Uncovering multiple Wolf-Rayet star-clusters and the ionized ISM in Mrk178: the closest metal-poor Wolf-Rayet HII galaxy

TL;DR

This study uses integral field spectroscopy to map and analyze the distribution of Wolf-Rayet stars and ionized gas in Mrk178, revealing new WR star-clusters, spatial variations in ISM properties, and insights into the ionization sources in this metal-poor galaxy.

Contribution

First spatially resolved detection of multiple Wolf-Rayet star-clusters in Mrk178, extending beyond its brightest knot, and refined methodology for analyzing ISM variations in metal-poor galaxies.

Findings

Detected blue and red WR bumps across the galaxy.

Identified at least 20 WR stars in the observed region.

Found spatially extended HeII emission beyond WR star locations.

Abstract

New integral field spectroscopy (IFS) has been obtained for the nearby metal-poor WR galaxy Mrk178 to examine the spatial correlation between its WR stars and the neighbouring ionized ISM. The strength of the broad WR features and its low metallicity make Mrk178 an intriguing object. We have detected the blue and red WR bumps in different locations across the FOV (~ 300 pc x 230 pc) in Mrk178. The study of the WR content has been extended, for the first time, beyond its brightest star-forming knot uncovering new WR star-clusters. Using SMC/LMC-template WR stars we empirically estimate a minimum of ~ 20 WR stars within the region sampled. Maps of the spatial distribution of the emission-lines and of the physical-chemical properties of the ionized ISM have been created and analyzed. Here we refine the statistical methodology by Perez-Montero et al.(2011) to probe the presence of variations in the ISM properties. An error-weighted mean of 12+log(O/H)=7.72 +/- 0.01 is taken as the representative oxygen abundance for Mrk178. A localized N and He enrichment, spatially correlated with WR stars, is suggested by this analysis. Nebular HeII4686 emission is shown to be spatially extended reaching well beyond the location of the WR stars. This spatial offset between WRs and HeII emission can be explained based on the mechanical energy input into the ISM by the WR star winds, and does not rule out WR stars as the HeII ionization source. We study systematic aperture effects on the detection and measurement of the WR features, using SDSS spectra combined with the power of IFS. In this regard, the importance of targeting low metallicity nearby systems is discussed.