PASSIVE AND STAR-FORMING GALAXIES AT 1.4 ⩽ z ⩽ 2.5 IN THE AEGIS FIELD

Using a simple two-color selection based on g-, z-, and K-band photometry, we choose from 1609 star-forming galaxies (sgzKs) and 422 passively evolving galaxies (pgzKs) at z ∼ 2 from a K-band-selected sample (KAB < 22.0) in an area of ∼0.44 deg2 of the All-wavelength Extended Groth Strip International Survey. The number of counts of pgzKs in our sample turn over at KAB ∼ 21.0, and both the number of faint and bright objects (including sgzKs and pgzKs) exceed the predictions of a recent semi-analytic model of galaxy formation; a more successful model is need to explain this diversity. We also find that the star formation rate (SFR) and specific SFR (sSFR) of sgzKs increases with redshift at all masses, implying that star-forming galaxies were much more active on average in the past. Moreover, the sSFR of massive galaxies is lower at all redshifts, suggesting that star formation contributes more to the mass growth of low-mass galaxies than to high-mass galaxies. From the Hubble Space Telescope Wide Field Camera 3 near-infrared imaging data we find that morphologies of z ∼ 2 galaxies not only have diffuse structures with lower G and higher M20 values, but also have single-object morphologies (higher G and lower M20), implying that there are morphological variety and different formation process for these galaxies at z ∼ 2. Finally, we also study the fraction of active galactic nuclei (AGNs) in the gzKs, 82 of 828 gzKs with four IRAC bands can be classified as AGNs (∼10%). Most of these AGN candidates have L0.5–10 keV > 1041 erg s−1.