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.
