The Wolf-Rayet star population in the dwarf galaxy NGC 625
  ABRIGED: Quantifying the number, type and distribution of W-R stars is a key
component in the context of galaxy evolution, since they put constraints on the
age of the star formation bursts. Nearby galaxies (d<5 Mpc) are particularly
relevant in this context since they fill the gap between studies in the Local
Group, where individual stars can be resolved, and galaxies in the Local Volume
and beyond. We intend to characterize the W-R star population in NGC625, a
low-metallicity dwarf galaxy suffering a currently declining burst of star
formation. Optical IFS data have been obtained with the VIMOS-IFU covering the
starburst region. We estimate the number of W-R stars using a linear
combination of 3 W-R templates: 1 early-type nitrogen (WN) star, 1 late-type WN
star and 1 carbon-type (WC) star (or oxygen-type (WO) star). Fits using several
ensembles of templates were tested. Results were confronted with: i) high
spatial resolution HST photometry; ii) numbers of W-R stars in nearby galaxies;
iii) model predictions. The W-R star population is spread over the main body of
the galaxy, not necessarily coincident with the overall stellar distribution.
Our best estimation for the number of W-R stars yields a total of 28 W-R stars
in the galaxy, out of which 17 are early- type WN, 6 are late-type WN and 5 are
WC stars. The width of the stellar features nicely correlates with the dominant
W-R type found in each aperture. The distribution of the different types of WR
in the galaxy is roughly compatible with the way star formation has propagated
in the galaxy, according to previous findings using HST images. Fits using
templates at the metallicity of the LMC yield more reasonable number of W-R
than those using templates at the metallicity of the SMC. Given the metallicity
of NGC 625, this suggests a non-linear relation between the metallicity and the
luminosity of the W-R spectral features.
