[PDF] High Resolution Analysis Of Extragalactic Globular Clusters eBook

Author : Ashley Chutter
Publisher :
Page : pages
File Size : 18,11 MB
Release : 2008
Category :
ISBN :

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High resolution spectra have been analyzed for two and three stars respectively in the candidate extragalactic globular clusters, NGC 5024 and NGC 5466, with the High-Resolution Spectrograph on the 9.2 m Hobby-Eberly Telescope. The goal of this investigation is to evaluate the proposed extragalactic origins of these two globular clusters. Evidence of a tidal tail in NGC 5466 (Belokurov et al., 2006) and the association of NGC 5024 with the Sagittarius stream (Martinez-Delgado et al., 2004) targeted the clusters as likely remnants of recent accretion events and thus potentially of extragalactic origin. Determination of their chemical abundance patterns could provide unique evidence to either support or dispute these claims. NGC 5024 has been associated with a proposed wrap in the Sagittarius stream which could be supported if the chemistry of NGC 5024 is similar to other clusters associated with the stream. NGC 5466 has the longest tidal tail known, which hints at an origin in a now dispersed dwarf spheroidal galaxy. Additional evidence for these clusters' capture origins has been compiled by Yoon & Lee (2002), demonstrating that these two low metallicity clusters, along with five others, are aligned in a single highly inclined plane in the outer halo. Confirmation that these clusters are remnants of dwarf galaxies would support a Galactic history which includes recent accretion events. Such evidence may bolster the cold dark matter hierarchical clustering scenario, which postulates the presence of a significant amount of substructure in the Milky Way. Unfortunately, at the metallicity of the target clusters ([Fe/H] = -1.9), the chemical distinction between Galactic stars and known dSph stars is not significant. The low [alpha/Fe] of dSph stars seen at higher metallicity is not apparent at [Fe/H] = -1.9 in either Galactic or dSph stars. Aside from a few mild discrepancies, NGC 5024 and NGC 5466 appear chemically similar to the Galactic field stars and globular clusters compiled by Pritzl et al. (2005). A moderate enhancement in the [Ba/Y] ratios relative to the halo field stars is the only positively detected chemical signature that is typically observed in dSph stars. Comparisons with Galactic GCs of similar age, metallicity and horizontal branch morphology (NGC 2298, NGC 6397 and NGC 5897) reveal a few other differences, but these could be attributed to systematic effects in the different analysis techniques. Although NGC 5024 has a similar metallicity to the GC Arp 2 that was stripped from the merging Sagittarius dwarf, neither Arp 2 (Mottini et al., 2008) nor the clusters in this study show any particularly unusual chemical abundance patterns. Thus, no conclusive evidence in support of or in opposition to the target clusters' proposed extragalactic origins has been discovered.

Author : Zachary Grove Jennings
Publisher :
Page : 272 pages
File Size : 31,29 MB
Release : 2017
Category :
ISBN : 9780355131499

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Globular Clusters (GCs) are powerful tools for understanding the formation of galaxies. GCs are located in the halos of galaxies and, due to their age and density, have borne witness to the major formation events of a galaxy's lifetime. One may study these objects using a wide array of techniques and datasets, including wide-field ground-based imaging, deep space-based imaging, and spectroscopy. All approaches involve tradeoffs, and in this work we consider a variety of ways to study GC systems in imaging data. We examine a wide-field HST/ACS mosaic of the nearby lenticular galaxy NGC 3115, selecting a high-quality GC sample using the superior resolution of the ACS data. We find strong color bimodality in the GC system of NGC 3115 and examine a number of trends in the properties of the GC system. Next, we consider the situation where one is limited to ground-based imaging, where contaminants to the GC population are a major concern. We detail a novel statistical methodology in which we treat the GC population and the contaminant population as a mixture model, and evaluate the model in a Bayesian context. We demonstrate the performance of the model on mock data, and note some areas where current analysis of GC systems may be missing information using traditional selection techniques. We also apply this Bayesian methodology to a subset of SLUGGS survey galaxies with high-quality photometry from either the MegaCam instrument on the Canada France-Hawaii Telescope or the SuprimeCam instrument on the Subaru Telescope. In most cases, the mixture model recovers the GC system well, often finding the traditional bimodality and providing well-calibrated statistical uncertainties for the global parameters of the GC system. Finally, we examine the object NGC 3628 UCD1, a star cluster slightly more massive than the largest GCs. We identify that UCD1 is located in a stellar stream around the galaxy NGC 3628, and therefore is in the process of being accreted. We characterize UCD1 both in wide-field SuprimeCam imaging and in Keck/ESI spectroscopy, and identify a number of interesting parallels between UCD1 and omegaCen, the largest Milky Way GC.

Author : Markus Kissler-Patig
Publisher : Springer Science & Business Media
Page : 382 pages
File Size : 20,27 MB
Release : 2003-07-21
Category : Science
ISBN : 9783540404729

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Dramatic progress is a trademark of the recent study of globular cluster systems. Considerations about the formation and evolution compose the first chapter, followed by a chapter on young star clusters. Then come four chapters reviewing the globular cluster system of early-type, late-type and dwarf galaxies, as well as of groups of galaxies. One chapter is dedicated to stellar population models and their applications to the field. Finally a chapter reviews the kinematics of galaxies derived from globular cluster systems and another their role in the context of galaxy formation and evolution studies. As a whole, the book gives an up-to-date view of the field at the beginning of the new decade, which will without doubt again bring significant progress in our understanding of globular cluster systems and galaxy formation and evolution.

Author : Tom Richtler
Publisher : Springer Science & Business Media
Page : 448 pages
File Size : 13,95 MB
Release : 2008-11-23
Category : Science
ISBN : 3540769617

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The principal question of whether and how globular clusters can contribute to a better understanding of galaxy formation and evolution is perhaps the main driving force behind the overall endeavour of studying globular cluster systems. Naturally, this splits up into many individual problems. The objective of the Joint ESO-FONDAP Workshop on Globular Clusters - Guides to Galaxies was to bring together researchers, both observational and theoretical, to present and discuss the most recent results. Topics covered in these proceedings are: internal dynamics of globular clusters and interaction with host galaxies (tidal tails, evolution of cluster masses), accretion of globular clusters, detailed descriptions of nearby cluster systems, ultracompact dwarfs, formations of massive clusters in mergers and elsewhere, the ACS Virgo survey, galaxy formation and globular clusters, dynamics and kinematics of globular cluster systems and dark matter-related problems. With its wide coverage of the topic, this book constitutes a valuable reference of the scientific knowledge of the field.

Author : Erin Marie O'Malley
Publisher :
Page : 390 pages
File Size : 42,59 MB
Release : 2017
Category :
ISBN :

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In recent years, evidence has grown for the existence of multiple stellar populations in globular clusters (GCs). However, questions remain regarding the nature of these populations. Photometric observations clearly show discrete populations while spectroscopic observations seem to show a continuous spread. This dissertation provides steps to better understanding GCs and the complexities associated with their evolution. Calibration of stellar evolution models at low metallicity is necessary for comparison to GCs. Accurate abundances of metal-poor subdwarfs are determined and used in this calibration. A Monte Carlo analysis is then performed in order to determine accurate distances, absolute ages, and integrated orbital trajectories for 24 GCs. These results are of critical importance as they not only incorporate the observational uncertainty, but also the uncertainty incurred by the models themselves. Lastly, high resolution spectra of three GCs (NGC 6681, NGC 6584 and NGC 7099) are obtained for a detailed abundance analysis of red giant branch stars. The high resolution and signal-to-noise achieved in these observations allows for the discovery of a statistically significant Na-O anticorrelation in all three clusters, the populations of which agree with those from photometric observations. Although we cannot determine precisely the nature of the polluters that were the predecessors to the enhanced populations, we do know that both s-process and r-process mechanisms contributed to the evolution and these results can be used to help constrain future models of GC polluter candidates

Author : Santi Cassisi
Publisher : John Wiley & Sons
Page : 506 pages
File Size : 44,32 MB
Release : 2013-08-29
Category : Science
ISBN : 3527665544

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The book discusses the theoretical path to decoding the information gathered from observations of old stellar systems. It focuses on old stellar systems because these are the fossil record of galaxy formation and provide invaluable information ont he evolution of cosmic structures and the universe as a whole. The aim is to present results obtained in the past few years for theoretical developments in low mass star research and in advances in our knowledge of the evolution of old stellar systems. A particularly representative case is the recent discovery of multiple stellar populations in galactic globular clusters that represents one of the hottest topics in stellar and galactic astrophysics and is discussed in detail. Santi Cassisi has authored about 270 scientific papers, 150 of them in peer-reviewed journals, and the title Evolution of Stars and Stellar Populations.