The Influence Of Environment And Mass On Galaxy Evolution

Galaxy clusters are among the most dense regions in the Universe. They are natural laboratories for galaxy evolution. The physical properties of mem-ber galaxies, such as morphologies, star formation rate and stellar ages, change dramatically from the core of a cluster to the outskirts. Studies focused on the impacts of environmental conditions on galaxies evolution search for the clues of how environmental conditions influence galaxy evolution in various environments, from cluster cores to sparse environments. The Sloan Digital Sky Survey provides a large local galaxy sample, including spectroscopic redshifts for more than1mil-lion galaxies. The spectroscopic sample enables the accurate measurements of galaxy environments. A great deal of works on galaxy environments are achieved based on SDSS, and this field is still active in astrophysics. In this thesis, we study the physical properties of a nearby galaxy cluster Abell671, based on the SDSS data and the multi-band photometry of BATC. In addition, we investigate a green valley galaxy sample selected from the COSMOS field and try to access the role of environments on the formation of this population.In Chapter2, we present a photometric and spectroscopic study of the n-earby galaxy cluster Abell0671(A671) with15intermediate-band filters in the Beijing-Arizona-Taiwan-Connecticut (BATC) system and the Sloan Digital Sky Survey (SDSS) data. After a cross-identification between the photometric data obtained from the BATC and SDSS, a list of985galaxies down to V-20.0mag in a view field of58’x58’is achieved, including103spectroscopically con-firmed member galaxies. The photometric redshift technique is applied to the galaxy sample for further membership determination. After the color-magnitude relation is taken into account,97galaxies brighter than hBATC=19.5mag are selected as new member galaxies. Based on the enlarged sample of cluster galax- ies, spatial distribution, dynamics of A671are investigated. The substructures of A671are well shown by the sample of bright members, but it appears less signif-icant based on the enlarged sample, which is mainly due to larger uncertainties in the line-of-sight velocities of the newly-selected faint members. The SDSS r-band luminosity function of A671is flat at faint magnitudes, with the faint end slope parameter a=-1.12. The SDSS spectra allow us to investigate the star for-mation history of bright cluster galaxies, and the galaxies in the core region are found to be older than those in the outskirts. No environmental effect is found for metallicities of the early-type galaxies (ETGs). Both mean stellar ages and metal-licities in bright member galaxies are found to be correlated strongly with their stellar masses assembled, and such correlations are dependent upon morphology. The possitive correlation between age and stellar mass supports the downsizing scenario. By comparing ETG absorption-line indices with the state-of-art stellar population models, we derive the relevant parameters of simple stellar population (such as age,[Fe/H],[Mg/Fe],[C/Fe],[N/Fe], and [Ca/Fe]). The ETGs at cluster center tend to have smaller Hβ indices, indicating that central ETGs are likely to be older. The distribution of total metallicity indicator,[MgFe]’, does not show any environmental effects. The relations between the simple stellar population parameters and velocity dispersion in A671are in good agreement with previous studies.Chapter3presents a research of morphologies, spectra and environments of≈2350"green valley" galaxies at0.2<z<1.0in the COSMOS field. The bi-modality of dust-corrected color is used to define "green valley"(thereafter, GV), which removes dusty star-forming galaxies from truly transiting galaxies between blue cloud and red sequence. Morphological parameters of green galaxies are intermediate between those of blue and red galaxy populations, both on the Gi-ni-Asymmetry and the Gini-M20planes. Approximately60%to70%green disk galaxies have intermediate or big bulges, and only5%to10%are pure disk system-s, based on the morphological classification with Zurich Estimator of Structural Types (ZEST). The obtained average spectra of green galaxies are intermediate between blue and red ones in terms of [O Ⅱ], Ha and Hβ emission lines. Stellar population synthesis on the average spectra show that green galaxies are average-ly older than blue galaxies, but younger than red galaxies. Green galaxies have similar projected galaxy density (Σ10) distribution with blue galaxies at z>0.7. At z<0.7, the fractions of M*<1O1O.OM⊙green galaxies located in dense en-vironment are found to be significantly larger than those of blue galaxies. The morphological and spectral properties of green galaxies are consistent with the transiting population between blue cloud and red sequence. The possible mecha-nisms for quenching star formation activities in green galaxies are discussed. The importance of AGN feedback cannot be well constrained in our study. Finally, our findings suggest that environment conditions, most likely starvation and ha-rassment, significantly affect the transformation of M*<*1010.0M⊙blue galaxies into red galaxies, especially at z<0.5.