We investigate the instantaneous star formation rates (SFRs) and extinction properties for a large (N = 274), near-infrared (NIR: 2.2 μm) + mid-infrared (MIR: 24 μm)-selected sample of normal to ultraluminous infrared galaxies (ULIRGs; 109 LIR/L☉ 1012.5) with z ~ 0.8 in the Spitzer Extragalactic First Look Survey (FLS). We combine 24 μm observations with high-resolution Keck DEIMOS spectroscopy to derive optical emission-line (Hα, Hβ, and [O II]) and infrared star formation rates (SFRopt and SFRIR, respectively). Comparison of SFR diagnostics reveals a wide extinction range (1.0 AV 4.0 mag) for this sample, even after removing spectroscopic and IRAC color-selected AGN candidates (≈12% of the sample). Objects with SFRs of a few M☉ yr-1 have extinction values consistent with normal spirals (AV ≈ 1.0 mag). By contrast, LIRGs at z 1, which comprise a fraction of our sample, have SFR ≈ 100 M☉ yr-1 and a mean AV ≈ 2.5 mag. This translates to a 97% mean [O II] λλ3727 attentuation and in extreme cases is as high as 99.7%. We derive an IR-luminosity-dependent A function [A = 0.75 log(LIR/L☉) - 6.35 mag] that we use to extinction correct our line luminosities. The resulting correlation between SFRIR and SFRopt has a dispersion of ~0.2 dex (semi-interquartile range). Comparison of the AV dependence on redshift and LIR reveals that for a fixed LIR, there is no significant AV evolution. Comparison to previous studies reveals a mean attenuation that is intermediate between that of local optical/UV- and radio-selected samples with a marginally stronger LIR dependence.
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