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Issue A&A
Volume 386, Number 1, April IV 2002
Page(s) 60 - 68
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20020078



A&A 386, 60-68 (2002)
DOI: 10.1051/0004-6361:20020078

$\vec{BeppoSAX}$ observations of LINER-2 galaxies

I. Georgantopoulos1, F. Panessa2, 3, A. Akylas1, 4, A. Zezas5, M. Cappi3 and A. Comastri6

1  Institute of Astronomy & Astrophysics, National Observatory of Athens, Palaia Penteli, 15236, Athens, Greece
2  Dipartimento di Astronomia, Universita di Bologna, via Ranzani 1, 40127, Bologna, Italy
3  Istituto Technologie e Studio delle Radiazioni Extraterrestri/CNR, via Gobetti 101, 40129, Bologna, Italy
4  Physics Department, University of Athens, Panepistimiopolis, Zografos, 15783, Athens, Greece
5  Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138, USA
6  Osservatorio Astronomico di Bologna, via Ranzani 1, 40127, Bologna, Italy

(Received 14 September 2001 / Accepted 15 January 2002)

Abstract
We present BeppoSAX observations of 6 "type-2" LINER and "transition" galaxies (NGC 3379, NGC 3627, NGC 4125, NGC 4374, NGC 5195 and NGC 5879) from the Ho et al. (1997) spectroscopic sample of nearby galaxies. All objects are detected in the 2-10 keV band, having luminosities in the range $ L_{2-10\,\rm keV}\sim 1\times10^{39}{-}1\times10^{40}$  $\rm erg~s^{-1}$. The PDS upper limits above 10 keV place constraints on the presence of a heavily obscured AGN in the case of NGC 3379 and NGC 4125. No significant variability is detected in any of the objects. The spectra are described in most cases by a simple power-law model with a spectral slope of $\Gamma \sim 1.7{-}2.5$ while there is evidence neither for a significant absorption above the Galactic nor for an FeK $_\alpha$ emission line. Therefore, based on the spectral properties alone, it is difficult to differentiate between a low-luminosity AGN or a star-forming galaxy scenario. However, imaging observations of NGC 3627 and NGC 5195 with Chandra ACIS-S reveal very weak nuclear sources while most of the X-ray flux originates either in off-nuclear point sources or in diffuse emission. The above clearly argue in favour of a star-forming origin for the bulk of the X-ray emission, at least in the above two sources.


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

Offprint request: I. Georgantopoulos, ig@astro.noa.gr

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