Probing Obscured Star Formation in Galaxy Clusters Using JWST Medium-band Images: 3.3 μm PAH Emitter Sample in A2744

Abstract

Star-forming galaxies in galaxy clusters play a crucial role in understanding the advanced stages of galaxy evolution within dense environments. We present a sample of 3.3 μ m polycyclic aromatic hydrocarbon (PAH)-bright galaxies in the A2744 galaxy cluster. Using F430M medium-band images, we select PAH emitters in the galaxy cluster, which capture the 3.3 μ m PAH emission at the redshift of A2744. Our multiwavelength study demonstrates consistent star formation rates (SFRs) derived from PAH emission and spectral energy distribution fitting, indicating that the 3.3 μ m PAH flux estimated from the medium-band image alone can reveal the entirety of star formation, immune to dust obscuration. We find that the PAH emitters are located in relatively low-mass surface density regions of A2744, with SFRs aligning with the field star-forming main sequence at z = 0.3. The PAH emission morphologies show more asymmetry than that of the F444W image when the asymmetry index is >0.4. With these results, we suggest that these star-forming galaxies in A2744 are in the stage of falling into the cluster from the field, and have not been quenched yet. We further explore a potential link between these galaxies and cosmic filaments being accreted onto the cluster, which may channel gas inflows to fuel star formation. JWST medium-band imaging provides a powerful new tool for identifying heavily dust-obscured star-forming populations. Future H I and low- J CO observations should be prioritized to resolve the cold gas kinematics and star formation processes in these systems, which would directly test the role of environmental stripping versus filamentary gas supply.

Keywords

• Polycyclic aromatic hydrocarbons
• Star formation
• Abell clusters
• Starburst galaxies