Spatially resolved PAH$_{3.3}$ emission and stellar ages in ram pressure stripped clumps at $z\sim0.3$

TL;DR

This study uses JWST/NIRCam PAH$_{3.3}$ mapping and spatially resolved UV-to-MIR SED fitting to investigate how ram pressure stripping affects dust and star formation in nine Abell 2744 galaxies at $z\,=\,0.306$. Eight galaxies show PAH$_{3.3}$ emission with disk truncation and extraplanar features up to 40 kpc in stripped tails; clumps in tails exhibit age gradients consistent with the fireball model, indicating sequential star formation as gas is stripped. PAH emission generally tracks local star formation and correlates with stellar mass, but the PAH-specific luminosity declines with age, and PAH-based SFRs align with SED-based SFRs within about 0.4 dex, albeit with a known age dependence that can overestimate SFR in very young or very old regions. The results provide the first detailed PAH analysis in cluster galaxies at intermediate redshift, demonstrating PAH survival during RPS and offering insights into dust fate and star formation in extreme environments. The findings support a scenario where PAHs are stripped with gas and participate in downstream star formation, while age gradients in clumps reinforce the fireball framework for tail formation and evolution."

Abstract

Ram pressure stripping (RPS) plays a crucial role in shaping galaxy evolution in dense environments, yet its impact on the molecular and dusty phases of the interstellar medium remains poorly understood. We present JWST/NIRCam $3.3\mathrm{μm}$ polycyclic aromatic hydrocarbon (PAH) emission maps for the nine most striking RPS galaxies in the Abell 2744 cluster at redshift $z_{cl}=0.306$, tracing the effects of environmental processes on small dust grains. Exploiting multi-band JWST/NIRCam and HST photometry, we performed a spatially resolved ultraviolet (UV) to mid-infrared (MIR) spectral energy distribution (SED) fitting to characterise stellar populations in both galactic disks and clumps detected in the stripped tails. We detected PAH$_{3.3}$ emission in eight of the nine galaxies at $5σ$, with morphologies revealing disk truncation and elongation along the RPS direction. In three galaxies, PAH$_{3.3}$ emission is also found in star-forming clumps embedded in the stripped tails up to a distance of $40\mathrm{kpc}$. Star formation rates inferred from PAH$_{3.3}$ emission are in agreement with those derived from SED fitting averaged over the past $100\mathrm{Myr}$ within an intrinsic scatter of $0.4\mathrm{dex}$, but the relation appears to be age-dependent. The spatial correlation between the PAH strength, stellar age, and star formation rate (SFR) is consistent across disks and tails and demonstrates that PAH-carrying molecules can survive and become stripped by ram pressure. Finally, age gradients revealed by the SED fitting provide observational evidence of the fireball model in star-forming, stripped clumps of galaxies at $z \sim 0.3$. This work represents the first detailed study of PAH emission in cluster galaxies, offering new insights into the fate of dust and star formation in extreme environments.

Figures (17)

• Figure 1: Colour composite images of the RPS galaxies analysed in this work, obtained from JWST data. We used F070W, F115W, and F200W filters for the blue, green, and red channels, respectively. The white arrows represent the RPS directions and the red ellipses indicate the galaxy disks, as described in Sect. \ref{['sec:disk-rps']}. The green square in galaxy 9856 indicates a clump with a spectroscopic redshift from MUSE (Astrodeep IDs 9962). In the upper left corner, the physical scale is reported. The white contour is the $\mathrm{H\alpha}$ mask from Moretti:2020, when available. The galaxies are organised as follows: first, the RPS galaxies identified by Moretti:2022; next, those from Watson:2025; and finally, the ones identified by this work. North is up, east is left.
• Figure 2: F200W image of the Abell 2744 field. The nine RPS galaxies analysed in this work, labelled with their IDs, are indicated in red. The centres of the dark matter halos from the lensing model of Furtak:2022 are shown in magenta.
• Figure 3: JWST/Prism spectrum of the galaxy 12875 Vulcani:2025 (black line) and a subset of the JWST and HST filter bandpasses. The complete set of filters used is found in Appendix \ref{['app:filters']}. The filters used to extract the PAH flux are red coloured: F335M and F480M are used to model the continuum flux. F430M is the filter in which the PAH band falls at the cluster redshift.
• Figure 4: Voronoi binning (in blue) and clumps identification in a portion of the galaxy 10685. The leaves from astrodendro with $N_{min}=30$ are shown in purple; in red, the ellipses traced from the leaves; in yellow, the clumps. Each elongated astrodendro leaf produces a clump association, which is visible as a series of circular clumps. In a clump association, each circle corresponds to a different clump. The scale of the image is shown in the top-right corner. In this image, both the identified clumps inside and outside the galactic disk are visible.
• Figure 5: $\mathrm{PAH_{3.3}}\ $ emission maps for all galaxies in the sample. For each galaxy, an RGB image composite of F070W (blue), F115W (green), and F200W (red) filters with the $5\sigma$ significance PAH map of the galaxy (superimposed in purple) is shown on the left. The red ellipses indicate the galaxy disks. The arrow indicates the RPS direction. The surface brightness map of the $\mathrm{PAH_{3.3}}\ $ emission is shown on the right. The gold and blue contours indicate the leading and trailing galactic regions with brightness greater than $5\sigma_{bkg}$, respectively. The $A_\mathrm{RPS}$ is the ram pressure asymmetry of the PAH map as defined in Sect. \ref{['sec:A-rps']}. The blue hatched region in galaxy 10685 represents the masked area. North is up, east is left.