Since Hubble (1926, 1936) categorized galaxies according to their shapes, galaxy morphology has been used as a fundamental parameter in studies of galaxy formation and evolutionary processes. However, many galaxies have unusual morphologies and do not belong to any Hubble type. Most of these peculiar galaxies are interacting systems and had their forms distorted by tidal forces. Therefore, interactions between galaxies are a major evolution mechanism which transforms galaxy morphology during their evolution. The so-called Toomre's sequence (Toomre 1977) is a perfect example of what happens to galaxy morphology during different stages of interaction. Numerical simulations of the encounter between galaxies has established that gravitational interaction can not only originate tidal damage to spiral structures but also merge two disk galaxies in one final product which resembles an elliptical galaxy (Toomre & Toomre 1972, see Barnes & Hernquist 1992 for a review). In order to establish whether an encounter will originate a merger or not it is necessary to determine the physical properties and dynamics of the interaction. In principle, all systems made of galaxies with comparable mass and which are in elliptical bound orbits end as a merger but not necessarily within the Hubble time (Binney & Tremaine 1987; Junqueira & de Freitas Pacheco 1994).
If mergers are frequent in galaxy evolution we should be able to find mergers in progress such as NGC 7252 and/or traces of the effect produced by this phenomenon. For instance, the most commonly associated features invoked by merger theory are bars, isophotes twisting, color gradient, shells, inner structures, dust, starbursts, AGN's, etc (Schweizer 1983; Noguchi 1988; Bender et al. 1989; Forbes & Thomson 1992). However, to what degree are the galaxy properties influenced by interactions with its neighbors is still an open issue. For instance, interaction involving at least one gas-rich galaxy may result in activity which may range from global starbusts to nuclear ones and to AGN's, however it is unclear whether there is a transition between these three features (Fritze-v. Alvensleben 1996; Keel 1996).
One of the most striking evidences for galaxy evolution is the faint blue galaxies excess at , i.e. the Buchter & Oemler effect (Butcher & Oemler 1978, 1984). In order to explain this effect, galaxy evolution models need a mechanism for creating disturbed galaxies with enhanced star formation and explain why they occur more frequently at this redshift (Moore et al. 1996). Moreover, they have to address the question of morphology evolution and an identification of the remnants of the distorted blue galaxies in the local Universe. These issues have been the focus of major research efforts, largely triggered by the Hubble Deep Field observations (Williams et al. 1996) and the 10 m class telescope data which are becoming available now. However, despite the efforts made so far, fundamental questions, such as when, where and how galaxies form and evolve remain controversial. For instance, in hierarchical models for galaxy formation an individual galaxy may pass through various phases of disk or spheroid during its lifetime (Baugh et al. 1996). The authors claim that about 50% of all ellipticals (but only about 15% of spirals) would have undergone a major merger during the redshift interval . However, the high degree of uniformity in ellipticals star formation history indicates that these objects must have formed at (Bower et al. 1992).
An essential step towards answering these questions is understanding the properties of interacting galaxies in the local universe and comparing it with the more distant objects. We have started a long-term project focusing on these issues. Our first step was to select a sample of faint interacting galaxies in pairs and groups. By faint we mean galaxies that are within 19<mR<22 and by interacting we mean angular separations of (see Infante et al. 1996; de Mello et al. 1997a,b for more details). Among the more interesting results we find is the excess of faint pairs at intermediate redshift .
In this paper we present a continuation of our previous work. We present a database of nearby pairs of galaxies that will be used in the future to compare with pairs at intermediate redshifts.