... rates

Tables 3, 4 and Fig. 1 are only available in electronic form at http://www.edpsciences.org

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... algorithm

The automatic algorithm performs aperture photometry around the selected UV sources using increasing radii. The adopted aperture is selected when the magnitude stabilizes. More details about this procedure are given in Moulinec (1989).

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... 17 mag

The UV magnitudes will always be referred in the AB system defined as  $AB_{\nu} = -2.5 \log f_{\nu} - 48.6$, where $f_{\nu}$ is expressed in erg cm^-2 s^-1 Hz^-1.

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... USNO/FOCA photometry

Details about the uncertainties of the USNO-B1.0 photometry are given in Appendix A.

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... candidates

Optical frames from the blue DSS plates centered at these objects are available upon request: jorge.iglesias@oamp.fr

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... respectively

m028-817 is misclassified as a cluster galaxy in SIMBAD based on the report of Brosch et al. (1998), but in this paper the authors clearly classify this object as the star TON 140.

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... database

The LEDA database assumes  H₀ = 75 km s^-1 Mpc^-1.

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... method

We call the attention of the reader to the fact that the  $1/V_{\rm max}$ method suffers from systematic errors in the derived parameters of the LF for small samples of galaxies (see Willmer 1997 for details).

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... sample

Although in the case that any of the four dubious objects listed in Sect. 3.1 were confirmed galaxies they would show a very low dust content.

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