SpitzerMid‐Infrared Spectroscopy of Infrared Luminous Galaxies atz∼ 2. I. The Spectra

We present the mid-infrared (MIR) spectra obtained with the Spitzer InfraRedSpectrograph (IRS) for a sample of 52 sources, selected as infrared luminous,z>1 candidates in the Extragalactic First Look Survey (XFLS). The sampleselection criteria are f(24um) > 0.9mJy, nu fnu(24um)/nu fnu(8um) > 3.16 and nufnu(24um)/nu fnu(0.7um) > 10. Of the 52 spectra, 47 (90%) produced measurableredshifts based solely on the mid-IR spectral features, with the majority(35/47=74%) at 1.5 1. Their$L_{1600\AA}$ and $L_{\rm IR}$ suggest that our sample is among the mostluminous and most dust enshrouded systems of its epoch . Our study has revealeda significant population of dust enshrouded galaxies at z~2, whose enormousenergy output, comparable to that of quasars, is generated by AGN as well asstarburst. This IR luminous population has very little overlap with sub-mm andUV-selected populations (Abridged).Comment: Accepted by the ApJ. In vol. 658, March, 200