Research On Wolf-Rayet Galaxies And The Stellar Initial Mass Function With Integral Field Spectroscopy

This thesis aims to take advantage of the recent integral field spectroscopy(IFS)survey,SDSS(Sloan Digital Sky Survey)-? Mapping Nearby Galaxies at Apache Point Observatory(MaNGA)survey,to search for Wolf-Rayet(WR)galaxies,which is a rare type of galaxy that hosts living high-mass stars(namely WR stars).Then we extract the information of WR stellar population from spectra in order to investigate whether the stellar initial mass function(IMF)varies with metallicity.The large field of view of IFS surveys is beneficial for WR galaxy searching,for they can cover the outskirts of galactic disks where more recent star formation is expected to happen.Our search procedure includes identifying H II regions in each MaNGA galaxy,stacking spectra for each H II region to increase the signal-to-noise ratio,conducting full spectral fitting for each stacked spectrum,and finally visually identifying emission features from WR stellar winds(i.e.the so-called "blue bump" in the wavelength window of 4600-4750(?))from residual spectra after continuum subtraction.We have identified 267 WR regions distributed in 90 WR galaxies.We have studied the basic properties of these WR galaxies.For the first time,we estimate the stellar mass function of WR galaxies and the detection rate of WR galaxies as a function of host galaxy's stellar mass.We then study the stellar population properties of WR galaxies,discovering most WR galaxies are very blue and very high in star formation rate.We also study WR galaxies' morphological and structural parameters.We find most WR galaxies are late-type galaxies and there are also a few S0 early-type WR galaxies.Regarding structural parameters,the asymmetry and fraction of mergers are both higher than the general population.This indicates the starburst or recent star formation activities of WR galaxies can be correlated with galaxy interaction.We put together the newly established WR catalog and two WR catalogs from literature and try to use them for constraining the IMF.The IMF is a key ingredient in our understanding of galaxy formation and evolution.The function form,the power law index and the possible variation of the IMF are all uncertain.We adopt Starburst99 and Binary Population and Spectral Synthesis(BPASS)models in two different ways to compare models with data — with parameterized WR feature and through Bayesian full spectral fitting.We conclude that under the condition of singular evolution,the IMF has a significant trend with metallicity.For metal-poor spectra,the model predictions with a flatter IMF is more consistent with data;for metal-rich spectra,a steeper IMF is needed.Under the condition of binary evolution,we see the same trend but with slightly lower significance level.