As hosts of living high-mass stars, Wolf-Rayet (WR) regions or WR galaxies are ideal objects for constraining the high-mass end of the stellar initial mass function (IMF). We construct a large sample of 910 WR galaxies/regions that cover a wide range of stellar metallicity, by combining three catalogs of WR galaxies/regions as previously selected from the SDSS and SDSS-IV/MaNGA surveys. We measure the equivalent width of the WR blue bump at ~4650 r{A} from each spectrum, and make comparisons with predictions of both singular population models in Starburst99 and binary population models in BPASS. We have also applied a Bayesian inference code to perform full spectral fitting to the WR spectra using the singular and binary stellar population models from BPASS as spectral templates, and we make model selection for models of different IMF slopes based on the Bayesian evidence ratios. These analyses have consistently led to a positive correlation of IMF high-mass slope $alpha$ with stellar metallicity $Z$, i.e. with steeper IMF (more bottom-heavy) at higher metallicities, and the conclusion holds even when binary population models are adopted.
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