Jellyfish galaxy candidates at low redshift (1504.07105v3)

Abstract: Galaxies that are being stripped of their gas can sometimes be recognized from their optical appearance. Extreme examples of stripped galaxies are the so-called ``jellyfish galaxies'', that exhibit tentacles of debris material with a characteristic jellyfish morphology. We have conducted the first systematic search for galaxies that are being stripped of their gas at low-z (z=0.04-0.07) in different environments, selecting galaxies with varying degrees of morphological evidence for stripping. We have visually inspected B and V-band images and identified 344 candidates in 71 galaxy clusters of the OMEGAWINGS+WINGS sample and 75 candidates in groups and lower mass structures in the PM2GC sample. We present the atlas of stripping candidates and a first analysis of their environment and their basic properties, such as morphologies, star formation rates and galaxy stellar masses. Candidates are found in all clusters and at all clustercentric radii, and their number does not correlate with the cluster velocity dispersion sigma or X-ray luminosity L_X. Interestingly, convincing cases of candidates are also found in groups and lower mass haloes (10^{11}-10^{14} M_{sun}), although the physical mechanism at work needs to be securely identified. All the candidates are disky, have stellar masses ranging from log M/M_{sun} < 9 to > 11.5 and the majority of them form stars at a rate that is on average a factor of 2 higher (2.5 sigma) compared to non-stripped galaxies of similar mass. The few post-starburst and passive candidates have weak stripping evidence. We conclude that the stripping phenomenon is ubiquitous in clusters and could be present even in groups and low mass haloes. Further studies will reveal the physics of the gas stripping and clarify the mechanisms at work.

Jellyfish Galaxy Candidates at Low Redshift: An Analytical Perspective

The paper by Poggianti et al. presents an extensive investigation into the phenomenon of jellyfish galaxies at low redshifts ($z=0.04-0.07$). These galaxies, known for their distinct morphological features resembling jellyfish due to gas stripping, are studied across various environments, including galaxy clusters and less massive structures. This work contributes significantly to understanding galactic evolution, specifically focusing on environmental effects on gas dynamics within galaxies.

Summary of Methodology and Findings

The researchers undertake a systematic search within the OMEGAWINGS and WINGS cluster samples and the PM2GC sample for potential jellyfish galaxies. They employ visual inspection methods on B and V-band images, identifying 344 candidates in 71 clusters and 75 candidates in the PM2GC sample. The paper classifies candidates into five categories based on the visual evidence supporting gas stripping, from the most apparent cases (JClass 5) to the least obvious ones (JClass 1).

Key findings reveal that jellyfish candidates exist across all inspected clusters and at various clustercentric radii. The distribution of candidates does not show dependency on cluster mass indicators such as velocity dispersion or X-ray luminosity. This suggests that the stripping phenomenon is prevalent in clusters, extending even into groups and low-mass halos with masses ranging from $10^{11}$ to $10^{14} M_{\odot}$.

Implications on Galaxy Evolution

One of the critical implications of this research is the evidence supporting the ubiquity of the gas stripping process in different environments, implying diverse mechanisms at play. The discovery of jellyfish candidates in lower mass environments raises questions regarding the possible role of alternative stripping mechanisms outside traditional ram pressure stripping, which has often been associated mainly with massive clusters.

Furthermore, the observed star formation rates in jellyfish galaxies are approximately twice those in non-stripped galaxies of similar mass. This enhancement suggests that interactions with the cluster environment might trigger star formation before it becomes quenched, aligning with the complex narrative of starburst and post-starburst phases in galactic evolution.

Future Research Directions

The paper opens several avenues for future research. There is a significant need for high-resolution integral field spectroscopy to dissect the physical processes behind gas stripping. Such studies can elucidate the nature of star formation in tails, the duration, and the extent of stripping, as well as pin down the precise mechanisms responsible in different environmental settings.

The results also point toward a broader investigation of lower mass environments where alternative processes might induce similar morphological traits seen in clusters. Efforts like the forthcoming MUSE/VLT observations are expected to provide deeper insights into the physics governing these stripping processes.

In summation, Poggianti et al.'s work presents a substantial contribution to the understanding of environmental influences on galaxy evolution, while also paving the path for more detailed, physics-based explorations to unlock the complexities of galaxy transformation in diverse cosmic settings.