Journal articles: 'Star 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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Palouš, Jan, Richard Wünsch, Guillermo Tenorio-Tagle, and Sergyi Silich. "Origin of Star-to-Star Abundance Inhomogeneities in Star Clusters." Proceedings of the International Astronomical Union 4, S254 (June 2008): 233–38. http://dx.doi.org/10.1017/s1743921308027646.

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AbstractThe mass reinserted by young stars of an emerging massive compact cluster shows a bimodal hydrodynamic behaviour. In the inner part of the cluster, it is thermally unstable, while in its outer parts it forms an out-blowing wind. The chemical homogeneity/inhomogeneity of low/high mass clusters demonstrates the relevance of this solution to the presence of single/multiple stellar populations. We show the consequences that the thermal instability of the reinserted mass has to the galactic super-winds.

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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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Turner, D. G. "Are the Cepheids in Cluster Nuclei a Rare Breed?" International Astronomical Union Colloquium 82 (1985): 209–11. http://dx.doi.org/10.1017/s0252921100109340.

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As reviewed by Kholopov (1968), star counts for a variety of open clusters reveal the existence of low density coronal regions surrounding the nuclear concentrations of most star clusters. Such cluster coronae have diameters 2.5 to 5 times larger than the respective nuclear diameters for clusters which are poor to medium-rich in member stars, and have star densities only about 10% those observed in cluster nuclei. Cluster coronae therefore contain roughly 40% to 70% of the stars in an open cluster, and are subsequently a (or, more appropriately, the) major component of most star clusters.

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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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Fujii, Michiko S. "Inter-cluster velocity structures of star cluster complexes." Proceedings of the International Astronomical Union 14, S351 (May 2019): 197–99. http://dx.doi.org/10.1017/s1743921319007634.

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AbstractStar clusters are often born as star-cluster systems, which include several stellar clumps. Such star-cluster complexes could have formed from turbulent molecular clouds. Since Gaia Data Release 2 provided us high quality velocity data of individual stars in known star-cluster complexes, we now can compare the velocity structures of the observed star-cluster complexes with simulated ones. We performed a series of N-body simulations for the formation of star-cluster complexes starting from turbulent molecular clouds. We measured the inter-cluster velocity dispersions of our simulated star-cluster complexes and compared them with the Carina region and NGC 2264. We found that the Carina region and NGC 2264 formed from molecular clouds with a mass of ∼4 × 105M⊙ and ∼4 × 104M⊙, respectively. In our simulations, we also found that the maximum cluster mass (Mc,max) in the complex follows ${M_{{\rm{c}},{\rm{max}}}} = 0.{\rm{2}}0M_g^{0.76}$, where Mg is the initial gas mass.

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Larsen, Søren S. "Open, Massive and Globular Clusters — Part of the Same Family?" Symposium - International Astronomical Union 207 (2002): 421–27. http://dx.doi.org/10.1017/s0074180900224133.

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Populations of young star clusters show significant differences even among “normal” disk galaxies. In this contribution I discuss how properties of young cluster systems are related to those of their host galaxies, based on a recent study of clusters in a sample of 22 nearby spiral galaxies. Luminous young clusters similar to the “super” star clusters observed in starbursts and mergers exist in several of these galaxies, and it is found that the luminosity of the brightest star cluster as well as the specific luminosity of the cluster systems both correlate well with the host galaxy star formation rate. When considering star clusters in different environments the traditional distinction between “open”, “massive” and “globular” clusters breaks down, underscoring the need for a universal physical description of cluster formation.

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Fujii, M., M. Iwasawa, Y. Funato, and J. Makino. "Fully Self-Consistent N-body Simulation of Star Cluster in the Galactic Center." Proceedings of the International Astronomical Union 3, S246 (September 2007): 467–68. http://dx.doi.org/10.1017/s1743921308016177.

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AbstractWe have developed a new tree-direct hybrid algorithm, “Bridge”. It can simulate small scale systems embedded within large-N systems fully self-consistently. Using this algorithm, we have performed full N-body simulations of star clusters near the Galactic center (GC) and compared the orbital evolutions of the star cluster with those obtained by “traditional” simulations, in which the orbital evolution of the star clusters is calculated from the dynamical friction formula. We found that the inspiral timescale of the star cluster is shorter than that obtained with traditional simulations. Moreover, we investigated the eccentricities of particles escaped from the star cluster. Eccentric orbit of the star cluster can naturally explain the high eccentricities of the observed stars.

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Hurley, Jarrod R., Michael M. Shara, and Christopher A. Tout. "Star Clusters as Exotic Star Factories." International Astronomical Union Colloquium 187 (2002): 115–20. http://dx.doi.org/10.1017/s0252921100001305.

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AbstractIn light of recent N-body simulations performed using the GRAPE-6 special-purpose hardware we discuss the role of the star cluster environment in producing unusual stellar populations and the possibility that stars labelled exotic in the solar neighbourhood may be commonplace within star clusters.

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10

Da Costa, G. S. "Star Clusters in the Magellanic Clouds." Symposium - International Astronomical Union 190 (1999): 397–404. http://dx.doi.org/10.1017/s0074180900118406.

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Recent results for the old and intermediate-age star clusters of the Magellanic Clouds are reviewed. Highlights include new evidence that the LMC old clusters are as old the Galaxy's halo globular clusters and the persistence of the LMC cluster “Age Gap” despite field star evidence for significant star formation during the cluster age gap epoch. For the SMC new data confirm the lack of significant change in cluster abundances with age prior to ~4 Gyr ago.

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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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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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Giersz, Mirek, Abbas Askar, Long Wang, Arkadiusz Hypki, Agostino Leveque, and Rainer Spurzem. "MOCCA-SURVEY Database I: Dissolution of tidally filling star clusters harboring black hole subsystem." Proceedings of the International Astronomical Union 14, S351 (May 2019): 438–41. http://dx.doi.org/10.1017/s1743921319006690.

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AbstractWe investigate the dissolution process of star clusters embedded in an external tidal field and harboring a subsystem of stellar-mass black hole. For this purpose we analyzed the MOCCA models of real star clusters contained in the Mocca Survey Database I. We showed that the presence of a stellar-mass black hole subsystem in tidally filling star cluster can lead to abrupt cluster dissolution connected with the loss of cluster dynamical equilibrium. Such cluster dissolution can be regarded as a third type of cluster dissolution mechanism. We additionally argue that such a mechanism should also work for tidally under-filling clusters with a top-heavy initial mass function.

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Hwang, Narae, and Myung Gyoon Lee. "Tracing star cluster formation in the interacting galaxy M51." Proceedings of the International Astronomical Union 5, S266 (August 2009): 423–26. http://dx.doi.org/10.1017/s1743921309991591.

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AbstractWe present a study of star clusters in the interacting galaxy M51 using a star cluster catalog that includes about 3600 star clusters with mF555W < 23 mag, compiled by Hwang & Lee (2008). Combined with mF336W-band imaging data taken with the Hubble Space Telescope (HST)'s WFPC2 camera, we have derived the ages and masses of star clusters in M51 using theoretical population synthesis models. The cluster age distribution displays multiple peaks that correspond to the epochs of dynamical encounters predicted by theoretical model studies and the cluster-formation rate appears to increase around the same epochs.

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van den Bergh, S. "Star clusters in the Magellanic Clouds." Symposium - International Astronomical Union 148 (1991): 161–64. http://dx.doi.org/10.1017/s0074180900200259.

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Star clusters in the Magellanic Clouds (MCs) differ from those in the Galaxy in a number of respects: (1) the Clouds contain a class of populous open clusters that has no Galactic counterpart; (2) Cloud clusters have systematically larger radii rh than those in the Galaxy; (3) clusters of all ages in the Clouds are, on average, more flattened than those in the Galaxy. In the Large Magellanic Cloud (LMC) there appear to have been two distinct epochs of cluster formation. LMC globulars have ages of 12-15 Gyr, whereas most populous open clusters have ages <5 Gyr. No such dichotomy is observed for clusters in the Small Magellanic Cloud (SMC) The fact that the SMC exhibits no enhanced cluster formation at times of bursts of cluster formation in the LMC, militates against encounters between the Clouds as a cause for enhanced rates of star and cluster formation.

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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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Piatti, Andrés E. "A genuine Large Magellanic Cloud age gap star cluster." Monthly Notices of the Royal Astronomical Society: Letters 511, no. 1 (January 29, 2022): L72—L76. http://dx.doi.org/10.1093/mnrasl/slac010.

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ABSTRACT We confirm the existence of a second Large Magellanic Cloud (LMC) star cluster, KMHK 1592, with an age that falls in the middle of the so-called LMC star cluster age gap, a long period of time (∼4–11 Gyr) where no star cluster had been uncovered, except ESO 121-SC 03. The age (8.0 ± 0.5 Gyr) and the metallicity ([Fe/H] = −1.0 ± 0.2 dex) of KMHK 1592 were derived from the fit of theoretical isochrones to the intrinsic star cluster colour–magnitude diagram sequences, which were unveiled using a robust star-by-star membership probability procedure. Because of the relative low brightness of the star cluster, deep GEMINI GMOS images were used. We discuss the pros and cons of three glimpsed scenarios that could explain the presence of both LMC age gap star clusters in the outskirts of the LMC, namely: in situ star cluster formation, capture from the Small Magellanic Cloud, or accretion of a small dwarf galaxy.

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Li, Zhongmu, Yangyang Deng, Huanbin Chi, Jing Chen, Xuejie Liu, Chen Yan, Wen Chen, Wenkai Guo, and Tao Xia. "LISC Catalog of Star Clusters. I. Galactic Disk Clusters in Gaia EDR3." Astrophysical Journal Supplement Series 259, no. 1 (February 28, 2022): 19. http://dx.doi.org/10.3847/1538-4365/ac3c49.

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Abstract This work searches for the candidates of Galactic disk star clusters in Gaia Early Data Release 3 (Gaia EDR3) and determines their basic parameters from color–magnitude diagrams (CMDs). A friends-of-friends method for membership determination and stellar population models including binary stars (ASPS) and rotating stars are adopted. As a result, 868 new star cluster candidates are found, besides 2729 known ones. When checking the CMD of each candidate, 61 new candidates show main sequences including a turnoff, which suggests that they are real star clusters. The basic parameters, including distance modulus, color excess, metallicity, age (or age range), primordial binary fraction, and rotating star fraction, are determined carefully by fitting the morphologies of CMDs of 61 newly identified star clusters and 594 known star clusters, which have relatively clear main sequences. The CMDs are fitted in considerable detail to ensure the reliability of property parameters of clusters. All final results are included in a new star cluster catalog, which is named LI team’s Star Cluster (LISC), and the catalog is available in the Zenodo repository.

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Fujii, Michiko S., Takayuki R. Saitoh, Yutaka Hirai, and Long Wang. "SIRIUS project. III. Star-by-star simulations of star cluster formation using a direct N -body integrator with stellar feedback." Publications of the Astronomical Society of Japan 73, no. 4 (June 30, 2021): 1074–99. http://dx.doi.org/10.1093/pasj/psab061.

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Abstract One of the computational challenges of cluster formation simulations is resolving individual stars and simulating massive clusters with masses of more than 104 M⊙ without gravitational softening. Combining a direct N-body code with smoothed-particle hydrodynamics (SPH) code, we have developed a new code, ASURA+BRIDGE, in which we can integrate stellar particles without softening. We add a feedback model for H ii regions into this code, in which thermal and momentum feedback is given within the Strömgren radius. We perform N-body/SPH simulations of star cluster formation. Without softening, a portion of massive stars are ejected from the forming clusters. As a result, the stellar feedback works outside the clusters. This enhances/suppresses the star formation in initially sub-virial/super-virial clouds. We find that the formed star clusters are denser than currently observed open clusters, but the mass–density relation is consistent with or even higher than that which is estimated as an initial cluster density. We also find that some clusters have multiple peaks in their stellar age distribution as a consequence of their hierarchical formation. Irrespective of the virial ratio of molecular clouds, approximately one-third of stars remain in the star clusters after gas expulsion.

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Lee, Seong-Kook, Myungshin Im, Eunhee Ko, Changbom Park, Juhan Kim, Jaehyun Lee, and Minhee Hyun. "Star-formation Property of High Redshift Galaxies in Clusters: Perceptive View from Observation and Simulation." Proceedings of the International Astronomical Union 17, S373 (August 2021): 260–63. http://dx.doi.org/10.1017/s1743921322004409.

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AbstractThe evolution of star formation properties of galaxies depends on the environment where galaxies reside, and generally star formation of galaxies in dense environment decreases more quickly. Interestingly, the star formation property of high-redshift galaxies clusters vary largely even though they are at similar redshift. We have found that the large-scale environment surrounding each galaxy cluster can contribute to make this cluster-by-cluster variation. This correlation is found in the results from observational data as well as in the simulations of galaxy formation. We suggest the ‘Web-feeding model’ to explain this trend. Star-forming galaxies falling into the galaxy cluster from surrounding large-scale structure make the quiescent galaxy fraction of the cluster lower than relatively isolated 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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Pflamm-Altenburg, J., and P. Kroupa. "On the Origin of Complex Stellar Populations in Star Clusters." Proceedings of the International Astronomical Union 3, S246 (September 2007): 71–72. http://dx.doi.org/10.1017/s1743921308015330.

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AbstractThe existence of complex stellar populations in some star clusters challenges the understanding of star formation. E.g. the ONC or the sigma Orionis cluster host much older stars than the main bulk of the young stars. Massive star clusters (ω Cen, G1, M54) show metallicity spreads corresponding to different stellar populations with large age gaps. We show that (i) during star cluster formation field stars can be captured and (ii) very massive globular clusters can accrete gas from a long-term embedding inter stellar medium and restart star formation.

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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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Ishchenko, Marina, Peter Berczik, and Nina Kharchenko. "Dynamical evolution modeling of the Collinder 135 & UBC 7 binary star cluster." Proceedings of the International Astronomical Union 16, S362 (June 2020): 128–33. http://dx.doi.org/10.1017/s1743921322001661.

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AbstractThe purpose of the present work is a detailed investigation of the dynamical evolution of Collinder 135 and UBC 7 star clusters. We present a set of dynamical numerical simulations using realistic star cluster -body modeling technique with the forward integration of the star-by-star cluster models to the present day, based on best-available 3D coordinates and velocities obtained from the latest Gaia EDR3 data release. We have established that Collinder 135 and UBC 7 are probably a binary star cluster and have common origin. We carried out a full star-by-star N-body simulation of the stellar population of both clusters using the new algorithm of Single Stellar Evolution and performed a comparison of the results obtained in the observational data (like cumulative number counts), which showed a fairly good agreement.

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Alzate, Jairo A., Verónica Lora, Gustavo Bruzual, Luis Lomelí-Núñez, and Bernardo Cervantes Sodi. "Star cluster survival in dark matter haloes: an old cluster in Eridanus II?" Monthly Notices of the Royal Astronomical Society 505, no. 2 (May 11, 2021): 2074–86. http://dx.doi.org/10.1093/mnras/stab1322.

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ABSTRACT The star formation history and the internal dynamics of Milky Way satellite galaxies are often complicated. In the last years, a substantial fraction of the known faint dwarf satellites have been studied. Some of them show embedded stellar substructures, such as star clusters and even globular star clusters. In this work, we study Eridanus II, a dwarf spheroidal satellite that hosts a star cluster, using published and archival data from the Hubble Space Telescope Advanced Camera for Surveys. We employ a Bayesian hierarchical method to infer the star formation history of Eridanus II. We find that the bulk of the stars in Eridanus II are very old ($13.5_{-1}^{+0.5}$ Gyr) and quite metal-poor (Z = 0.000 01). We do not find any evidence of the presence of an intermediate age or young population in Eri II. We cannot date the embedded star cluster as a separate entity, but we find it likely that the cluster has a similar age and metallicity as the bulk of the stars in Eri II. The existence of an old star cluster in a dark matter dominated old metal-poor dwarf galaxy is of major importance to cast light on the dark matter distribution within dwarf galaxies. The existence of intermediate age stars is required by the recent detection of carbon stars in Eri II. Since no recent star formation is detected, blue-straggler fusions of lower mass stars are the most likely origin of the carbon star progenitors.

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Tan, Jonathan C. "Massive star and star cluster formation." Proceedings of the International Astronomical Union 2, S237 (August 2006): 258–64. http://dx.doi.org/10.1017/s1743921307001573.

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AbstractI review the status of massive star formation theories: accretion from collapsing, massive, turbulent cores; competitive accretion; and stellar collisions. I conclude the observational and theoretical evidence favors the first of these models. I then discuss: the initial conditions of star cluster formation as traced by infrared dark clouds; the cluster formation timescale; and comparison of the initial cluster mass function in different galactic environments.

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Jeon, Seyoung, Sukyoung K. Yi, Yohan Dubois, Aeree Chung, Julien Devriendt, San Han, Ryan A. Jackson, Taysun Kimm, Christophe Pichon, and Jinsu Rhee. "Star Formation History and Transition Epoch of Cluster Galaxies Based on the Horizon-AGN Simulation." Astrophysical Journal 941, no. 1 (December 1, 2022): 5. http://dx.doi.org/10.3847/1538-4357/ac9d8c.

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Abstract Cluster galaxies exhibit substantially lower star formation rates than field galaxies today, but it is conceivable that clusters were sites of more active star formation in the early universe. Herein, we present an interpretation of the star formation history (SFH) of group/cluster galaxies based on the large-scale cosmological hydrodynamic simulation, Horizon-AGN. We find that massive galaxies in general have small values of e-folding timescales of star formation decay (i.e., “mass quenching”) regardless of their environment, while low-mass galaxies exhibit prominent environmental dependence. In massive host halos (i.e., clusters), the e-folding timescales of low-mass galaxies are further decreased if they reside in such halos for a longer period of time. This “environmental quenching” trend is consistent with the theoretical expectation from ram pressure stripping. Furthermore, we define a “transition epoch” as where cluster galaxies become less star-forming than field galaxies. The transition epoch of group/cluster galaxies varies according to their stellar and host-cluster halo masses. Low-mass galaxies in massive clusters show the earliest transition epoch of ∼7.6 Gyr ago in lookback time. However, this decreases to ∼5.2 Gyr for massive galaxies in low-mass clusters. Based on our findings, we can describe a cluster galaxy’s SFH with regard to the cluster halo-to-stellar mass ratio.

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Freeman, K. C., D. C. Heggie, G. L. H. Harris, G. Lynga, P. E. Nissen, C. Pilachowski, and G. N. Salufcvadze. "Commission 37: Star Clusters and Associations." Transactions of the International Astronomical Union 19, no. 1 (1985): 521–45. http://dx.doi.org/10.1017/s0251107x0000660x.

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The last three years have been very productive for cluster research. This report, on activities in the field, has been compiled by the members of Commission 37. It begins with sections on recent meetings, and on data catalogs (G. Lynga). Detailed tables of work on associations (P.E. Nissen), open clusters (G.L.H. Harris) and globular clusters (R.E. White) are then given. A section on cluster dynamics (D.C. Heggie) follows, and the final section concerns present trends in cluster research (C. Pilachowski).

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Chiboucas, Kristin, Peter Ferguson, R. Brent Tully, David Carter, Steven Phillipps, and Eric Peng. "The UCD Population of the Coma Cluster." Proceedings of the International Astronomical Union 12, S316 (August 2015): 253–54. http://dx.doi.org/10.1017/s1743921315008893.

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AbstractUCDs are super massive star clusters found largely in dense regions but have also been found around individual galaxies and in smaller groups. Their origin is still under debate but consensus is that they formed either during major galaxy mergers as mergers of super massive star clusters, are simply the high mass end of the globular cluster luminosity function and formed in the same way as globular clusters, or that they formed from the threshing of galaxies and are remnant nuclear star clusters, which themselves may have formed from the mergers of globular star clusters within galaxies. We are attempting to disentangle these competing formation scenarios with a large survey of UCDs in the Coma cluster. Using ACS two-passband imaging from the HST/ACS Coma Cluster Treasury Survey, we are using colors and sizes to identify the UCD cluster members. With a large sample within the core region of the Coma cluster, we will use the population size, properties, and spatial distribution, and comparison with the Coma globular cluster and nuclear star cluster populations to discriminate between the threshing and globular cluster scenarios. In particular, previously we have found a possible correlation of UCD colors with host galaxy and a possible excess of UCDs around a non-central giant galaxy with an unusually large globular cluster population, both suggestive of a globular cluster origin. With a larger sample size, we are investigating whether the color correlation with host persists and whether the UCD population is consistent with, or in excess of, the bright end of the GCLF. We present initial results from the survey.

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Sills, Alison. "The emergence of multiple populations in radiation hydrodynamics simulations of cluster formation." Proceedings of the International Astronomical Union 14, S351 (May 2019): 337–40. http://dx.doi.org/10.1017/s1743921319006501.

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AbstractWe present a new approach to understanding star-to-star helium abundance variations within globular clusters. We begin with detailed radiation hydrodynamics simulations of cluster formation within giant molecular clouds, and investigate the conditions under which multiple populations could be created. Chemical enrichment occurs dynamically as the cluster is assembled. We test two extreme mechanisms for injection of enriched gas within the clusters, and find that realistic multiple populations can be formed in both mechanisms. The stochastic cluster formation histories are dictated by the inherent randomness of the timing and location of the formation of small clusters, which rapidly merge to build up the larger cluster, in combination with continual accretion of gas from the cloud. These cluster formation histories naturally produce a diversity of abundance patterns across the massive cluster population. We conclude that multiple populations are a natural outcome of the typical mode of star cluster formation.

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Sabbi, E., A. Nota, M. Sirianni, L. R. Carlson, M. Tosi, J. Gallagher, M. Meixner, et al. "Star formation in the Small Magellanic Cloud: the youngest star clusters." Proceedings of the International Astronomical Union 2, S237 (August 2006): 199–203. http://dx.doi.org/10.1017/s1743921307001469.

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AbstractWe recently launched a comprehensive ground based (ESO/VLT/NTT) and space (HST & SST) study of the present and past star formation in the Small Magellanic Cloud (SMC), in clusters and in the field, with the goal of understanding how star and cluster formation occur and propagate in an environment of low metallicity, with a gas and dust content that is significantly lower than in the Milky Way. In this paper, we present some preliminary results of the “young cluster” program, where we acquired deep F555W (~V), and F814W (~I) HST/ACS images of the four young and massive SMC star clusters: NGC 346, NGC 602, NGC 299, and NGC 376.

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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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Elmegreen, Bruce G. "The nature and nurture of star clusters." Proceedings of the International Astronomical Union 5, S266 (August 2009): 3–13. http://dx.doi.org/10.1017/s1743921309990809.

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AbstractStar clusters have hierarchical patterns in space and time, suggesting formation processes in the densest regions of a turbulent interstellar medium. Clusters also have hierarchical substructure when they are young, which makes them all look like the inner mixed parts of a pervasive stellar hierarchy. Young field stars share this distribution, presumably because some of them came from dissolved clusters and others formed in a dispersed fashion in the same gas. The fraction of star formation that ends up in clusters is apparently not constant, but may increase with interstellar pressure. Hierarchical structure explains why stars form in clusters and why many of these clusters are self-bound. It also explains the cluster mass function. Halo globular clusters share many properties of disk clusters, including what appears to be an upper cluster cutoff mass. However, halo globulars are self-enriched and often connected with dwarf galaxy streams. The mass function of halo globulars could have initially been like the power-law mass function of disk clusters, but the halo globulars have lost their low-mass members. The reasons for this loss are not understood. It could have happened slowly over time as a result of cluster evaporation, or it could have happened early after cluster formation as a result of gas loss. The latter model explains best the observation that the globular cluster mass function has no radial gradient in galaxies.

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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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Turner, Jean L., and Sara C. Beck. "Watching the Birth of Super Star Clusters." Symposium - International Astronomical Union 221 (2004): 125–30. http://dx.doi.org/10.1017/s0074180900241521.

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Subarcsecond infrared and radio observations yield important information about the formation of super star clusters from their surrounding gas. We discuss the general properties of ionized and molecular gas near young, forming SSCs, as illustrated by the prototypical young, forming super star cluster nebula in the dwarf galaxy NGC 5253. This super star cluster appears to have a gravitationally bound nebula, and the lack of molecular gas suggests a very high star formation efficiency, consistent with the formation of a large, bound cluster.

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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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Hußmann, Benjamin, Andrea Stolte, and Wolfgang Brandner. "Proper-motion measurements in the Quintuplet cluster." Proceedings of the International Astronomical Union 5, S266 (August 2009): 422. http://dx.doi.org/10.1017/s174392130999158x.

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AbstractThe three young, massive star clusters found in the Galactic Centre region (Young Nuclear Cluster, the Arches and Quintuplet clusters) are among the six most massive star clusters in our Galaxy, with masses similar to low-mass, extragalactic starburst clusters. The conditions for star formation in this region are extreme and likely comparable to those found in the Hii regions in starburst galaxies and tidal-interaction zones of mergers. As the inner Galactic star clusters can be resolved, they can serve as templates for extragalactic starburst clusters. With knowledge of the spectral types, masses and ages of the individual stars, their stellar population can be studied in detail, allowing derivation of their present-day mass function (PDMF). The Quintuplet cluster, with an age of about 4 Myr, is the most extended of the three clusters and also displays a lower spatial density. To determine its mass function correctly, the distinction between cluster and field stars is therefore of particular importance. We present the first determination of a proper-motion-membership sample for the Quintuplet cluster. By comparing two high-precision astrometric VLT/NACO data sets with a time baseline of 5 years, the displacement of the Quintuplet cluster relative to the field population was measured and a selection of the proper-motion cluster members could be established, from which the PDMF can be derived.

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Piskunov, A. E., A. Just, N. V. Kharchenko, P. Berczik, R. D. Scholz, S. Reffert, and S. X. Yen. "Global survey of star clusters in the Milky Way." Astronomy & Astrophysics 614 (June 2018): A22. http://dx.doi.org/10.1051/0004-6361/201732337.

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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.

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Parmentier, G., and A. Pasquali. "Rebounding Cores to Build Star Cluster Multiple Populations." Astrophysical Journal 924, no. 2 (January 1, 2022): 81. http://dx.doi.org/10.3847/1538-4357/ac32d8.

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Abstract We present a novel approach to the riddle of star cluster multiple populations. Stars form from molecular cores. But not all cores form stars. Following their initial compression, such “failed” cores re-expand, rather than collapsing. We propose that their formation and subsequent dispersal regulate the gas density of cluster-forming clumps and, therefore, their core and star formation rates. Clumps for which failed cores are the dominant core type experience star formation histories with peaks and troughs (i.e., discrete star formation episodes). In contrast, too few failed cores results in smoothly decreasing star formation rates. We identify three main parameters shaping the star formation history of a clump: the star and core formation efficiencies per free-fall time, and the timescale on which failed cores return to the clump gas. The clump mass acts as a scaling factor. We use our model to constrain the density and mass of the Orion Nebula Cluster progenitor clump, and to caution that the star formation histories of starburst clusters may contain close-by peaks concealed by stellar age uncertainties. Our model generates a great variety of star formation histories. Intriguingly, the chromosome maps and O–Na anticorrelations of old globular clusters also present diverse morphologies. This prompts us to discuss our model in the context of globular cluster multiple stellar populations. More massive globular clusters exhibit stronger multiple stellar population patterns, which our model can explain if the formation of the polluting stars requires a given stellar mass threshold.

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Feldmeier-Krause, A., N. Neumayer, R. Schödel, A. Seth, P. T. de Zeeuw, C. J. Walcher, N. Lützgendorf, M. Kissler-Patig, M. Hilker, and H. Kuntschner. "The Assembly History of the Milky Way Nuclear Star Cluster." Proceedings of the International Astronomical Union 12, S316 (August 2015): 50–54. http://dx.doi.org/10.1017/s1743921315009412.

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AbstractWithin the central 10 pc of our Galaxy lies a dense cluster of stars, the nuclear star cluster. This cluster forms a distinct component of our Galaxy. Nuclear star clusters are common objects and are detected in ~ 75% of nearby galaxies. It is, however, not fully understood how nuclear star clusters form. The Milky Way nuclear star cluster is the closest of its kind. At a distance of only 8 kpc we can spatially resolve its stellar populations and kinematics much better than in external galaxies. This makes the Milky Way nuclear star cluster the perfect local reference object for understanding the structure and assembly history of nuclear star clusters in general. There are of the order of 107 stars within the central 10 pc of the Galactic center. Most of these stars are several Gyr old late-type stars. However, there are also more than 100 hot early-type stars in the central parsec of the Milky Way, with ages of only a few Myr. Beyond a projected distance of 0.5 pc of the Galactic center, the density of young stars was largely unknown, since only very few spectroscopic observations existed so far. We covered the central >4 pc2 (0.75 sq.arcmin) of the Galactic center using the integral-field spectrograph KMOS (VLT). We extracted more than 1,000 spectra from individual stars and identified >20 new early-type stars based on their spectra. We studied the spatial distribution of the different populations and their kinematics to put constraints on the assembly history of the Milky Way nuclear star cluster.

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Neumayer, Nadine. "Nuclear Star Clusters." Proceedings of the International Astronomical Union 12, S316 (August 2015): 84–90. http://dx.doi.org/10.1017/s1743921316007018.

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AbstractThe centers of galaxies host two distinct, compact components: massive black holes and nuclear star clusters. Nuclear star clusters are the densest stellar systems in the universe, with masses of ~ 107M⊙and sizes of ~ 5pc. They are almost ubiquitous at the centres of nearby galaxies with masses similar to, or lower than the Milky Way. Their occurrence both in spirals and dwarf elliptical galaxies appears to be a strong function of total galaxy light or mass. Nucleation fractions are up to 100% for total galaxy magnitudes of MB= −19mag or total galaxy luminosities of about LB= 1010L⊙and falling nucleation fractions for both smaller and higher galaxy masses. Although nuclear star clusters are so common, their formation mechanisms are still under debate. The two main formation scenarios proposed are the infall and subsequent merging of star clusters and the in-situ formation of stars at the center of a galaxy. Here, I review the state-of-the-art of nuclear star cluster observations concerning their structure, stellar populations and kinematics. These observations are used to constrain the proposed formation scenarios for nuclear star clusters. Constraints from observations show, that likely both cluster infall and in-situ star formation are at work. The relative importance of these two mechanisms is still subject of investigation.

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Ivanov, Valentin D., Maria Messineo, Qingfeng Zhu, Don Figer, J. Borissova, R. Kurtev, and G. R. Ivanov. "Infrared surveys of Galactic star clusters." Proceedings of the International Astronomical Union 5, S266 (August 2009): 203–10. http://dx.doi.org/10.1017/s1743921309991062.

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AbstractMany attempts have been made to carry out a complete observational census of Milky Way star clusters based on recent near- and mid-infrared surveys. However, more clusters are still being discovered, indicating that existing catalogs are incomplete. We attempt to estimate the total number of supermassive (SM; Mcl ≥ 104 M⊙) clusters in the Galaxy, and to improve the yield from the automated cluster searches. Assuming that the ‘local’ census of SM clusters is complete, and that their surface density accross the disk follows that of the stars, we predict that the Milky Way contains ≥81 ± 21 SM clusters. We apply a cluster-detection algorithm to the 2mass Point Source Catalog after a preliminary color and/or magnitude selection of the point sources to improves the surface-density cluster-to-field contrast. Our algorithm identified 94 new candidates, and re-identified 34 known clusters. During the visual inspection, we detected an additional 41 new candidates, and re-identified 32 known objects. Preliminary characterization suggests that the new list may contain red-supergiant, open and globular clusters.

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Lee, Joowon, and Jihye Shin. "Dynamical modeling of the Arches cluster using Fokker-Planck calculations." Proceedings of the International Astronomical Union 10, S312 (August 2014): 241–42. http://dx.doi.org/10.1017/s1743921315007905.

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AbstractThe Arches cluster is a young, compact, and massive star cluster located in ~30pc away from the Galactic Center in projection. The cluster is located in the extreme environment of the Galactic Center, making it an excellent target for understanding the effects of star-forming environment on the mass function of star clusters. In this study, we estimate the initial condition (mass, concentration parameter, and galactocentric radius) of the Arches cluster by comparing Fokker-Planck calculations with observed velocity dispersion, surface density and mass function data.

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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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Choksi, Nick, and J. M. Diederik Kruijssen. "On the initial mass–radius relation of stellarclusters." Monthly Notices of the Royal Astronomical Society 507, no. 4 (September 10, 2021): 5492–506. http://dx.doi.org/10.1093/mnras/stab2514.

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ABSTRACT Young stellar clusters across nearly five orders of magnitude in mass appear to follow a power-law mass–radius relationship (MRR), $R_{\star }\propto M_{\star }^{\alpha }$, with α ≈ 0.2–0.33. We develop a simple analytic model for the cluster mass–radius relation. We consider a galaxy disc in hydrostatic equilibrium, which hosts a population of molecular clouds that fragment into clumps undergoing cluster formation and feedback-driven expansion. The model predicts a mass–radius relation of $R_{\star }\propto M_{\star }^{1/2}$ and a dependence on the kpc-scale gas surface density $R_{\star }\propto \Sigma _{\rm g}^{-1/2}$, which results from the formation of more compact clouds (and cluster-forming clumps within) at higher gas surface densities. This environmental dependence implies that the high-pressure environments in which the most massive clusters can form also induce the formation of clusters with the smallest radii, thereby shallowing the observed MRR at high-masses towards the observed $R_{\star }\propto M_{\star }^{1/3}$. At low cluster masses, relaxation-driven expansion induces a similar shallowing of the MRR. We combine our predicted MRR with a simple population synthesis model and apply it to a variety of star-forming environments, finding good agreement. Our model predicts that the high-pressure formation environments of globular clusters at high redshift naturally led to the formation of clusters that are considerably more compact than those in the local Universe, thereby increasing their resilience to tidal shock-driven disruption and contributing to their survival until the present day.

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Hislop, Jessica M., Thorsten Naab, Ulrich P. Steinwandel, Natalia Lahén, Dimitrios Irodotou, Peter H. Johansson, and Stefanie Walch. "The challenge of simulating the star cluster population of dwarf galaxies with resolved interstellar medium." Monthly Notices of the Royal Astronomical Society 509, no. 4 (November 23, 2021): 5938–54. http://dx.doi.org/10.1093/mnras/stab3347.

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ABSTRACT We present results on the star cluster properties from a series of high resolution smoothed particles hydrodynamics (SPH) simulations of isolated dwarf galaxies as part of the griffin project. The simulations at sub-parsec spatial resolution and a minimum particle mass of 4 M⊙ incorporate non-equilibrium heating, cooling, and chemistry processes, and realize individual massive stars. The simulations follow feedback channels of massive stars that include the interstellar-radiation field variable in space and time, the radiation input by photo-ionization and supernova explosions. Varying the star formation efficiency per free-fall time in the range ϵff = 0.2–50${{\ \rm per\ cent}}$ neither changes the star formation rates nor the outflow rates. While the environmental densities at star formation change significantly with ϵff, the ambient densities of supernovae are independent of ϵff indicating a decoupling of the two processes. At low ϵff, gas is allowed to collapse more before star formation, resulting in more massive, and increasingly more bound star clusters are formed, which are typically not destroyed. With increasing ϵff, there is a trend for shallower cluster mass functions and the cluster formation efficiency Γ for young bound clusters decreases from $50 {{\ \rm per\ cent}}$ to $\sim 1 {{\ \rm per\ cent}}$ showing evidence for cluster disruption. However, none of our simulations form low mass (<103 M⊙) clusters with structural properties in perfect agreement with observations. Traditional star formation models used in galaxy formation simulations based on local free-fall times might therefore be unable to capture star cluster properties without significant fine tuning.

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Nayak, P. K., A. Subramaniam, S. Choudhury, and Ram Sagar. "Star clusters in the Magellanic Clouds." Astronomy & Astrophysics 616 (August 2018): A187. http://dx.doi.org/10.1051/0004-6361/201732227.

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Aims. We aim to estimate the age and reddening parameters of already identified star clusters within the Small Magellanic Cloud (SMC) in a consistent way using available photometric data, classify them based on their mass and strength, and study their spatiotemporal distribution. Methods. We have used a semi-automated quantitative method, developed in the first paper of this series (Paper I), to estimate the cluster parameters using the V and I band photometric data from the Optical Gravitational Lensing Experiment (OGLE) III survey. Results. We estimated parameters of 179 star clusters (17 are newly parameterised) and classified them into four groups. We present an online catalogue of parameters as well as cleaned and isochrone-fitted colour magnitude diagrams of 179 clusters. We compiled age information of 468 clusters by combining previous studies with our catalogue, to study their spatio-temporal distribution. Most of the clusters located in the southern part of the SMC are in the age range 600 Myr–1.25 Gyr, whereas, the clusters younger than 100 Myr are mostly found in the northern SMC, with the central SMC showing continuous cluster formation. The peak of the cluster age distribution is identified at 130 ± 35 Myr, very similar to the Large Magellanic Cloud (LMC) in Paper I. Conclusions. We suggest that the burst of cluster formation at 130 Myr is due to the most recent LMC-SMC interaction. 90% of the studied sample is found to have mass < 1700 M⊙, suggesting that the SMC is dominated by low mass clusters. There is tentative evidence for compact clusters in the LMC when compared to those in the Galaxy and the SMC. A progressive shifting of cluster location from the south to north of the SMC is identified in last ~600 Myr. The details of spatio-temporal distribution of clusters presented in two videos as part of this study can be used as a tool to constrain details of the recent LMC-SMC interactions.

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Farias, Juan P., Jonathan C. Tan, and Sourav Chatterjee. "Star cluster formation from turbulent clumps. II. Gradual star cluster formation." Monthly Notices of the Royal Astronomical Society 483, no. 4 (December 20, 2018): 4999–5019. http://dx.doi.org/10.1093/mnras/sty3470.

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Portegies Zwart, S. F., S. L. W. McMillan, P. Hut, and J. Makino. "Star cluster ecology -- IV. Dissection of an open star cluster: photometry." Monthly Notices of the Royal Astronomical Society 321, no. 2 (February 21, 2001): 199–226. http://dx.doi.org/10.1046/j.1365-8711.2001.03976.x.

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Portegies Zwart, Simon F., Piet Hut, Stephen L. W. McMillan, and Junichiro Makino. "Star cluster ecology – V. Dissection of an open star cluster: spectroscopy." Monthly Notices of the Royal Astronomical Society 351, no. 2 (June 21, 2004): 473–86. http://dx.doi.org/10.1111/j.1365-2966.2004.07709.x.

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Journal articles on the topic 'Star cluster'

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