Narrow-line AGN in the ISO-2MASS survey *
Astronomisches Institut Ruhr-Universität Bochum (AIRUB), Universitätsstraße 150, 44780 Bochum, Germany e-mail: email@example.com
2 Thüringer Landessternwarte Tautenburg (TLS), Sternwarte 5, 07778 Tautenburg, Germany
3 European Southern Observatory (ESO), Karl-Schwarzschild-Str. 2, 85748 Garching, Germany
4 Instituto de Astronomía, Universidad Católica del Norte (UCN), Avenida Angamos 0610, Antofagasta, Chile
5 Harvard-Smithsonian Center for Astrophysics (CfA), 60 Garden Street, Cambridge, MA-02138, USA
6 HERSCHEL Science Centre, ESA, Noordwijk, PO Box 299, 2200 AG Noordwijk, The Netherlands
7 IPAC, California Institute of Technology (Caltech), 770 South Wilson Avenue, Pasadena, CA-91125, USA
Accepted: 23 December 2006
Context.A long-standing challenge of observational AGN research is to find type 2 quasars, the luminous analogues of Seyfert-2 galaxies.
Aims.We search for luminous narrow-line type 2 AGN, characterise their properties, and compare them with broad-line type 1 AGN.
Methods.Combining the ISOCAM parallel survey at 6.7 μm with 2MASS, we have selected AGN via near-mid-infrared colours caused by the hot nuclear dust emission. We performed spectroscopy in the optical and, for a subset of the sample, also in the mid-infrared with Spitzer.
Results.We find nine type 2 AGN at redshift , three of them have even quasar-like  luminosities. At the given redshift and luminosity range the number of type 2 AGN is at least as high as that of type 1s. At we did not find type 2 AGN, probably because the hottest dust emission, still covered by the NIR filters, is obscured. The optical spectra of the type 2 host galaxies show young and old stellar populations. Only one object is an ultraluminous infrared galaxy with starburst. The 5–38 μm spectra of the two type 2 sources observed show a strong continuum with PAH emission in one case and silicate absorption in the other case.
Conclusions. The near-mid-infrared selection is a successful strategy to find luminous type 2 AGN at low z. The objects exhibit a large range of properties so that it is difficult to infer details by means of popular SED fitting with simple average templates.
Key words: galaxies: active / galaxies: quasars: general / infrared: galaxies
Based on observations made with ESO telescopes at La Silla and Paranal (IDs 072.B-0144, 075.A-0345, and 075.A-0374), with the 4-m Blanco telescope at Cerro Tololo Inter-American Observatory (CTIO is part of the National Optical Astronomy Observatories, which are operated by the Association of Universities for Research in Astronomy, under contract with the National Science Foundation), with the 2.2-m telescope at the Centro Astronómico Hispano Alemán (CAHA) Calar Alto, operated jointly by the Max-Planck Institut für Astronomie and the Instituto de Astrofísica de Andalucía (CSIC), with the 1.9-m telescope at the South African Astrophysical Observatory (SAAO), and with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA.
© ESO, 2007