scholarly journals Young massive star clusters: achievements and challenges

2009 ◽  
Vol 5 (S266) ◽  
pp. 49-57 ◽  
Author(s):  
Richard de Grijs
Keyword(s):  
Massive Star ◽  
Initial Conditions ◽  
Cluster Formation ◽  
Star Clusters ◽  
Dynamical Evolution ◽  
Mass Function ◽  
Large Magellanic Cloud ◽  
Initial Mass Function ◽  
Ongoing Research ◽  
Mass Segregation

AbstractIn spite of significant recent and ongoing research efforts, most of the early evolution and long-term fate of young massive star clusters remain clouded in uncertainties. Here, I discuss our understanding of the initial conditions of star cluster formation and the importance of initial substructure for the subsequent dynamical-evolution and mass-segregation timescales. I also assess our current understanding of the (initial) binary fraction in star clusters and the shape of the stellar initial mass function at the low-mass end in the low-metallicity environment of the Large Magellanic Cloud. Finally, I question the validity of our assumptions leading to dynamical cluster mass estimates. I conclude that it seems imperative that observers, modellers and theorists combine efforts and exchange ideas and data freely for the field to make a major leap forward.

scholarly journals The Mass Function of Young Star Clusters in our Galaxy and Nearby Galaxies: Is It Universal?

2002 ◽  
Vol 207 ◽  
pp. 515-524
Author(s):  
Ram Sagar
Keyword(s):  
Star Clusters ◽  
Dynamical Evolution ◽  
Mass Function ◽  
Young Star ◽  
Initial Mass Function ◽  
Galactocentric Distance ◽  
Photometric Observations ◽  
Nearby Galaxies ◽  
Mass Segregation ◽  
Young Star Clusters

Mass functions (MFs) derived from photometric observations of young star clusters of our Galaxy, the Magellanic Clouds (MCs), M31 and M33 have been used to investigate the question of universality of the initial mass function and presence of mass segregation in these systems. Observational determination of the MF slope of young star clusters have an inherent uncertainty of at least ∼ 1.0 dex in the Milky Way and of ∼ 0.4 dex in the MCs. There is no obvious dependence of the MF slope on either galactocentric distance or age of the young star clusters or on the spatial concentration of the stars formed or on the galactic characteristics including metallicity. Effects of mass segregation have been observed in a good number of young stellar groups of our Galaxy and MCs. As their ages are much smaller than their dynamical evolution times, star formation processes seem to be responsible for the observed mass segregation in them.

scholarly journals The life and death of star clusters

2006 ◽  
Vol 2 (S237) ◽  
pp. 222-229 ◽  
Author(s):  
B. C. Whitmore
Keyword(s):  
Massive Star ◽  
Cluster Formation ◽  
Star Clusters ◽  
Mass Function ◽  
Initial Mass Function ◽  
Merging Galaxies ◽  
Life And Death ◽  
Large Numbers ◽  
Super Star Clusters ◽  
Massive Clusters

AbstractIt is generally believed that most stars are born in groups and clusters, rather than in the field. It has also been demonstrated that merging galaxies produce large numbers of young massive star clusters, sometimes called super star clusters. Hence, understanding what triggers the formation of these young massive clusters may provide important information about what triggers the formation of stars in general. In recent years it has become apparent that most clusters do not survive more than ≈10 Myr (i.e., “infant mortality”). Hence, it is just as important to understand the disruption of star clusters as it is to understand their formation if we want to understand the demographics of both star clusters and field stars. This talk will first discuss what triggers star cluster formation in merging galaxies (primarily in the Antennae galaxies), will then demonstrate that most of the faint objects detected in the Antennae are clusters rather than individual stars (which shows that the initial mass function was a power law rather than a Gaussian), and will then outline a general framework designed to empirically fit observations of both star clusters and field stars in a wide variety of galaxies from mergers to quiescent spirals.

scholarly journals Dynamical Evolution of Mass-Segregated Clusters

2007 ◽  
Vol 3 (S246) ◽  
pp. 181-185
Author(s):  
Enrico Vesperini ◽  
Steve McMillan ◽  
Simon Portegies Zwart
Keyword(s):  
Mass Loss ◽  
Density Profile ◽  
Stellar Evolution ◽  
Star Clusters ◽  
Dynamical Evolution ◽  
Mass Function ◽  
Initial Mass Function ◽  
Initial Evolution ◽  
Stellar Initial Mass Function ◽  
Mass Segregation

AbstractWe present the results of a survey of N-body simulations aimed at exploring the implications of primordial mass segregation on the dynamical evolution of star clusters. We show that, in a mass-segregated cluster, the effect of early mass loss due to stellar evolution is, in general, more destructive than for an unsegregated cluster with the same density profile and leads to shorter lifetimes, a faster initial evolution toward less concentrated structure and flattening of the stellar initial mass function.

scholarly journals The elephant in the room: the importance of the details of massive star formation in molecular clouds

2019 ◽  
Vol 488 (2) ◽  
pp. 2970-2975 ◽  
Author(s):  
Michael Y Grudić ◽  
Philip F Hopkins
Keyword(s):  
Star Formation ◽  
Molecular Clouds ◽  
Massive Star ◽  
Initial Conditions ◽  
Mass Function ◽  
Initial Mass Function ◽  
Giant Molecular Clouds ◽  
Massive Star Formation ◽  
Average Mass ◽  
Sampling Schemes

Abstract Most simulations of galaxies and massive giant molecular clouds (GMCs) cannot explicitly resolve the formation (or predict the main-sequence masses) of individual stars. So they must use some prescription for the amount of feedback from an assumed population of massive stars (e.g. sampling the initial mass function, IMF). We perform a methods study of simulations of a star-forming GMC with stellar feedback from UV radiation, varying only the prescription for determining the luminosity of each stellar mass element formed (according to different IMF sampling schemes). We show that different prescriptions can lead to widely varying (factor of ∼3) star formation efficiencies (on GMC scales) even though the average mass-to-light ratios agree. Discreteness of sources is important: radiative feedback from fewer, more-luminous sources has a greater effect for a given total luminosity. These differences can dominate over other, more widely recognized differences between similar literature GMC-scale studies (e.g. numerical methods, cloud initial conditions, presence of magnetic fields). Moreover the differences in these methods are not purely numerical: some make different implicit assumptions about the nature of massive star formation, and this remains deeply uncertain in star formation theory.

scholarly journals Young Star Clusters in the LMC

1992 ◽  
Vol 45 (4) ◽  
pp. 407
Author(s):  
KC Freeman
Keyword(s):  
Mass Loss ◽  
Globular Clusters ◽  
Star Clusters ◽  
Dynamical Evolution ◽  
Mass Function ◽  
Young Star ◽  
Stellar Mass ◽  
Initial Mass Function ◽  
Initial Mass ◽  
Young Star Clusters

The young globular star clusters in the LMC offer us insights into the formation and early dynamical evolution of globular clusters which are unobtainable from the old globular clusters in our Galaxy. Because these young clusters are so young and populous, they provide an opportunity to measure the upper end of the initial mass function by direct means and also through the dynamical effects of stellar mass loss on the structure of the clusters.

scholarly journals Global survey of star clusters in the Milky Way

2018 ◽  
Vol 614 ◽  
pp. A22 ◽  
Author(s):  
A. E. Piskunov ◽  
A. Just ◽  
N. V. Kharchenko ◽  
P. Berczik ◽  
R.-D. Scholz ◽  
...  
Keyword(s):  
Milky Way ◽  
Cluster Formation ◽  
Formation Rate ◽  
Age Distribution ◽  
Star Clusters ◽  
Mass Function ◽  
Spatial Variations ◽  
Initial Mass Function ◽  
Initial Mass ◽  
Formation History

Context. The all-sky Milky Way Star Clusters (MWSC) survey provides uniform and precise ages, along with other relevant parameters, for a wide variety of clusters in the extended solar neighbourhood. Aims. In this study we aim to construct the cluster age distribution, investigate its spatial variations, and discuss constraints on cluster formation scenarios of the Galactic disk during the last 5 Gyrs. Methods. Due to the spatial extent of the MWSC, we have considered spatial variations of the age distribution along galactocentric radius RG, and along Z-axis. For the analysis of the age distribution we used 2242 clusters, which all lie within roughly 2.5 kpc of the Sun. To connect the observed age distribution to the cluster formation history we built an analytical model based on simple assumptions on the cluster initial mass function and on the cluster mass-lifetime relation, fit it to the observations, and determined the parameters of the cluster formation law. Results. Comparison with the literature shows that earlier results strongly underestimated the number of evolved clusters with ages t ≳ 100 Myr. Recent studies based on all-sky catalogues agree better with our data, but still lack the oldest clusters with ages t ≳ 1 Gyr. We do not observe a strong variation in the age distribution along RG, though we find an enhanced fraction of older clusters (t > 1 Gyr) in the inner disk. In contrast, the distribution strongly varies along Z. The high altitude distribution practically does not contain clusters with t < 1 Gyr. With simple assumptions on the cluster formation history, the cluster initial mass function and the cluster lifetime we can reproduce the observations. The cluster formation rate and the cluster lifetime are strongly degenerate, which does not allow us to disentangle different formation scenarios. In all cases the cluster formation rate is strongly declining with time, and the cluster initial mass function is very shallow at the high mass end.

scholarly journals The dynamical importance of binary systems in young massive star clusters

2015 ◽  
Vol 12 (S316) ◽  
pp. 222-227
Author(s):  
Richard de Grijs ◽  
Chengyuan Li ◽  
Aaron M. Geller
Keyword(s):  
Binary Systems ◽  
Hubble Space Telescope ◽  
Star Clusters ◽  
Dynamical Evolution ◽  
Large Magellanic Cloud ◽  
Cluster Center ◽  
Dynamical Mass ◽  
Mass Segregation ◽  
Cluster Cores

AbstractCharacterization of the binary fractions in star clusters is of fundamental importance for many fields in astrophysics. Observations indicate that the majority of stars are found in binary systems, while most stars with masses greater than 0.5M⊙ are formed in star clusters. In addition, since binaries are on average more massive than single stars, in resolved star clusters these systems are thought to be good tracers of (dynamical) mass segregation. Over time, dynamical evolution through two-body relaxation will cause the most massive objects to migrate to the cluster center, while the relatively lower-mass objects remain in or migrate to orbits at greater radii. This process will globally dominate a cluster’s stellar distribution. However, close encounters involving binary systems may disrupt ‘soft’ binaries. This process will occur more frequently in a cluster’s central, dense region than in its periphery, which may mask the effects of mass segregation. Using high resolution Hubble Space Telescope observations, combined with sophisticated N-body simulations, we investigate the radial distributions of the main-sequence binary fractions in massive young Large Magellanic Cloud star clusters. We show that binary disruption may play an important role on very short timescales, depending on the environmental conditions in the cluster cores. This may lead to radial binary fractions that initially decline in the cluster centers, which is contrary to the effects expected from dynamical mass segregation.

scholarly journals The massive star Initial Mass function

2003 ◽  
Vol 212 ◽  
pp. 642-651 ◽  
Author(s):  
Daniel Schaerer
Keyword(s):  
Massive Star ◽  
Current Knowledge ◽  
Star Clusters ◽  
Mass Function ◽  
Initial Mass Function ◽  
H Ii Regions ◽  
Star Forming ◽  
Star Forming Regions ◽  
Super Star Clusters ◽  
The Imf

We review our current knowledge on the IMF in nearby environments, massive star forming regions, super star clusters, starbursts and alike objects from studies of integrated light, and discuss the various techniques used to constrain the IMF. In most cases, including UV-optical studies of stellar features and optical-IR analysis of nebular emission, the data is found to be compatible with a ‘universal’ Salpeter-like IMF with a high upper mass cut-off over a large metallicity range. In contrast, near-IR observations of nuclear starbursts and LIRG show indications of a lowerMupand/or a steeper IMF slope, for which no alternate explanation has yet been found. Also, dynamical mass measurements of seven super star clusters provide so far no simple picture of the IMF. Finally, we present recent results of a direct stellar probe of the upper end of the IMF in metal-rich H ii regions, showing no deficiency of massive stars at high metallicity, and determining a lower limit ofMup≳ 60 – 90 M⊙.

Young, old, massive: Steps to understanding globular cluster formation

2019 ◽  
Vol 14 (S351) ◽  
pp. 3-12
Author(s):  
William E. Harris
Keyword(s):  
Galaxy Evolution ◽  
Globular Clusters ◽  
Massive Star ◽  
Cluster Formation ◽  
Star Clusters ◽  
Dynamical Evolution ◽  
Mass Range ◽  
High Mass ◽  
Theoretical Modelling ◽  
Giant Molecular Clouds

AbstractOn observational grounds we now know a huge amount about the characteristics of massive star clusters in galaxies of all types, from the smallest dwarfs to the most massive giants and even into the Intracluster Medium. The old globular clusters (GCs) in particular exhibit a high degree of uniformity across all these environments in their physical properties including scale size, luminosity distribution, metallicity distribution, and age. As survivors of a long period of dynamical evolution, they are “unusual, but not special” among star clusters.The past few years have seen major advances in theoretical modelling that are starting to reveal how these massive star clusters formed in the early stages of galaxy evolution. Several suites of models point to their emergence in GMCs (Giant Molecular Clouds), which provide the turbulent big reservoirs of gas within which star clusters can be built. At cluster masses ∼105M⊙ and above, clusters form hierarchically through a nearly equal combination of direct gas accretion, and mergers with smaller clusters scattered throughout the GMC. GCs and YMCs (young massive clusters) in this high mass range should therefore be composite systems right from birth. To make such high-mass clusters, host GMCs of ∼107M⊙ are needed, and these are most commonly found in galaxies at redshifts z ≳ 2.

scholarly journals Mass to light ratios of Large Magellanic Cloud clusters

1991 ◽  
Vol 148 ◽  
pp. 191-192 ◽  
Author(s):  
Mario Mateo ◽  
Douglas Welch ◽  
Phil Fischer
Keyword(s):  
Globular Clusters ◽  
Massive Star ◽  
Large Range ◽  
Temporal Evolution ◽  
Star Clusters ◽  
Dynamical Evolution ◽  
Large Magellanic Cloud ◽  
Magellanic Cloud ◽  
Cloud Clusters ◽  
Large Numbers

The massive star clusters of the Large Magellanic Cloud (LMC) are ideal laboratories for the study of the dynamical evolution of rich stellar systems. Not only do they contain large numbers of stars but, unlike the Galactic globular clusters, LMC clusters span a large range in age. Here we describe a continuing project to determine the temporal evolution of the mass-to-light (M/L) ratio of LMC clusters and present some preliminary results.

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