Moreover, ages, metallicities and [α/Fe] abundances of a sub-sample of 60 bright globular clusters (GCs) with high S/N spectroscopy show a multi-modal distribution in the correlation space of these three parameters, confirming heterogeneous stellar populations in the halo of NGC 1399. In the Hydra I cluster very blue GCs were identified. They are not uniformly distributed around the central galaxies. 3-color photometry including the U-band reveals that some of them are of intermediate age. Their location coincides with a group of dwarf galaxies under disruption. This is evidence of a structurally young stellar halo “still in formation”, which is also supported by kinematic measurements of the halo light that point to a kinematically disturbed system. The most massive GCs divide into generally more extended ultra-compact dwarf galaxies (UCDs) and genuine compact GCs. In both clusters, the spatial distribution and kinematics of UCDs are different from those of genuine GCs. Assuming that some UCDs represent nuclei of stripped galaxies, the properties of those UCDs can be used to trace the assembly of nucleated dwarf galaxies into the halos of central cluster galaxies. We show via semi-analytical approaches within a cosmological simulation that only the most massive UCDs in Fornax-like clusters can be explained by stripped nuclei, whereas the majority of lower mass UCDs belong to the star cluster family.

scholarly journals Modeling and analysis of medium-resolution integrated-light spectra of globular clusters in dwarf galaxies

2019 ◽  
Vol 14 (S351) ◽  
pp. 165-169
Author(s):  
Margarita E. Sharina ◽  
Vladislav V. Shimansky
Keyword(s):  
Chemical Composition ◽  
Globular Clusters ◽  
Dwarf Galaxies ◽  
Synthesis Method ◽  
Host Galaxies ◽  
Modeling And Analysis ◽  
Physical Conditions ◽  
Light Spectra ◽  
Medium Resolution ◽  
Key Points

AbstractThe study of ages, helium mass fraction (Y) and chemical composition of globular clusters in dwarf galaxies is important for understanding the physical conditions at the main evolutionary stages of the host galaxies and for constraining the build-up histories of large galaxies. We present the analysis of integrated-light spectra of 8 extragalactic and 20 Galactic globular clusters (GCs) using our population synthesis method. We calculate synthetic spectra of GCs according to the defined stellar mass functions using model atmospheres and stellar parameters ([Fe/H], Teff, and logg) set by theoretical isochrones. The main advantage of our method is the ability to determine not only chemical composition but also the age and mean Y in a cluster by modelling and analysis of Balmer absorption lines. The knowledge of Y and anomalies of light elements in star clusters is one of the key points for understanding the phenomenon of multiple stellar populations.

scholarly journals The Ghosts of Galaxies: Tidal Debris in Clusters

2004 ◽  
Vol 217 ◽  
pp. 70-76
Author(s):  
Michael D. Gregg ◽  
Michael J. West
Keyword(s):  
Globular Clusters ◽  
Surface Brightness ◽  
Large Scale ◽  
Dwarf Galaxies ◽  
Cluster Formation ◽  
X Ray ◽  
Cluster Evolution ◽  
Low Surface Brightness ◽  
Intergalactic Space ◽  
Formation And Evolution

Gravitational interactions in rich clusters can strip material from the outer parts of galaxies or even completely disrupt entire systems, giving rise to large scale, low surface brightness ghostly features stretching across intergalactic space. The nearby Coma and Centaurus clusters both have striking examples of galaxy ghosts, in the form of 100 kpc-long plumes of intergalactic debris. By searching HST archival images, we have found numerous other examples of galaxy ghosts in rich clusters at low redshift, evidence that galaxy destruction and recycling are ubiquitous, important in cluster formation and evolution, and continue to mold clusters at the present epoch. Many ghosts appear in X-ray bright clusters, perhaps signaling a connection with energetic subcluster mergers.The fate of such material has important ramifications for cluster evolution. Our new HST WFPC2 V & I images of a portion of the Centaurus plume reveal that it contains an excess of discrete objects with −12 < MV < −6, consistent with being globular clusters or smaller dwarf galaxies. This tidally liberated material is being recycled directly into the intracluster population of stars, dwarf galaxies, globular clusters, and gas, which may have been built largely from a multitude of similar events over the life of the cluster.

scholarly journals The Stellar Populations in Local Group Dwarf Galaxies

1995 ◽  
Vol 164 ◽  
pp. 175-180
Author(s):  
Abhijit Saha
Keyword(s):  
Star Formation ◽  
Globular Clusters ◽  
Formation Rate ◽  
Stellar System ◽  
Mass Function ◽  
Open Clusters ◽  
Initial Mass Function ◽  
Star Formation History ◽  
Physical Parameters ◽  
Stellar Content

The aim of the study of the populations in a stellar system is to understand and be able to describe the stellar content of a system in terms of physical parameters such as the age, star formation history, chemical enrichment history, initial mass function (IMF), environment, and dynamical history of the system. This is done given an understanding of stellar evolution and the ability to express the outcome in “observer parameters”, particularly a color-magnitude diagram (CMD), kinematics, and metallicity. From this perspective, the simplest systems are the galactic clusters and the globular clusters, where all the component stars are coeval and of the same metallicity. The current state of knowledge for these are discussed by others in this conference. We proceed to the next level of complexity (where metallicities are not necessarily all the same, and nor are the stars all coeval), and try to decompose their stellar content, particularly in terms of star formation rate and metallicity. In this regard the two classes of objects that come to mind are the dwarf spheroidals, and the dwarf irregulars. Both these classes of objects are more massive than the open clusters and globular clusters, and show evidence of complexities in their star formation histories, without being so convolved as to make such a study intractable. As we shall see, recent studies along these lines have presented some puzzling problems. Moreover, these are the smallest independent galaxies, and the study of star formation in these is likely to shed light on the history and formation of larger and more complex galaxies.

scholarly journals An Update on the ACS Virgo and Fornax Cluster Surveys

2007 ◽  
Vol 3 (S246) ◽  
pp. 377-386 ◽  
Author(s):  
Patrick Côté ◽  
Laura Ferrarese ◽  
Andrés Jordán ◽  
John P. Blakeslee ◽  
Chin-Wei Chen ◽  
...  
Keyword(s):  
Globular Clusters ◽  
Milky Way ◽  
Dwarf Galaxies ◽  
Hubble Space Telescope ◽  
Structural Parameters ◽  
Star Clusters ◽  
Early Type ◽  
Space Telescope ◽  
Fornax Cluster ◽  
Selection Of

AbstractWe present a brief update on the ACS Virgo and Fornax Cluster Surveys —Hubble Space Telescopeprograms to obtainACSimaging for 143 early-type galaxies in the two galaxy clusters nearest to the Milky Way. We summarize a selection of science highlights from the surveys as including new results on the central structure of early-type galaxies, the apparent continuity of photometric and structural parameters between dwarf and giant galaxies, and the properties of globular clusters, diffuse star clusters and ultra-compact dwarf galaxies.

scholarly journals Ages and chemical compositions of massive clusters in NGC147 and M31

2015 ◽  
Vol 12 (S316) ◽  
pp. 347-348
Author(s):  
Margarita Sharina ◽  
Vladislav Shimansky
Keyword(s):  
Globular Clusters ◽  
Light Element ◽  
Mass Function ◽  
Stellar Atmospheres ◽  
Element Abundance ◽  
Chemical Compositions ◽  
Element Abundances ◽  
Light Spectra ◽  
Medium Resolution ◽  
Red Giant

AbstractWe present estimates of ages, [Fe/H], helium content (Y) and abundances of C, N, Mg, Ca, and several other elements for the following globular clusters (GCs): GC7 in NGC147, and Mayall II, Mackey 1 and Mackey 6 in M31. Medium-resolution integrated-light spectra of the GCs were conducted with the 6m telescope. To derive the ages and abundances for the GCs we carried out their population synthesis using model stellar atmospheres, the Padova YZVAR isochrones and the Chabrier mass function. We compare the results with the corresponding data obtained using the same method for several massive Galactic GCs. We show that the differences in the light-element abundances between GCs with similar ages and metallicities may reach 0.5-0.6 dex. The corresponding differences for other elements are usually 2-3 times smaller. We suggest that at least partially the detected differences may be due to light-element abundance variations in the atmospheres of high-luminosity red giant branch stars as a consequence of the transportation of the produced elements to the surface layers.

scholarly journals The building blocks of the Milky Way halo using APOGEE and Gaia or Is the Galaxy a typical galaxy?

2019 ◽  
Vol 14 (S351) ◽  
pp. 170-173 ◽  
Author(s):  
Ricardo P. Schiavon ◽  
J. Ted Mackereth ◽  
Joel Pfeffer ◽  
Rob A. Crain ◽  
Jo Bovy
Keyword(s):  
Numerical Simulations ◽  
Globular Clusters ◽  
Milky Way ◽  
Galactic Halo ◽  
Dwarf Galaxies ◽  
Stellar Populations ◽  
Building Blocks ◽  
Stellar Content ◽  
The Galaxy ◽  
Milky Way Halo

AbstractWe summarise recent results from analysis of APOGEE/Gaia data for stellar populations in the Galactic halo, disk, and bulge, leading to constraints on the contribution of dwarf galaxies and globular clusters to the stellar content of the Milky Way halo. Intepretation of the extant data in light of cosmological numerical simulations suggests that the Milky Way has been subject to an unusually intense accretion history at z ≳ 1.5.

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