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We present Spitzer/IRS spectral mapping observations of the luminous infraredgalaxy (LIRG) Arp299 (IC694 + NGC3690) covering the central 45arcsec ~ 9kpc.The integrated mid-IR spectrum of Arp299 is similar to that of local starburstsdespite its strongly interacting nature and high infrared luminosity, L_IR ~6x10^11 Lsun. This is explained because the star formation (probed by e.g. high[NeIII]15.56micron/[NeII]micron line ratios) is spread across at least 6-8kpc.Moreover, a large fraction of this star formation is taking place in youngregions of moderate mid-IR optical depths such as the C+C' complex in theoverlap region between the two galaxies and in HII regions in the disks of thegalaxies. It is only source A, the nuclear region of IC694, that shows thetypical mid-IR characteristics of ultraluminous infrared galaxies (ULIRGs, L_IR> 10^12 Lsun), that is, very compact (less than 1kpc) and dust-enshrouded starformation resulting in a deep silicate feature and moderate equivalent widthsof the PAHs. The nuclear region of NGC3690, known as source B1, hosts alow-luminosity AGN and is surrounded by regions of star formation. Although thehigh excitation [NeV]14.32micron line typical of AGN is not detected in B1, itsupper limit is consistent with the value expected from the X-ray luminosity.The AGN emission is detected in the form of a strong hot dust component thataccounts for 80-90% of the 6micron luminosity of B1. The similarity between theArp299 integrated mid-IR spectrum and those of high-z ULIRGs suggests thatArp299 may represent a local example, albeit with lower IR luminosity andpossibly higher metallicity, of the star-formation processes occurring athigh-z.

The Extreme Star Formation Activity of Arp299 Revealed by Spitzer IRS Spectral Mapping