Stellar Bars in Jellyfish Galaxies: Statistical Insights into the Combined Role of Bars and Environment

TL;DR

This study investigates how internal bars and external ram pressure stripping (RPS) jointly affect central star formation in jellyfish galaxies, using a large SDSS-based dataset. By classifying galaxies by bar presence and RPS signatures and constructing mass- and environment-matched control samples, the authors analyze radial $u-r$ colour profiles as proxies for sSFR. They find that barred galaxies, especially those undergoing RPS, exhibit flatter central colour profiles and bluer cores, with the strongest signatures when bars and RPS act together; after controlling for mass and environment, the central rejuvenation signal persists but is less pronounced. The results demonstrate that bars amplify environmental effects on the stellar populations of cluster galaxies, highlighting the interplay between secular bar-driven inflows and hydrodynamic stripping in shaping galaxy evolution in dense environments.

Abstract

Recent observational studies suggest that the interplay between internal and environmental mechanisms, in particular, the combined action of stellar bars and ram pressure stripping (RPS) may influence central star formation activity in jellyfish galaxies. However, current evidence relies on small samples, leaving open whether bars play a significant role during stripping. In this study, we analyse a sample about five times larger than those used in previous works, comprising 176 galaxies identified as RPS candidates based on optical morphological indicators such as asymmetries, debris tails, and displaced star-forming regions. To assess the impact of these processes, we examine radial $u-r$ colour profiles from SDSS imaging as tracers of the specific star formation rate (sSFR). We classify galaxies by bar presence and RPS signatures, and construct comparison samples through stepwise matching in stellar mass and environment to disentangle the individual and combined effects of bars and RPS on stellar population gradients. Our results show that central rejuvenation signals emerge in RPS candidate galaxies, becoming most evident when bars and RPS act together. Barred RPS galaxies are systematically bluer at all radii than their non-RPS counterparts, while unbarred systems display only mild or no central differences, suggesting that the observable outcome of RPS depends on the stripping stage. Furthermore, barred galaxies exhibit flatter central colour profiles than unbarred ones -- a robust signature across all matched configurations. These findings highlight the key role of bars in amplifying environmental effects on the stellar populations of jellyfish galaxies, underscoring how internal structures can modulate the observable signatures of environmental processes in galaxies.

Figures (8)

• Figure 1: Projected phase–space diagram illustrating the distribution of galaxies in $\Delta V_{cl}/\sigma_{cl}$ (line-of-sight velocity offset from the cluster mean normalized by the cluster velocity dispersion) versus $r_{cl}/r_{vir}$ (projected clustercentric distance normalized by the virial radius). Top-left panel: galaxies affected by RPS, including both barred and unbarred types. Top-right panel: galaxies from the comparison (NRPS) sample, categorized into barred and unbarred. Bottom-left panel: barred galaxies split into RPS and NRPS subsamples. Bottom-right panel: unbarred galaxies split in the same way.
• Figure 2: Representative examples of visually classified galaxies from our samples. The top row shows RPS galaxies and the bottom row NRPS galaxies, each split into unbarred (left) and barred (right) categories. Images are $g+r+z$ colour composites from the DESI Legacy Imaging Surveys (Data Release 9; Dey+2019).
• Figure 3: Workflow followed to construct the final galaxy samples. The process consists of successive cross-matches with SDSS public value-added catalogs, indicating the number of galaxies retained at each step. The final stage includes the bar classification (Section \ref{['sec: bar_identification']}), leading to the working samples of late-type, face-on galaxies without AGN. Acronyms (KIAS-VAGC, NSA, MPA-JHU) are defined in Section \ref{['sec: data']}, and further details on the bar classification procedure are provided in Section \ref{['sec: bar_identification']}.
• Figure 4: Violin plots illustrating the distribution of stellar masses in galaxies before and after the matching process. The upper panels distinguish between RPS and NRPS galaxies, further categorized into barred (red) and unbarred (blue) types. The bottom panels differentiate galaxies based on the presence of bars, further divided into barred (red) and unbarred (blue) galaxies.
• Figure 5: Violin plots illustrating the distribution of stellar masses ($M_\ast$), projected cluster distance ($r_{cl}/r_{vir}$), and line-of-sight velocity ($\Delta V_{cl} / \sigma_{cl}$) of galaxies before and after the matching process. The panels distinguish between galaxies affected by RPS and NRPS, further categorizing them into barred (red) and unbarred (blue) types. Additionally, galaxies are differentiated based on the presence of bars, with further subdivisions into those affected (green) and unaffected (black) by RPS.