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This paper presents a method for finding ram pressure stripped (RPS) galaxy candidates by performing a morphological analysis of galaxy images obtained from the Legacy survey. We consider a sample of about 600 galaxies located in different environments such as groups and clusters, tidally interacting pairs and the field. The sample includes 160 RPS previously classified in the literature into classes from J1 to J5, based on the increasing level of disturbances. Our morphological analysis was done using the astromorphlib software followed by the inspection of diagnostic diagrams involving combinations of different parameters like the asymmetry (A), concentration (C), Sérsic index (n), and bulge strength parameters |$F(G,\, M_{20})$|⁠. We found that some of those diagrams display a distinct region in which galaxies classified as J3, J4, and J5 decouples from isolated galaxies. We call this region as the morphological transition zone and we also found that tidally interacting galaxies in pairs are predominant within this zone. Nevertheless, after visually inspecting the objects in the morphological transition zone to discard obvious contaminants, we ended up with 33 bona fide new RPS candidates in the studied nearby groups and clusters (Hydra, Fornax, and CLoGS sample), of which one-third show clear evidence of unwinding arms. Future works may potentially further increase significantly the samples of known RPS using such method. [ABSTRACT FROM AUTHOR]

Theoretical and observational studies have suggested that ram-pressure stripping (RPS) by the intracluster medium can be enhanced during cluster interactions, boosting the formation of the 'jellyfish' galaxies. In this work, we study the incidence of galaxies undergoing RPS in 52 clusters of different dynamical states. We use optical data from the WINGS/OmegaWINGS surveys and archival X-ray data to characterize the dynamical state of our cluster sample, applying eight different proxies. We then compute the number of RPS candidates relative to the infalling population of blue late-type galaxies within a fixed circular aperture in each cluster. We find no clear correlation between the fractions of RPS candidates and the different cluster dynamical state proxies considered. These fractions also show no apparent correlation with cluster mass. To construct a dynamical state classification closer to a merging 'sequence', we perform a visual classification of the dynamical states of the clusters, combining information available in optical, X-ray, and radio wavelengths. We find a mild increase in the RPS fraction in interacting clusters with respect to all other classes (including post-mergers). This mild enhancement could hint at a short-lived enhanced RPS in ongoing cluster mergers. However, our results are not statistically significant due to the low galaxy numbers. We note this is the first homogeneous attempt to quantify the effect of cluster dynamical state on RPS using a large cluster sample, but even larger (especially wider) multiwavelength surveys are needed to confirm the results. [ABSTRACT FROM AUTHOR]

The ratio of calcium ii H plus Hϵ to calcium ii K inverts as a galaxy stellar population moves from being dominated by older stars to possessing more A and B class stars. This ratio – the H:K ratio – can serve as an indicator of stellar populations younger than 200 Myr. In this work, we provide a new method to determine H:K, and apply it to spectra taken of cluster galaxies in Abell 3888. Although H:K is on average systematically lower for the cluster than for a wider field sample, we show that H:K does not have a simple relationship with other indices such as the equivalent widths of Hδ and [O  ii ] beyond having a high value for strong [O  ii ] emission. Moreover, strongly inverted galaxies with H:K > 1.1 have no preferred location within the cluster and are only slightly lower in their velocity dispersions around the cluster compared to strongly emitting [O  ii ] galaxies. Our results indicate that selecting galaxies on H:K inversion results in a heterogeneous sample formed via a mixture of pathways that likely includes, but may not be limited to, merging spiral galaxies, and quiescent galaxies accreting lower mass, gas-rich companions. In concert with other selection criteria, H:K can provide a means to select a more 'pure' passive sample or to aid in the selection of highly star-forming galaxies, especially where other spectral line indicators such as H α may not have been observed. [ABSTRACT FROM AUTHOR]