CALIBRATING THE STAR FORMATION RATE ATz∼ 1 FROM OPTICAL DATA

Abstract

We present a star-formation rate calibration based on optical data that is consistent with average observed rates in both the red and blue galaxy populations at z~1. The motivation for this study is to calculate SFRs for DEEP2 Redshift Survey galaxies in the 0.7<z<1.4 redshift range, but our results are generally applicable to similar optically-selected galaxy samples without requiring UV or IR data. Using SFRs fit from UV/optical SEDs in the AEGIS survey, we explore the behavior of restframe B-band magnitude, observed [OII] luminosity, and restframe (U-B) color with SED-fit SFR for both red sequence and blue cloud galaxies. We find that a SFR calibration can be calculated for all z~1 DEEP2 galaxies using a simultaneous fit in M_B and restframe colors with residual errors that are within the SFR measurement error. The resulting SFR calibration produces fit residual errors of 0.3 dex RMS scatter for the full color-independent sample with minimal correlated residual error in L[OII] or stellar mass. We then compare the calibrated z~1 SFRs to two diagnostics that use L[OII] as a tracer in local galaxies and correct for dust extinction at intermediate redshifts through either galaxy B-band luminosity or stellar mass. We find that a L[OII] - M_B SFR calibration commonly used in the literature agrees well with our calculated SFRs after correcting for the average B-band luminosity evolution in L* galaxies. However, we find better agreement with a local L[OII]-based SFR calibration that includes stellar mass to correct for reddening effects, indicating that stellar mass is a better tracer of dust extinction for all galaxy types and less affected by systematic evolution than galaxy luminosity from z=1 to the current epoch.