scholarly journals Inverting the dynamical evolution of globular clusters: clues to their origin

2015 ◽  
Vol 12 (S316) ◽  
pp. 214-221
Author(s):  
Mark Gieles ◽  
Poul Alexander
Keyword(s):  
Power Law ◽  
Globular Clusters ◽  
Milky Way ◽  
Dynamical Evolution ◽  
Mass Function ◽  
Initial Mass Function ◽  
Scaling Relations ◽  
Galactocentric Distance ◽  
Cluster Density ◽  
Bivariate Dependence

AbstractScaling relations for globular clusters (GC) differ from the scaling relations for pressure supported (elliptical) galaxies. In this contribution we discuss the relative importance of nature and nurture in the establishment of the scaling between cluster density (or radius), mass and Galactocentric distance for the Milky Way GCs. We show that energy diffusion by stellar encounters (i.e. two-body relaxation) is the dominant mechanism in shaping the bivariate dependence of density on mass and Galactocentric distance for GCs with masses ≲ 106M⊙, and it can not be excluded that GCs formed with similar scaling relations as the more massive ultra-compact dwarf galaxies (UCDs). To explore the initial properties that give rise to the distributions of these quantities, we developed a fast cluster evolution model (Evolve Me A Cluster of StarS, emacss) and use it in a hierarchical Bayesian framework to fit a parameterised model for the initial properties of Milky Way GCs to the observed present-day properties. The best-fit cluster initial mass function is substantially flatter (power-law with index − 0.6 ± 0.2) than what is observed for young massive clusters (YMCs) forming in the nearby Universe (power-law with index − 2). This result is driven by the metal-poor GCs, a slightly steeper CIMF is allowed when considering the metal-rich GCs separately (α ≃ −1.2 ± 0.4). If stellar mass loss and two-body relaxation in the Milky Way tidal field are the dominant disruption mechanisms, then GCs formed differently from YMCs.

scholarly journals On the temporal evolution of the stellar mass function of Galactic clusters

2009 ◽  
Vol 5 (S266) ◽  
pp. 81-86
Author(s):  
Guido De Marchi ◽  
Francesco Paresce ◽  
Simon Portegies Zwart
Keyword(s):  
Power Law ◽  
Globular Clusters ◽  
Dynamical Evolution ◽  
Mass Function ◽  
Stellar Mass ◽  
Initial Mass Function ◽  
Dissolution Time ◽  
Power Law Distribution ◽  
Galactic Clusters ◽  
Characteristic Mass

AbstractWe show that we can obtain a good fit to the present-day stellar-mass functions of a large sample of young and old Galactic clusters with a tapered Salpeter power-law distribution function with an exponential truncation of the form dN/dm ∝ mα [1 − exp(−m/mc)β]. The average value of the power-law index α is ~−2.2, very close to the Salpeter value of −2.3, while the characteristic mass, mc, is in the range 0.1–0.6M⊙ and does not seem to vary in any systematic way with the present cluster parameters such as metal abundance, total cluster mass or central concentration. However, the characteristic mass shows a remarkable correlation with the dynamical age of the cluster, namely mc/M⊙ ≃ 0.15 + 0.5 × t3/4dyn, where tdyn is the dynamical time, taken as the ratio of cluster age and dissolution time. The small scatter around this correlation is likely due to uncertainties on the estimated value of tdyn. We attribute the observed trend to the onset of mass segregation through two-body relaxation in a tidal environment, causing preferential loss of low-mass stars from the cluster and hence a drift of the characteristic mass towards higher values. If dynamical evolution is indeed at the origin of the observed trend, it seems plausible that globular clusters, now with mc ≃ 0.35M⊙, were born with a stellar mass function very similar to that measured today in the youngest Galactic clusters and with a value of mc around 0.15 M⊙. This is consistent with the absence of a turn-over in the mass function of the Galactic bulge down to the observational limit at ~0.2M⊙ and argues for the universality of the initial mass function of Population I and II stars.

scholarly journals Dynamical evolution of star clusters with top-heavy IMF

2019 ◽  
Vol 14 (S351) ◽  
pp. 447-450
Author(s):  
Hosein Haghi ◽  
Ghasem Safaei ◽  
Akram H. Zonoozi ◽  
Pavel Kroupa
Keyword(s):  
Globular Clusters ◽  
Milky Way ◽  
Massive Stars ◽  
Star Clusters ◽  
Dynamical Evolution ◽  
Mass Function ◽  
Initial Mass Function ◽  
Dissolution Time ◽  
Theoretical Studies ◽  
Cloud Density

AbstractSeveral observational and theoretical studies suggest that the initial mass function (IMF) slope for massive stars in globular clusters (GCs) depends on the initial cloud density and metallicity, such that the IMF becomes increasingly top-heavy with decreasing metallicity and increasing the gas density of the forming object. Using N-body simulations of GCs starting with a top-heavy IMF and undergo early gas expulsion within a Milky Way-like potential, we show how such a cluster would evolve. By varying the degree of top-heaviness, we calculate the dissolution time and the minimum cluster mass needed for the cluster to survive after 12 Gyr of evolution.

scholarly journals The Influence of Gas Expulsion on the Evolution of Star Clusters

2007 ◽  
Vol 3 (S246) ◽  
pp. 36-40
Author(s):  
H. Baumgardt ◽  
P. Kroupa
Keyword(s):  
Globular Clusters ◽  
Milky Way ◽  
Three Dimensional ◽  
Star Clusters ◽  
Dynamical Evolution ◽  
Mass Function ◽  
Star Cluster ◽  
Dissolution Mechanism ◽  
Large Set ◽  
Cluster Systems

AbstractWe present new results on the dynamical evolution and dissolution of star clusters due to residual gas expulsion and the effect this has on the mass function and other properties of star cluster systems. To this end, we have carried out a large set of N-body simulations, varying the star formation efficiency, gas expulsion time scale and strength of the external tidal field, obtaining a three-dimensional grid of models which can be used to predict the evolution of individual star clusters or whole star cluster systems by interpolating between our runs. When applied to the Milky Way globular cluster system, we find that gas expulsion is the main dissolution mechanism for star clusters, destroying about 80% of all clusters within a few 10s of Myers. Together with later dynamical evolution, it seems possible to turn an initial power-law mass function into a log-normal one with properties similar to what has been observed for the Milky Way globular clusters.

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 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 Is it possible to reconcile extragalactic IMF variations with a universal Milky Way IMF?

2019 ◽  
Vol 485 (4) ◽  
pp. 4852-4862 ◽  
Author(s):  
Dávid Guszejnov ◽  
Philip F Hopkins ◽  
Andrew S Graus
Keyword(s):  
Star Formation ◽  
Power Law ◽  
Milky Way ◽  
Extreme Environments ◽  
Mass Function ◽  
Initial Mass Function ◽  
Star Formation History ◽  
Arbitrary Power ◽  
Power Law Function ◽  
The Imf

Abstract One of the most robust observations of the stellar initial mass function (IMF) is its near-universality in the Milky Way and neighbouring galaxies. But recent observations of early-type galaxies can be interpreted to imply a ‘bottom-heavy’ IMF, while others of ultrafaint dwarfs could imply a ‘top-heavy’ IMF. This would impose powerful constraints on star formation models. We explore what sort of ‘cloud-scale’ IMF models could possibly satisfy these constraints. We utilize simulated galaxies that reproduce (broadly) the observed galaxy properties, while they also provide the detailed star formation history and properties of each progenitor star-forming cloud. We then consider generic models where the characteristic mass of the IMF is some arbitrary power-law function of progenitor cloud properties, along with well-known literature IMF models which scale with Jeans mass, ‘turbulent Bonnor–Ebert mass’, temperature, the opacity limit, metallicity, or the ‘protostellar heating mass’. We show that no IMF models currently in the literature – nor any model where the turnover mass is an arbitrary power-law function of a combination of cloud temperature/density/size/metallicity/velocity dispersion/magnetic field – can reproduce the claimed IMF variation in ellipticals or dwarfs without severely violating observational constraints in the Milky Way. Specifically, they predict too much variation in the ‘extreme’ environments of the Galaxy compared to that observed. Either the IMF varies in a more complicated manner, or alternative interpretations of the extragalactic observations must be explored.

scholarly journals Dynamical Evolution of Globular Clusters in Hierarchical Cosmology

2007 ◽  
Vol 3 (S246) ◽  
pp. 403-407
Author(s):  
Oleg Y. Gnedin ◽  
José L. Prieto
Keyword(s):  
Galaxy Formation ◽  
Power Law ◽  
Molecular Clouds ◽  
Globular Clusters ◽  
High Redshift ◽  
Dynamical Evolution ◽  
Mass Function ◽  
Giant Molecular Clouds ◽  
Log Normal ◽  
The Masses

AbstractWe probe the evolution of globular clusters that could form in giant molecular clouds within high-redshift galaxies. Numerical simulations demonstrate that the large and dense enough gas clouds assemble naturally in current hierarchical models of galaxy formation. These clouds are enriched with heavy elements from earlier stars and could produce star clusters in a similar way to nearby molecular clouds. The masses and sizes of the model clusters are in excellent agreement with the observations of young massive clusters. Do these model clusters evolve into globular clusters that we see in our and external galaxies? In order to study their dynamical evolution, we calculate the orbits of model clusters using the outputs of the cosmological simulation of a Milky Way-sized galaxy. We find that at present the orbits are isotropic in the inner 50 kpc of the Galaxy and preferentially radial at larger distances. All clusters located outside 10 kpc from the center formed in the now-disrupted satellite galaxies. The spatial distribution of model clusters is spheroidal, with a power-law density profile consistent with observations. The combination of two-body scattering, tidal shocks, and stellar evolution results in the evolution of the cluster mass function from an initial power law to the observed log-normal distribution.

scholarly journals Radial variation of the stellar mass functions in the globular clusters M15 and M30: clues of a non-standard IMF?

2020 ◽  
Vol 499 (2) ◽  
pp. 2390-2400
Author(s):  
M Cadelano ◽  
E Dalessandro ◽  
J J Webb ◽  
E Vesperini ◽  
D Lattanzio ◽  
...  
Keyword(s):  
Globular Clusters ◽  
Hubble Space Telescope ◽  
Dynamical Evolution ◽  
Mass Function ◽  
Initial Mass Function ◽  
Radial Variation ◽  
Wide Field ◽  
Data Set ◽  
Central Regions ◽  
Mass Segregation

ABSTRACT We exploit a combination of high-resolution Hubble Space Telescope and wide-field ESO-VLT observations to study the slope of the global mass function (αG) and its radial variation (α(r)) in the two dense, massive and post core-collapse globular clusters M15 and M30. The available data set samples the clusters’ main sequence down to ∼0.2 M⊙ and the photometric completeness allows the study of the mass function between 0.40 M⊙ and 0.75 M⊙ from the central regions out to their tidal radii. We find that both clusters show a very similar variation in α(r) as a function of clustercentric distance. They both exhibit a very steep variation in α(r) in the central regions, which then attains almost constant values in the outskirts. Such a behaviour can be interpreted as the result of long-term dynamical evolution of the systems driven by mass-segregation and mass-loss processes. We compare these results with a set of direct N-body simulations and find that they are only able to reproduce the observed values of α(r) and αG at dynamical ages (t/trh) significantly larger than those derived from the observed properties of both clusters. We investigate possible physical mechanisms responsible for such a discrepancy and argue that both clusters might be born with a non-standard (flatter/bottom-lighter) initial mass function.

Dynamical effects on the stellar mass function of multiple stellar populations in globular clusters

2019 ◽  
Vol 14 (S351) ◽  
pp. 346-349
Author(s):  
Enrico Vesperini ◽  
Jongsuk Hong ◽  
Jeremy J. Webb ◽  
Franca D’Antona ◽  
Annibale D’Ercole
Keyword(s):  
Globular Clusters ◽  
First Generation ◽  
Cluster Formation ◽  
Dynamical Evolution ◽  
Mass Function ◽  
Stellar Mass ◽  
Initial Mass Function ◽  
Cluster Center ◽  
Mixing Rate ◽  
Multiple Population

AbstractWe present a brief summary of the results of a study of the effects of dynamical evolution on the stellar mass function of multiple-population globular clusters. Theoretical studies have predicted that the process of multiple-population cluster formation results in a system in which second-generation (2G) stars are initially more centrally concentrated than first-generation (1G) stars. In the study presented here, we have explored the implications of the initial differences between the 2G and 1G structural properties for the evolution of the local (measured at different distances from a cluster center) and global mass function. We have studied both systems in which 1G and 2G stars start with the same initial mass function (IMF) and systems in which 1G and 2G stars have different IMFs. Finally we have explored the evolution of the spatial mixing and found that the multiscale nature of the clusters studied leads to a dependence of the mixing rate on the stellar mass.

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