We present Spitzer /IRS spectral mapping observations of the luminous infrared galaxy ( LIRG ) Arp 299 ( IC 694 + NGC 3690 ) covering the central \sim 45 \arcsec \sim 9 { kpc } .
The integrated mid-IR spectrum of Arp 299 is similar to that of local starbursts despite its strongly interacting nature and high infrared luminosity , L _ { IR } \sim 6 \times 10 ^ { 11 } { L } _ { \odot } .
This is explained because the star formation ( probed by e.g .
high [ NeIII ] 15.56 \mu m/ [ NeII ] 12.81 \mu m line ratios ) is spread across at least 6-8 kpc .
Moreover , a large fraction of this star formation is taking place in young regions of moderate mid-IR optical depths such as the C+C ^ { \prime } complex in the overlap region between the two galaxies and in H ii regions in the disks of the galaxies .
It is only source A , the nuclear region of IC 694 , that shows the typical mid-IR characteristics of ultraluminous infrared galaxies ( ULIRGs , L _ { IR } > 10 ^ { 12 } { L } _ { \odot } ) , that is , very compact ( less than 1 kpc ) and dust-enshrouded star formation resulting in a deep silicate feature and moderate equivalent widths of the PAHs .
The nuclear region of NGC 3690 , known as source B1 , hosts a low-luminosity AGN and is surrounded by regions of star formation .
Although the high excitation [ NeV ] 14.32 \mu m line typical of AGN is not detected in B1 , its upper 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 that accounts for 80 - 90 \% of the 6 \mu m luminosity of B1 .
The similarity between the Arp 299 integrated mid-IR spectrum and those of high- z ULIRGs suggests that Arp 299 may represent a local example , albeit with lower IR luminosity and possibly higher metallicity , of the star-formation processes occurring at high- z .