THE [O II] λ3727 LUMINOSITY FUNCTION AT z ∼ 1

We measure the evolution of the [O II] lambda 3727 luminosity function (LF) at 0.75 < z < 1.45 using high-resolution spectroscopy of similar to 14,000 galaxies observed by the Deep Extragalactic Evolutionary Probe 2 galaxy redshift survey. We find that brighter than L-[O II] = 10(42) erg s(-1) the LF is well represented by a power law dN/dL alpha L-alpha with slope alpha similar to -3. The number density of [O II]-emitting galaxies above this luminosity declines by a factor of greater than or similar to 2.5 between z similar to 1.35 and z similar to 0.84. In the limit of no number-density evolution, the characteristic [O II] luminosity, L*([O II]), defined as the luminosity where the space density equals 10(-3.5) dex(-1) Mpc(-3), declines by a factor of similar to 1.8 over the same redshift interval. Assuming that L-[O II] is proportional to the star formation rate (SFR), and negligible change in the typical dust attenuation in galaxies at fixed [O II] luminosity, the measured decline in L*([O II]) implies a similar to 25% per Gyr decrease in the amount of star formation in galaxies during this epoch. Adopting a faint-end power-law slope of -1.3 +/- 0.2, we derive the comoving SFR density in four redshift bins centered around z similar to 1 by integrating the observed [O II] LF using a local, empirical calibration between L-[O II] and SFR, which statistically accounts for variations in dust attenuation and metallicity among galaxies. We find that our estimate of the SFR density at z similar to 1 is consistent with previous measurements based on a variety of independent SFR indicators.