中国科学院云南天文台机构知识库

We present research on the morphologies, spectra, and environments of approximate to 2350 "green valley" galaxies at 0.2 < z < 1.0 in the COSMOS field. The bimodality of dust-corrected NUV-r(+) color is used to define " green valley"; it removes dusty star-forming galaxies from galaxies that are truly transitioning between the blue cloud and the red sequence. Morphological parameters of green galaxies are intermediate between those of blue and red galaxy populations, both on the Gini-asymmetry and the Gini-M-20 planes. Approximately 60%-70% of green disk galaxies have intermediate or big bulges, and only 5%-10% are pure disk systems, based on morphological classification using the Zurich Estimator of Structural Types. The obtained average spectra of green galaxies are intermediate between blue and red ones in terms of [OII], H alpha, and H beta emission lines. Stellar population synthesis on the average spectra shows that green galaxies are on average older than blue galaxies but younger than red galaxies. Green galaxies and blue galaxies have similar projected galaxy density (Sigma(10)) distributions at z > 0.7. At z < 0.7, the fractions of M-* < 10(10.0) M-circle dot green galaxies located in a dense environment are found to be significantly larger than those of blue galaxies. The morphological and spectral properties of green galaxies are consistent with the transitioning population between the blue cloud and the red sequence. The possible mechanisms for quenching star formation activities in green galaxies are discussed. The importance of active galactic nucleus feedback cannot be well constrained in our study. Finally, our findings suggest that environmental conditions, most likely starvation and harassment, significantly affect the transformation of M-* < 10(10.0) M-circle dot blue galaxies into red galaxies, especially at z < 0.5.