  The cosmological evolution of X-ray-selected and optically selected Active
Galactic Nuclei (AGNs) show different behaviours interpreted in terms of two
different populations. The difference is evident mainly for low luminosity AGNs
(LLAGNs), many of which are lost by optical photometric surveys. We are
conducting a spectroscopical study of a composite sample of AGN candidates
selected in SA57 following different searching techniques, to identify low
luminosity AGNs and break down the sample into different classes of objects.
AGN candidates were obtained through optical variability and/or X-ray emission.
Of special interest are the extended variable objects, which are expected to be
galaxies hosting LLAGNs. Among the 26 classified objects a fair number (9) show
typical AGN spectra. 10 objects show Narrow Emission Line Galaxy spectra, and
in most of them (8/10) optical variability suggests the presence of LLAGNs.
