FEAST: JWST/NIRCam view of the Resolved Stellar Populations of the Interacting Dwarf Galaxies NGC~4485/NGC~4490 (2509.01740v1)

Abstract: We present new JWST/NIRCam observations of the interacting dwarf galaxy system NGC 4485/NGC 4490 (a.k.a. Arp 269), obtained as part of the Cycle 1 Feedback in Emerging extrAgalactic Star clusTers (FEAST) program. NGC 4485 and NGC 4490 form the closest known pair of interacting late-type dwarf galaxies (at $\sim 7.4$ Mpc), excluding the Magellanic Clouds. Near-infrared color-magnitude diagrams (CMDs) reveal a wide range of stellar populations in both galaxies, including young ($\lesssim 200$ Myr) upper main sequence stars, core helium-burning stars, and oxygen-rich asymptotic giant branch (AGB) stars. We also identify intermediate-age ($\sim 200$ Myr -- $1$ Gyr) carbon-rich AGB stars and a well-populated old ($\gtrsim 1$ Gyr) red giant branch (RGB). The CMDs show two distinct bursts of star formation beginning $\sim 30$ Myr and $\sim 200$ Myr ago, the latter consistent with the most recent pericenter passage predicted by N-body simulations. The spatial distribution of stars reveals a tidal bridge extending from NGC 4485 and connecting to the disk of NGC 4490. Compact star-forming regions are seen along NGC 4490's spiral arms, possibly originating from its infrared nucleus. A significant metallicity gradient is observed in the young stellar populations forming the bridge. These findings suggest that during the last pericenter passage, gas was stripped from NGC 4485 via tidal forces or ram pressure, accreted by NGC 4490, and mixed with in-situ material, fueling ongoing star formation. This system provides a unique nearby laboratory for studying how tidal interactions shape the star formation and chemical enrichment history of dwarf galaxies.