5 HII galaxies showing only nebular HeII emission

 HII regions ("local'' or extragalactic objects) and HII galaxies showing nebular HeII 4686 HeII $\lambda$4686 are considered to be quite rare (e.g. Garnett et al. 1991). Although not intended as a complete inventory these authors quote only 17 objects drawn from the studies of dwarf emission-line galaxies by Kunth & Sargent (1983) and Campbell et al. (1986). Many new observations revealing nebular HeII 4686 HeII $\lambda$4686 emission have since been found, mostly in the sample of Izotov and collaborators (see Sect. 2).

  

Table 2: List of extragalactic HII regions with nebular HeII

In Table 3 we list extragalactic HII regions showing HeII 4686 HeII $\lambda$4686 emission which is entirely attributed to nebular emission processes. In some cases, however, WR signatures are suspected by some authors; see Col. 8 for references. We restrict ourself to objects from the Terlevich et al. (1991) catalogue analysed by various authors and the sample of Izotov and collaborators, since these constitute the largest available samples of such objects. All except one object (Pox 105) from Kunth & Sargent (1983) showing HeII 4686 HeII $\lambda$4686 emission was later classified as a WR galaxy (Kunth & Joubert 1985 and references in Sect. 3). From the four emission line galaxies with narrow HeII 4686 HeII $\lambda$4686 emission listed by Conti (1991, his Table 2) three are now classified as WR galaxies (see Table 1); the presence of a broad HeII 4686 HeII $\lambda$4686 component due to WR stars is suspected in the Seyfert 2 galaxy Pox 52 (Kunth et al. 1987).

From the 12 objects of Campbell et al. (1986) for which a measurement is available, six remain in this category, although two additional objects are suspected to show broad HeII. In the other objects from Campbell et al., WR features have been found by other investigators (see Sect. 3), in part also in re-analysis of the same observational data (e.g. Masegosa et al. 1991).

From the sample of Izotov and collaborators (including 60 objects published up to 1998, i.e. including Izotov & Thuan 1998), 40 show nebular HeII. However only 9 objects (listed in Table 3) reveal no broad 4686 component according to these studies and the reanalysis of Guseva et al. (1998).