FEAST: Spatially Resolved Star Formation History of the NGC 4485/NGC 4490 System and its Tidal Bridge from JWST/NIRCam Color Magnitude Diagrams

Giacomo Bortolini; Matteo Correnti; Angela Adamo; Michele Cignoni; Monica Tosi; Göran Östlin; Arjan Bik; Daniela Calzetti; John M. Cannon; Flavia Dell'Agli; Bruce G. Elmegreen; Helena Faustino Vieira; Kathryn Grasha; Kelsey E. Johnson; Thomas S. -Y. Lai; Drew Lapeer; Sean T. Linden; Matteo Messa; Alex Pedrini; Julia Roman-Duval; Elena Sabbi; Linda J. Smith

arXiv · 2610.29405

FEAST: Spatially Resolved Star Formation History of the NGC 4485/NGC 4490 System and its Tidal Bridge from JWST/NIRCam Color Magnitude Diagrams

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Abstract

We present the spatially resolved star formation history (SFH) of the interacting, low-mass, gas-rich galaxy pair NGC 4485/NGC 4490, based on deep JWST/NIRCam imaging obtained as part of the FEAST program. Using resolved stars' near-infrared color-magnitude diagrams (CMDs) and the SFERA 2.0 CMD fitting code, we reconstruct the SFH of the system, including the tidal bridge connecting the two galaxies. We find that recent star formation is widespread across the system, extending beyond the main bodies of the galaxies into the tidal bridge and other off-center areas. In particular, a significant fraction of the recent star formation in NGC 4485 occurs outside its central region. All major regions of the system exhibit two prominent episodes of enhanced star formation, occurring around 0.5-1 Gyr and 10-30 Myr ago, with the tidal bridge showing the largest increase relative to its average star formation rate. These peaks in star formation activity occur a few hundred million years after the epochs of the first and second pericenter passages predicted by independent dynamical models, supporting a scenario in which repeated tidal interactions triggered the observed bursts through gas redistribution and compression. Our results place direct observational constraints on the formation history of NGC 4485/NGC 4490 and provide evidence for the important role of galaxy interactions in driving spatially extended, bursty star formation in low-mass galaxies.

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Giacomo Bortolini, Matteo Correnti, Angela Adamo, Michele Cignoni, Monica Tosi, Göran Östlin, Arjan Bik, Daniela Calzetti, John M. Cannon, Flavia Dell'Agli, Bruce G. Elmegreen, Helena Faustino Vieira, Kathryn Grasha, Kelsey E. Johnson, Thomas S. -Y. Lai, Drew Lapeer, Sean T. Linden, Matteo Messa, Alex Pedrini, Julia Roman-Duval, Elena Sabbi, Linda J. Smith. 2026-10-21. FEAST: Spatially Resolved Star Formation History of the NGC 4485/NGC 4490 System and its Tidal Bridge from JWST/NIRCam Color Magnitude Diagrams. https://arxiv.org/abs/2610.29405

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