Mid-infrared spectroscopy of high-redshift submillimeter galaxies:: First results

We present mid-infrared spectra of five submillimeter galaxies at taken with the Spitzer Space z p 0.65-2.38 Telescope. Four of these sources, at, have strong PAH features and their composite spectrum is well z <= 1.5 fitted by an M82-like spectrum with an additional power-law component consistent with that expected from AGN activity. Based on comparison with local templates of the 7.7 mu m PAH equivalent width and the PAH-to-infrared luminosity ratio, we conclude that these galaxies host both star formation and AGN activity, with star formation dominating the bolometric luminosity. The source at displays a Mrk 231-type broad emission feature z = 2.38 at rest frame similar to 8 mm that does not conform to the typical 7.7 mu m/8.6 mm PAH complex in starburst galaxies, suggesting a more substantial AGN contribution.