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Issue A&A
Volume 460, Number 1, December II 2006
Page(s) 45 - 57
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20054756



A&A 460, 45-57 (2006)
DOI: 10.1051/0004-6361:20054756

X-ray nature of the LINER nuclear sources

O. González-Martín1, J. Masegosa1, I. Márquez1, M. A. Guerrero1, and D. Dultzin-Hacyan2

1  Instituto de Astrofísica de Andalucía, CSIC, Apartado Postal 3004, 18080 Granada, Spain
    e-mail: omaira@iaa.es
2  Instituto de Astronomía, UNAM, Apartado Postal 70-264, 04510 México D.F., México

(Received 22 December 2005 / Accepted 17 May 2006 )

Abstract
We report the results from a homogeneous analysis of the X-ray (Chandra ACIS) data available for a sample of 51 LINER galaxies selected from the catalogue by Carrillo et al. (1999, Rev. Mex. Astron. Astrofis., 35, 187) and representative of the population of bright LINER sources. The nuclear X-ray morphology has been classified by their nuclear compactness in the hard band (4.5-8.0 keV) into 2 categories: active galactic nuclei (AGN) candidates (with a clearly identified unresolved nuclear source) and starburst (SB) candidates (without a clear nuclear source). Sixty percent of the total sample are classified as AGNs, with a median luminosity of ${L_{\rm X}(2{-}10~\rm keV)=2.5\times\rm 10^{40}~erg~s^{-1}}$, which is an order of magnitude higher than for SB-like nuclei. The spectral fitting allows us to conclude that most of the objects need a non-negligible power-law contribution. When no spectral fitting can be performed (data with a low signal-to-noise ratio), the color-color diagrams allow us to roughly estimate physical parameters, such as column density, temperature of the thermal model, or spectral index for a power-law, and therefore to better constrain the origin of the X-ray emission. The X-ray morphology, the spectra, and the color-color diagrams together allow us to conclude that a high percentage of LINER galaxies, at least $\approx$60%, could host AGN nuclei, although contributions from high-mass X-ray binaries or ultra-luminous X-ray sources cannot be ruled out for some galaxies.


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



© ESO 2006


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