The spatial structure and dynamical state of the open cluster NGC 2112

This paper investigates the spatial structure and dynamical state of the old open cluster NGC 2112 based on likely cluster members from Gaia Early Data Release 3. Using the Density-Based Spatial Clustering of Applications with Noise (DBSCAN) algorithm, we find 1193 likely cluster members down to G ∼ 21 mag within a radius of 1.°5 from the cluster center. These likely cluster members can be divided into 865 core members and 328 border members by DBSCAN. We find that the core members are, on average, significantly brighter and more centrally concentrated than the border members. This suggests the existence of clear mass segregation within the cluster. We find that the outer regions of the cluster exhibit a slightly elongated shape, which may be caused by external tidal perturbations. We estimate a distance of D = 1108 ± 3 pc for the cluster based on bright core members. We find that NGC 2112 has a cluster radius of Rcl ∼ 40′ (∼12.9 pc) and a core radius of $R_{\rm c} \sim {4{^{\prime }_{.}}8} \pm {0{^{\prime }_{.}}2}$ (∼1.5 pc). This indicates that NGC 2112 has a central concentration parameter of C = log (Rcl/Rc) ∼ 0.92, which is significantly larger than previously thought. In addition, we estimate a total mass of Mcl = 858 ± 12 M⊙ and an initial mass of Mini = (2.2 ± 0.5) × 104 M⊙ for the cluster. This implies that NGC 2112 may have lost more than $90\%$ of its initial mass. Based on the obtained distance and kinematical data, we also calculate the Galactic orbit of the cluster.

The Three Hundred Project: Dynamical state of galaxy clusters and morphology from multi-wavelength synthetic maps

We study the connection between morphology and dynamical state of the simulated galaxy clusters in z ∈ [0, 1.031] from The Three Hundred Project. We quantify cluster dynamical state using a combination of dynamical indicators from theoretical measures and compare this combined parameter, χ, with the results from morphological classifications. The dynamical state of the cluster sample shows a continuous distribution from dynamically relaxed, more abundant at lower redshift, to hybrid and disturbed. The dynamical state presents a clear dependence on the radius, with internal regions more relaxed than outskirts. The morphology from multi-wavelength mock observation of clusters in X-ray, optical, and Sunyaev-Zel’dovich (SZ) effect images, is quantified by M – a combination of six parameters for X-ray and SZ maps and the offsets between the optical position of the Brightest Central Galaxy (BCG) and the X-ray/SZ centroids. All the morphological parameters are highly correlated with each other, while they show a moderately strong correlation with the dynamical χ parameter. The X-ray or SZ peaks are less affected by the dynamical state than centroids, which results in reliable tracers of the cluster density peak. The principal source of contamination in the relaxed cluster fraction, inferred from morphological parameters, is due to dynamically hybrid clusters. Compared to individual parameters, which consider only one aspect of cluster property (e.g. only clumping or asymmetry), the combined morphological and dynamical parameters (M and χ) collect more information and provide a single and more accurate estimation of the cluster dynamical state.

Changes in geometrical aspects of a simple model of cilia synchronization control the dynamical state, a possible mechanism for switching of swimming gaits in microswimmers

Active oscillators, with purely hydrodynamic coupling, are useful simple models to understand various aspects of motile cilia synchronization. Motile cilia are used by microorganisms to swim and to control the flow fields in their surroundings; the patterns observed in cilia carpets can be remarkably complex, and can be changed over time by the organism. It is often not known to what extent the coupling between cilia is due to just hydrodynamic forces, and neither is it known if it is biological or physical triggers that can change the dynamical collective state. Here we treat this question from a very simplified point of view. We describe three possible mechanisms that enable a switch in the dynamical state, in a simple scenario of a chain of oscillators. We find that shape-change provides the most consistent strategy to control collective dynamics, but also imposing small changes in frequency produces some unique stable states. Demonstrating these effects in the abstract minimal model proves that these could be possible explanations for gait switching seen in ciliated micro organisms like Paramecium and others. Microorganisms with many cilia could in principle be taking advantage of hydrodynamic coupling, to switch their swimming gait through either a shape change that manifests in decreased coupling between groups of cilia, or alterations to the beat style of a small subset of the cilia.

Probing Saraswati’s heart: evaluating the dynamical state of the massive galaxy cluster A2631 through a comprehensive weak-lensing and dynamical analysis

ABSTRACT In this work, we investigate the dynamical state of the galaxy cluster Abell 2631, a massive structure located at the core of the Saraswati supercluster. To do this, we first solve a tension found in the literature regarding the weak-lensing mass determination of the cluster. We do this through a comprehensive weak-lensing analysis, exploring the power of the combination of shear and magnification data sets. We find $M_{200}^{\rm wl} = 8.7_{-2.9}^{+2.5} \times 10^{14}$ M⊙. We also determined the mass based on the dynamics of spectroscopic members, corresponding to $M_{200}^{\rm dy} = 12.2\pm 3.0 \times 10^{14}$ M⊙, consistent within a 68 per cent CL with the weak-lensing estimate. The scenarios provided by the mass distribution and dynamics of galaxies are reconciled with those provided by X-ray observations in a scenario where A2631 is observed at a late stage of merging.