2005ApJ...633..748R

Using the extensive multiwavelength data in the GOODS-North field, including our ground-based rest-frame UV spectroscopy and near-IR imaging, we construct and draw comparisons between samples of optical and near-IR selected star-forming and passively evolving galaxies at redshifts 1.4≲z≲2.6. We find overlap at the 70%-80% level in samples of z∼2 star-forming galaxies selected by their optical (U_nGR) and near-IR (BzK) colors when subjected to common K-band limits. Deep Chandra data indicate a ∼25% AGN fraction among near-IR selected objects, much of which occurs among near-IR bright objects (K_s<20; Vega). Using X-rays as a proxy for the bolometric star formation rate (SFR) and stacking the X-ray emission for the remaining (non-AGN) galaxies, we find that the SFR distributions of U_nGR, BzK, and J-K_s>2.3 galaxies (i.e., distant red galaxies; DRGs) are very similar as a function of K_s_, with K_s<20 galaxies having <SFR≳120 M_☉/yr, a factor of 2-3 higher than those with K_s>20.5. The absence of X-ray emission from the reddest DRGs and BzK galaxies with (z-K)_AB≳3 indicates that they must have declining star formation histories to explain their red colors and low SFRs. While the M/L ratio of passively evolving galaxies may be larger on average, the Spitzer IRAC data indicate that their inferred stellar masses do not exceed the range spanned by optically selected galaxies, suggesting that the disparity in current SFR may not indicate a fundamental difference between optical and near-IR selected massive galaxies (M^*>10¹¹ M_☉). We consider the contribution of optical, near-IR, and submillimeter selected galaxies to the star formation rate density (SFRD) at z∼2, taking into account sample overlap. The SFRD in the interval 1.4≲z≲2.6 of U_nGR and BzK galaxies to K_s=22 and DRGs to K_s=21 is ∼0.10±0.02 M_☉/yr/Mpc3. Optically selected galaxies to R=25.5 and K_s=22.0 account for ∼70% of this total. Greater than 80% of radio-selected submillimeter galaxies to S_850µm∼4 mJy with redshifts 1.4<z<2.6 satisfy either one or more of the BX/BM, BzK, and DRG criteria.