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Session 63 - Surveys of Galaxies.
Oral session, Thursday, January 08
Georgetown,
Large redshift surveys offer us unprecedented data sets for the study of galactic properties as a function of environment, as well as helping us probe the geometry of the universe. We present a new investigation of the environmental effects on galactic morphological and star formation properties, using a sample of 16377 galaxies, taken from the Las Campanas Redshift Survey (LCRS; Shectman et. al 1996).
The data set consists of a large number of galaxies in a range of environments continuously spanning from field to cluster. Thus, not only it gives us good general statistics, it also enables us to investigate environmental effects without combing multiple data sets of heterogeneous data quality, which is one of the major source of uncertainties among the previous environmental studies. In addition to the popular cluster/field subdivision, we further introduce a ``richness'' criterion to investigate possible unique role of poor cluster, or group environments on the galactic properties. This further subdivision is very important, since poor clusters might host very unique ``merging'' environments for galaxies by their relatively low galaxy velocity dispersions. Furthermore, and more importantly, we also expand our research from any type of essentially ``membership'' studies to a new, full ``general'' environmental investigation by decoupling local galaxy density from the membership. This decoupling is very crucial for constraining the physical processes responsible for the observed environmental dependencies of morphological and star formation properties. To further minimize serious uncertainties associated with conventional environmental studies, we characterize morphological properties by using objective qualitative measures of galactic light profiles which are all automatically measured, rather than using the eye ball Hubble type-based characterizations, which are inherently subjective and often star formation-contaminated estimates of galactic morphologies.
