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Draft version Preprint typeset using L ATEX style emulateapj v. 6/6/04 THE NATURE OF COMPOSITE SEYFERT/STAR-FORMING GALAXIES REVEALED BY X-RAY OBSERVATIONS

By Francesca Panessa, Anna Wolter, Silvia Pellegrini, Antonella Fruscione, Loredana Bassani, Della Ceca, Giorgio G. C. Palumbo and Ginevra Trinchieri

Abstract

This paper presents new Chandra and BeppoSAX observations aimed at investigating the optical/Xray mismatch in the enigmatic class of the Composite galaxies, discovered by a cross-correlation of IRAS and ROSAT all sky survey catalogues. These galaxies have been classified as star-forming objects on the basis of their optical spectra, while the detection of weak broad wings in the Hα emission in a few of them and their high X-ray luminosity in the ROSAT band indicated the presence of an active nucleus. The analysis of Chandra observations for 4 Composites has revealed nuclear point-like sources, with a typical AGN spectrum (Γ ∼ 1.7-1.9) and little intrinsic absorption. A strong flux variability has been observed on different time scales, in particular most of the sources were brighter at the ROSAT epoch. Although of relative low luminosity for the AGN class (L2−10keV ∼ 3-60 × 10 41 erg/s), the active nucleus is nevertheless dominant in the X-ray domain. At other wavelengths it appears to be overwhelmed by the starburst and/or host galaxy light, yielding the Composite classification for these objects

Year: 2005
OAI identifier: oai:CiteSeerX.psu:10.1.1.317.5432
Provided by: CiteSeerX
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