Dobrycheva D. Morphological content and color indices bimodality of a new galaxy sample at the redshifts z < 0.1.

The thesis deals with a study of the morphological content and color indices bimodality of a new sample of 317018 galaxies with absolute magnitudes -24m < Mr < -13m at the redshifts z < 0.1 from the SDSS DR9. At the first time the criteria for morphological classification on the base of relations between color indices and one of such parameters as the inverse concentration index, absolute magnitude, de Vaucouleurs radius or scale radius are proposed. It is allowed us to distinguish galaxies into three morphological classes: 1) early types - elliptical and lenticular, E-S0; 2) spirals, Sa-Scd; 3) last spirals, Sd-Sdm, and irregular galaxies, Im/BCG. Applying machine learning methods and two dimensional diagrams likely the color indices and one of the aforementioned parameters, we set the morphological content of galaxies from SDSS DR9 sample at z < 0.1. The 3D Voronoi tessellation method was applied to determine the environmental density of galaxies at redshifts 0.02 < z < 0.1. It is found that the share of early-type galaxies (with quenching star formation) decrease with a redshift as compare with a share of the late types. When the environmental density of the central galaxies is higher, it is more probably that the central galaxies are of the early morphological types. It is also shown that the higher the environmental density near the central galaxy, the more likely that it has an early morphological type. For studying the pairs of galaxies, we restricted our sample by the redshift as 0.02 < z < 0.06 to avoid the selection effect. It was found a statistically significant increase of the E-E pair's fraction among close pairs of our sample. We have no found such excess among more distant pairs of different morphological content. Correlation of color indices of galaxies in close pairs, the Holmberg effect, isn't found for the closest galaxy pairs at 0.02 < z < 0.06, even in the case when one component of a pair is of early type. So, figuring manifestations of the Holmberg effect in its original interpretation seems no longer modern.