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As hosts of living high-mass stars, Wolf-Rayet (WR) regions or WR galaxiesare ideal objects for constraining the high-mass end of the stellar initialmass function (IMF). We construct a large sample of 910 WR galaxies/regionsthat cover a wide range of stellar metallicity (from Z~0.001 up to Z~0.03), bycombining three catalogs of WR galaxies/regions previously selected from theSDSS and SDSS-IV/MaNGA surveys. We measure the equivalent widths of the WR bluebump at ~4650 A for each spectrum. They are compared with predictions fromstellar evolutionary models Starburst99 and BPASS, with different IMFassumptions (high-mass slope {\alpha} of the IMF ranging from 1.0 up to 3.3).Both singular evolution and binary evolution are considered. We also use aBayesian inference code to perform full spectral fitting to WR spectra withstellar population spectra from BPASS as fitting templates. We then make modelselection among different {\alpha} assumptions based on Bayesian evidence.These analyses have consistently led to a positive correlation of IMF high-massslope {\alpha} with stellar metallicity Z, i.e. with steeper IMF (morebottom-heavy) at higher metallicities. Specifically, an IMF with {\alpha}=1.00is preferred at the lowest metallicity (Z~0.001), and a Salpeter or evensteeper IMF is preferred at the highest metallicity (Z~0.03). These conclusionshold even when binary population models are adopted.

Wolf-Rayet galaxies in SDSS-IV MaNGA. II. Metallicity dependence of the high-mass slope of the stellar initial mass function