Star Formation Property Of Galaxies And Its Environmental Effect

To study the star formation properties of galaxies is one of the major tasks of extragalactic astronomy. The current star formation rates (SFRs) of galaxies and the variation with morphology environment and some physical properties of galaxies are crucial in our understanding of the evolution of galaxies. With the development of observational technology, the SFR measurement becomes more accurate. A large number of galaxies spectroscopically observed by the Sloan Digital Sky Survey (SDSS) impels a great progress in this field.The cluster of galaxies Abell2199 is covered by the SDSS. The physical parameters of 290 bright member galaxies derived from the SDSS data analyses by Brinchmann et al. (2004) allow a detailed study on the star formation properties of galaxies within a cluster at intermediate redshift. In this thesis we perform a morphological classification on the basis of the SDSS imaging and spectral data, and investigate the morphological dependence of the star formation rates (SFRs) for these member galaxies.Based on the morphological classification for 290 member galaxies in Abell 2199, relations of the star formation rates (SFRs) with morphology and relevant physical properties of cluster galaxies are studied. A tight correlation between the SFR normalized by stellar mass (SFR/M_*) and the Ha equivalent width are found. The correlations ofSFR/M_* with the continuum break strength at 4000A and stellar mass (M_*) are alsoconfirmed. These cluster galaxies show no significant environmental effect in their star formation activities, which suggests that Abell 2199 is still at an active stage of dynamical evolution, far from the status of dynamical equilibrium.By comparing the physical parameters of cluster galaxies and field galaxies, such as concentration index, specific star formation rate, stellar mass, and metallicity, the star formation properties of galaxies within different gravitational environments are studied. It is show that highly concentrated galaxies dominate in galaxy clusters, and less massive galaxies are predominately field galaxies. The correlations of the specific star formation rate with stellar mass and metallicity are found. Additionally, both field and cluster galaxies with z < 0.1 show significant effect of cosmic evolution.In order to observe how the star formation activities in galaxies varies with gravitational environment, we study the variation of star formation and the chemical evolution in galaxies with local density. The number of neighbor galaxies (N) within a distance of～1 h^-1 Mpc to a given galaxy is defined to describe the local density. The specific star formation rate (SFR/M_*) declines monotonously with a increasing density,and chemical enrichment shows different behaviors at different local densities. For the galaxies in low-density regions (N < 10), the slope and correlation coefficient of metallicity-mass relation tends to decrease as the local density increases, indicating that the chemical enrichment is being depressed in a denser environment. For the galaxies in high-density regions (N > 10), however, the slope and correlation coefficient of metallicity-mass relation becomes scattered and uncertain, showing that the chemical enrichment for cluster galaxies might have been strongly disturbed by the local gravitational potential. This suggests that main physical mechanisms which have exerted an influence on the star formation and chemical enrichment of galaxies are different in different local gravitational environments.