The Wolf-Rayet star population in the dwarf galaxy NGC 625

Context. Quantifying the number, type, and distribution of Wolf-Rayet (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 (distances â=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. Aims. We intend to characterise the W-R star population in one of these systems, NGC 625, which is a low-metallicity dwarf galaxy suffering a currently declining burst of star formation. Methods. Optical integral field spectroscopy (IFS) data have been obtained with the VIMOS-IFU and the HR-Orange and HR-Blue gratings at the Very Large Telescope covering the starburst region of NGC 625. Ancillary Hubble Space Telescope (HST) images in the F555W and F814W bands are also used for comparison. We estimate the number of W-R stars using a linear combination of three W-R templates: one early-Type nitrogen (WN) star, one late-Type WN star, and one 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; and iii) model predictions. Results. The W-R star population is spread over the main body of the galaxy and is 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, six are late-Type WN, and five 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 high spatial resolution with the HST. Fits using templates at the metallicity of the Large Magellanic Cloud yield more reasonable number of W-R than those using templates at the metallicity of the Small Magellanic Cloud. Given the metallicity of NGC 625, this suggests a non-linear relation between the metallicity and luminosity of the W-R spectral features. © ESO, 2017.We thank John M. Cannon and Kristy McQuinn for making the HST photometry of NGC 625 available to us. Based on observations carried out at the European Southern Observatory, Paranal (Chile), programme 086.B-0042. A.M.-I. grateful to ESO Garching, where part of this work was carried out, for their hospitality and funding via their visitor programme. A.M.-I. acknowledges support from the Spanish PNAYA through project AYA2015-68217-P and from BMBF through the Erasmus-F project (grant number 05 A12BA1). M. R. acknowledges support by the research projects AYA2014-53506-P from the Spanish Minister de Economia y Competitividad, from the European Regional Development Funds (FEDER) and the Junta de Andalucia (Spain) grants FQM108. This paper uses the plotting package jmaplot9, developed by Jesus Maiz-Apellaniz. This research made use of the NASA/IPAC Extragalactic Database (NED), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration