EDP Sciences
Free access
Volume 446, Number 2, February I 2006
Page(s) 459 - 470
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20053893
A&A 446, 459-470 (2006)
DOI: 10.1051/0004-6361:20053893

X-ray spectral survey with XMM-Newton of a complete sample of nearby Seyfert galaxies

M. Cappi1, F. Panessa2, L. Bassani1, M. Dadina1, G. DiCocco1, A. Comastri3, R. Della Ceca4, A. V. Filippenko5, F. Gianotti1, L. C. Ho6, G. Malaguti1, J. S. Mulchaey6, G. G. C. Palumbo7, E. Piconcelli8, W. L. W. Sargent9, J. Stephen1, M. Trifoglio1 and K. A. Weaver10

1  INAF-IASF Sezione di Bologna, via Gobetti 101, 40129 Bologna, Italy
    e-mail: cappi@bo.iasf.cnr.it
2  Instituto de Fisica de Cantabria (CSIC-UC), Avda de los Castros, 39005 Santander, Spain
3  INAF- Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy
4  INAF- Osservatorio Astronomico di Brera, via Brera 28, 20121 Milano, Italy
5  Department of Astronomy, University of California, Berkeley, CA 94720-3411, USA
6  Carnegie Observatories, 813 Santa Barbara Street, Pasadena, CA 91101, USA
7  Dipartimento di Astronomia, Universita' degli Studi di Bologna, via Ranzani 1, 40127 Bologna, Italy
8  XMM-Newton Science Operation Center/RSSD-ESA, Apartado 50727, 28080 Madrid, Spain
9  Department of Astronomy, California Institute of Technology, Pasadena, CA 91125, USA
10  Laboratory for High Energy Astrophysics, NASA's Goddard Space Flight Center, Greenbelt, MD 20771, USA

(Received 23 July 2005 / Accepted 28 September 2005 )

Results obtained from an X-ray spectral survey of nearby Seyfert galaxies using XMM-Newton are reported. The sample was optically selected, well defined, complete in B magnitude, and distance limited: it consists of the nearest ($D \la22$ Mpc) 27 Seyfert galaxies (9 of type 1, 18 of type 2) taken from the Ho et al. (1997a, ApJS, 112, 315) sample. This is one of the largest atlases of hard X-ray spectra of low-luminosity active galaxies ever assembled. All nuclear sources except two Seyfert 2s are detected between 2 and 10 keV, half for the first time ever, and average spectra are obtained for all of them. Nuclear luminosities reach values down to 1038 erg s-1. The shape of the distribution of X-ray parameters is affected by the presence of Compton-thick objects ($\ga$30% among type 2s). The latter have been identified either directly from their intense FeK line and flat X-ray spectra, or indirectly with flux diagnostic diagrams which use isotropic indicators. After taking into account these highly absorbed sources, we find that (i) the intrinsic X-ray spectral properties (i.e., spectral shapes and luminosities above 2 keV) are consistent between type 1 and type 2 Seyferts, as expected from "unified models"; (ii) Seyfert galaxies as a whole are distributed fairly continuously over the entire range of $N_{\rm H}$, between 1020 and 1025 cm-2; and (iii) while Seyfert 1s tend to have lower $N_{\rm H}$ and Seyfert 2s tend to have the highest, we find 30% and 10% exceptions, respectively. Overall the sample is of sufficient quality to well represent the average intrinsic X-ray spectral properties of nearby active galactic nuclei, including a proper estimate of the distribution of their absorbing columns. Finally, we conclude that, with the exception of a few cases, the present study agrees with predictions of unified models of Seyfert galaxies, and extends their validity down to very low luminosities.

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

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