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1
Kroupa, Pavel. "Star-cluster formation and evolution." Proceedings of the International Astronomical Union 2, S237 (August 2006): 230–37. http://dx.doi.org/10.1017/s1743921307001524.
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AbstractStar clusters are observed to form in a highly compact state and with low star-formation efficiencies, and only 10 per cent of all clusters appear to survive to middle- and old-dynamical age. If the residual gas is expelled on a dynamical time the clusters disrupt. Massive clusters may then feed a hot kinematical stellar component into their host-galaxy's field population thereby thickening galactic disks, a process that theories of galaxy formation and evolution need to accommodate. If the gas-evacuation time-scale depends on cluster mass, then a power-law embedded-cluster mass function may transform within a few dozen Myr to a mass function with a turnover near 105M, thereby possibly explaining this universal empirical feature. Discordant empirical evidence on the mass function of star clusters leads to the insight that the physical processes shaping early cluster evolution remain an issue of cutting-edge research.
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Parmentier, Geneviève. "Early dynamical evolution of star cluster systems." Proceedings of the International Astronomical Union 5, S266 (August 2009): 87–94. http://dx.doi.org/10.1017/s1743921309990913.
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AbstractViolent relaxation, the protocluster dynamical response to the expulsion of its residual star-forming gas, is a short albeit crucial episode in the evolution of star clusters and star cluster systems. Because it is heavily driven by cluster-formation and environmental conditions, it is a potentially highly rewarding phase in terms of probing star formation and galaxy evolution. In this contribution, I review how cluster-formation and environmental conditions affect the shape of the young cluster mass function and the relation between the present star-formation rate of galaxies and the mass of their young, most massive cluster.
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Vesperini, Enrico. "Star cluster dynamics." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 368, no. 1913 (February 28, 2010): 829–49. http://dx.doi.org/10.1098/rsta.2009.0260.
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Dynamical evolution plays a key role in shaping the current properties of star clusters and star cluster systems. A detailed understanding of the effects of evolutionary processes is essential to be able to disentangle the properties that result from dynamical evolution from those imprinted at the time of cluster formation. In this review, I focus my attention on globular clusters, and review the main physical ingredients driving their early and long-term evolution, describe the possible evolutionary routes and show how cluster structure and stellar content are affected by dynamical evolution.
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Zepf, Stephen E. "The Formation and Evolution of Star Clusters and Galaxies." Highlights of Astronomy 13 (2005): 347–49. http://dx.doi.org/10.1017/s1539299600015938.
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AbstractThis paper addresses the questions of what we have learned about how and when dense star clusters form, and what studies of star clusters have revealed about galaxy formation and evolution. One important observation is that globular clusters are observed to form in galaxy mergers and starbursts in the local universe, which both provides constraints on models of globular cluster formation, and suggests that similar physical conditions existed when most early-type galaxies and their globular clusters formed in the past. A second important observation is that globular cluster systems typically have bimodal color distributions. This was predicted by merger models, and indicates an episodic formation history for elliptical galaxies. A third and very recent result is the discovery of large populations of intermediate age globular clusters in several elliptical galaxies through the use of optical to near-infrared colors. These provide an important link between young cluster systems observed in starbursts and mergers and old cluster systems. This continuum of ages of the metal-rich globular cluster systems also indicates that there is no special age or epoch for the formation of the metal-rich globular clusters, which comprise about half of the cluster population. The paper concludes with a brief discussion of recent results on the globular cluster – low-mass X-ray binary connection.
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Gieles, Mark. "Star cluster disruption." Proceedings of the International Astronomical Union 5, S266 (August 2009): 69–80. http://dx.doi.org/10.1017/s1743921309990895.
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AbstractStar clusters are often used as tracers of major star-formation events in external galaxies as they can be studied out to much greater distances than individual stars. It is vital to understand their evolution if they are used to derive, for example, the star-formation history of their host galaxy. More specifically, we want to know how cluster lifetimes depend on their environment and on structural properties such as mass and radius. This review presents a theoretical overview of the early evolution of star clusters and the consequent long-term survival chances. It is suggested that clusters forming with initial densities of ≳104 M⊙ pc−3 survive the gas expulsion, or ‘infant mortality,’ phase. At ~10Myr, they are bound and have densities of ~103±1 M⊙ pc−3. After this time, they are stable against expansion through stellar evolution, encounters with giant molecular clouds and will most likely survive for another Hubble time if they are located in a moderate tidal field. Clusters with lower initial densities (≲100 M⊙ pc−3) will disperse into the field within a few 10s of Myrs. Some discussion is given on how extragalactic star cluster populations, and especially their age distributions, can be used to gain insight into disruption.
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Clarke, C. J. "Star Formation in Large N Clusters." Symposium - International Astronomical Union 207 (2002): 489–98. http://dx.doi.org/10.1017/s0074180900224297.
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We focus here on the gas dynamics of cluster formation and the early stellar dynamical evolution of young clusters. We point out that the condition that a cloud can fragment into a large number of pieces places rather particular constraints on its initial state; we also review the processes that shape the stellar IMF in cluster formation simulations. We show how N-body calculations and observations can be combined to discover the properties of clusters at the point at which they first become stellar dynamical (as opposed to gas dynamical systems). Finally, we touch on the question of how proto-cluster clouds are assembled and reopen the issue of whether dark matter may play a role in globular cluster formation.
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Fensch, Jérémy, Pierre-Alain Duc, Médéric Boquien, Debra M. Elmegreen, Bruce G. Elmegreen, Frédéric Bournaud, Elias Brinks, et al. "Massive star cluster formation and evolution in tidal dwarf galaxies." Astronomy & Astrophysics 628 (August 2019): A60. http://dx.doi.org/10.1051/0004-6361/201834403.
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Context. The formation of globular clusters remains an open debate. Dwarf starburst galaxies are efficient at forming young massive clusters with similar masses as globular clusters and may hold the key to understanding their formation. Aims. We study star cluster formation in a tidal debris, including the vicinity of three tidal dwarf galaxies, in a massive gas-dominated collisional ring around NGC 5291. These dwarfs have physical parameters that differ significantly from local starbursting dwarfs. They are gas rich, highly turbulent, their gas metallicity is already enriched up to half solar values, and they are expected to be free of dark matter. The aim is to study massive star cluster formation in this as yet unexplored type of environment. Methods. We used imaging from the Hubble Space Telescope using broadband filters that cover the wavelength range from the near-ultraviolet to the near-infrared. We determined the masses and ages of the cluster candidates by using the spectral energy distribution-fitting code CIGALE. We considered age-extinction degeneracy effects on the estimation of the physical parameters. Results. We find that the tidal dwarf galaxies in the ring of NGC 5291 are forming star clusters with an average efficiency of ∼40%, which is similar to blue compact dwarf galaxies. We also find massive star clusters for which the photometry suggests that they were formed at the very birth of the tidal dwarf galaxies. These clusters have survived for several hundred million years. Therefore our study shows that extended tidal dwarf galaxies and compact clusters may be formed simultaneously. In the specific case observed here, the young star clusters are not massive enough to survive for a Hubble time. However, it may be speculated that similar objects at higher redshift, with a higher star formation rate, might form some of the long-lived globular clusters.
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Lada, Charles J. "The physics and modes of star cluster formation: observations." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 368, no. 1913 (February 28, 2010): 713–31. http://dx.doi.org/10.1098/rsta.2009.0264.
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Stellar clusters are born in cold and dusty molecular clouds and the youngest clusters are embedded to various degrees in a dusty dark molecular material. Such embedded clusters can be considered protocluster systems. The most deeply buried examples are so heavily obscured by dust that they are only visible at infrared wavelengths. These embedded protoclusters constitute the nearest laboratories for a direct astronomical investigation of the physical processes of cluster formation and early evolution. I review the present state of empirical knowledge concerning embedded-cluster systems and discuss the implications for understanding their formation and subsequent evolution to produce bound stellar clusters.
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Anders, Peter, Uta Fritze –. v. Alvensleben, and Richard de Grijs. "Young Star Clusters: Progenitors of Globular Clusters!?" Highlights of Astronomy 13 (2005): 366–68. http://dx.doi.org/10.1017/s1539299600015987.
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AbstractStar cluster formation is a major mode of star formation in the extreme conditions of interacting galaxies and violent starbursts. Young clusters are observed to form in a variety of such galaxies, a substantial number resembling the progenitors of globular clusters in mass and size, but with significantly enhanced metallicity. From studies of the metal-poor and metal-rich star cluster populations of galaxies, we can therefore learn about the violent star formation history of these galaxies, and eventually about galaxy formation and evolution. We present a new set of evolutionary synthesis models of our GALEV code, with special emphasis on the gaseous emission of presently forming star clusters, and a new tool to compare extensive model grids with multi-color broad-band observations to determine individual cluster masses, metallicities, ages and extinction values independently. First results for young star clusters in the dwarf starburst galaxy NGC 1569 are presented. The mass distributions determined for the young clusters give valuable input to dynamical star cluster system evolution models, regarding survival and destruction of clusters. We plan to investigate an age sequence of galaxy mergers to see dynamical destruction effects in process.
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Randriamanakoto, Zara, and Petri Väisänen. "Young massive clusters in Arp 299." Proceedings of the International Astronomical Union 14, S351 (May 2019): 143–46. http://dx.doi.org/10.1017/s1743921319007701.
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AbstractBecause of their young ages and compact densities, young massive star clusters (YMCs) are widely considered as potential proto-globular clusters. They are ubiquitous in environments with ongoing star formation activity such as interacting luminous infrared galaxies. To determine the galactic environmental effects on the star cluster formation and evolution, we study the YMC population of Arp 299 (NGC 3690E/NGC 3690W) using data taken with the HST WFC3/UVIS camera. By fitting the multiband photometry with the Yggdrasil models, we derive the star cluster masses, ages and extinction. While the cluster mass-galactocentric radius relation of NGC 3690E indicates that there could be an influence of the gas density distribution on the cluster formation, the age distribution of the western component suggests that YMCs in that galaxy endure stronger disruption mechanisms. With a cluster formation efficiency of 19 percent, star formation happening in bound clusters in Arp 299 is 3–5 times higher than that of a typical normal spiral.
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Baumgardt, H., and P. Kroupa. "The Influence of Gas Expulsion on the Evolution of Star Clusters." Proceedings of the International Astronomical Union 3, S246 (September 2007): 36–40. http://dx.doi.org/10.1017/s1743921308015238.
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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.
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Grijs, Richard de. "“Super” Star Clusters." Highlights of Astronomy 13 (2005): 363–65. http://dx.doi.org/10.1017/s1539299600015975.
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AbstractThe production of “super star clusters” (SSCs; luminous, compact star clusters) seems to be a hallmark of intense star formation, particularly in interacting and star-burst galaxies. Their sizes, luminosities, and mass estimates are entirely consistent with what is expected for young Milky Way-type globular clusters (GCs). SSCs are important because of what they can tell us about GC formation and evolution (e.g., initial characteristics and early survival rates). They are also of prime importance as probes of the formation and (chemical) evolution of their host galaxies, and of the initial mass function in the extreme environments required for cluster formation. Recent evidence lends support to the scenario that Milky Way-type GCs (although more metal rich), which were once thought to be the oldest building blocks of galaxies, are still forming today.
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Smith, R., J. I. Davies, and A. Nelson. "Tidal Influences on Cluster Dwarf Evolution." Proceedings of the International Astronomical Union 3, S244 (June 2007): 378–80. http://dx.doi.org/10.1017/s1743921307014366.
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AbstractUsing N-Body/Treecode, SPH simulations, including a self regulating Star Formation-feedback model, the influence of cluster tidal forces on infalling dwarf irregulars is investigated. Results suggest that an encounter with the cluster potential can disrupt a rotating disk causing morphological transformation of the gaseous component, resulting in an enhancement of star formation rates (SFRs) of up to an order of magnitude.
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Santiago, Basílio X. "The star clusters of the Magellanic System." Proceedings of the International Astronomical Union 4, S256 (July 2008): 69–80. http://dx.doi.org/10.1017/s1743921308028287.
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AbstractMore than 50 years have elapsed since the first studies of star clusters in the Magellanic Clouds. The wealth of data accumulated since then has not only revealed a large cluster system, but also a diversified one, filling loci in the age, mass and chemical abundance parameter space which are complementary to Galactic clusters. Catalogs and photometric samples currently available cover most of the cluster mass range. The expectations of relatively long cluster disruption timescales in the Clouds have been confirmed, allowing reliable assessments of the cluster initial mass function and of the cluster formation rate in the Clouds. Due to their proximity to the Galaxy, Magellanic clusters are also well resolved into stars. Analysis of colour—magnitude diagrams (CMDs) of clusters with different ages, masses and metallicities are useful tools to test dynamical effects such as mass loss due to stellar evolution, two-body relaxation, stellar evaporation, cluster interactions and tidal effects. The existence of massive and young Magellanic clusters has provided insight into the physics of cluster formation. The magnitudes and colours of different stellar types are confronted with stellar evolutionary tracks, thus constraining processes such as convective overshooting, stellar mass-loss, rotation and pre main-sequence evolution. Finally, the Magellanic cluster system may contribute with nearby and well studied counterparts of recently proposed types of extragalactic clusters, such as Faint Fuzzies and Diffuse Star Clusters.
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Assmann, P., M. Fellhauer, and M. I. Wilkinson. "Star clusters as building blocks for dSph galaxy formation." Proceedings of the International Astronomical Union 5, S266 (August 2009): 353–56. http://dx.doi.org/10.1017/s174392130999127x.
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AbstractWe study numerically the formation of dSph galaxies. Intense starbursts, e.g., in gas-rich environments, typically produce a few to a few hundred young star clusters within a region of just a few hundred pc. The dynamical evolution of these star clusters may explain the formation of the luminous component of dwarf spheroidal (dSph) galaxies. Here, we perform a numerical experiment to show that the evolution of star cluster complexes in dark-matter haloes can explain the formation of the luminous components of dSph galaxies.
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Baumgardt, Holger, Junichiro Makino, and Simon Portegies Zwart. "Formation and Evolution of Massive Black Holes in Star Clusters." Highlights of Astronomy 13 (2005): 350–53. http://dx.doi.org/10.1017/s153929960001594x.
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AbstractWe present results of N-body simulations on the formation of massive black holes by run-away merging in young star clusters and the later dynamical evolution of star clusters containing massive black holes. We determine the initial conditions necessary for run-away merging to form a massive black hole and study the equilibrium profile that is established in the cluster center as a result of the interaction of stars with the central black hole. Our results show that star clusters which contain black holes have projected luminosity profiles that can be fitted by standard King models. The presence of massive black holes in (post-)core collapse clusters is therefore ruled out by our simulations.
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Anders, Peter, Uta Fritze-V. Alvensleben, and Richard de Grijs. "Young Star Clusters: Clues to Galaxy Formation and Evolution." Symposium - International Astronomical Union 217 (2004): 210–11. http://dx.doi.org/10.1017/s0074180900197529.
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Young clusters are observed to form in a variety of interacting galaxies and violent starbursts, a substantial number resembling the progenitors of the well-studied globular clusters in mass and size. By studying young clusters in merger remnants and peculiar galaxies, we can therefore learn about the violent star formation history of these galaxies. We present a new set of evolutionary synthesis models of our GALEV code specifically developed to include the gaseous emission of presently forming star clusters, and a new tool that allows to determine individual cluster metallicities, ages, extinction values and masses from a comparison of a large grid of model Spectral Energy Distributions (SEDs) with multi-color observations. First results for the newly-born clusters in NGC 1569 are presented.
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Sabbi, Elena, Linda J. Smith, Lynn R. Carlson, Antonella Nota, Monica Tosi, Michele Cignoni, Jay S. Gallagher, Marco Sirianni, and Margaret Meixner. "Time resolved star formation in the SMC: the youngest star clusters." Proceedings of the International Astronomical Union 4, S256 (July 2008): 244–49. http://dx.doi.org/10.1017/s1743921308028512.
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AbstractThe two young clusters NGC 346 and NGC 602 in the Small Magellanic Cloud provide us with the opportunity to study and the efficiency of feedback mechanism at low metallicity, as well as the impact of local and global conditions in cluster formation and evolution. I describe the latest results from a multi-wavelength, large-scale study of these two clusters. HST/ACS images reveal that the clusters have very different structures: NGC 346 is composed by a number of sub-clusters which appear coeval with ages of 3 ± 1 Myr, strongly suggesting formation by the hierarchical fragmentation of a turbulent molecular cloud (Nota et al. 2006; Sabbi et al. 2007a). NGC 602, on the contrary, appears as a single small cluster of OB stars surrounded by pre-main sequence stars. For both clusters high-resolution spectroscopy of the ionized gas shows little evidence for gas motions. This suggests that at the low SMC metallicity, the winds from the hottest stars are not powerful enough to sweep away the residual gas. Instead we find that stellar radiation is the dominant process shaping the interstellar environment of NGC 346 and NGC 602.
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Carraro, Giovanni, Richard de Grijs, Bruce Elmegreen, Peter Stetson, Barbara Anthony-Twarog, Simon Goodwin, Douglas Geisler, and Dante Minniti. "HIGHLIGHTS OF COMMISSION 37 SCIENCE RESULTS." Proceedings of the International Astronomical Union 11, T29A (August 2015): 502–21. http://dx.doi.org/10.1017/s174392131600096x.
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AbstractIt is widely accepted that stars do not form in isolation but result from the fragmentation of molecular clouds, which in turn leads to star cluster formation. Over time, clusters dissolve or are destroyed by interactions with molecular clouds or tidal stripping, and their members become part of the general field population. Star clusters are thus among the basic building blocks of galaxies. In turn, star cluster populations, from young associations and open clusters to old globulars, are powerful tracers of the formation, assembly, and evolutionary history of their parent galaxies. Although their importance (e.g., in mapping out the Milky Way) had been recognised for decades, major progress in this area has only become possible in recent years, both for Galactic and extragalactic cluster populations. Star clusters are the observational foundation for stellar astrophysics and evolution, provide essential tracers of galactic structure, and are unique stellar dynamical environments. Star formation, stellar structure, stellar evolution, and stellar nucleosynthesis continue to benefit and improve tremendously from the study of these systems. Additionally, fundamental quantities such as the initial mass function can be successfully derived from modelling either the Hertzsprung-Russell diagrams or the integrated velocity structures of, respectively, resolved and unresolved clusters and cluster populations. Star cluster studies thus span the fields of Galactic and extragalactic astrophysics, while heavily affecting our detailed understanding of the process of star formation in dense environments. This report highlights science results of the last decade in the major fields covered by IAU Commission 37: Star clusters and associations. Instead of focusing on the business meeting - the out-going president presentation can be found here:http://www.sc.eso.org/gcarraro/splinter2015.pdf- this legacy report contains highlights of the most important scientific achievements in the Commission science area, compiled by 5 well expert members.
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Randriamanakoto, Zara, and Petri Väisänen. "The SUNBIRD survey: characterizing the super star cluster populations of intensely star-forming galaxies." Proceedings of the International Astronomical Union 12, S316 (August 2015): 70–76. http://dx.doi.org/10.1017/s1743921315010510.
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AbstractSuper star clusters (SSCs) represent the youngest and most massive form of known gravitationally bound star clusters in the Universe. They are born abundantly in environments that trigger strong and violent star formation. We investigate the properties of these massive SSCs in a sample of 42 nearby starbursts and luminous infrared galaxies. The targets form the sample of the SUperNovae and starBursts in the InfraReD (SUNBIRD) survey that were imaged using near-infrared (NIR) K-band adaptive optics mounted on the Gemini/NIRI and the VLT/NaCo instruments. Results from i) the fitted power-laws to the SSC K-band luminosity functions, ii) the NIR brightest star cluster magnitude − star formation rate (SFR) relation and iii) the star cluster age and mass distributions have shown the importance of studying SSC host galaxies with high SFR levels to determine the role of the galactic environments in the star cluster formation, evolution and disruption mechanisms.
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Kodama, Tadayuki, Masao Hayashi, Yusei Koyama, Ken-ichi Tadaki, Ichi Tanaka, and Rhythm Shimakawa. "Mahalo-Subaru: Mapping Star Formation at the Peak Epoch of Massive Galaxy Formation." Proceedings of the International Astronomical Union 8, S295 (August 2012): 74–77. http://dx.doi.org/10.1017/s1743921313004353.
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AbstractMAHALO-Subaru (MApping HAlpha and Lines of Oxygen with Subaru) is our on-going large programme which aims to investigate how the star forming activities in galaxies are propagated as a function of time, mass, and environment. We are targeting 10 clusters and proto-clusters at 0.4<z<2.6, and two general fields (GOODS-N and SXDF-CANDELS) with Suprime-Cam and MOIRCS by utilizing our unique sets of narrow-band filters. The narrow-band imaging can map out star forming galaxies with the redshifted Halpha and/or [OII] emission lines from our targets, and thus providing relatively unbiased views of star forming activities across time and environment. We have almost completed narrow-band imaging of our targets, and found that star forming activity is very high even in the proto-cluster cores (z≳1.5), and that the peak of star formation is shifted outwards with time, indicating the inside-out formation of clusters. Moreover, we have identified many “red” emitters especially in high density regions at z>2, which suggests that the mode of star formation and/or the activation of AGN are dependent on environment, and thus holding the key to the environmental effects at the early stage of cluster galaxies formation and evolution.
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Webb, Jeremy J., and Alison Sills. "The initial properties of young star clusters in M83." Monthly Notices of the Royal Astronomical Society 501, no. 2 (December 12, 2020): 1933–39. http://dx.doi.org/10.1093/mnras/staa3832.
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ABSTRACT The initial sizes and masses of massive star clusters provide information about the cluster formation process and also determine how cluster populations are modified and destroyed, which have implications for using clusters as tracers of galaxy assembly. Young massive cluster populations are often assumed to be unchanged since cluster formation; therefore, their distributions of masses and radii are used as the initial values. However, the first few hundred million years of cluster evolution does change both cluster mass and cluster radius, through both internal and external processes. In this paper, we use a large suite of N-body cluster simulations in an appropriate tidal field to determine the best initial mass and initial size distributions of young clusters in the nearby galaxy M83. We find that the initial masses follow a power-law distribution with a slope of −2.7 ± 0.4 , and the half-mass radii follow a lognormal distribution with a mean of 2.57 ± 0.04 pc and a dispersion of 1.59 ± 0.01 pc. The corresponding initial projected half-light radius function has a mean of 2.7 ± 0.3 pc and a dispersion of 1.7 ± 0.2 pc. The evolution of the initial mass and size distribution functions is consistent with mass-loss and expansion due to stellar evolution, independent of the external tidal field and the cluster’s initial density profile. Observed cluster sizes and masses should not be used as the initial values, even when clusters are only a few hundred million years old.
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Harris, William E. "Young, old, massive: Steps to understanding globular cluster formation." Proceedings of the International Astronomical Union 14, S351 (May 2019): 3–12. http://dx.doi.org/10.1017/s1743921319006495.
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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.
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Konstantopoulos, I. S., N. Bastian, M. Gieles, and H. J. G. L. M. Lamers. "Constraining star cluster disruption mechanisms." Proceedings of the International Astronomical Union 5, S266 (August 2009): 433–37. http://dx.doi.org/10.1017/s1743921309991621.
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AbstractStar clusters are found in all sorts of environments, and their formation and evolution is inextricably linked to the star-formation process. Their eventual destruction can result from a number of factors at different times, but the process can be investigated as a whole through the study of cluster age distributions. Observations of populous cluster samples reveal a distribution following a power law of index approximately −1. In this work, we use M33 as a test case to examine the age distribution of an archetypal cluster population and show that it is, in fact, the evolving shape of the mass detection limit that defines this trend. That is to say, any magnitude-limited sample will appear to follow a dN/dτ = τ−1 relation, while cutting the sample according to mass gives rise to a composite structure, perhaps implying a dependence of the cluster disruption process on mass. In the context of this framework, we examine different models of cluster disruption from both theoretical and observational perspectives.
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Portegies Zwart, Simon F. "The formation of intermediate mass black holes." Symposium - International Astronomical Union 208 (2003): 145–56. http://dx.doi.org/10.1017/s0074180900207109.
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We study the growth rate of stars in dense star clusters by stellar collisions. Our analytic calculations are in good agreement with direct N-body simulations with up to 65536 stars performed on the GRAPE family of computers. We find that star clusters with a half mass relaxation time ≲ 20 Myr are dominated by stellar collisions. The first collision occurs at the moment of core collapse. The collision dominated phase last until the cluster dissolves in the tidal field of the Galaxy or mass loss by stellar evolution arrests core collapse. The majority of collisions occur with the same star resulting in the uncontrolled growth of a super massive object. This object can grow up to ∼ 0.08% of the mass of the entire star cluster. This mass ratio is comparable to the ratio of the mass of Galactic bulges to their central black hole. Star clusters which are older than about 4 Myr and with a half mass relaxation time ≲ 80 Myr are expected to contain the remnant of a phase of uncontrolled growth in their cores.
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de Grijs, Richard. "A revolution in star cluster research: setting the scene." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 368, no. 1913 (February 28, 2010): 693–711. http://dx.doi.org/10.1098/rsta.2009.0253.
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Star clusters and their stellar populations play a significant role in the context of galaxy evolution, across space (from local to high redshift) and time (from currently forming to fossil remnants). We are now within reach of answering a number of fundamental questions that will have a significant impact on our understanding of key open issues in contemporary astrophysics, ranging from the formation, assembly and evolution of galaxies to the details of the star-formation process. Our improved understanding of the physics driving star cluster formation and evolution has led to the emergence of crucial new open questions that will most probably be tackled in a systematic way in the next decade.
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Adamo, Angela. "The Imprints Of Galactic Environment On Cluster Formation and Evolution." Proceedings of the International Astronomical Union 12, S316 (August 2015): 17–24. http://dx.doi.org/10.1017/s1743921315010571.
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AbstractYoung star clusters (YSCs) appear to be a ubiquitous product of star formation in local galaxies, thus, they can be used to study the star formation process at work in their host galaxies. Moreover, YSCs are intrinsically brighter that single stars, potentially becoming the most important tracers of the recent star formation history in galaxies in the local Universe. In local galaxies, we also witness the presence of a large population of evolved star clusters, commonly called globular clusters (GCs). GCs peak formation history is very close to the redshift (z ~ 2) when the cosmic star formation history reached the maximum. Therefore, GCs are usually associated to extreme star formation episodes in high-redshift galaxies. It is yet not clear whether YSCs and GCs share a similar formation process (same physics under different interstellar medium conditions) and evolution process, and whether the former can be used as progenitor analogs of the latter. In this invited contribution, I review general properties of YSC populations in local galaxies. I will summarise some of the current open questions in the field, with particular emphasis to whether or not galactic environments, where YSCs form, leave imprints on the nested populations. The importance of this rapidly developing field can be crucial in understanding GC formation and possibly the galactic environment condition where this ancient population formed.
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Fall, S. Michael, and Qing Zhang. "Formation and Disruption of Globular Star Clusters." Symposium - International Astronomical Union 207 (2002): 566–76. http://dx.doi.org/10.1017/s0074180900224388.
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In the first part of this article, we review observations of the mass and luminosity functions of young and old star cluster systems. We also review some of the physical processes that may determine the characteristic mass of globular clusters and the form of their mass function. In the second part of this article, we summarize our models for the disruption of clusters and the corresponding evolution of the mass function. Much of our focus here is on understanding why the mass function of globular clusters has no more than a weak dependence on radius within their host galaxies.
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Román-Zúñiga, Carlos G., Elizabeth A. Lada, and Bruno Ferreira. "A Near-infrared Survey of the Rosette Complex: Clues of Early Cluster Evolution." Proceedings of the International Astronomical Union 3, S246 (September 2007): 46–49. http://dx.doi.org/10.1017/s1743921308015251.
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AbstractThe majority of stars in our galaxy are born in embedded clusters, which can be considered the fundamental units of star formation. We have recently surveyed the star forming content of the Rosette Complex using FLAMINGOS in order to investigate the properties of its embedded clusters. We discuss the results of our near-infrared imaging survey. In particular, we on the first evidence for the early evolution and expansion of the embedded clusters. In addition we present data suggesting a temporal sequence of cluster formation across the cloud and discuss the influence of the HII region on the star forming history of the Rosette.
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Li, Hui, and Oleg Gnedin. "Formation and evolution of globular clusters in cosmological simulations." Proceedings of the International Astronomical Union 14, S351 (May 2019): 34–39. http://dx.doi.org/10.1017/s1743921319007646.
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AbstractIn a series of three papers, we introduced a novel cluster formation model that describes the formation, growth, and disruption of star clusters in high-resolution cosmological simulations. We tested this model on a Milky Way-sized galaxy and found that various properties of young massive clusters, such as the mass function and formation efficiency, are consistent with observations in the local universe. Interestingly, most massive clusters – globular cluster candidates – are preferentially formed during major merger events. We follow the dynamical evolution of clusters in the galactic tidal field. Due to tidal disruption, the cluster mass function evolves from initial power law to a peaked shape. The surviving clusters at z = 0 show a broad range of metallicity [Fe/H] from -3 to -0.5. A robust prediction of the model is the age–metallicity relation, in which metal-rich clusters are systematically younger than metal-poor clusters by up to 3 Gyr.
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Ladeyschikov, D. A., M. S. Kirsanova, A. M. Sobolev, M. Thomasson, V. Ossenkopf-Okada, M. Juvela, S. A. Khaibrakhmanov, and E. A. Popova. "The link between gas and stars in the S254–S258 star-forming region." Monthly Notices of the Royal Astronomical Society 506, no. 3 (July 1, 2021): 4447–64. http://dx.doi.org/10.1093/mnras/stab1821.
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ABSTRACT The paper aims to study relation between the distributions of the young stellar objects (YSOs) of different ages and the gas-dust constituents of the S254–S258 star formation complex. This is necessary to study the time evolution of the YSO distribution with respect to the gas and dust compounds that are responsible for the birth of the young stars. For this purpose, we use correlation analysis between different gas, dust, and YSO tracers. We compared the large-scale CO, HCO+, near-IR extinction, and far-IR Herschel maps with the density of YSOs of the different evolutionary classes. The direct correlation analysis between these maps was used together with the wavelet-based spatial correlation analysis. This analysis reveals a much tighter correlation of the gas-dust tracers with the distribution of class I YSOs than with that of class II YSOs. We argue that class I YSOs that were initially born in the central bright cluster S255-IR (both N and S parts) during their evolution to class II stage (∼2 Myr) had enough time to travel through the whole S254–S258 star formation region. Given that the region contains several isolated YSO clusters, the evolutionary link between these clusters and the bright central S255-IR (N and S) cluster can be considered. Despite the complexity of the YSO cluster formation in the non-uniform medium, the clusters of class II YSOs in the S254-258 star formation region can contain objects born in the different locations of the complex.
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Bekki, Kenji. "Star cluster dynamics in galaxies." Proceedings of the International Astronomical Union 5, S266 (August 2009): 219–30. http://dx.doi.org/10.1017/s1743921309991086.
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AbstractI present a review of star cluster (SC) dynamics in galaxies, with special emphasis on the effects of global galactic dynamics on SC formation and evolution. I particularly discuss (i) dynamical friction processes affecting SCs in galaxies of different masses, (ii) formation of stellar galactic nuclei and massive globular clusters (GCs) through multiple merging of SCs, (iii) interactions between giant molecular clouds (GMCs) and SCs, (iv) SC destruction due to the strong tidal fields in galaxy mergers and (v) the formation of low-mass dwarfs from numerous SCs. I also discuss some recent observational results on SC mass functions in dwarf galaxies and physical properties of GC systems in luminous galaxies based on recent results of numerical simulations of SC dynamics in galaxies.
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Shukirgaliyev, Bekdaulet, Genevieve Parmentier, Peter Berczik, and Andreas Just. "Star Clusters in the Galactic tidal field, from birth to dissolution." Proceedings of the International Astronomical Union 14, S351 (May 2019): 507–11. http://dx.doi.org/10.1017/s1743921319006781.
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AbstractWe study the evolution of star clusters in the Galactic tidal field starting from their birth in molecular clumps. Our model clusters form according to the local-density-driven cluster formation model in which the stellar density profile is steeper than that of gas. As a result, clusters resist the gas expulsion better than predicted by earlier models.We vary the impact of the Galactic tidal field λ, considering different Galactocentric distances (3-18 kpc), as well as different cluster sizes. Our model clusters survive the gas expulsion independent of λ.We investigated the relation between the cluster mass at the onset of secular evolution and their dissolution time. The model clusters formed with a high star-formation efficiency (SFE) follow a tight mass-dependent dissolution relation, in agreement with previous theoretical studies. However, the low-SFE models present a shallower mass-dependent relation than high-SFE clusters, and most dissolve before reaching 1 Gyr (cluster teenage mortality).
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Decressin, T. "Formation of globular clusters with multiple populations." Proceedings of the International Astronomical Union 12, S316 (August 2015): 281–86. http://dx.doi.org/10.1017/s1743921315010613.
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AbstractSpectroscopic and photometric evidences have led to a complete revision of our understanding of globular clusters with the discovery of multiple stellar populations which differ chemically. Whereas some stars have a chemical composition similar to fields stars, others show large star-to-star variations in light elements (Li to Al) while their composition in iron and heavy elements stay constant. This peculiar chemical pattern can be explained by self-pollution of the intracluster gas occurring in the early evolution of clusters. Here the possible impact from a first generation of fast rotating stars to the early evolution of globular clusters is presented. The high rotation velocity will allow the stars to rotate at the break-up velocity and release matter enrich in H-burning which in turn will produce new stars with a chemical composition in agreement with observations. The massive stars have also an important role to clear the cluster from the remaining gas left after the star formation episodes. If the gas expulsion is fast enough, the strong change in the potential well will lead to the loss of stars occupying the outer part of the cluster. As second generation stars are preferentially born in the cluster centre, the ratio of second to first generation stars will increase over time to match the present ratio determined by observations. Considerations on the properties of low-mass stars still present in globular clusters will also be presented.
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Belczynski, K., A. Askar, M. Arca-Sedda, M. Chruslinska, M. Donnari, M. Giersz, M. Benacquista, et al. "The origin of the first neutron star – neutron star merger." Astronomy & Astrophysics 615 (July 2018): A91. http://dx.doi.org/10.1051/0004-6361/201732428.
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The first neutron star-neutron star (NS-NS) merger was discovered on August 17, 2017 through gravitational waves (GW170817) and followed with electromagnetic observations. This merger was detected in an old elliptical galaxy with no recent star formation. We perform a suite of numerical calculations to understand the formation mechanism of this merger. We probe three leading formation mechanisms of double compact objects: classical isolated binary star evolution, dynamical evolution in globular clusters, and nuclear cluster formation to test whether they are likely to produce NS-NS mergers in old host galaxies. Our simulations with optimistic assumptions show current NS-NS merger rates at the level of 10−2 yr−1 from binary stars, 5 × 10−5 yr−1 from globular clusters, and 10−5 yr−1 from nuclear clusters for all local elliptical galaxies (within 100 Mpc3). These models are thus in tension with the detection of GW170817 with an observed rate of 1.5−1.2+3.2 yr−1 (per 100 Mpc3; LIGO/Virgo 90% credible limits). Our results imply that either the detection of GW170817 by LIGO/Virgo at their current sensitivity in an elliptical galaxy is a statistical coincidence; that physics in at least one of our three models is incomplete in the context of the evolution of stars that can form NS-NS mergers; or that another very efficient (unknown) formation channel with a long delay time between star formation and merger is at play.
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Pérez-Martínez, J. M., B. Ziegler, A. Böhm, and M. Verdugo. "Galaxy kinematics across different environments in the RXJ1347−1145 cluster complex." Astronomy & Astrophysics 637 (May 2020): A30. http://dx.doi.org/10.1051/0004-6361/201936243.
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Aims. In order to understand the role of the different processes that drive galaxy evolution in clusters, we need comprehensive studies that simultaneously examine several of the most important physical properties of galaxies. In this work we study the interplay between the kinematic state and star formation activity of galaxies in the RXJ1347−1145 cluster complex at z ∼ 0.45. Methods. We used VLT/VIMOS to obtain slit spectra for 95 galaxies across the 40′ × 40′ area where the RXJ1347−1145 cluster complex resides. We determined the cluster membership of our targets by identifying one or more of the available emission lines within the wavelength range. Our spectroscopy is complemented with archival SUBARU/Suprime-Cam deep photometric observations in five optical bands (B, V, Rc, Ic, z′). We examined the kinematic properties of our sample attending to the degree of distortion of the extracted rotation curves. Regular rotating galaxies were included in our Tully–Fisher analysis while the distorted ones were used to study the role of cluster-specific interactions with respect to star formation and AGN activity. Results. Our analysis confirmed the cluster membership for approximately half of our targets. We report a higher fraction of galaxies with irregular gas kinematics in the cluster environment than in the field. Cluster galaxies with regular rotation display a moderate brightening in the B-band Tully–Fisher relation compatible with the gradual evolution of the stellar populations with lookback time, and no significant evolution in the stellar-mass Tully–Fisher relation, in line with previous studies at similar redshift. Average specific star formation rate values are slightly lower in our cluster sample (−0.15 dex) with respect to the main sequence of star-forming galaxies, confirming the role of the environment in the early quenching of star formation in clusters. Finally, we carried out an exploratory observational study on the stellar-to-halo mass relation finding that cluster galaxies tend to have slightly lower stellar mass values for a fixed halo mass compared to their field counterparts.
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Grudić, Michael Y., J. M. Diederik Kruijssen, Claude-André Faucher-Giguère, Philip F. Hopkins, Xiangcheng Ma, Eliot Quataert, and Michael Boylan-Kolchin. "A model for the formation of stellar associations and clusters from giant molecular clouds." Monthly Notices of the Royal Astronomical Society 506, no. 3 (July 5, 2021): 3239–58. http://dx.doi.org/10.1093/mnras/stab1894.
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ABSTRACT We present a large suite of magnetohydrodynamic simulations of turbulent, star-forming giant molecular clouds (GMCs) with stellar feedback, extending previous work by simulating 10 different random realizations for each point in the parameter space of cloud mass and size. It is found that once the clouds disperse due to stellar feedback, both self-gravitating star clusters and unbound stars generally remain, which arise from the same underlying continuum of substructured stellar density, i.e. the hierarchical cluster formation scenario. The fraction of stars that are born within gravitationally bound star clusters is related to the overall cloud star formation efficiency set by stellar feedback, but has significant scatter due to stochastic variations in the small-scale details of the star-forming gas flow. We use our numerical results to calibrate a model for mapping the bulk properties (mass, size, and metallicity) of self-gravitating GMCs on to the star cluster populations they form, expressed statistically in terms of cloud-level distributions. Synthesizing cluster catalogues from an observed GMC catalogue in M83, we find that this model predicts initial star cluster masses and sizes that are in good agreement with observations, using only standard IMF and stellar evolution models as inputs for feedback. Within our model, the ratio of the strength of gravity to stellar feedback is the key parameter setting the masses of star clusters, and of the various feedback channels direct stellar radiation (photon momentum and photoionization) is the most important on GMC scales.
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Panwar, Neelam, A. K. Pandey, Manash R. Samal, Paolo Battinelli, K. Ogura, D. K. Ojha, W. P. Chen, and H. P. Singh. "Young Cluster Berkeley 59: Properties, Evolution, and Star Formation." Astronomical Journal 155, no. 1 (January 3, 2018): 44. http://dx.doi.org/10.3847/1538-3881/aa9f1b.
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Chatterjee, Sourav, Meagan Morscher, Carl L. Rodriguez, Bharat Pattabiraman, and Frederic A. Rasio. "Effects of Stellar-Mass Black Holes on Massive Star Cluster Evolution." Proceedings of the International Astronomical Union 12, S316 (August 2015): 234–39. http://dx.doi.org/10.1017/s1743921315010674.
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AbstractRecent observations have revealed the existence of stellar mass black hole (BH) candidates in some globular clusters (GC) in the Milky Way and in other galaxies. Given that the detection of BHs is challenging, these detections likely indicate the existence of large populations of BHs in these clusters. This is in direct contrast to the past understanding that at most a handful of BHs may remain in old GCs due to quick mass segregation and rapid mutual dynamical ejection. Modern realistic star-by-star numerical simulations suggest that the retention fraction of BHs is typically much higher than what was previously thought. The BH dynamics near the cluster center leads to dynamical formation of new binaries and dynamical ejections, and acts as a persistent and significant energy source for these clusters. We have started exploring effects of BHs on the global evolution and survival of star clusters. We find that the evolution as well as survival of massive star clusters can critically depend on the details of the initial assumptions related to BH formation physics, such as natal kick distribution, and the initial stellar mass function (IMF). In this article we will present our latest results.
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Gouliermis, Dimitrios A., and Sacha Hony. "NGC 346: Looking in the Cradle of a Massive Star Cluster." Proceedings of the International Astronomical Union 12, S316 (August 2015): 117–22. http://dx.doi.org/10.1017/s1743921316008759.
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AbstractHow does a star cluster of more than few 10,000 solar masses form? We present the case of the cluster NGC 346 in the Small Magellanic Cloud, still embedded in its natal star-forming region N66, and we propose a scenario for its formation, based on observations of the rich stellar populations in the region. Young massive clusters host a high fraction of early-type stars, indicating an extremely high star formation efficiency. The Milky Way galaxy hosts several young massive clusters that fill the gap between young low-mass open clusters and old massive globular clusters. Only a handful, though, are young enough to study their formation. Moreover, the investigation of their gaseous natal environments suffers from contamination by the Galactic disk. Young massive clusters are very abundant in distant starburst and interacting galaxies, but the distance of their hosting galaxies do not also allow a detailed analysis of their formation. The Magellanic Clouds, on the other hand, host young massive clusters in a wide range of ages with the youngest being still embedded in their giant HII regions. Hubble Space Telescope imaging of such star-forming complexes provide a stellar sampling with a high dynamic range in stellar masses, allowing the detailed study of star formation at scales typical for molecular clouds. Our cluster analysis on the distribution of newly-born stars in N66 shows that star formation in the region proceeds in a clumpy hierarchical fashion, leading to the formation of both a dominant young massive cluster, hosting about half of the observed pre–main-sequence population, and a self-similar dispersed distribution of the remaining stars. We investigate the correlation between stellar surface density (and star formation rate derived from star-counts) and molecular gas surface density (derived from dust column density) in order to unravel the physical conditions that gave birth to NGC 346. A power law fit to the data yields a steep correlation between these two parameters with a considerable scatter. The fraction of stellar over the total (gas plus young stars) mass is found to be systematically higher within the central 15 pc (where the young massive cluster is located) than outside, which suggests variations in the star formation efficiency within the same star-forming complex. This trend possibly reflects a change of star formation efficiency in N66 between clustered and non-clustered star formation. Our findings suggest that the formation of NGC 346 is the combined result of star formation regulated by turbulence and of early dynamical evolution induced by the gravitational potential of the dense interstellar medium.
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Olsen, K. A. G., P. W. Hodge, M. Mateo, E. W. Olszewski, R. A. Schommer, N. B. Suntzeff, and A. R. Walker. "Results from HST Observations of Six LMC Globular Cluster Fields." Symposium - International Astronomical Union 190 (1999): 448–49. http://dx.doi.org/10.1017/s0074180900118534.
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We present deep HST color-magnitude diagrams of fields centered on the six old LMC globular clusters NGC 1754, NGC 1835, NGC 1898, NGC 1916, NGC 2005, and NGC 2019. Separate cluster and field star CMDs are shown. The time of formation of the LMC is studied from an analysis of the cluster CMDs. Based on a comparison of the CMDs with sequences of the Milky Way clusters M3, M5, and M55, we suggest that the LMC formed its first stars at the same time as the Milky Way to within 1 Gyr. We find additional evidence that these LMC globular clusters are as old as the oldest Milky Way clusters through a comparison of our data with the horizontal branch evolutionary models of Lee, Demarque, & Zinn (1994).The evolution of the LMC following its formation is studied through an analysis of the field star CMDs. Through an automated comparison with stellar evolution models, we extract the star formation histories implied by the CMDs. Our best-fit star formation histories imply that the LMC has been actively forming stars over the last 4 Gyr, in agreement with previous field star studies. The four fields that lie in the Bar also contain significant numbers of stars with ages of 4–8 Gyr in the best-fit cases. The most notable disagreement between the best-fit models and observed CMDs is in the color of the red giant branch.
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Tan, Jonathan C., Suzanne N. Shaske, and Sven Van Loo. "Molecular Clouds: Internal Properties, Turbulence, Star Formation and Feedback." Proceedings of the International Astronomical Union 8, S292 (August 2012): 19–28. http://dx.doi.org/10.1017/s1743921313000173.
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AbstractAll stars are born in molecular clouds, and most in giant molecular clouds (GMCs), which thus set the star formation activity of galaxies. We first review their observed properties, including measures of mass surface density, Σ, and thus mass,M. We discuss cloud dynamics, concluding most GMCs are gravitationally bound. Star formation is highly clustered within GMCs, but overall is very inefficient. We compare properties of star-forming clumps with those of young stellar clusters (YSCs). The high central densities of YSCs may result via dynamical evolution of already-formed stars during and after star cluster formation. We discuss theoretical models of GMC evolution, especially addressing how turbulence is maintained, and emphasizing the importance of GMC collisions. We describe how feedback limits total star formation efficiency, ε, in clumps. A turbulent and clumpy medium allows higher ε, permitting formation of bound clusters even when escape speeds are less than the ionized gas sound speed.
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Vanbeveren, Dany. "Close pairs: keys to comprehension of star cluster evolution." Proceedings of the International Astronomical Union 5, S266 (August 2009): 293–303. http://dx.doi.org/10.1017/s1743921309991165.
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AbstractIn this review I first summarize why binaries are key objects in the study of stellar populations, to understand the evolution of star clusters and galaxies, and thus to understand the universe. I then focus on four specific topics: (i)the formation (through binaries) and evolution of very massive stars in dense clusters and the importance of stellar-wind mass loss. I discuss preliminary computations of wind mass-loss rates of very massive stars performed with the Munich hydrodynamical code and the influence of these new rates on the possible formation of an intermediate-mass black hole in the cluster MGG 11 in M82;(ii)the evolution of intermediate-mass binaries in a starburst with special emphasis on the variation of the supernova (SN) Ia rate (i.e., on the delayed time distribution of SNe Ia). A comparison with SN Ia rates in elliptical galaxies may provide important clues to SN Ia models as well as to the evolution of SN Ia progenitors;(iii)the evolution of double-neutron-star mergers in a starburst (i.e., the delayed time distribution of these mergers) and what this tells us about the suggestion that these mergers may be important production sites of r-process elements;(iv)the possible effect of massive binaries on the self-enrichment of globular clusters.
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Rieder, Steven, Clare Dobbs, Thomas Bending, Kong You Liow, and James Wurster. "The formation and early evolution of embedded star clusters in spiral galaxies." Monthly Notices of the Royal Astronomical Society 509, no. 4 (November 26, 2021): 6155–68. http://dx.doi.org/10.1093/mnras/stab3425.
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ABSTRACT We present Ekster, a new method for simulating star clusters from birth in a live galaxy simulation that combines the smoothed-particle hydrodynamics (SPH) method Phantom with the N-body method PeTar. With Ekster, it becomes possible to simulate individual stars in a simulation with only moderately high resolution for the gas, allowing us to study whole sections of a galaxy rather than be restricted to individual clouds. We use this method to simulate star and star cluster formation in spiral arms, investigating massive giant molecular clouds (GMCs) and spiral arm regions with lower mass clouds, from two galaxy models with different spiral potentials. After selecting these regions from pre-run galaxy simulations, we re-sample the particles to obtain a higher resolution. We then re-simulate these regions for 3 Myr to study where and how star clusters form. We analyse the early evolution of the embedded star clusters in these regions. We find that the massive GMC regions, which are more common with stronger spiral arms, form more massive clusters than the sections of spiral arms containing lower mass clouds. Clusters form both by accreting gas and by merging with other proto-clusters, the latter happening more frequently in the denser GMC regions.
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Whitmore, Bradley C. "The Evolution of Young Star Clusters in Merging Galaxies." Symposium - International Astronomical Union 186 (1999): 251–60. http://dx.doi.org/10.1017/s0074180900112719.
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The formation of young star clusters in merging galaxies is, by now, well established. The new challenge is to use these young clusters as a tool to address some of the outstanding questions. For example, what fraction of these young clusters become globular clusters? Is this enough to explain the difference in the specific globular cluster frequencies for spirals and ellipticals? What is it about the collision between two gas-rich galaxies that triggers giant molecular clouds to form star clusters? Can the star clusters be used to age date merger remnants and establish a convincing evolutionary connection between merging spirals and elliptical galaxies? This review will focus on the last of these items.
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Kruijssen, J. M. Diederik. "Are globular clusters the natural outcome of regular high-redshift star formation?" Proceedings of the International Astronomical Union 10, S312 (August 2014): 147–54. http://dx.doi.org/10.1017/s1743921315007759.
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AbstractWe summarise the recent progress in understanding the formation and evolution of globular clusters (GCs) in the context of galaxy formation and evolution. It is discussed that an end-to-end model for GC formation and evolution should capture four different phases: (1) star and cluster formation in the high-pressure interstellar medium of high-redshift galaxies, (2) cluster disruption by tidal shocks in the gas-rich host galaxy disc, (3) cluster migration into the galaxy halo, and (4) the final evaporation-dominated evolution of GCs until the present day. Previous models have mainly focussed on phase 4. We present and discuss a simple model that includes each of these four steps – its key difference with respect to previous work is the simultaneous addition of the high-redshift formation and early evolution of young GCs, as well as their migration into galaxy haloes. The new model provides an excellent match to the observed GC mass spectrum and specific frequency, as well as the relations of GCs to the host dark matter halo mass and supermassive black hole mass. These results show (1) that the properties of present-day GCs are reproduced by assuming that they are the natural outcome of regular high-redshift star formation (i.e. they form according to same physical processes that govern massive cluster formation in the local Universe), and (2) that models only including GC evaporation strongly underestimate their integrated mass loss over a Hubble time.
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Lovisari, Lorenzo, Tatiana F. Laganá, Katharina Borm, Gerrit Schellenberger, and Thomas H. Reiprich. "METALS IN THE ICM: WITNESSES OF CLUSTER FORMATION AND EVOLUTION." Acta Polytechnica 53, A (December 18, 2013): 579–82. http://dx.doi.org/10.14311/ap.2013.53.0579.
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The baryonic composition of galaxy clusters and groups is dominated by a hot, X-ray emitting Intra-Cluster Medium (ICM). The mean metallicity of the ICM has been found to be roughly 0.3 ÷ 0.5 times the solar value, therefore a large fraction of this gas cannot be of purely primordial origin. Indeed, the distribution and amount of metals in the ICM is a direct consequence of the past history of star formation in the cluster galaxies and of the processes responsible for the injection of enriched material into the ICM. We here shortly summarize the current views on the chemical enrichment, focusing on the observational evidence in terms of metallicity measurements in clusters, spatial metallicity distribution and evolution, and expectations from future missions.
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Giersz, Mirek, Nathan Leigh, Michael Marks, Arkadiusz Hypki, and Abbas Askar. "Monte Carlo modeling of globular star clusters: many primordial binaries and IMBH formation." Proceedings of the International Astronomical Union 10, S312 (August 2014): 213–22. http://dx.doi.org/10.1017/s1743921315007838.
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AbstractWe will discuss the evolution of star clusters with a large initial binary fraction, up to 95%. The initial binary population is chosen to follow the invariant orbital-parameter distributions suggested by Kroupa (1995). The Monte Carlo MOCCA simulations of star cluster evolution are compared to the observations of Milone et al. (2012) for photometric binaries. It is demonstrated that the observed dependence on cluster mass of both the binary fraction and the ratio of the binary fractions inside and outside of the half mass radius are well recovered by the MOCCA simulations. This is due to a rapid decrease in the initial binary fraction due to the strong density-dependent destruction of wide binaries described by Marks, Kroupa & Oh (2011). We also discuss a new scenario for the formation of intermediate mass black holes in dense star clusters. In this scenario, intermediate mass black holes are formed as a result of dynamical interactions of hard binaries containing a stellar mass black hole, with other stars and binaries. We will discuss the necessary conditions to initiate the process of intermediate mass black hole formation and the dependence of its mass accretion rate on the global cluster properties.
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Hut, Piet. "Binary Formation and Interactions with Field Stars." Symposium - International Astronomical Union 113 (1985): 231–49. http://dx.doi.org/10.1017/s0074180900147412.
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Binaries provide an energy source in dense stellar systems. Exothermic gravitational interactions in star clusters can play a role similar to that of nuclear reactions in single stars. These gravitational interactions can be modeled in a laboratory setting, in the form of numerical binary-single star and binary-binary scattering experiments. Gravitational cross sections obtained this way can be applied to model star cluster evolution, just as nuclear cross sections are used as input data in stellar evolution calculations. References are given to detailed descriptions of gravitational cross sections, and a useful new example of an application is given: the rate at which hard binaries form in a homogeneous stellar background, as the solution of an integral equation describing the combined effects of creation, destruction, hardening and softening of binaries.
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Venuti, L., L. Prisinzano, G. G. Sacco, E. Flaccomio, R. Bonito, F. Damiani, G. Micela, et al. "The Gaia-ESO Survey and CSI 2264: Substructures, disks, and sequential star formation in the young open cluster NGC 2264." Astronomy & Astrophysics 609 (December 22, 2017): A10. http://dx.doi.org/10.1051/0004-6361/201731103.
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Context. Reconstructing the structure and history of young clusters is pivotal to understanding the mechanisms and timescales of early stellar evolution and planet formation. Recent studies suggest that star clusters often exhibit a hierarchical structure, possibly resulting from several star formation episodes occurring sequentially rather than a monolithic cloud collapse. Aims. We aim to explore the structure of the open cluster and star-forming region NGC 2264 (~3 Myr), which is one of the youngest, richest and most accessible star clusters in the local spiral arm of our Galaxy; we link the spatial distribution of cluster members to other stellar properties such as age and evolutionary stage to probe the star formation history within the region. Methods. We combined spectroscopic data obtained as part of the Gaia-ESO Survey (GES) with multi-wavelength photometric data from the Coordinated Synoptic Investigation of NGC 2264 (CSI 2264) campaign. We examined a sample of 655 cluster members, with masses between 0.2 and 1.8 M⊙ and including both disk-bearing and disk-free young stars. We used Teff estimates from GES and g,r,i photometry from CSI 2264 to derive individual extinction and stellar parameters. Results. We find a significant age spread of 4–5 Myr among cluster members. Disk-bearing objects are statistically associated with younger isochronal ages than disk-free sources. The cluster has a hierarchical structure, with two main blocks along its latitudinal extension. The northern half develops around the O-type binary star S Mon; the southern half, close to the tip of the Cone Nebula, contains the most embedded regions of NGC 2264, populated mainly by objects with disks and ongoing accretion. The median ages of objects at different locations within the cluster, and the spatial distribution of disked and non-disked sources, suggest that star formation began in the north of the cluster, over 5 Myr ago, and was ignited in its southern region a few Myr later. Star formation is likely still ongoing in the most embedded regions of the cluster, while the outer regions host a widespread population of more evolved objects; these may be the result of an earlier star formation episode followed by outward migration on timescales of a few Myr. We find a detectable lag between the typical age of disk-bearing objects and that of accreting objects in the inner regions of NGC 2264: the first tend to be older than the second, but younger than disk-free sources at similar locations within the cluster. This supports earlier findings that the characteristic timescales of disk accretion are shorter than those of disk dispersal, and smaller than the average age of NGC 2264 (i.e., ≲3 Myr). At the same time, we note that disks in the north of the cluster tend to be shorter-lived (~2.5 Myr) than elsewhere; this may reflect the impact of massive stars within the region (notably S Mon), that trigger rapid disk dispersal. Conclusions. Our results, consistent with earlier studies on NGC 2264 and other young clusters, support the idea of a star formation process that takes place sequentially over a prolonged span in a given region. A complete understanding of the dynamics of formation and evolution of star clusters requires accurate astrometric and kinematic characterization of its population; significant advance in this field is foreseen in the upcoming years thanks to the ongoing Gaia mission, coupled with extensive ground-based surveys like GES.