Environmental cluster effects and galaxy evolution: The H i properties of the Abell clusters A85/A496/A2670

Abstract

We study the impact of local environment on the transformation of spiral galaxies in three nearby (z < 0.08) Abell clusters: A85/A496/A2670. These systems were observed in H i with the Very Large Array, covering a volume extending beyond the virial radius and detecting 10, 58, 38 galaxies, respectively. High fractions (0.40–0.86) of bright spirals [log(M*/M⊙) = 9 − 10] are not detected in H i. We provide further evidence of environmental effects consisting in significant fractions (0.10–0.33) of abnormal objects and a number of red (passive) spirals, suggesting an ongoing process of quenching. Ram-pressure profiles, and the sample of the brightest spirals used as test particles for environmental effects, indicate that ram-pressure plays an important role in stripping and transforming late-types. Phase-space diagrams and our search for substructures helped to trace the dynamical stage of the three systems. This was used to compare the global cluster effects vs. pre-processing, finding that the former is the dominating mechanism in the studied clusters. By contrasting the global distribution of H i normal vs. H i disturbed spirals in the combined three clusters, we confirm the expected correlation of disturbed objects located, on average, at shorter projected radii. However, individual clusters do not necessarily follow this trend and we show that A496 and A2670 present an atypical behavior. In general we provide conclusive evidence about the dependence of the transformation of infalling spirals on the ensemble of cluster properties like mass, ICM density, dynamical stage and surrounding large-scale structure.

Tracing the Assembly Histories of Galaxy Clusters in the Nearby Universe

“…After homogenizing the galaxy coordinates by applying the match with photometric data, and after defining the different centers and correcting for superposed clusters, we proceeded to check the membership of the galaxies in their respective clusters using a more robust approach. The principle is simple: considering that, in a gravitationally-bound system, the galaxies must have velocities that do not exceed the escape velocity, their distribution in a projected phase-space (PPS) diagram, formed by the LOS velocity as a function of projected cluster-centric distance, e.g., Figure 1, must be enclosed within a trumpet-shaped curve, usually called "caustic", as defined by the escape velocity (e.g., Regös & Geller 1989;López-Gutiérrez et al 2022). Details about the method for defining and fitting caustics are presented in Chow-Martínez (2019).…”

“…Note that, differing from the traditional way substructures are identified by this test, we do not consider only specific concentrations of galaxies with high δ values in the projected distribution. 14 Specifically, when ∆/N c > 1.2, we analyse both the 3D distribution of galaxies in RA, Dec and v local and the respective 2D PPS diagram to identify, in the former, the volume separation surfaces between the substructures (e.g., López-Gutiérrez et al 2022). In this pseudo-3D volume, substructure members are more smoothly distributed, defining a more isolated locus (local concentration) than in a RA-Dec-z-volume, while in the PPS they show the typical caustics-shape distribution.…”