Galaxy cluster mergers as triggers for the formation of jellyfish galaxies: case study of the A901/2 system

The A901/2 system is a rare case of galaxy cluster interaction, in which two galaxy clusters and two smaller groups are seen in route of collision with each other simultaneously. Within each of the four substructures, several galaxies with features indicative of jellyfish morphologies have been observed. In this paper, we propose a hydrodynamic model for the merger as a whole, compatible with its diffuse X-ray emission, and correlate the gas properties in this model with the locations of the jellyfish galaxy candidates in the real system. We find that jellyfish galaxies seem to be preferentially located near a boundary inside each subcluster where diffuse gas moving along with the subcluster and diffuse gas from the remainder of the system meet. The velocity change in those boundaries is such that a factor of up to $\sim$1000 increase in the ram pressure takes place within a few hundred kpc, which could trigger the high rate of gas loss necessary for a jellyfish morphology to emerge. A theoretical treatment of ram pressure stripping in the environment of galaxy cluster mergers has not been presented in the literature so far; we propose that this could be a common scenario for the formation of jellyfish morphologies in such systems.Comment: Accepted for publication in MNRAS. 10 pages, 9 figure

Sloshing Simulations of the galaxy cluster Abell 1644

Recent collision events between galaxy clusters exhibit peculiar morphologies in the intracluster medium. That seems to be the case of Abell 1644, a nearby galaxy cluster (z = 0:047), composed by three main structures: the southern cluster that shows a spiral-like morphology A1644S, the northern cluster seen in X-ray observations A1644N1, and the recently discovered substructure A1644N2. By means of N-body hydrodynamical simulations, we attempt to reconstruct the dynamical history of the system. These simulations resulted in two specific scenarios: (i) The collision between A1644S and A1644N2, with an inclination in relation to the plane of the sky of 20∘. Our best model reaches the best morphology 2 Gyr after the pericentric passage, and shows a good agreement with observations; (ii) The collision between A1644S and A1644N1. This scenario was evaluated in two instants of time: in the first passage after the pericentric passage; and after apoapsis, when the cluster returns when reaching the maximum separation. This approach of collision between A1644S/N1 did not give rise to results as satisfactory as the scenario A1644S/N2, due to great disturbances in density and mismatching temperature maps. As a complementary study, we perform a three-cluster simulation using as base the best-fitting model A1644S/N2. We tried to reproduce the current state of A1644 with the three main structures, resulting in a good agreement to the global morphology of the observations. Thus, we find that the more likely scenario is a collision between A1644S and A1644N2, where A1644N1 may be present as long as it does not greatly interfere in the formation of the spiral feature.Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Colisões recentes entre aglomerados de galáxias exibem morfologias peculiares no meio intraaglomerado. Esse parece ser o caso de Abell 1644, um aglomerado próximo (z = 0:047) composto por três principais estruturas: o aglomerado ao sul que apresenta uma morfologia espiral, A1644S; o aglomerado ao norte, presente em observações de raios-X, A1644N1; e a subestrutura recém descoberta pela análise de lentes gravitacionais fracas, A1644N2. Por meio de simulações hidrodinâmicas de N-corpos, propõe-se uma possível reconstrução da história dinâmica do sistema. Tais simulações resultaram em dois cenários específicos: (i) A colisão entre A1644S e A1644N2, com inclinação em relação ao plano do céu de 20∘. O modelo final apresentado alcança a melhor morfologia 2 Gyr após a passagem pericêntrica, e demonstra boa concordância quantitativa e qualitativa com os dados observacionais. (ii) A colisão entre A1644S e A1644N1. Esse cenário foi avaliado em dois instantes de tempo: na primeira passagem após a passagem pericêntrica; e após o apoapsis, quando o aglomerado retorna ao atingir o máximo afastamento; Tal abordagem de colisão entre A1644S/N1 não demonstrou resultados tão satisfatórios quanto o cenário de A1644S/N2, devido a grandes perturbações na densidade e discordâncias entre os mapas de temperatura. Um estudo complementar é realizado através de simulações de três corpos, utilizando como base o melhor modelo de colisão entre A1644S/N2. Tentou-se reproduzir o estado atual de A1644 com suas três principais estruturas, resultando em um cenário de bom acordo com a morfologia global das observações. Assim, acredita-se que é mais provável uma colisão entre A1644S e A1644N2, onde A1644N1 pode estar presente desde que não interfira na formação da estrutura espiral

Galaxy cluster optical mass proxies from probabilistic memberships

Robust galaxy cluster mass estimates are fundamental for constraining cosmological parameters from counts. For this reason, it is essential to search for tracers that, independent of the cluster's dynamical state, have a small intrinsic scatter and can be easily inferred from observations. This work uses a simulated data set to focus on photometric properties and explores different optical mass proxies including richness, optical luminosity, and total stellar mass. We have developed a probabilistic membership assignment that makes minimal assumptions about the galaxy cluster properties, limited to a characteristic radius, velocity dispersion, and spatial distribution. Applying the estimator to over 919 galaxy clusters with z(phot )for stellar mass. We also discuss membership assignment, completeness and purity, and the consequences of small centre and redshift offsets. We conclude that the application of our method for photometric surveys delivers competitive cluster mass proxies.Peer reviewe