Based On The Sloan Digital Sky Survey, A Large Sample Of Wolf - Rayet Galaxy Study

Wolf-Rayet (WR) galaxies are a subset of emission line galaxies whose integrated spectra show broad emission lines from WR stars. As lifetime of WR stars are very short, their appearance imply that the WR galaxies are undergoing present or very recent star formation, so they are ideal objects for studing the early phases of starbursts, determining burst properties, the shape of the IMF at high mass end, and the mechanism triggering the burst et al. To do this, there is a good way that constructing a WR galaxies sample, and analysing them statistically. Before release of the data of the SDSS, the samples are usually small, and arc lack of completeness and consistency, therefore it is hard to give a reliable conclusion. In this thesis, using the data release of the SDSS, we construct two large WR galaxies samples and give some interesting results. The thesis consists of five chapters.In Chapter 1, we firstly introduce some basic properties and method of classification of the WR stars, then the basic properties and the recent studies of of WR galaxies, and also our progress on this topic.In Chapter 2, we first introduce previous results of initial mass function (IMF), and then introduce the sample selection and analyses based on SDSS DR3, and our studying on the metallicity dependence of the IMF. The sample consists of 174 objects. By comparing these observed WR features and Hβemission lines with predictions by evolutionary synthesis, we have found a clear dependence of the IMF slope on metallicity in that the IMF slope increases with increasing metallicity. We have carefully examine the possible sources of systematic error either in models or in our observational measurements and shown that these sources do not change our main results. Such dependence has been probed by many previous studies, but it is much more pronounced in this paper due to the improvement in the observational data.In Chapter 3, in order to better understand the particular properties of WR galaxies, and also to construct a large enough sample for analysising the clustering of WR galaxies, we update the data to SDSS DR4. The new sample consists of 866 objects, we compare their physical parameters with two samples of star forming galaxies, one consists of all star forming galaxies (SFG1) and the other consists of star forming galaxies whoseα(4650) are steeper. We find that, compared with SFG1, WR galaxies and SFG2 are lower in redshift, smaller in D4000, bluer in color, higher in mean star formation rate (SFR/M_*), poorer in metallicity and less dusty. Compared with SFG2, WR galaxies are still smaller in D4000, bluer in color and higher in SFR/M_*, while quite similar distributions of metallicity, concentration and dusty, and quite similar position in the BPT diagram. These comparisons may put some restrictions on theoretical models.In Chapter 4, we have analysed, for the first time, the clustering properties of WR galaxies, using the sample constructed in Chapter 3. When compared to the underlying star-forming galaxies and the reference galaxies, W-R galaxies are the least strongly clustered on scales larger than～0.1 h^-1 Mpc. We wish to isolate the effect of the W-R features, and so we compare the measurement to that of control samples of non-W-R star-forming galaxies that are closely matched in redshift, luminosity, concentration, star formation rate and mean stellar age, as measured by the 4000-A break strength (D₄₀₀₀). This close matching is important because previous work has established that the clustering of galaxies depends strongly on these properties. One can see that, on scales larger than a few Mpc, the clustering amplitude of W-R galaxies does not differ significantly any more from that of similar but non-W-R galaxies. In contrast, the difference on intermediate scales still exists, in the sense that the ratio between the two cross-correlations appears to exhibit a pronounced 'dip' at scales between 100 h^-1kpc and 1 h^-1Mpc. We have done a lot of check and believe this anti-bias is true. Based on the following observational and theoretical considerations, we speculate that this anti-bias can be interpreted by W-R galaxies residing preferentially at the centers of their dark matter haloes.The summary and future discussions are presented in the last Chapter.