Characterizing the Star Cluster Populations in Stephan’s Quintet Using HST and JWST Observations

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Abstract
Stephan’s Quintet (SQ) is a local compact galaxy group system that exhibits significant star formation activity. A history of tidal interactions between its four member galaxies and a recent collision between an intruder galaxy and the original group are associated with active star formation, particularly in many shocked regions in the intragroup medium. Using an existing star cluster candidate (SCC) catalog constructed from Hubble Space Telescope (HST) UV/optical images, we integrate flux measurements from five near-infrared filters (F090W, F150W, F200W, F277W, and F356W) obtained from JWST NIRCam observations in 2022. Leveraging the extended photometric baseline from HST and JWST, spanning ∼300 to ∼3500 nm, we perform spectral energy distribution (SED) fitting using the C igale code to derive reliable estimates of age, mass, and extinction for the 1588 high-confidence SCCs. We confirm earlier results that very young SCCs (∼a few Myr) are predominantly located along previously identified shock regions near the merging galaxies, while older (>100 Myr) and globular clusters are more widely distributed. Our analysis shows that near-IR photometry helps break the age–extinction degeneracy, reclassifying many SCCs from older to younger, moderately dust-extincted clusters when added to HST-based SED fits. We also observe a strong spatial correlation between young clusters and CO-traced molecular gas, although active star formation is present in several regions with no detectable CO. We find that the two prominent epochs of star formation, around 5 and 200 Myr, correspond to the two major interaction events in SQ that gave rise to the observed extended tidal features.

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