7 Summary of the results

The dedicated search for ELGs on the blue objective prism plates revealed a large number of intrinsically faint galaxies, and with small linear sizes. Surface photometry of a subsample of 139 ELGs show that nearly 25% of them have almost unresolved stellar images and quasi-stellar SB profiles. Those unresolved galaxies could not have been separated from stars by traditional morphological surveys.

Among the studied ELGs there is a higher percentage of isolated galaxies than in the study of Vennik et al. ([1996]). The 15 isolated ELGs are intrinsically faint and small ELGs. Isolated ELGs show, consequently, a slightly higher fraction of quasi-stellar SB profiles.

SB profile decomposition into disk and excess light components has been performed for most but the unresolved ELGs. ELGs show more SB profiles with (central) light excess, when compared to those in the morphological surveys, because of the bright H II regions in the ELGs. Among the resolved dwarf ELGs ( $M_{ B} \geq -16.5$) an underlying stellar disk component has been detected for most of them, at least marginally. The underlying disks of the isolated ELGs are of lower SB and have larger scale lengths than the non-isolated ELGs of the same luminosity. Consiquently, the isolated galaxies could have lower stellar (i.e. baryonic) density than the clustered galaxies. For a full discussion of this issue the baryonic content in gaseous (H I) form has to be considered, and recent studies (Hopp [1998]) suggest that this content might be unsually high in these galaxies.

The observed ELGs are blue in B-R, which should be expected since the objects were selected from blue plates. Our small sample does not reveal any significant colour differences between isolated and non-isolated ELGs. Nearly half of the sample shows reliable radial colour changes. The frequency of raising outwards and decreasing outwards colour index profiles is nearly equal, but depends slightly on the intrinsic luminosity and on the profile type (i.e. morphology) of the ELGs.

The preliminary results concerning the (marginally detected) underlying stellar components in the dwarf ELGs should be confirmed by measurements on deeper frames, obtained in good seeing conditions.

A detailed comparison to the results of other photometric studies of dwarf and/or emission line galaxies like e.g. Salzer et al. ([1989]), Telles et al. ([1997]), Vader & Chaboyer ([1994]), Vitores et al. ([1996]), Cruzen et al. ([1997]) will be postponed to a main journal paper.

Acknowledgements

We would like to thank Dr. A.P. Fairall for the careful review of this manuscript. We gratefully acknowledge Prof. H. Elsässer for interesting discussions and Dr. G.M. Richter for using his software package. J.V. acknowledges the financial support and hospitality of the Max-Planck-Institute for Astronomy during several visits. This research has made use of the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.