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2 Searches for WR galaxies

 Few systematic searches for WR populations outside the Local Group (or "WR galaxies'') have been undertaken. In this section we briefly summarise the studies explicitly devoted to the detection of WR signatures. A list of candidate WR galaxies resulting from some of these searches or found loosely in the literature is provided in Sect. 6. The WR galaxies issued from the searches described below are included in our list and represent the vast majority of detections. Let us now briefly summarise the properties of the spectroscopic and narrow-band imaging searches.

2.1 Spectroscopic searches

The first search for WR features in giant HII regions of nearby galaxies was carried out by D'Odorico et al. (1983). The latest update from their study is summarised by Rosa & D'Odorico (1986). Data from their work was included in the quantitative analysis by Arnault et al. (1989).

The most detailed search was undertaken by Kunth & Joubert (1985) from a sample of 45 "lazy'' galaxies (blue emission-line galaxies forming stars by intermittent short bursts) from various sources. In their statistical approach they measure the excess emission above the continuum between 4600-4711 Å (rest wavelength) after subtracting a typical nebular contamination taken as a function of the excitation level and abundance. Their search yielded 19 regions (15 different objects) with excess emission above 0.8 $\sigma$.

A systematic search for a broad WR bump in all the HII galaxies included in the catalogue of Terlevich et al. (1991) was presented by Masegosa et al. (1991). Earlier publications using a subset of the same observational data had also reported some WR detections and nebular HeII 4686 HeII $\lambda$4686 (Campbell & Smith 1986; Campbell et al. 1986). Positive detections were considered by Masegosa et al. when the "blue bump'' was at least 1 $\sigma$ over the continuum level and clearly discernible from the nebular HeII 4686 HeII $\lambda$4686 line. Their search yielded 37 detections ($\sim$ 10% of the sample); 14 of these objects have spectra with a spectral resolution of $\mathrel{\mathchoice {\vcenter{\offinterlineskip\halign{\hfil
$\displaystyle ... 5 Å FWHM, which the authors estimate to be "good enough'' to reliably detect WR stars. Only these objects (their Table 2) were included in our list as confirmed WR galaxies. The remaining objects are classified here as "candidates'' (Sect. 6).

Recently Pindao (1998) and Pindao et al. (1999) have reanalysed the spectra from the Terlevich et al. catalogue and $\mathrel{\mathchoice {\vcenter{\offinterlineskip\halign{\hfil
$\displaystyle ... 100 additional emission line galaxies for their WR content. Objects with a clear detection of broad HeII 4686 HeII $\lambda$4686 are retained as WR galaxies here (See Pindao 1998. The detection level corresponds to $\mathrel{\mathchoice {\vcenter{\offinterlineskip\halign{\hfil
$\displaystyle ... 0.8 $\sigma$, i.e. category 4 of Pindao et al. 1999). Category 3 objects (WR bump detection at $\sim$ 0.5 $\sigma$) from Pindao et al. (1999) are classified here as "WR candidates''.

Robledo-Rella & Conti (1993) presented a search for WR features in a selected sample of northern HII galaxies; candidates are given in Sect. 6.

First results from a new search for WR signatures in young starbursts have been presented by Contini (1996) and Kovo & Contini (1998).

An ongoing systematic search for WR galaxies has been mentioned by Huang et al. (1998).

According to Izotov (1998, private communication) the observational data gathered primarily for accurate determinations of the helium abundance since 1993 (see Izotov et al. 1994, 1996, 1997a; Thuan et al. 1995; Izotov & Thuan 1998) are being systematically re-analysed for their WR content (Guseva et al. 1998; Izotov et al. 1998). Adding 10 newly observed objects, their sample mostly including blue compact galaxies consists of $\sim$ 70 spectra. While the initial sample contained essentially very metal-poor objects, metallicities up to $\sim$ solar are now also included. The majority of the WR detections have been mentioned in the above papers; in total Guseva et al. (1998) and Izotov et al. (1998) find 41 WR galaxies, defined by broad emission between $\sim$ 4620 - 4700 Å. Often several broad features are pointed out in the blue bump (HeII 4686 HeII $\lambda$4686, NIII $\lambda$4640, but also other lines they identify as NIII $\lambda$4510, NII $\lambda$4565, NV $\lambda$4605, 4620, CIV $\lambda$4658). According to their study 28 spectra also show broad CIV $\lambda$5808. Finally, few detections of broad HeII $\lambda$5412, CIII $\lambda$5696, and also CII $\lambda$4267 are signaled. We retain all except one WR galaxy (Mrk 1026 = NGC 848 showing no broad HeII 4686 HeII $\lambda$4686) from their study.

2.2 Narrow-band imaging and others

Drissen et al. (1993) have conducted a search for HeII 4686 HeII $\lambda$4686 emission via narrow-band imagery in four low mass galaxies (GR8, NGC 2366, IC 2574, NGC 1569). Two of them are now confirmed WR galaxies (see above), IC 2574 remains to be studied spectroscopically, and GR8 yielded negative results (no HeII).

Schmidt-Kaler & Feitzinger (1984) initiated a search for 30 Dor and NGC 604 like objects based on POSS, ESO-Blue, and SRC film. To the best of our knowledge results from this survey have not been published.

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