EDP Sciences
Free access
Volume 477, Number 2, January II 2008
Page(s) 473 - 479
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20078727

A&A 477, 473-479 (2008)
DOI: 10.1051/0004-6361:20078727

Optical spectroscopy of active galactic nuclei in SA57

D. Trevese1, V. Zitelli2, F. Vagnetti3, K. Boutsia1, 4, and G. M. Stirpe2

1  Dipartimento di Fisica, Università di Roma "La Sapienza", P.le A. Moro 2, 00185 Roma, Italy
    e-mail: dario.trevese@roma1.infn.it
2  INAF - Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy
3  Dipartimento di Fisica, Universitá di Roma "Tor Vergata", via della Ricerca Scientifica 1, 00133 Roma, Italy
4  European Southern Observatory, Karl-Schwarzschild-Straße 2, 85748 Garching, Germany

(Received 24 September 2007 / Accepted 17 October 2007)

Context.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.
Aims.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.
Methods.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.
Results.Among the 26 classified objects a fair number (9) show typical AGN spectra. Ten objects show Narrow Emission Line Galaxy spectra, and in most of them (8/10) optical variability suggests the presence of LLAGNs.

Key words: galaxies: active -- galaxies: nuclei -- galaxies: Seyfert -- X-rays: galaxies

© ESO 2007