Journal articles on the topic 'Galaxy clusters'
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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, no. 1 (March 22, 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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Benavides, José A., Laura V. Sales, and Mario G. Abadi. "Accretion of galaxy groups into galaxy clusters." Monthly Notices of the Royal Astronomical Society 498, no. 3 (September 2, 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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Gal-Yam, A., D. Maoz, K. Sharon, F. Prada, P. Guhathakurta, and A. V. Filippenko. "Supernovae in Galaxy Clusters." International Astronomical Union Colloquium 192 (2005): 367–71. http://dx.doi.org/10.1017/s025292110000943x.
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SummaryWe present the results of several surveys for supernovae (SNe) in galaxy clusters. SNe discovered in deep, archival HST images were used to measure the cluster SN Ia rate to z = 1. A search for SNe in nearby (0.06 ≤ z ≤ 0.2) Abell galaxy clusters yielded 15 SNe, 12 of which were spectroscopically confirmed. Of these, 7 are cluster SNe Ia, which we will use to measure the SN Ia rate in nearby clusters. This search has also discovered the first convincing examples of intergalactic SNe. We conclude with a brief description of ongoing and future cluster SN surveys.
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Gouin, C., N. Aghanim, V. Bonjean, and M. Douspis. "Probing the azimuthal environment of galaxies around clusters." Astronomy & Astrophysics 635 (March 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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Yoo, Jaewon, Jongwan Ko, Cristiano G. Sabiu, Jihye Shin, Kyungwon Chun, Ho Seong Hwang, Juhan Kim, M. James Jee, Hyowon Kim, and Rory Smith. "Comparison of Spatial Distributions of Intracluster Light and Dark Matter." Astrophysical Journal Supplement Series 261, no. 2 (July 27, 2022): 28. http://dx.doi.org/10.3847/1538-4365/ac7142.
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Abstract In a galaxy cluster, the relative spatial distributions of dark matter, member galaxies, gas, and intracluster light (ICL) may connote their mutual interactions over the cluster’s evolution. However, it is a challenging problem to provide a quantitative measure for matching the shapes between two multidimensional scalar distributions. We present a novel methodology, named the weighted overlap coefficient (WOC), to quantify the similarity of two-dimensional spatial distributions. We compare the WOC with a standard method known as the modified Hausdorff distance (MHD) method. We find that our method is robust, and performs well even with the existence of multiple substructures. We apply our methodology to search for a visible component whose spatial distribution resembles that of dark matter. If such a component could be found to trace the dark-matter distribution with high fidelity for more relaxed galaxy clusters, then the similarity of the distributions could also be used as a dynamical stage estimator of the cluster. We apply the method to six galaxy clusters at different dynamical stages, simulated within a GRT simulation, which is an N-body simulation using the galaxy replacement technique. Among the various components (stellar particles, galaxies, ICL), the ICL+brightest cluster galaxy (BCG) component most faithfully traced the dark-matter distribution. Among the sample galaxy clusters, the relaxed clusters show stronger similarity in the spatial distribution of the dark matter and ICL+BCG than the dynamically young clusters, while the results of the MHD method show a weaker trend with the dynamical stages.
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Henriksen, Mark J., and Prajwal Panda. "Exploiting Machine Learning and Disequilibrium in Galaxy Clusters to Obtain a Mass Profile." Astrophysical Journal Letters 961, no. 2 (January 25, 2024): L36. http://dx.doi.org/10.3847/2041-8213/ad1ede.
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Abstract We use 3D k-means clustering to characterize galaxy substructure in the A2146 cluster of galaxies (z = 0.2343). This method objectively characterizes the cluster’s substructure using projected position and velocity data for 67 galaxies within a 2.305 Mpc circular region centered on the cluster's optical center. The optimal number of substructures is found to be four. Four distinct substructures with rms velocity typical of galaxy groups or low-mass subclusters, when compared to cosmological simulations of galaxy cluster formation, suggest that A2146 is in the early stages of formation. We utilize this disequilibrium, which is so prevalent in galaxy clusters at all redshifts, to construct a radial mass distribution. Substructures are bound but not virialized. This method is in contrast to previous kinematical analyses, which have assumed virialization, and ignored the ubiquitous clumping of galaxies. The best-fitting radial mass profile is much less centrally concentrated than the well-known Navarro–Frenk–White profile, indicating that the dark-matter-dominated mass distribution is flatter pre-equilibrium, becoming more centrally peaked in equilibrium through the merging of the substructure.
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Cohn, J. D. "Galaxy subgroups in galaxy clusters." Monthly Notices of the Royal Astronomical Society 419, no. 2 (October 21, 2011): 1017–27. http://dx.doi.org/10.1111/j.1365-2966.2011.19756.x.
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Kosiba, Matej, Maggie Lieu, Bruno Altieri, Nicolas Clerc, Lorenzo Faccioli, Sarah Kendrew, Ivan Valtchanov, et al. "Multiwavelength classification of X-ray selected galaxy cluster candidates using convolutional neural networks." Monthly Notices of the Royal Astronomical Society 496, no. 4 (June 17, 2020): 4141–53. http://dx.doi.org/10.1093/mnras/staa1723.
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ABSTRACT Galaxy clusters appear as extended sources in XMM–Newton images, but not all extended sources are clusters. So, their proper classification requires visual inspection with optical images, which is a slow process with biases that are almost impossible to model. We tackle this problem with a novel approach, using convolutional neural networks (CNNs), a state-of-the-art image classification tool, for automatic classification of galaxy cluster candidates. We train the networks on combined XMM–Newton X-ray observations with their optical counterparts from the all-sky Digitized Sky Survey. Our data set originates from the XMM CLuster Archive Super Survey (X-CLASS) survey sample of galaxy cluster candidates, selected by a specially developed pipeline, the XAmin, tailored for extended source detection and characterization. Our data set contains 1707 galaxy cluster candidates classified by experts. Additionally, we create an official Zooniverse citizen science project, The Hunt for Galaxy Clusters, to probe whether citizen volunteers could help in a challenging task of galaxy cluster visual confirmation. The project contained 1600 galaxy cluster candidates in total of which 404 overlap with the expert’s sample. The networks were trained on expert and Zooniverse data separately. The CNN test sample contains 85 spectroscopically confirmed clusters and 85 non-clusters that appear in both data sets. Our custom network achieved the best performance in the binary classification of clusters and non-clusters, acquiring accuracy of 90 per cent, averaged after 10 runs. The results of using CNNs on combined X-ray and optical data for galaxy cluster candidate classification are encouraging, and there is a lot of potential for future usage and improvements.
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Lee, Jong Chul, Ho Seong Hwang, and Hyunmi Song. "Searching for Mg ii absorbers in and around galaxy clusters." Monthly Notices of the Royal Astronomical Society 503, no. 3 (March 5, 2021): 4309–19. http://dx.doi.org/10.1093/mnras/stab637.
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ABSTRACT To study environmental effects on the circumgalactic medium (CGM), we use the samples of redMaPPer galaxy clusters, background quasars, and cluster galaxies from the Sloan Digital Sky Survey (SDSS). With ∼82 000 quasar spectra, we detect 197 Mg ii absorbers in and around the clusters. The detection rate per quasar is 2.7 ± 0.7 times higher inside the clusters than outside the clusters, indicating that Mg ii absorbers are relatively abundant in clusters. However, when considering the galaxy number density, the absorber-to-galaxy ratio is rather low inside the clusters. If we assume that Mg ii absorbers are mainly contributed by the CGM of massive star-forming galaxies, a typical halo size of cluster galaxies is smaller than that of field galaxies by 30 ± 10 per cent. This finding supports that galaxy haloes can be truncated by interaction with the host cluster.
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Kuchner, Ulrike, Roan Haggar, Alfonso Aragón-Salamanca, Frazer R. Pearce, Meghan E. Gray, Agustín Rost, Weiguang Cui, Alexander Knebe, and Gustavo Yepes. "An inventory of galaxies in cosmic filaments feeding galaxy clusters: galaxy groups, backsplash galaxies, and pristine galaxies." Monthly Notices of the Royal Astronomical Society 510, no. 1 (November 27, 2021): 581–92. http://dx.doi.org/10.1093/mnras/stab3419.
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ABSTRACT Galaxy clusters grow by accreting galaxies from the field and along filaments of the cosmic web. As galaxies are accreted they are affected by their local environment before they enter (pre-processing), and traverse the cluster potential. Observations that aim to constrain pre-processing are challenging to interpret because filaments comprise a heterogeneous range of environments including groups of galaxies embedded within them and backsplash galaxies that contain a record of their previous passage through the cluster. This motivates using modern cosmological simulations to dissect the population of galaxies found in filaments that are feeding clusters, to better understand their history, and aid the interpretation of observations. We use zoom-in simulations from The ThreeHundred project to track haloes through time and identify their environment. We establish a benchmark for galaxies in cluster infall regions that supports the reconstruction of the different modes of pre-processing. We find that up to 45 per cent of all galaxies fall into clusters via filaments (closer than 1 h−1Mpc from the filament spine). 12 per cent of these filament galaxies are long-established members of groups and between 30 and 60 per cent of filament galaxies at R200 are backsplash galaxies. This number depends on the cluster’s dynamical state and sharply drops with distance. Backsplash galaxies return to clusters after deflecting widely from their entry trajectory, especially in relaxed clusters. They do not have a preferential location with respect to filaments and cannot collapse to form filaments. The remaining pristine galaxies (∼30–60 per cent) are environmentally affected by cosmic filaments alone.
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Casas, Madeline C., Ky Putnam, Adam B. Mantz, Steven W. Allen, and Taweewat Somboonpanyakul. "Optical Photometric Indicators of Galaxy Cluster Relaxation." Astrophysical Journal 967, no. 1 (May 1, 2024): 14. http://dx.doi.org/10.3847/1538-4357/ad41de.
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Abstract The most dynamically relaxed clusters of galaxies play a special role in cosmological studies as well as astrophysical studies of the intracluster medium (ICM) and active galactic nucleus feedback. While high-spatial-resolution imaging of the morphology of the ICM has long been the gold standard for establishing a cluster’s dynamical state, such data are not available from current or planned surveys, and thus require separate, pointed follow-up observations. With optical and/or near-IR photometric imaging, and red-sequence cluster finding results from those data, expected to be ubiquitously available for clusters discovered in upcoming optical and millimeter-wavelength surveys, it is worth asking how effectively photometric data alone can identify relaxed cluster candidates, before investing in, e.g., high-resolution X-ray observations. Here we assess the ability of several simple photometric measurements, based on the redMaPPer cluster finder run on Sloan Digital Sky Survey data, to reproduce X-ray classifications of dynamical state for an X-ray selected sample of massive clusters. We find that two simple metrics contrasting the bright central galaxy (BCG) to other cluster members can identify a complete sample of relaxed clusters with a purity of ∼40% in our data set. Including minimal ICM information in the form of a center position increases the purity to ∼60%. However, all three metrics depend critically on correctly identifying the BCG, which is presently a challenge for optical red-sequence cluster finders.
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Trudeau, A., C. Garrel, J. Willis, M. Pierre, F. Gastaldello, L. Chiappetti, S. Ettori, et al. "The XXL Survey." Astronomy & Astrophysics 642 (October 2020): A124. http://dx.doi.org/10.1051/0004-6361/202038982.
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Context. Distant galaxy clusters provide an effective laboratory in which to study galaxy evolution in dense environments and at early cosmic times. Aims. We aim to identify distant galaxy clusters as extended X-ray sources that are coincident with overdensities of characteristically bright galaxies. Methods. We used optical and near-infrared data from the Hyper Suprime-Cam and VISTA Deep Extragalactic Observations (VIDEO) surveys to identify distant galaxy clusters as overdensities of bright, zphot ≥ 0.8 galaxies associated with extended X-ray sources detected in the ultimate XMM extragalactic survey (XXL). Results. We identify a sample of 35 candidate clusters at 0.80 ≤ z ≤ 1.93 from an approximately 4.5 deg2 sky area. This sample includes 15 newly discovered candidate clusters, ten previously detected but unconfirmed clusters, and ten spectroscopically confirmed clusters. Although these clusters host galaxy populations that display a wide variety of quenching levels, they exhibit well-defined relations between quenching, cluster-centric distance, and galaxy luminosity. The brightest cluster galaxies (BCGs) within our sample display colours that are consistent with a bimodal population composed of an old and red sub-sample together with a bluer, more diverse sub-sample. Conclusions The relation between galaxy masses and quenching seem to already be in place at z ∼ 1, although there is no significant variation in the quenching fraction with the cluster-centric radius. The BCG bimodality might be explained by the presence of a younger stellar component in some BCGs, but additional data are needed to confirm this scenario.
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Bogdán, Ákos, Lorenzo Lovisari, Patrick Ogle, Orsolya E. Kovács, Thomas Jarrett, Christine Jones, William R. Forman, and Lauranne Lanz. "Detection of a Superluminous Spiral Galaxy in the Heart of a Massive Galaxy Cluster." Astrophysical Journal 930, no. 2 (May 1, 2022): 138. http://dx.doi.org/10.3847/1538-4357/ac62cd.
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Abstract It is well established that brightest cluster galaxies (BCGs), residing in the centers of galaxy clusters, are typically massive and quenched galaxies with cD or elliptical morphology. An optical survey suggested that an exotic galaxy population, superluminous spiral and lenticular galaxies, could be the BCGs of some galaxy clusters. Because the cluster membership and the centroid of a cluster cannot be accurately determined based solely on optical data, we followed up a sample of superluminous disk galaxies and their environments using XMM-Newton X-ray observations. Specifically, we explored seven superluminous spiral and lenticular galaxies that are candidate BCGs. We detected massive galaxy clusters around five superluminous disk galaxies and established that one superluminous spiral, 2MASX J16273931+3002239, is the central BCG of a galaxy cluster. The temperature and total mass of the cluster are kT 500 = 3.55 − 0.20 + 0.18 keV and M 500 = (2.39 ± 0.19) × 1014 M ⊙. We identified the central galaxies of the four clusters that do not host superluminous disk galaxies at their cores, and established that the centrals are massive elliptical galaxies. However, for two of the clusters, the offset superluminous spirals are brighter than the central galaxies, implying that the superluminous disk galaxies are the brightest cluster galaxies. Our results demonstrate that superluminous disk galaxies are rarely the central systems of galaxy clusters. This is likely because galactic disks are destroyed by major mergers, which are more frequent in high-density environments. We speculate that the disks of superluminous disk galaxies in cluster cores may have been reformed due to mergers with gas-rich satellites.
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Rasheed, Mariwan A., and Mohamad A. Brza. "Color-Magnitude and Luminosity Function in Galaxy Clusters." International Journal of Scientific Research 2, no. 7 (June 1, 2012): 15–18. http://dx.doi.org/10.15373/22778179/july2013/160.
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Berkovskyi, M., E. Panko, and N. Miroshnik. "GALAXY CLUSTER MERGERS: THE USE OF THE COMPUTER MODELING." Odessa Astronomical Publications 36 (December 4, 2023): 5–8. http://dx.doi.org/10.18524/1810-4215.2023.36.289962.
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We show the possibilities of the methods of computer modeling of the galaxy cluster merger process with different initial parameters for the investigation of the features of the clusters after colliding. We considered the galaxy clusters as evolving objects including through collisions. Computer modeling of galaxy cluster mergers and comparing its results with observational data makes it possible to determine the evolutionary status of real clusters with complex internal structures. Within the study, we analyzed in detail a series of models of the galaxy clusters’ merger consequences by ZuHone under different initial conditions like mass ratio, initial collision parameter, or plasma coefficient β. The considered time intervals were from 0 to 4.8 billion years, from 0 to 6 billion years, and from 0 to 10 billion years, depending on the initial conditions. Based on the images of the simulated galaxy clusters, maps of the distribution of the total mass density and X-ray radiation were created and compared with observations. We showed a good perspective to use this catalog for studying galaxy clusters having compound inner structure.
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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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Varga, T. N., D. Gruen, S. Seitz, N. MacCrann, E. Sheldon, W. G. Hartley, A. Amon, et al. "Synthetic galaxy clusters and observations based on Dark Energy Survey Year 3 Data." Monthly Notices of the Royal Astronomical Society 509, no. 4 (November 18, 2021): 4865–85. http://dx.doi.org/10.1093/mnras/stab3269.
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ABSTRACT We develop a novel data-driven method for generating synthetic optical observations of galaxy clusters. In cluster weak lensing, the interplay between analysis choices and systematic effects related to source galaxy selection, shape measurement, and photometric redshift estimation can be best characterized in end-to-end tests going from mock observations to recovered cluster masses. To create such test scenarios, we measure and model the photometric properties of galaxy clusters and their sky environments from the Dark Energy Survey Year 3 (DES Y3) data in two bins of cluster richness $\lambda \in [30; 45)$, $\lambda \in [45; 60)$ and three bins in cluster redshift ($z\in [0.3; 0.35)$, $z\in [0.45; 0.5)$ and $z\in [0.6; 0.65)$. Using deep-field imaging data, we extrapolate galaxy populations beyond the limiting magnitude of DES Y3 and calculate the properties of cluster member galaxies via statistical background subtraction. We construct mock galaxy clusters as random draws from a distribution function, and render mock clusters and line-of-sight catalogues into synthetic images in the same format as actual survey observations. Synthetic galaxy clusters are generated from real observational data, and thus are independent from the assumptions inherent to cosmological simulations. The recipe can be straightforwardly modified to incorporate extra information, and correct for survey incompleteness. New realizations of synthetic clusters can be created at minimal cost, which will allow future analyses to generate the large number of images needed to characterize systematic uncertainties in cluster mass measurements.
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Godłowski, W., and F. Baier. "Galaxy Orientation in Some Abell Clusters." Symposium - International Astronomical Union 186 (1999): 410. http://dx.doi.org/10.1017/s0074180900113245.
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We analyze a sample of galaxies in a region of three rich Abell Clusters. The data are taken from the Edinburgh Catalogue of the cluster. First, we divide the whole cluster area into different parts according to the assumed subclusters. Now we can find the position angles of the cluster and subclusters. We find strong evidence that the position angles of galaxies within our clusters are aligned to a large extent. For the cluster A754, position angles of galaxies tend to be perpendicular to the direction of the position angle of the cluster. Consequently, the angular momentum of galaxies are preferentially perpendicular to the cluster plane. For the cluster A14, position angles of galaxies tend to be parallel to the direction of the position angle of the cluster. Consequently, the angular momentum of galaxies are preferentially parallel to the cluster plane. For the cluster A3667 we obtain a more complicated picture suggesting that the alignment of galaxies in this cluster may have a different shape. From the distribution of the positions angles of galaxies we also found evidence for possible subclustering inside the whole cluster. This result is confirmed by the investigation of the distribution of the vectors normal to the galactic planes. Moreover we confirm the existence of a “line of sight” effect, originally found by Godłowski &, Ostrowski (1996) for galaxies belonging to the clusters in the Tully Catalogue (1988), for the clusters in our basic catalog.
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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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de Andres, Daniel, Weiguang Cui, Florian Ruppin, Marco De Petris, Gustavo Yepes, Ichraf Lahouli, Gianmarco Aversano, Romain Dupuis, and Mahmoud Jarraya. "Mass Estimation of Planck Galaxy Clusters using Deep Learning." EPJ Web of Conferences 257 (2022): 00013. http://dx.doi.org/10.1051/epjconf/202225700013.
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Galaxy cluster masses can be inferred indirectly using measurements from X-ray band, Sunyaev-Zeldovich (SZ) effect signal or optical observations. Unfortunately, all of them are affected by some bias. Alternatively, we provide an independent estimation of the cluster masses from the Planck PSZ2 catalog of galaxy clusters using a machine-learning method. We train a Convolutional Neural Network (CNN) model with the mock SZ observations from The Three Hundred (the300) hydrodynamic simulations to infer the cluster masses from the real maps of the Planck clusters. The advantage of the CNN is that no assumption on a priory symmetry in the cluster’s gas distribution or no additional hypothesis about the cluster physical state are made. We compare the cluster masses from the CNN model with those derived by Planck and conclude that the presence of a mass bias is compatible with the simulation results.
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Zarodnyuk, A., E. Trofimova, A. Solovyov, and D. Gradoboev. "Galaxy Clusters Reconstruction." Journal of Physics: Conference Series 1740 (January 2021): 012017. http://dx.doi.org/10.1088/1742-6596/1740/1/012017.
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Bahk, Hyeonguk, and Ho Seong Hwang. "UPCluster-SZ: The Updated Catalog of Galaxy Clusters from the List of Planck Sunyaev–Zel’dovich Sources." Astrophysical Journal Supplement Series 272, no. 1 (April 23, 2024): 7. http://dx.doi.org/10.3847/1538-4365/ad323f.
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Abstract We present the updated galaxy cluster catalog of the second Planck catalog of Sunyaev–Zel’dovich sources (PSZ2) through the compilation of the data for clusters and galaxies with spectroscopically measured redshifts in the literature. The original version of PSZ2 comprises 1653 Sunyaev–Zel’dovich (SZ) sources, of which 1203 have been validated as genuine galaxy clusters, while the remaining 450 sources are yet to be validated. To increase the number of genuine clusters in PSZ2, we first update the validations of the cluster candidates and their redshift information using the data compiled for the confirmed clusters and the member galaxies in the literature. We then use the galaxy redshift data in the fields of the remaining cluster candidates by searching for possible member galaxies with measured spectroscopic redshifts around the SZ centroids. In this search process, we classify clusters as strong candidates if they contain more than nine galaxies within a 4500 km s−1 velocity range and within 15′ around the SZ centroids. This process results in the validation of 139 new genuine clusters, the update of redshift information on 399 clusters, and the identification of 10 strong candidates, which increases the number of validated clusters up to 1334 among the 1653 SZ sources. Our updated galaxy cluster catalog will be very useful for studies of galaxy formation and cosmology through a combination with other all-sky surveys including the Wide-field Infrared Survey Explorer and SPHEREx.
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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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Koulouridis, Elias. "The AGN dependence on cluster mass." Proceedings of the International Astronomical Union 14, S342 (May 2018): 145–48. http://dx.doi.org/10.1017/s1743921318005124.
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AbstractWe present the results of a study of the AGN density in a homogeneous and well studied sample of 167 bona-fide X-ray galaxy clusters (0.1<z<0.5). Our aim is to study the AGN activity in 167 XXL X-ray galaxy clusters as a function of the cluster mass and the location of the AGN in the cluster. We report a significant AGN excess in our low-mass cluster sub-sample between 0.5r500 and 2r500. In contrast, the high-mass sub-sample presents no AGN excess. The AGN excess in poor clusters indicates AGN triggering, supporting previous studies that reported enhanced galaxy merging in the cluster outskirts. This effect is probably prevented by high velocity dispersions in high-mass clusters. Comparing also with previous studies of massive or high-redshift clusters, we conclude that the AGN fraction in cluster galaxies anti-correlates strongly with cluster mass.
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Lee, Seong-Kook, Myungshin Im, Minhee Hyun, Bomi Park, Jae-Woo Kim, Dohyeong Kim, and 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, no. 1 (September 16, 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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Sarron, F., C. Adami, F. Durret, and C. Laigle. "Pre-processing of galaxies in cosmic filaments around AMASCFI clusters in the CFHTLS." Astronomy & Astrophysics 632 (November 26, 2019): A49. http://dx.doi.org/10.1051/0004-6361/201935394.
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Context. Galaxy clusters and groups are thought to accrete material along the preferred direction of cosmic filaments. These structures have proven difficult to detect because their contrast is low, however, and only a few studies have focused on cluster infall regions. Aims. We detect cosmic filaments around galaxy clusters using photometric redshifts in the range 0.15 < z < 0.7. We characterise galaxy populations in these structures to study the influence of pre-processing by cosmic filaments and galaxy groups on star formation quenching. Methods. We detected cosmic filaments in the Canada-France-Hawaii Telescope Legacy Survey (CFHTLS) T0007 data, focusing on regions around clusters of the AMASCFI CFHTLS cluster sample. The filaments were reconstructed with the discrete persistent structure extractor (DISPERSE) algorithm in photometric redshift slices. We show that this reconstruction is reliable for a CFHTLS-like survey at 0.15 < z < 0.7 using a mock galaxy catalogue. We split our galaxy catalogue into two populations (passive and star forming) using the LePhare spectral energy density fitting algorithm and worked with two redshift bins (0.15 < z ≤ 0.4 and 0.4 < z < 0.7). Results. We showed that the AMASCFI cluster connectivity (i.e. the number of filaments that is connected to a cluster) increases with cluster mass M200. Filament galaxies outside R200 are found to be closer to clusters at low redshift, regardless of the galaxy type. Passive galaxies in filaments are closer to clusters than star-forming galaxies in the low redshift bin alone. The passive fraction of galaxies decreases with increasing clustercentric distance up to d ∼ 5 cMpc. Galaxy groups and clusters that are not located at nodes of our reconstruction are mainly found inside cosmic filaments. Conclusions. These results give clues for pre-processing in cosmic filaments that could be due to smaller galaxy groups. This trend could be further explored by applying this method to larger photometric surveys such as the Hyper Suprime-Cam Subaru Strategic Program (HSC-SPP) or Euclid.
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Tucker, Gregory S., and J. B. Peterson. "Alignment of Clusters with Brightest Member Galaxies." Symposium - International Astronomical Union 130 (1988): 546. http://dx.doi.org/10.1017/s0074180900136757.
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We have obtained CCD images of the brightest elliptical galaxy in 27 clusters of galaxies with redshifts z < 0.1. For each galaxy we fitted elliptical isophotes to the galaxy image. We also measured the position angle of each cluster from the Palomar Observatory Sky Survey (POSS) prints. We find only marginal evidence for alignment of brightest cluster members (BCM) with their parent clusters, but we find that our CCD isophotes are well aligned with the POSS image.
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Wittman, David, Drake Foote, and Nathan Golovich. "Brightest Cluster Galaxy Alignments in Merging Clusters." Astrophysical Journal 874, no. 1 (March 27, 2019): 84. http://dx.doi.org/10.3847/1538-4357/ab0a0a.
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Lubin, Lori M. "Clusters in the Optical." Highlights of Astronomy 13 (2005): 286–90. http://dx.doi.org/10.1017/s1539299600015811.
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AbstractI present a brief review of studies of galaxy clusters in the optical. Clusters of galaxies were historically detected in the optical, and this selection provided the first large, statistical samples of clusters. I describe how these samples have been instrumental in characterizing the properties of the local cluster population, tracing large scale structure, and constraining cosmology. More sophisticated cluster detection techniques in the optical have now made it possible to detect large numbers of clusters up to z ~ 1.4. I describe these advances and discuss how large-area and deep surveys are being used to determine the evolution in the global cluster properties and the properties of cluster galaxy populations.
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Ibarra-Medel, Héctor J., Maritza Lara-López, and Omar López-Cruz. "Galaxy and Mass Assembly (GAMA): Selection of the Most Massive Clusters." Proceedings of the International Astronomical Union 11, S308 (June 2014): 215–16. http://dx.doi.org/10.1017/s174392131600990x.
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AbstractWe have developed a galaxy cluster finding technique based on the Delaunay Tessellation Field Estimator (DTFE) combined with caustic analysis. Our method allows us to recover clusters of galaxies within the mass range of $10^{12}$ to $10^{16}\ \mathcal{M}_{\odot}$. We have found a total of 113 galaxy clusters in the Galaxy and Mass Assembly survey (GAMA). In the corresponding mass range, the density of clusters found in this work is comparable to the density traced by clusters selected by the thermal Sunyaev Zel'dovich Effect; however, we are able to cover a wider mass range. We present the analysis of the two-point correlation function for our cluster sample.
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Beyene, Fitsum Woldegerima, and Remudin Reshid Mekuria. "Non-thermal radio emission from dark matter annihilation processes in simulated Coma like galaxy clusters." Proceedings of the International Astronomical Union 15, S356 (October 2019): 385–87. http://dx.doi.org/10.1017/s1743921320003518.
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AbstractTaking secondary particles produced from dark matter (DM) annihilation process to the origin of the extended diffuse radio emission observed in galaxy clusters, we studied both their morphology and radio spectral profile using simulated Coma like galaxy clusters. We have considered a neutralino annihilation channel dominated by $b\overline b $ species with a branching ratio of 1 and neutralino mass of 35 GeV with annihilation cross-section of 1×10-26 cm3 s-1. The radio emission maps produced for the two simulated galaxy clusters which are based on the MUsic SImulation of galaxy Clusters (MUSIC) dataset reveal the observed radio halo morphology showing radio emission both from the central regions of the cluster and substructures lying out off cluster centre. The flux density curve is in a good agreement for ν ≤ 2 GHz with the obsevational values for the Coma cluster of galaxies showing a small deviation at higher frequencies.
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Aguena, M., C. Benoist, L. N. da Costa, R. L. C. Ogando, J. Gschwend, H. B. Sampaio-Santos, M. Lima, et al. "The WaZP galaxy cluster sample of the dark energy survey year 1." Monthly Notices of the Royal Astronomical Society 502, no. 3 (February 16, 2021): 4435–56. http://dx.doi.org/10.1093/mnras/stab264.
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ABSTRACT We present a new (2+1)D galaxy cluster finder based on photometric redshifts called Wavelet Z Photometric (WaZP) applied to DES first year (Y1A1) data. The results are compared to clusters detected by the South Pole Telescope (SPT) survey and the redMaPPer cluster finder, the latter based on the same photometric data. WaZP searches for clusters in wavelet-based density maps of galaxies selected in photometric redshift space without any assumption on the cluster galaxy populations. The comparison to other cluster samples was performed with a matching algorithm based on angular proximity and redshift difference of the clusters. It led to the development of a new approach to match two optical cluster samples, following an iterative approach to minimize incorrect associations. The WaZP cluster finder applied to DES Y1A1 galaxy survey (1511.13 deg2 up to mi = 23 mag) led to the detection of 60 547 galaxy clusters with redshifts 0.05 < z < 0.9 and richness Ngals ≥ 5. Considering the overlapping regions and redshift ranges between the DES Y1A1 and SPT cluster surveys, all sz based SPT clusters are recovered by the WaZP sample. The comparison between WaZP and redMaPPer cluster samples showed an excellent overall agreement for clusters with richness Ngals (λ for redMaPPer) greater than 25 (20), with 95 per cent recovery on both directions. Based on the cluster cross-match, we explore the relative fragmentation of the two cluster samples and investigate the possible signatures of unmatched clusters.
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Bilton, Lawrence E., Matthew Hunt, Kevin A. Pimbblet, and Elke Roediger. "The rotational profiles of cluster galaxies." Monthly Notices of the Royal Astronomical Society 490, no. 4 (October 21, 2019): 5017–32. http://dx.doi.org/10.1093/mnras/stz2927.
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ABSTRACT We compile two samples of cluster galaxies with complimentary hydrodynamic and N-body analysis using flash code to ascertain how their differing populations drive their rotational profiles and to better understand their dynamical histories. We select our main cluster sample from the X-ray Galaxy Clusters Database (BAX), which are populated with Sloan Digital Sky Survey (SDSS) galaxies. The BAX clusters are tested for the presence of substructures, acting as proxies for core mergers, culminating in sub-samples of eight merging and 25 non-merging galaxy clusters. An additional sample of 12 galaxy clusters with known dumbbell components is procured using galaxy data from the NASA/IPAC Extragalactic Database (NED) to compare against more extreme environments. BAX clusters of each sample are stacked on to a common RA–Dec. space to produce rotational profiles within the range of 0.0–2.5 r200. Merging stacks possess stronger core rotation at ≲0.5r200 primarily contributed by a red galaxy sub-population from relaxing core mergers; this is alongside high rotational velocities from blue galaxy sub-populations, until they mix and homogenize with the red sub-populations at ∼r200, indicative of an infalling blue galaxy sub-population with interactive mixing between both sub-populations at ≳ r200. flash code is utilized to simulate the merger phase between two originally independent clusters and test the evolution of their rotational profiles. Comparisons with the dumbbell clusters leads to the inference that the peculiar core rotations of some dumbbell clusters are the result of the linear motions of core galaxies relaxing on to the potential during post second infall.
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Xu, Weiwei, Miriam E. Ramos-Ceja, Florian Pacaud, Thomas H. Reiprich, and Thomas Erben. "Catalog of X-ray-selected extended galaxy clusters from the ROSAT All-Sky Survey (RXGCC)." Astronomy & Astrophysics 658 (February 2022): A59. http://dx.doi.org/10.1051/0004-6361/202140908.
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Context. There is a known tension between cosmological parameter constraints obtained from the primary cosmic microwave background and those drawn from galaxy cluster samples. One possible explanation for this discrepancy may be that the incomplete character of detected clusters is higher than estimated and, as a result, certain types of groups or galaxy clusters have been overlooked in the past. Aims. We aim to search for galaxy groups and clusters with particularly extended surface brightness distributions by creating a new X-ray-selected catalog of extended galaxy clusters from the ROSAT All-Sky Survey (RASS), based on a dedicated source detection and characterization algorithm that is optimized for extended sources. Methods. Our state-of-the-art algorithm includes multi-resolution filtering, source detection, and characterization. On the basis of extensive simulations, we investigated the detection efficiency and sample purity. We used previous cluster catalogs in X-ray and other bands, as well as spectroscopic and photometric redshifts of galaxies to identify clusters. Results. We report a catalog of galaxy clusters at high galactic latitude based on the ROSAT All-sky Survey, known as the RASS-based extended X-ray Galaxy Cluster Catalog, which includes 944 groups and clusters. Of this number, 641 clusters have been previously identified based on intra-cluster medium (ICM) emission (Bronze), 154 known optical and infrared clusters are detected as X-ray clusters for the first time (Silver) and 149 are identified as clusters for the first time (Gold). Based on 200 simulations, the contamination ratio of the detections that were identified as clusters by ICM emission and the detections that were identified as optical and infrared clusters in previous work is 0.008 and 0.100, respectively. Compared with the Bronze sample, the Gold+Silver sample is less luminous, less massive, and exhibits a flatter surface brightness profile. Specifically, the median flux in [0.1−2.4] keV band for Gold+Silver and Bronze sample is 2.496 × 10−12 erg s−1 cm−2 and 4.955 × 10−12 erg s−1 cm−2, respectively. The median value of β (the slope of cluster surface brightness profile) is 0.76 and 0.83 for the Gold+Silver and Bronze sample, respectively.
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Schimd, C., and M. Sereno. "Morphology of relaxed and merging galaxy clusters: analytical models for monolithic Minkowski functionals." Monthly Notices of the Royal Astronomical Society 502, no. 3 (February 1, 2021): 3911–21. http://dx.doi.org/10.1093/mnras/stab274.
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ABSTRACT Galaxy clusters exhibit a rich morphology during the early and intermediate stages of mass assembly, especially beyond their boundary. A classification scheme based on shapefinders deduced from the Minkowski functionals is examined to fully account for the morphological diversity of galaxy clusters, including relaxed and merging clusters, clusters fed by filamentary structures, and cluster-pair bridges. These configurations are conveniently treated with idealized geometric models and analytical formulas, some of which are novel. Examples from CLASH and LC2 clusters and observed cluster-pair bridges are discussed.
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Strazzullo, V. "Galaxies in most dense environments at redshift 1.4." Proceedings of the International Astronomical Union 8, S295 (August 2012): 61. http://dx.doi.org/10.1017/s1743921313004316.
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AbstractAt a cosmic time when galaxy clusters start showing evidence of a still active galaxy population, the X-ray luminous, massive cluster XMMU J2235-2557 at z=1.39, already hosts massive, quiescent, early-type galaxies on a tight red sequence dominating the cluster core. XMMU J2235-2557 is among the most massive of the very distant clusters, which may explain the evolved status of the system itself, and of its host galaxy populations. It remains a unique laboratory to observe environment-biased galaxy evolution already 9 billion years ago.
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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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Soltis, John, Michelle Ntampaka, John F. Wu, John ZuHone, August Evrard, Arya Farahi, Matthew Ho, and Daisuke Nagai. "A Machine-learning Approach to Enhancing eROSITA Observations." Astrophysical Journal 940, no. 1 (November 1, 2022): 60. http://dx.doi.org/10.3847/1538-4357/ac9b1b.
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Abstract The eROSITA X-ray telescope, launched in 2019, is predicted to observe roughly 100,000 galaxy clusters. Follow-up observations of these clusters from Chandra, for example, will be needed to resolve outstanding questions about galaxy cluster physics. Deep Chandra cluster observations are expensive, and it is unfeasible to follow up every eROSITA cluster, therefore the objects that are chosen for follow-up must be chosen with care. To address this, we have developed an algorithm for predicting longer-duration, background-free observations, based on mock eROSITA observations. We make use of the hydrodynamic cosmological simulation Magneticum, simulate eROSITA instrument conditions using SIXTE, and apply a novel convolutional neural network to output a deep Chandra-like “super observation” of each cluster in our simulation sample. Any follow-up merit assessment tool should be designed with a specific use case in mind; our model produces observations that accurately and precisely reproduce the cluster morphology, which is a critical ingredient for determining a cluster’s dynamical state and core type. Our model will advance our understanding of galaxy clusters by improving follow-up selection, and it demonstrates that image-to-image deep learning algorithms are a viable method for simulating realistic follow-up observations.
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Govoni, Federica, and Matteo Murgia. "Magnetic Fields in Galaxy Clusters." Highlights of Astronomy 13 (2005): 322–26. http://dx.doi.org/10.1017/s1539299600015884.
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AbstractMagnetic fields in galaxy clusters can be investigated using a variety of techniques. Recent studies including radio halos, Inverse Compton hard X-ray emissions and Faraday rotation measure, are briefly outlined. A numerical approach for investigating cluster magnetic fields strength and structure is presented. It consists of producing simulated rotation measure, radio halo images, and radio halo polarization, obtained from 3-dimensional multi-scale cluster magnetic field models, and comparing with observations.
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Huang, Mei-Ling, and Lin-wen Chen. "Co-Evolution of Brightest Cluster Galaxies and Galaxy Activity in the Host Clusters." Proceedings of the International Astronomical Union 5, S267 (August 2009): 110. http://dx.doi.org/10.1017/s1743921310005715.
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AbstractWe have identified ~500 relatively relaxed galaxy clusters at low redshift (z < 0.3) from the maxBCG catalog with double radio lobes at the center; about 200 radio counterparts of brightest cluster galaxies (BCGs) of these clusters appear to be wide-angle tailed (WAT) radio sources, indicating ongoing interaction between its host galaxy and the surrounding ICM. Our analysis suggests that the radio power of WAT is positively correlated with the optical luminosities of host BCGs, and increases with redshift; whereas the cluster ellipticity-radio galaxy fraction relation shows no obvious difference between WAT and non-WAT clusters.
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Arnaboldi, Magda, and Ortwin Gerhard. "JD2 - Diffuse Light in Galaxy Clusters." Proceedings of the International Astronomical Union 5, H15 (November 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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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, no. 2 (March 1, 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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Giocoli, Carlo, Federico Marulli, Lauro Moscardini, Mauro Sereno, Alfonso Veropalumbo, Lorenzo Gigante, Matteo Maturi, et al. "AMICO galaxy clusters in KiDS-DR3." Astronomy & Astrophysics 653 (September 2021): A19. http://dx.doi.org/10.1051/0004-6361/202140795.
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Context. The large-scale mass distribution around dark matter haloes hosting galaxy clusters provides sensitive cosmological information. Aims. In this work we make use of a large photometric galaxy cluster sample, constructed from the public Third Data Release of the Kilo-Degree Survey, and the corresponding shear signal, to assess cluster masses and test the concordance Λ-cold dark matter (ΛCDM) model. In particular, we study the weak gravitational lensing effects on scales beyond the cluster virial radius, where the signal is dominated by correlated and uncorrelated matter density distributions along the line of sight. The analysed catalogue consists of 6962 galaxy clusters, in the redshift range 0.1 ≤ z ≤ 0.6 and with signal-to-noise ratios higher than 3.5. Methods. We perform a full Bayesian analysis to model the stacked shear profiles of these clusters. The adopted likelihood function considers both the small-scale one-halo term, used primarily to constrain the cluster structural properties, and the two-halo term, that can be used to constrain cosmological parameters. Results. We find that the adopted modelling is successful in assessing both the cluster masses and the total matter density parameter, ΩM, when fitting shear profiles up to the largest available scales of 35 Mpc h−1. Moreover, our results provide a strong observational evidence of the two-halo signal in the stacked gravitational lensing of galaxy clusters, further demonstrating the reliability of this probe for cosmological studies. The main result of this work is a robust constraint on ΩM, assuming a flat ΛCDM cosmology. We get ΩM = 0.29 ± 0.02, estimated from the full posterior probability distribution, consistent with the estimates from cosmic microwave background experiments.
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Barkhouse, W. A., H. K. C. Yee, and O. López-Cruz. "Photometric Properties of Low-Redshift Galaxy Clusters." Symposium - International Astronomical Union 201 (2005): 435–36. http://dx.doi.org/10.1017/s0074180900216549.
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A recent comprehensive photometric survey of 45 low-z X-ray selected Abell clusters (López-Cruz 1997) has measured significant variations in the faint end slope of the luminosity function (LF). This result indicates that dwarf galaxies (dGs) comprise a different fraction of the cluster population as a function cluster environment. Clusters having a central “cD-like” galaxy have a flatter faint end slope than non-cD clusters. Also, cD clusters were found to have a dwarf-to-giant ratio (D/ G) which was smaller than non-cD clusters. López-Cruz et al. (1997) has suggested that the light contained in cD envelopes can be accounted for by assuming that it is produced from stars that originally formed dGs. In this simple model, the D/ G would be expected to increase with radial distance from the cluster centre due to the decrease in the disruptive forces.
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White, Raymond E. "Globular clusters belonging to galaxy clusters." Monthly Notices of the Royal Astronomical Society 227, no. 1 (July 1987): 185–95. http://dx.doi.org/10.1093/mnras/227.1.185.
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Zinn, Robert. "An Overview of the Globular Cluster System of the Galaxy." Symposium - International Astronomical Union 126 (1988): 37–48. http://dx.doi.org/10.1017/s0074180900042376.
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Harlow Shapley (1918) used the positions of globular clusters in space to determine the dimensions of our Galaxy. His conclusion that the Sun does not lie near the center of the Galaxy is widely recognized as one of the most important astronomical discoveries of this century. Nearly as important, but much less publicized, was his realization that, unlike stars, open clusters, HII regions and planetary nebulae, globular clusters are not concentrated near the plane of the Milky Way. His data showed that the globular clusters are distributed over very large distances from the galactic plane and the galactic center. Ever since this discovery that the Galaxy has a vast halo containing globular clusters, it has been clear that these clusters are key objects for probing the evolution of the Galaxy. Later work, which showed that globular clusters are very old and, on average, very metal poor, underscored their importance. In the spirit of this research, which started with Shapley's, this review discusses the characteristics of the globular cluster system that have the most bearing on the evolution of the Galaxy.
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Lim, Sungsoon, Narae Hwang, and Myung Gyoon Lee. "Star clusters in the starburst galaxy M82." Proceedings of the International Astronomical Union 5, S266 (August 2009): 454–57. http://dx.doi.org/10.1017/s1743921309991682.
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AbstractWe present a study of star clusters in the starburst galaxy M82 using the BVI mosaic images taken with the Hubble Space Telescope's Advanced Camera for Surveys. We have selected about 850 clusters with V < 23 mag based on their morphological information. The brightest cluster is as bright as V ~ 16.5 mag (MV ~ −11.2 mag) and most clusters are fainter than V = 18 mag (MV = −9.7 mag). The V-band luminosity function is represented by a power law with a slope α ~ −2.0 in the range of −9.5 < MV < −7 mag. The star clusters in M82 are mainly distributed in the galaxy's disk. However, about a dozen clusters are found far from the disk and are considered to belong to the halo of M82. The color–magnitude diagrams of star clusters show that most star clusters are highly reddened. We have derived the age of the star clusters using a spectral-energy-distribution fitting method with Bruzual & Charlot simple stellar population models. We discuss the age distribution as well as the photometric properties of the star clusters in regard to the formation history of the M82 cluster population.
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de los Rios, Martín, Héctor J. Martínez, Valeria Coenda, Hernán Muriel, Andrés N. Ruiz, Cristian A. Vega-Martínez, and Sofía A. Cora. "ROGER: Reconstructing orbits of galaxies in extreme regions using machine learning techniques." Monthly Notices of the Royal Astronomical Society 500, no. 2 (October 28, 2020): 1784–94. http://dx.doi.org/10.1093/mnras/staa3339.
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ABSTRACT We present the ROGER (Reconstructing Orbits of Galaxies in Extreme Regions) code, which uses three different machine learning techniques to classify galaxies in, and around, clusters, according to their projected phase-space position. We use a sample of 34 massive, M200 > 1015h−1M⊙, galaxy clusters in the MultiDark Planck 2 (MDLP2) simulation at redshift zero. We select all galaxies with stellar mass M⋆ ≥ 108.5h−1M⊙, as computed by the semi-analytic model of galaxy formation SAG, that are located in, and in the vicinity of, these clusters and classify them according to their orbits. We train ROGER to retrieve the original classification of the galaxies from their projected phase-space positions. For each galaxy, ROGER gives as output the probability of being a cluster galaxy, a galaxy that has recently fallen into a cluster, a backsplash galaxy, an infalling galaxy, or an interloper. We discuss the performance of the machine learning methods and potential uses of our code. Among the different methods explored, we find the K-Nearest Neighbours algorithm achieves the best performance.
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Knebe, Alexander, Matías Gámez-Marín, Frazer R. Pearce, Weiguang Cui, Kai Hoffmann, Marco De Petris, Chris Power, Roan Haggar, and Robert Mostoghiu. "The Three Hundred project: shapes and radial alignment of satellite, infalling, and backsplash galaxies." Monthly Notices of the Royal Astronomical Society 495, no. 3 (May 21, 2020): 3002–13. http://dx.doi.org/10.1093/mnras/staa1407.
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ABSTRACT Using 324 numerically modelled galaxy clusters, we investigate the radial and galaxy–halo alignment of dark matter subhaloes and satellite galaxies orbiting within and around them. We find that radial alignment depends on distance to the centre of the galaxy cluster but appears independent of the dynamical state of the central host cluster. Furthermore, we cannot find a relation between radial alignment of the halo or galaxy shape with its own mass. We report that backsplash galaxies, i.e. objects that have already passed through the cluster radius but are now located in the outskirts, show a stronger radial alignment than infalling objects. We further find that there exists a population of well radially aligned objects passing very close to the central cluster’s centre that were found to be on highly radial orbit.
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Cariddi, S., M. D’Onofrio, G. Fasano, B. M. Poggianti, A. Moretti, M. Gullieuszik, D. Bettoni, and M. Sciarratta. "Characterization of Omega-WINGS galaxy clusters." Astronomy & Astrophysics 609 (January 2018): A133. http://dx.doi.org/10.1051/0004-6361/201731605.
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Context. Galaxy clusters are the largest virialized structures in the observable Universe. Knowledge of their properties provides many useful astrophysical and cosmological information. Aims. Our aim is to derive the luminosity and stellar mass profiles of the nearby galaxy clusters of the Omega-WINGS survey and to study the main scaling relations valid for such systems. Methods. We merged data from the WINGS and Omega-WINGS databases, sorted the sources according to the distance from the brightest cluster galaxy (BCG), and calculated the integrated luminosity profiles in the B and V bands, taking into account extinction, photometric and spatial completeness, K correction, and background contribution. Then, by exploiting the spectroscopic sample we derived the stellar mass profiles of the clusters. Results. We obtained the luminosity profiles of 46 galaxy clusters, reaching r200 in 30 cases, and the stellar mass profiles of 42 of our objects. We successfully fitted all the integrated luminosity growth profiles with one or two embedded Sérsic components, deriving the main clusters parameters. Finally, we checked the main scaling relation among the clusters parameters in comparison with those obtained for a selected sample of early-type galaxies (ETGs) of the same clusters. Conclusions. We found that the nearby galaxy clusters are non-homologous structures such as ETGs and exhibit a color–magnitude (CM) red-sequence relation very similar to that observed for galaxies in clusters. These properties are not expected in the current cluster formation scenarios. In particular the existence of a CM relation for clusters, shown here for the first time, suggests that the baryonic structures grow and evolve in a similar way at all scales.