Mapping the ionized gas of the metal-poor HII galaxy PHL 293B with MEGARA

Abstract

Here we report the first spatially resolved spectroscopic study for the galaxy PHL 293B using the high-resolution GTC/MEGARA integral field unit (IFU). PHL 293B is a local, extremely metal-poor, high ionization galaxy. This makes PHL 293B an excellent analogue for galaxies in the early Universe. The MEGARA aperture (∼ 12.5” × 11.3”) covers the entire PHL 293B main body and its far-reaching ionized gas. We created and discussed maps of all relevant emission lines, line ratios and physical-chemical properties of the ionized ISM. The narrow emission gas appears to be ionized mainly by massive stars according to the observed diganostic line ratios, regardless of the position across the MEGARA aperture. We detected low intensity broad emission components and blueshifted absorptions in the Balmer lines (Hα,Hβ) which are located in the brightest zone of the galaxy ISM. A chemically homogeneity, across hundreds of parsecs, is observed in O/H. We take the oxygen abundance 12+log (O/H) = 7.64 ± 0.06 derived from the PHL 293B integrated spectrum as the representative metallicity for the galaxy. Our IFU data reveal for the first time that the nebular HeIIλ4686 emission from PHL 293B is spatially extended and coincident with the ionizing stellar cluster, and allow us to compute its absolute HeII ionizing photon flux. Wolf-Rayet bumps are not detected excluding therefore Wolf-Rayet stars as the main HeII excitation source. The origin of the nebular HeIIλ4686 is discussed.