1 Introduction

It is expected that, in a nearby future, extragalactic photographic Schmidt surveys will be superseded by CCD-based observations that will go much deeper and are free from the well-known caveats of photographic emulsions. However the giant CCD mosaic detectors that are needed to cover a field of several square degrees are either just beginning operations or still under development. Further, the technical problem due to the field curvature of Schmidt telescopes have prevented the complete coverage of their field with CCDs and lead to build special telescopes based on different optical designs dedicated to CCD wide-field imaging. Therefore, several groups in the recent years have pursued efforts on classical photographic surveys, still fairly well adapted to the statistical study of the galaxian population in the nearby Universe, especially in the field of active galaxy search. Aside from continuing surveys begun long ago and producing large numbers of objects in very homogeneous data bases, such as the Case survey (Pesch & Sanduleak 1983) or the Kiso survey (Takase & Miyauchi-Isobe 1984), other attempts have been directed to a more complete retrieval of the information content of the Schmidt plates, thanks to the capabilities of modern digitization machines and subsequent digital image processing systems. The UC Madrid survey (Zamorano et al. 1994; Gallego et al. 1995), the Montreal Blue Galaxy survey (Coziol et al. 1993, 1994), and the Hamburg Schmidt survey (Hopp et al. 1995; Popescu et al. 1996) are examples of these improvements that enable to go beyond the information content of previous catalogs.

Except for far-infrared selected samples, the search for active galaxies with conventional ground-based telescopes has always been inspired by two basic ideas: to search for emission line spectra or to search for an ultraviolet excess in the continuum of the objects. The two major facets of "activity'' in a galaxy are the non-thermal Seyfert-like nuclear phenomena and the enhanced stellar formation producing massive ionizing and rich hot main-sequence stars. They are known to produce uv-excess, or at least enhanced blue color, and emission lines. However, the emission lines could be of small equivalent widths in an active object, and therefore very difficult to detect. For instance if the star formation burst is seen in an evolved state most of the ionizing fraction of the newborn population has already disappeared. An ideal survey aimed at detecting the totality of the active galaxy population should therefore search for emission lines (including H$\alpha$,which in some objects is the only line with substantial equivalent width in the visible), search for ultraviolet excess in the continuum, and be carefully cross-correlated with a deep far-infrared survey to add the dusty objects that escape detection in the visible because of considerable extinction of the active areas.

As a first step to build a sample of "Starburst Galaxies'' as complete as possible without constraints either on the morphology or on the cause and/or age of the starburst phenomenon, we have conducted a Schmidt photographic survey using the two modes of selection: ultraviolet excess and emission lines (as for the 2nd Byurakan: Markarian & Stepanian 1983 and Case surveys: Pesch & Sanduleak 1983; Salzer et al. 1995). This allows us to get galaxies experiencing a recent and strong starburst as well as those showing an old dying burst. One of the aim was to get the maximum astrophysical information output directly from the Schmidt plates without any CCD follow-up. For that purpose we have developed specific procedures to process the digitized plates (Surace & Comte 1994, hereafter referred as Paper I).

The present paper focusses on the part of the data reduction not discussed in Paper I (determination of spectrophotometric parameters from the Schmidt photographic low-resolution spectra), an estimate of the completeness of the spectroscopic survey on 2 fields (46.5 square degrees) and contains a catalog of the 92 emission line objects found in these two fields.