The Spitzer Spirals, Bridges, and Tails Interacting Galaxy Survey: Interaction-Induced Star Formation in the Mid-Infrared

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We present Spitzer mid-infrared imaging of a sample of 35 tidally distorted premerger interacting galaxy pairs selected from the Arp Atlas. We compare their global mid-infrared properties with those of normal galaxies from the SINGS Spitzer Legacy survey, and separate the disk emission from that of the tidal features. The [8.0 μm] - [24 μm], [3.6 μm] - [24 μm], and [5.8 μm] - [8.0 μm] colors of these optically selected interacting galaxies are redder on average than those of spirals, implying enhancements to the mass-normalized star formation rates (SFRs) of a factor of ∼2. Furthermore, the 24 μm emission in the Arp galaxies is more centrally concentrated than that in the spirals, suggesting that gas is being concentrated into the inner regions and fueling central star formation. No significant differences can be discerned in the shorter wavelength Spitzer colors of the Arp galaxies compared to the spirals, and thus these quantities are less sensitive to star formation enhancements. No strong trend of Spitzer color with pair separation is visible in our sample; this may be because our sample was selected to be tidally disturbed. The tidal features contribute ≤ 10% of the total Spitzer fluxes on average. The SFRs implied for the Arp galaxies by the Spitzer 24 μm luminosities are relatively modest, ∼1 M⊙ yr-1 on average.