Speaker
Description
I will present new JWST/NIRCam observations of the interacting dwarf galaxies 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 ~8 Mpc), excluding the Magellanic Clouds. This system offers a unique opportunity to study how interactions and mergers shape the star formation and chemical evolution of dwarf galaxies at high spatial resolution. Such studies are fundamental to understanding how interactions and mergers sculpt the stellar content and regulate the star-formation activity of galaxies.
Thanks to the exquisite sensitivity and resolution of JWST, we resolved for the first time the individual stars in these galaxies and constructed their deep color–magnitude diagrams (CMDs). We identified a broad range of stellar populations in both galaxies, allowing us to probe all epochs of their evolutionary history. In particular, we found a very young and massive population (age < 30 Myr, M > 8 M⊙) of red supergiant stars forming a striking tidal bridge extending from NGC 4485 toward the disk of NGC 4490. We also detected a well-populated intermediate-age population of oxygen- and carbon-rich AGB stars, as well as an old (age > 1 Gyr) red giant branch population.
Using the state-of-the-art stellar population synthesis code SFERA2.0 (Bortolini et al. 2024), we derived the star formation histories of both galaxies and of the tidal bridge, and compared them with previous n-body simulations (Pearson et al. 2018). We find two synchronized peaks in the star formation activity in both galaxies: one very recent episode occurring 10–30 Myr ago, and another between 100 Myr and 1 Gyr ago. Our findings suggest that during the last pericenter passage (likely happened around 250 Myr ago), gas was stripped from NGC 4485 via tidal stripping, accreted by NGC 4490 and mixed with in-situ material, fueling the ongoing star formation.
These results highlight how JWST’s superior resolution and near-infrared sensitivity open new windows onto the star-formation processes of nearby dwarf galaxies, which can also help us shed light on galaxy formation and evolution at high redshift.