Wolf-Rayet galaxies in SDSS-IV MaNGA. I. Catalog construction and sample properties

Wolf-Rayet (WR) galaxies are a rare population of galaxies that host living high-mass stars during their WR phase (i.e. WR stars) and are thus expected to provide interesting constraints on the stellar Initial Mass Function, massive star formation, stellar evolution models, etc. Spatially resolved spectroscopy should in principle provide a more efficient way of identifying WR galaxies than single-fiber surveys of galactic centers such as SDSS-I & II, as WR stars should be more preferentially found in discs. Using IFU data from the ongoing SDSS-IV MaNGA survey, we have performed a thorough search for WR galaxies. We first identify H II regions in each datacube and carry out full spectral fitting to the stacked spectra. We then visually inspect the residual spectrum of each H II region and identify WR regions that present a significant "blue bump" at 4600-4750 A. The resulting WR catalog includes 267 WR regions of ~500pc (radius) sizes, distributed in 90 galaxies from the current sample of MaNGA (MaNGA Product Launch 7). We find WR regions are exclusively found in galaxies that show bluest colors and highest star formation rates for their mass. Most WR galaxies have late-type morphologies and show relatively large asymmetry in their images, implying that WR regions are more preferentially found in interacting/merging galaxies. We estimate the stellar mass function of WR galaxies and the mass-dependent detection rate. The detection rate of WR galaxies is typically ~2%, with weak dependence on stellar mass. This detection rate is about 40 times higher than previous studies with SDSS single fiber data, and by a factor of 2 lower than the CALIFA-based WR catalog. We make comparisons with SDSS and CALIFA studies, and conclude that different detection rates can be explained mainly by three factors: spatial coverage, spectral signal-to-noise ratio, and redshift ranges of the parent sample.