Spectroscopic Survey of 1.4 GHz and 24 μm Sources in the Spitzer First Look Survey with WIYN Hydra

We present an optical spectroscopic survey of 24 μm and 1.4 GHz sources, detected in the Spitzer extragalactic First Look Survey (FLS), using the multifiber spectrograph, Hydra, on the WIYN telescope. We have obtained spectra for 772 sources, with flux densities above 0.15 mJy in the infrared and 0.09 mJy in the radio. The redshifts measured in this survey are mostly in the range 0 < z < 0.4, with a distribution peaking at z ~ 0.2. Detailed spectral analysis of our sources reveals that the majority are emission-line star-forming galaxies, with star formation rates in the range 0.2-200 M☉ yr-1. The rates estimated from the Hα line fluxes are found to be on average consistent with those derived from the 1.4 GHz luminosities. For these star-forming systems, we find that the 24 μm and 1.4 GHz flux densities follow an infrared-radio correlation, which can be characterized by a value of q24 = 0.83, with a 1 σ scatter of 0.31. Our WIYN Hydra database of spectra nicely complements those obtained by the Sloan Digital Sky Survey in the region at lower redshift, as well as the MMT Hectospec survey by Papovich et al. in 2006, and brings the redshift completeness to 70% for sources brighter than 2 mJy at 24 μm. Applying the classical 1/Vmax method, we derive new 24 μm and 1.4 GHz luminosity functions, using all known redshifts in the FLS. We find evidence for evolution in both the 1.4 GHz and 24 μm luminosity functions in the redshift range 0 < z < 1. The redshift catalog and spectra presented in this paper are available at the Spitzer FLS Web site.