Large-scale star formation triggering in the low-mass ARP 82 system: A nearby example of galaxy downsizing based on UV/optical/mid-IR imaging

Abstract

As part of our Spitzer Spirals, Bridges, and Tails project to help understand the effects of galaxy interactions on star formation, we analyze Galaxy Evolution Explorer UV, Southeastern Association for Research in Astronomy optical, and Spitzer IR images of the interacting galaxy pair Arp 82 (NGC 2535/6) and compare to a numerical simulation of the interaction. We investigate the multiwavelength properties of several individual star-forming complexes (clumps). Using optical and UV colors, EW(Hα), and population synthesis models we constrain the ages of the clumps and find that the median clump age is ~9 Myr. The clumps have masses ranging from a few; x 10^6 to 10^9 M☉. In general, the clumps in the tidal features have ages similar to those in the spiral region, but are less massive. The clumps provide 33%, 36%, and 70% of the far-UV, 8.0 µm, and 24 µm emission, respectively. The 8 and 24 µm luminosities are used to estimate the far-IR luminosities and the star formation rates of the clumps. The total clump star formation rate is ~2.0 ± 0.8M☉yr^-1, while the entire Arp 82 system is forming stars at a rate of ~4.9 ± 2.0 M☉ yr^-1. We find, for the first time, stars in the H I arc to the southeast of the NGC 2535 disk. Population synthesis models indicate that all of the observed populations have young to intermediate ages. We conclude that, although the gas disks and some old stars may have formed early on, the progenitors may have been of late-type or low surface brightness, and the evolution of these galaxies seems to have halted until the recent encounter.

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