中国科学院云南天文台机构知识库

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 similar to 2 from a K-band-selected sample (K-AB < 22.0) in an area of similar to 0.44 deg(2) of the All-wavelength Extended Groth Strip International Survey. The number of counts of pgzKs in our sample turn over at K-AB similar to 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 similar to 2 galaxies not only have diffuse structures with lower G and higher M-20 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 similar to 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 (similar to 10%). Most of these AGN candidates have L0.5-10 keV > 10(41) erg s(-1).