Articles de revues : « Galaxy formation clusters »

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Larson, Richard B. « Galaxy Formation and Cluster Formation ». Symposium - International Astronomical Union 126 (1988) : 311–21. http://dx.doi.org/10.1017/s007418090004256x.

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A primary motivation for studying globular clusters is that, as the oldest known galactic fossils, they trace the earliest stages of galactic evolution; indeed, they may hold the key to understanding galaxy formation. Thus it is clearly of great importance to learn how to read the fossil record. To do this, we need to understand something about how the globular clusters themselves formed. Were they the first bound objects to form, or did they form in larger pre-existing systems of which they are just small surviving fragments? If the latter, what were the prehistoric cluster-forming systems like? And how did they manage to produce objects like globular clusters?

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Blau, Steven K. « Galaxy clusters in formation ». Physics Today 68, n^o 6 (juin 2015) : 20. http://dx.doi.org/10.1063/pt.3.2807.

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Kravtsov, Andrey V., et Stefano Borgani. « Formation of Galaxy Clusters ». Annual Review of Astronomy and Astrophysics 50, n^o 1 (22 septembre 2012) : 353–409. http://dx.doi.org/10.1146/annurev-astro-081811-125502.

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Robertson, Andrew. « The galaxy–galaxy strong lensing cross-sections of simulated ΛCDM galaxy clusters ». Monthly Notices of the Royal Astronomical Society : Letters 504, n^o 1 (22 mars 2021) : L7—L11. http://dx.doi.org/10.1093/mnrasl/slab028.

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ABSTRACT We investigate a recent claim that observed galaxy clusters produce an order of magnitude more galaxy–galaxy strong lensing (GGSL) than simulated clusters in a Λ cold dark matter (CDM) cosmology. We take galaxy clusters from the c-eagle hydrodynamical simulations and calculate the expected amount of GGSL for sources placed behind the clusters at different redshifts. The probability of a source lensed by one of the most massive c-eagle clusters being multiply imaged by an individual cluster member is in good agreement with that inferred for observed clusters. We show that numerically converged results for the GGSL probability require higher resolution simulations than had been used previously. On top of this, different galaxy formation models predict cluster substructures with different central densities, such that the GGSL probabilities in ΛCDM cannot yet be robustly predicted. Overall, we find that GGSL within clusters is not currently in tension with the ΛCDM cosmological model.

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Neumayer, Nadine. « Nuclear Star Clusters ». Proceedings of the International Astronomical Union 12, S316 (août 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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Anders, Peter, Uta Fritze –. v. Alvensleben et 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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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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Benavides, José A., Laura V. Sales et Mario G. Abadi. « Accretion of galaxy groups into galaxy clusters ». Monthly Notices of the Royal Astronomical Society 498, n^o 3 (2 septembre 2020) : 3852–62. http://dx.doi.org/10.1093/mnras/staa2636.

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ABSTRACT We study the role of group infall in the assembly and dynamics of galaxy clusters in ΛCDM. We select 10 clusters with virial mass M200 ∼ 1014 $\rm M_\odot$ from the cosmological hydrodynamical simulation Illustris and follow their galaxies with stellar mass M⋆ ≥ 1.5 × 108 $\rm M_\odot$. A median of ${\sim}38{{\ \rm per\ cent}}$ of surviving galaxies at z = 0 is accreted as part of groups and did not infall directly from the field, albeit with significant cluster-to-cluster scatter. The evolution of these galaxy associations is quick, with observational signatures of their common origin eroding rapidly in 1–3 Gyr after infall. Substructure plays a dominant role in fostering the conditions for galaxy mergers to happen, even within the cluster environment. Integrated over time, we identify (per cluster) an average of 17 ± 9 mergers that occur in infalling galaxy associations, of which 7 ± 3 occur well within the virial radius of their cluster hosts. The number of mergers shows large dispersion from cluster to cluster, with our most massive system having 42 mergers above our mass cut-off. These mergers, which are typically gas rich for dwarfs and a combination of gas rich and gas poor for M⋆ ∼ 1011 $\rm M_\odot$, may contribute significantly within ΛCDM to the formation of specific morphologies, such as lenticulars (S0) and blue compact dwarfs in groups and clusters.

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Elbaz, D. « Infrared Observations of Galaxy Clusters ». Highlights of Astronomy 11, n^o 2 (1998) : 1128–30. http://dx.doi.org/10.1017/s1539299600019754.

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The evolution of galaxy clusters from their formation due to the merging of sub structures, the bulk of star formation and subsequent chemical enrichment of the intra-cluster medium, is expected to be quite recent (z<l-2) in the hierarchical clustering scenario (White & Frenk 1991).

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Danieli, Shany, Pieter van Dokkum, Sebastian Trujillo-Gomez, J. M. Diederik Kruijssen, Aaron J. Romanowsky, Scott Carlsten, Zili Shen et al. « NGC 5846-UDG1 : A Galaxy Formed Mostly by Star Formation in Massive, Extremely Dense Clumps of Gas ». Astrophysical Journal Letters 927, n^o 2 (1 mars 2022) : L28. http://dx.doi.org/10.3847/2041-8213/ac590a.

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Abstract It has been shown that ultra-diffuse galaxies (UDGs) have higher specific frequencies of globular clusters, on average, than other dwarf galaxies with similar luminosities. The UDG NGC 5846-UDG1 is among the most extreme examples of globular cluster–rich galaxies found so far. Here we present new Hubble Space Telescope observations and analysis of this galaxy and its globular cluster system. We find that NGC 5846-UDG1 hosts 54 ± 9 globular clusters, three to four times more than any previously known galaxy with a similar luminosity and higher than reported in previous studies. With a galaxy luminosity of L V,gal ≈ 6 × 107 L ⊙ (M ⋆ ≈ 1.2 × 108 M ⊙) and a total globular cluster luminosity of L V,GCs ≈ 7.6 × 106 L ⊙, we find that the clusters currently comprise ∼13% of the total light. Taking into account the effects of mass loss from clusters during their formation and throughout their lifetime, we infer that most of the stars in the galaxy likely formed in globular clusters, and very little to no “normal” low-density star formation occurred. This result implies that the most extreme conditions during early galaxy formation promoted star formation in massive and dense clumps, in contrast to the dispersed star formation observed in galaxies today.

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Lindholmer, Mikkel O., et Kevin A. Pimbblet. « Redshift measurement through star formation ». Astronomy & ; Astrophysics 629 (23 août 2019) : A7. http://dx.doi.org/10.1051/0004-6361/201833046.

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In this work we use the property that, on average, star formation rate increases with redshift for objects with the same mass – the so called galaxy main sequence – to measure the redshift of galaxy clusters. We use the fact that the general galaxy population forms both a quenched and a star-forming sequence, and we locate these ridges in the SFR–M⋆ plane with galaxies taken from the Sloan Digital Sky Survey in discrete redshift bins. We fitted the evolution of the galaxy main sequence with redshift using a new method and then subsequently apply our method to a suite of X-ray selected galaxy clusters in an attempt to create a new distance measurement to clusters based on their galaxy main sequence. We demonstrate that although it is possible in several galaxy clusters to measure the main sequences, the derived distance and redshift from our galaxy main sequence fitting technique has an accuracy of σz = ±0.017 ⋅ (z + 1) and is only accurate up to z ≈ 0.2.

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Hwang, Narae, et Myung Gyoon Lee. « Tracing star cluster formation in the interacting galaxy M51 ». Proceedings of the International Astronomical Union 5, S266 (août 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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Li, Yuexing, Mordecai-Mark Mac Low et Ralf S. Klessen. « Globular Cluster Formation in Galaxy Mergers ». Highlights of Astronomy 13 (2005) : 205. http://dx.doi.org/10.1017/s1539299600015719.

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AbstractWe present preliminary results of a high resolution simulation of globular cluster formation in a galaxy merger using GADGET (Springel et al. 2001). A barotropic equation of state (Li et al 2003) is implemented to include effects of cooling and heating. After one orbital period, a dozen proto-globular clusters are identified in the tidal tails.

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Arnaboldi, Magda, et Ortwin Gerhard. « JD2 - Diffuse Light in Galaxy Clusters ». Proceedings of the International Astronomical Union 5, H15 (novembre 2009) : 97–110. http://dx.doi.org/10.1017/s174392131000846x.

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AbstractDiffuse intracluster light (ICL) has now been observed in nearby and in intermediate redshift clusters. Individual intracluster stars have been detected in the Virgo and Coma clusters and the first color-magnitude diagram and velocity measurements have been obtained. Recent studies show that the ICL contains of the order of 10% and perhaps up to 30% of the stellar mass in the cluster, but in the cores of some dense and rich clusters like Coma, the local ICL fraction can be high as 40%-50%. What can we learn from the ICL about the formation of galaxy clusters and the evolution of cluster galaxies? How and when did the ICL form? What is the connection to the central brightest cluster galaxy? Cosmological N-body and hydrodynamical simulations are beginning to make predictions for the kinematics and origin of the ICL. The ICL traces the evolution of baryonic substructures in dense environments and can thus be used to constrain some aspects of cosmological simulations that are most uncertain, such as the modeling of star formation and the mass distribution of the baryonic component in galaxies.

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Anders, Peter, Uta Fritze-V. Alvensleben et 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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Brodie, Jean P., et Jay Strader. « Extragalactic Globular Clusters and Galaxy Formation ». Annual Review of Astronomy and Astrophysics 44, n^o 1 (septembre 2006) : 193–267. http://dx.doi.org/10.1146/annurev.astro.44.051905.092441.

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Laganá, T. F., G. B. Lima Neto, F. Andrade-Santos et E. S. Cypriano. « Star formation efficiency in galaxy clusters ». Astronomy & ; Astrophysics 485, n^o 3 (15 mai 2008) : 633–44. http://dx.doi.org/10.1051/0004-6361:20079168.

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Cohn, J. D., et Martin White. « The formation histories of galaxy clusters ». Astroparticle Physics 24, n^o 4-5 (décembre 2005) : 316–33. http://dx.doi.org/10.1016/j.astropartphys.2005.07.006.

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Gnedin, Oleg Y. « Modeling Formation of Globular Clusters : Beacons of Galactic Star Formation ». Proceedings of the International Astronomical Union 6, S270 (mai 2010) : 381–84. http://dx.doi.org/10.1017/s1743921311000676.

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AbstractModern hydrodynamic simulations of galaxy formation are able to predict accurately the rates and locations of the assembly of giant molecular clouds in early galaxies. These clouds could host star clusters with the masses and sizes of real globular clusters. I describe current state-of-the-art simulations aimed at understanding the origin of the cluster mass function and metallicity distribution. Metallicity bimodality of globular cluster systems appears to be a natural outcome of hierarchical formation and gradually declining fraction of cold gas in galaxies. Globular cluster formation was most prominent at redshifts z > 3, when massive star clusters may have contributed as much as 20% of all galactic star formation.

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Chun, Kyungwon, Jihye Shin, Rory Smith, Jongwan Ko et Jaewon Yoo. « The Formation of the Brightest Cluster Galaxy and Intracluster Light in Cosmological N-body Simulations with the Galaxy Replacement Technique ». Astrophysical Journal 943, n^o 2 (1 février 2023) : 148. http://dx.doi.org/10.3847/1538-4357/aca890.

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Abstract We investigate the formation channels of the intracluster light (ICL) and the brightest cluster galaxy (BCG) in clusters at z = 0. For this, we perform multi-resolution cosmological N-body simulations using the “galaxy replacement technique.” We study the formation channels of the ICL and BCG as a function of distance from the cluster center and the dynamical state of the clusters at z = 0. To do this, we trace back the stars of the ICL and BCG, and identify the stellar components in which they existed when they first fell into the clusters. We find that the progenitors of the ICL and BCG in the central region of the cluster fell earlier and with a higher total mass ratio of the progenitors to the cluster compared to the outer region. This causes a negative radial gradient in the infall time and total mass ratio of the progenitors. Although stellar mass of the progenitors does not show the same radial gradient in all clusters, massive galaxies (M gal > 1010 M ⊙ h−1) are the dominant formation channel of the ICL and BCG for all clusters, except for our most relaxed cluster. For clusters that are dynamically more unrelaxed, we find that the progenitors of the ICL and BCG fall into their clusters more recently, and with a higher mass and mass ratio. Furthermore, we find that the diffuse material of massive galaxies and group-mass halos that is formed by preprocessing contributes significantly to the ICL in the outer region of the unrelaxed clusters.

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Gouin, C., N. Aghanim, V. Bonjean et M. Douspis. « Probing the azimuthal environment of galaxies around clusters ». Astronomy & ; Astrophysics 635 (mars 2020) : A195. http://dx.doi.org/10.1051/0004-6361/201937218.

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Galaxy clusters are connected at their peripheries to the large-scale structures by cosmic filaments that funnel accreting material. These filamentary structures are studied to investigate both environment-driven galaxy evolution and structure formation and evolution. In the present work, we probe in a statistical manner the azimuthal distribution of galaxies around clusters as a function of the cluster-centric distance, cluster richness, and star-forming or passive galaxy activity. We performed a harmonic decomposition in large photometric galaxy catalogue around 6400 SDSS clusters with masses M > 1014 solar masses in the redshift range of 0.1 < z < 0.3. The same analysis was performed on the mock galaxy catalogue from the light cone of a Magneticum hydrodynamical simulation. We used the multipole analysis to quantify asymmetries in the 2D galaxy distribution. In the inner cluster regions at R < 2R500, we confirm that the galaxy distribution traces an ellipsoidal shape, which is more pronounced for richest clusters. In the outskirts of the clusters (R = [2 − 8]R500), filamentary patterns are detected in harmonic space with a mean angular scale mmean = 4.2 ± 0.1. Massive clusters seem to have a larger number of connected filaments than lower-mass clusters. We also find that passive galaxies appear to trace the filamentary structures around clusters better. This is the case even if the contribution of star-forming galaxies tends to increase with the cluster-centric distance, suggesting a gradient of galaxy activity in filaments around clusters.

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Brodie, Jean P. « Constraints on Galaxy Formation from Extragalactic Globular Clusters ». Symposium - International Astronomical Union 187 (2002) : 175–84. http://dx.doi.org/10.1017/s0074180900113907.

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The merger model for elliptical galaxy formation has received increasing attention since it was first suggested by Toomre & Toomre (1972). Van den Bergh (1984) pointed out a problem with the idea that elliptical galaxies were formed by simply combining two, or more, spiral galaxies. He noted that the specific frequency (SN, number of globular clusters per unit galaxy light) is systematically lower for spirals than for ellipticals. Schweizer (1987) suggested that globular clusters might be expected to form in the merger process, thereby alleviating or possibly eliminating the SN problem. Ashman & Zepf (1992) developed this idea into a merger model for globular cluster formation with testable predictions.

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Lee, Seong-Kook, Myungshin Im, Minhee Hyun, Bomi Park, Jae-Woo Kim, Dohyeong Kim et Yongjung Kim. « More connected, more active : galaxy clusters and groups at z ∼ 1 and the connection between their quiescent galaxy fractions and large-scale environments ». Monthly Notices of the Royal Astronomical Society 490, n^o 1 (16 septembre 2019) : 135–55. http://dx.doi.org/10.1093/mnras/stz2564.

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ABSTRACT High-redshift galaxy clusters, unlike local counterparts, show diverse star formation activities. However, it is still unclear what keeps some of the high-redshift clusters active in star formation. To address this issue, we performed a multiobject spectroscopic observation of 226 high-redshift (0.8 < z < 1.3) galaxies in galaxy cluster candidates and the areas surrounding them. Our spectroscopic observation reveals six to eight clusters/groups at z ∼ 0.9 and z ∼ 1.3. The redshift measurements demonstrate the reliability of our photometric redshift measurements, which in turn gives credibility for using photometric redshift members for the analysis of large-scale structures (LSSs). Our investigation of the large-scale environment (∼10 Mpc) surrounding each galaxy cluster reveals LSSs – structures up to ∼10 Mpc scale – around many of, but not all, the confirmed overdensities and the cluster candidates. We investigate the correlation between quiescent galaxy fraction of galaxy overdensities and their surrounding LSSs, with a larger sample of ∼20 overdensities including photometrically selected overdensities at 0.6 < z < 0.9. Interestingly, galaxy overdensities embedded within these extended LSSs show a lower fraction of quiescent galaxies ($\sim 20{{\ \rm per\ cent}}$) than isolated ones at similar redshifts (with a quiescent galaxy fraction of $\sim 50 {{\ \rm per\ cent}}$). Furthermore, we find a possible indication that clusters/groups with a high quiescent galaxy fraction are more centrally concentrated. Based on these results, we suggest that LSSs are the main reservoirs of gas and star-forming galaxies to keep galaxy clusters fresh and extended in size at z ∼ 1.

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Fujita, Yutaka, Keiichi Umetsu, Elena Rasia, Massimo Meneghetti, Megan Donahue, Elinor Medezinski, Nobuhiro Okabe, Marc Postman et Stefano Ettori. « The new fundamental plane dictating galaxy cluster evolution ». Proceedings of the International Astronomical Union 15, S341 (novembre 2019) : 271–72. http://dx.doi.org/10.1017/s1743921319001376.

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AbstractIn this study, we show that the characteristic radius rs, mass Ms, and the X-ray temperature, TX, of galaxy clusters form a thin plane in the space of (log rs, log Ms, log TX). This tight correlation indicates that the cluster structure including the temperature is affected by the formation time of individual clusters. Numerical simulations show that clusters move along the fundamental plane as they evolve. The plane and the cluster evolution within the plane can be explained by a similarity solution of structure formation. The angle of the plane shows that clusters have not achieved “virial equilibrium”. The details of this study are written in Fujita et al. (2018a,b).

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Zepf, Stephen E. « Formation Scenarios for Globular Clusters and Their Host Galaxies ». Symposium - International Astronomical Union 207 (2002) : 653–63. http://dx.doi.org/10.1017/s0074180900224492.

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This review focuses on how galaxies and their globular cluster systems form. I first discuss the now fairly convincing evidence that some globular clusters form in galaxy starbursts/mergers. One way these observations are valuable is they place important constraints on the physics of the formation of globular clusters. Moreover, it is natural to associate the typically metal-rich clusters forming in mergers with the substantial metal-rich population of globulars around ellipticals, thereby implying an important role for galaxy mergers in the evolution of elliptical galaxies. I also highlight some new observational efforts aimed at constraining how and when elliptical galaxies and their globular cluster systems formed. These include systematic studies of the number of globular clusters around galaxies as a function of morphological type, studies of the kinematics of globular cluster populations in elliptical galaxies, and a variety of observational programs aimed at constraining the relative ages of globular clusters within galaxies as a function of cluster metallicity. The understanding of the formation of globular cluster systems and their host galaxies has grown dramatically in recent years, and the future looks equally promising.

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Elmegreen, Bruce G. « Triggering the Formation of Young Clusters ». Symposium - International Astronomical Union 207 (2002) : 390–400. http://dx.doi.org/10.1017/s0074180900224108.

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Star formation is triggered in essentially three ways: (1) the pressures from existing stars collect and squeeze nearby dense gas into gravitationally unstable configurations, (2) random compression from supersonic turbulence makes new clouds and clumps, some of which are gravitationally unstable, and (3) gravitational instabilities in large parts of a galaxy disk make giant new clouds and spiral arms that fragment by the other two processes into a hierarchy of smaller star-forming pieces. Examples of each process are given. Most dense clusters in the solar neighborhood were triggered by external stellar pressures. Most clusters and young stars on larger scales are organized into hierarchical patterns with an age-size correlation, suggestive of turbulence. Beads-on-a-string of star formation in spiral arms and resonance rings indicate gravitational instabilities. The turbulence model explains the mass spectrum of clusters, the correlation between the fraction of star formation in the form of clusters and the star formation rate, found by Larsen & Richtler, and the correlation between the size of the largest cluster and the number of clusters in a galaxy.

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Khosroshahi, Habib G., et T. J. Ponman. « Fossil Galaxy Groups ; Scaling Relations, Galaxy Properties and Formation of BCGs ». Proceedings of the International Astronomical Union 2, S235 (août 2006) : 214. http://dx.doi.org/10.1017/s174392130600620x.

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AbstractWe study fossil galaxy groups, their hot gas and the galaxy properties. Fossils are more X-ray luminous than non-fossil groups, however, they fall comfortably on the conventional L-T relation of galaxy groups and clusters indicating that their X-ray luminosity and temperature are both boosted, arguably, as a result of their early formation. The central dominant galaxy in fossils have optical luminosity comparable to the brightest cluster galaxies (BCGs), however, the isophotal shapes of the central galaxy in fossils are non-boxy in contrast to the isophotes of majority of the BCGs.

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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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Rieder, Steven, Clare Dobbs, Thomas Bending, Kong You Liow et James Wurster. « The formation and early evolution of embedded star clusters in spiral galaxies ». Monthly Notices of the Royal Astronomical Society 509, n^o 4 (26 novembre 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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Assmann, P., M. Fellhauer et M. I. Wilkinson. « Star clusters as building blocks for dSph galaxy formation ». Proceedings of the International Astronomical Union 5, S266 (août 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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Hashimoto, Tetsuya, Tomotsugu Goto, Rieko Momose, Chien-Chang Ho, Ryu Makiya, Chia-Ying Chiang et Seong Jin Kim. « A young galaxy cluster in the old Universe ». Monthly Notices of the Royal Astronomical Society 489, n^o 2 (12 août 2019) : 2014–29. http://dx.doi.org/10.1093/mnras/stz2182.

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ABSTRACT Galaxies evolve from a blue star-forming phase into a red quiescent one by quenching their star formation activity. In high-density environments, this galaxy evolution proceeds earlier and more efficiently. Therefore, local galaxy clusters are dominated by well-evolved red elliptical galaxies. The fraction of blue galaxies in clusters monotonically declines with decreasing redshift, i.e. the Butcher–Oemler effect. In the local Universe, observed blue fractions of massive clusters are as small as ≲0.2. Here we report a discovery of a ‘blue cluster’ that is a local galaxy cluster with an unprecedentedly high fraction of blue star-forming galaxies yet hosted by a massive dark matter halo. The blue fraction is 0.57, which is 4.0σ higher than those of the other comparison clusters under the same selection and identification criteria. The velocity dispersion of the member galaxies is 510 km s−1, which corresponds to a dark matter halo mass of 2.0$^{+1.9}_{-1.0}\times 10^{14}$ M⊙. The blue fraction of the cluster is more than 4.7σ beyond the standard theoretical predictions including semi-analytic models of galaxy formation. The probability to find such a high blue fraction in an individual cluster is only 0.003 per cent, which challenges the current standard frameworks of the galaxy formation and evolution in the ΛCDM universe. The spatial distribution of galaxies around the blue cluster suggests that filamentary cold gas streams can exist in massive haloes even in the local Universe. However these cold streams have already disappeared in the theoretically simulated local universes.

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Spergel, David N. « Textures and Galaxy Formation ». Highlights of Astronomy 9 (1992) : 705–8. http://dx.doi.org/10.1017/s153929960001011x.

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AbstractTextures will produce positively skewed non-Gaussian primordial fluctuations. This implies that galaxies and quasars formed earlier in this model than in a Gaussian model with the same power spectrum. The model also predicts the existence of more high velocity dispersion clusters and richer superclusters. We describe the texture model and our numerical simulations of the origin of structure in the model.

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Hattori, M. « A Metal Enriched Dark Cluster of Galaxies at Z = 1 ». Symposium - International Astronomical Union 187 (2002) : 129–38. http://dx.doi.org/10.1017/s0074180900113841.

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Looking for and studying very distant galaxy clusters, clusters at z > 1, are one of the prime subjects of the modern observational cosmology. If the metallicity of the hot intra-cluster medium in very distant galaxy clusters is measured for example, it provides fruitful informations for us to understand the formation and evolution of galaxies. However, difficulty of the study is that there is few confirmed very distant galaxy clusters yet. We first have to search for very distant clusters but it requires very deep observations. A random selection of sky is not practical. We have to select the sky. In this article, it is demonstrated that missing lens problem has close connection with very distant cluster of galaxies and dark lens searches could open a new window for studying very distant cluster of galaxies.

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Durret, Florence, Christophe Adami et Tatiana F. Laganá. « Environmental Effects on Galaxy Luminosity Functions in Clusters ». Proceedings of the International Astronomical Union 6, S277 (décembre 2010) : 9–12. http://dx.doi.org/10.1017/s1743921311022356.

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AbstractThe formation and evolution of galaxies is strongly influenced by environment, particularly in clusters, where galaxy luminosity functions vary in shape with the dynamical state of the cluster (relaxed or in various stages of merging), with the photometric band considered and with the position in the cluster. We present here results concerning the optical GLFs in several relaxed and merging clusters.

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Kroupa, Pavel. « Star-cluster formation and evolution ». Proceedings of the International Astronomical Union 2, S237 (août 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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Fujita, Yutaka, Megan Donahue, Stefano Ettori, Keiichi Umetsu, Elena Rasia, Massimo Meneghetti, Elinor Medezinski, Nobuhiro Okabe et Marc Postman. « Halo Concentrations and the Fundamental Plane of Galaxy Clusters ». Galaxies 7, n^o 1 (2 janvier 2019) : 8. http://dx.doi.org/10.3390/galaxies7010008.

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According to the standard cold dark matter (CDM) cosmology, the structure of dark halos including those of galaxy clusters reflects their mass accretion history. Older clusters tend to be more concentrated than younger clusters. Their structure, represented by the characteristic radius r s and mass M s of the Navarro–Frenk–White (NFW) density profile, is related to their formation time. In this study, we showed that r s , M s , and the X-ray temperature of the intracluster medium (ICM), T X , form a thin plane in the space of ( log r s , log M s , log T X ) . This tight correlation indicates that the ICM temperature is also determined by the formation time of individual clusters. Numerical simulations showed that clusters move along the fundamental plane as they evolve. The plane and the cluster evolution within the plane could be explained by a similarity solution of structure formation of the universe. The angle of the plane shows that clusters have not achieved “virial equilibrium” in the sense that mass/size growth and pressure at the boundaries cannot be ignored. The distribution of clusters on the plane was related to the intrinsic scatter in the halo concentration–mass relation, which originated from the variety of cluster ages. The well-known mass–temperature relation of clusters ( M Δ ∝ T X 3 / 2 ) can be explained by the fundamental plane and the mass dependence of the halo concentration without the assumption of virial equilibrium. The fundamental plane could also be used for calibration of cluster masses.

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Fahrion, K., M. Lyubenova, G. van de Ven, M. Hilker, R. Leaman, J. Falcón-Barroso, A. Bittner et al. « Diversity of nuclear star cluster formation mechanisms revealed by their star formation histories ». Astronomy & ; Astrophysics 650 (juin 2021) : A137. http://dx.doi.org/10.1051/0004-6361/202140644.

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Nuclear star clusters (NSCs) are the densest stellar systems in the Universe and are found in the centres of all types of galaxies. They are thought to form via mergers of star clusters such as ancient globular clusters (GCs) that spiral to the centre as a result of dynamical friction or through in situ star formation directly at the galaxy centre. There is evidence that both paths occur, but the relative contribution of either channel and their correlation with galaxy properties are not yet constrained observationally. Our aim was to derive the dominant NSC formation channel for a sample of 25 nucleated galaxies, mostly in the Fornax galaxy cluster, with stellar masses between Mgal ∼ 108 and 1010.5 M⊙ and NSC masses between MNSC ∼ 105 and 108.5 M⊙. Using Multi-Unit Spectroscopic Explorer data from the Fornax 3D survey and the ESO archive, we derived star formation histories, mean ages, and metallicities of NSCs, and compared them to the host galaxies. In many low-mass galaxies, the NSCs are significantly more metal poor than their hosts, with properties similar to GCs. In contrast, in the massive galaxies we find diverse star formation histories and cases of ongoing or recent in situ star formation. Massive NSCs (> 107 M⊙) occupy a different region in the mass–metallicity diagram than lower-mass NSCs and GCs, indicating a different enrichment history. We find a clear transition of the dominant NSC formation channel with both galaxy and NSC mass. We hypothesise that while GC accretion forms the NSCs of the dwarf galaxies, central star formation is responsible for the efficient mass build up in the most massive NSCs in our sample. At intermediate masses both channels can contribute. The transition between these formation channels seems to occur at galaxy masses Mgal ∼ 109 M⊙ and NSC masses MNSC ∼ 107 M⊙.

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Kissler-Patig, Markus. « Metal-rich and Metal-poor Globular Clusters in Ellipticals : Did we Learn Anything ? or Constraints on Galaxy Formation and Evolution from Globular Cluster Sub-populations ». Symposium - International Astronomical Union 207 (2002) : 207–17. http://dx.doi.org/10.1017/s0074180900223760.

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A brief review on globular cluster sub-populations in galaxies, and their constraints on galaxy formation and evolution is given. The metal-poor and metal-rich sub-populations are put in a historical context, and their properties, as known to date, are summarized. We review why the study of these sub-populations is extremely useful for the study of galaxy formation and evolution, but highlight a few caveats with the current interpretations. We re-visit the current globular cluster system formation scenarios and show how they boil down to a single scenario for the metal-poor clusters (namely the formation in “universal”, small fragments at high z) and that a hierarchical formation seems favored for the metal-rich clusters.

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Barger, A. J., A. Aragón-Salamanca, R. S. Ellis, W. J. Couch, I. Smail et R. M. Sharples. « Starburst Cycle in Distant Clusters ». Symposium - International Astronomical Union 171 (1996) : 341. http://dx.doi.org/10.1017/s0074180900232609.

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A major puzzle in observational cosmology is the physical origin of a significant excess population of blue galaxies in the cores of distant rich galaxy clusters. This ‘Butcher-Oemler’ effect is now known to be a widespread starburst-related phenomenon. We test whether various spectral and photometrically-defined galaxy classes might represent different stages within a single cycle of star-formation. We compare the numbers of galaxies in various categories for three z = 0.31 clusters, AC103, AC114, and AC118, with evolutionary models generated according to the Bruzual & Chariot (1993) isochrone spectral synthesis code, assuming that some fraction of the model cluster population is viewed either before or during a secondary burst of star formation. We find good agreement between the model predictions and the number density of spectroscopically-confirmed members in the H δ versus B – R plane for a cluster population in which 30 per cent of the member galaxies have undergone secondary bursts of star formation within the last ∼ 2 Gyr prior to observation. As an additional check, we analyse a larger Kn–limited sample from newly-acquired infrared images and find good agreement between the models and the data in the U – I versus I – Kn plane for the same active cluster fraction. We conclude that the unusual galaxy population in distant clusters can be explained by a single cycle in which about 30 per cent of the cluster population experienced a secondary burst of star-formation within the last ∼ 2 Gyr.

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Davies, Roger L., A. Beifiori, R. Bender, M. Cappellari, J. Chan, R. Houghton, T. Mendel et al. « The KMOS Galaxy Clusters Project ». Proceedings of the International Astronomical Union 10, S311 (juillet 2014) : 110–15. http://dx.doi.org/10.1017/s174392131500349x.

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AbstractKMOS is a cryogenic infrared spectrograph fed by twentyfour deployable integral field units that patrol a 7.2 arcminute diameter field of view at the Nasmyth focus of the ESO VLT. It is well suited to the study of galaxy clusters at 1 < z < 2 where the well understood features in the restframe V-band are shifted into the KMOS spectral bands. Coupled with HST imagining, KMOS offers a window on the critical epoch for galaxy evolution, 7-10 Gyrs ago, when the key properties of cluster galaxies were established. We aim to investigate the size, mass, morphology and star formation history of galaxies in the clusters. Here we describe the instrument, discuss the status of the observations and report some preliminary results.

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Combes, Francoise. « Molecular gas filamentary structures in galaxy clusters ». Proceedings of the International Astronomical Union 14, S342 (mai 2018) : 77–84. http://dx.doi.org/10.1017/s1743921318003915.

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AbstractRecent molecular line observations with ALMA and NOEMA in several Brightest Cluster Galaxies (BCG) have revealed the large-scale filamentary structure at the center of cool core clusters. These filaments extend over 20-100kpc, they are tightly correlated with ionized gas (Hα, [NII]) emission, and have characteristic shapes: either radial and straight, or also showing a U-turn, like a horse-shoe structure. The kinematics is quite regular and laminar, and the derived infall time is much longer than the free-fall time. The filaments extend up to the radius where the cooling time becomes larger than the infall time. Filaments can be perturbed by the sloshing of the BCG in its cluster, and spectacular cooling wakes have been observed. Filaments tend to occur at the border of cavities driven in the X-ray gas by the AGN radio jets. Observations of cool core clusters support the thermal instability scenario, which accounts for the multiphase medium in the upper atmospheres of BCG, where the right balance between heating and cooling is reached, and a chaotic cold gas accretion occurs. Molecular filaments are also seen associated to ram-pressure stripped spiral galaxies in rich galaxy clusters, and in jet-induced star formation, suggesting a very efficient molecular cloud formation even in hostile cluster environments.

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Rieder, Steven, Clare Dobbs, Thomas Bending, Kong You Liow et James Wurster. « Simulating star formation in spiral galaxies ». Proceedings of the International Astronomical Union 16, S362 (juin 2020) : 105–10. http://dx.doi.org/10.1017/s1743921322001892.

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AbstractWe present Ekster, a new method for simulating the formation and dynamics of individual stars in a relatively low-resolution gas background. Here, we use Ekster to simulate star cluster formation in two different regions from each of two galaxy models with different spiral potentials. We simulate these regions for 3 Myr to study where and how star clusters form. We find that massive GMC regions form more massive clusters than sections of spiral arms. Additionally we find that 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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Cohen, Seth A., Ryan C. Hickox, Gary A. Wegner, Maret Einasto et Jaan Vennik. « STAR FORMATION AND SUBSTRUCTURE IN GALAXY CLUSTERS ». Astrophysical Journal 783, n^o 2 (24 février 2014) : 136. http://dx.doi.org/10.1088/0004-637x/783/2/136.

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David, Laurence P., et George R. Blumenthal. « The efficiency of galaxy formation in clusters ». Astrophysical Journal 389 (avril 1992) : 510. http://dx.doi.org/10.1086/171227.

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Bekki, Kenji, Warrick J. Couch, Duncan A. Forbes et M. A. Beasley. « Formation of Globular Clusters in Galaxy Mergers ». Highlights of Astronomy 13 (2005) : 191–92. http://dx.doi.org/10.1017/s1539299600015598.

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AbstractOur numerical simulations first demonstrate that the pressure of ISM in a major merger becomes so high (> 105 kB K cm-3) that GMCs in the merger can collapse to form globular clusters (GCs) within a few Myr. The star formation efficiency within a GMC in galaxy mergers can rise up from a few percent to ~ 80 percent, depending on the shapes and the temperature of the GMC. This implosive GC formation due to external high pressure of warm/hot ISM can be more efficient in the tidal tails or the central regions of mergers. The developed clusters have King-like profiles with an effective radius of a few pc. The structural, kinematical, and chemical properties of these GC systems can depend on the orbital and chemical properties of major mergers.

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Li, Yuexing, Mordecai-Mark Mac Low et Ralf S. Klessen. « Formation of Globular Clusters in Galaxy Mergers ». Astrophysical Journal 614, n^o 1 (14 septembre 2004) : L29—L32. http://dx.doi.org/10.1086/425320.

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Strader, Jay, Jean P. Brodie et Duncan A. Forbes. « Metal-Poor Globular Clusters and Galaxy Formation ». Astronomical Journal 127, n^o 6 (juin 2004) : 3431–36. http://dx.doi.org/10.1086/420995.

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Anders, Peter, Uta Fritze –. v. Alvensleben et Richard de Grijs. « Young Star Clusters : Metallicity Tracers in External Galaxies ». Highlights of Astronomy 13 (2005) : 667–69. http://dx.doi.org/10.1017/s1539299600017354.

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AbstractStar cluster formation is a major mode of star formation in the extreme conditions of interacting galaxies and violent star bursts. These newly-formed clusters are built from recycled gas, pre-enriched to various levels within the interacting galaxies. Hence, star clusters of different ages represent a fossil record of the chemical enrichment history of their host galaxy, as well as of the host galaxy’s violent star formation history. 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 to analyze multi-color observations with our models. First results for newly-born clusters in the dwarf star-burst galaxy NGC 1569 are presented.

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Nulsen, P. E. J. « Gas and Galaxy Formation ». Publications of the Astronomical Society of Australia 16, n^o 1 (1999) : 3–7. http://dx.doi.org/10.1071/as99003.

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AbstractThe theory of galaxy formation is reviewed briefly. From the evidence of clusters today, the primordial gas fraction was 20% or more. Thus, while the Universe is dominated by dark matter, gas plays an appreciable role in galaxy formation. Collapses of dwarf protogalaxies produce predominantly cold gas. It is argued that, in such cold collapses, the collapsed gas is largely self-gravitating. As a result, gas processes play a critical role in determining the visible structure of galaxies.

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Forbes, Duncan A. « Globular Clusters in Elliptical Galaxies : Constraints on Mergers ». Symposium - International Astronomical Union 186 (1999) : 181–84. http://dx.doi.org/10.1017/s0074180900112495.

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There exists a relationship between globular cluster mean metallicity and parent galaxy luminosity (e.g. Brodie & Huchra 1991; Forbes et al. 1996), which appears to be similar to that between stellar metallicity and galaxy luminosity. The globular cluster relation has a similar slope but is offset by about 0.5 dex to lower metallicity. The similarity of these relations suggests that both the globular cluster system and their parent galaxy have shared a common chemical enrichment history. If we can understand the formation and evolution of the globulars, we will also learn something about galaxy formation. With this aim in mind we have created the SAGES (Study of the Astrophysics of Globular clusters in Extragalactic Systems) project. Project members include Brodie, Elson, Forbes, Freeman, Grillmair, Huchra, Kissler–Patig and Schroder. We are using HST Imaging and Keck spectroscopy to study extragalactic globular cluster systems. Further details are given at http://www.ucolick.org/~mkissler/Sages/sages.html.

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