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Astron. Astrophys. 364, 53-69 (2000)

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Broad band properties of medium and low [FORMULA] early type galaxies

G. Trinchieri 1, S. Pellegrini 2, A. Wolter 1, G. Fabbiano 3 and F. Fiore 4

1 Osservatorio Astronomico di Brera, Via Brera 28, 20121 Milano, Italy
2 Dipartimento di Astronomia, Università di Bologna, Via Ranzani 1, 40127 Bologna, Italy
3 Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138, USA
4 Osservatorio Astronomico di Roma, Via dell'Osservatorio, 00044 Monteporzio Catone, Italy

Received 13 July 2000 / Accepted 28 September 2000


We have measured the spectral properties of five galaxies of low to intermediate L[FORMULA] ratios with BeppoSAX and ASCA. A hard component (kT [FORMULA] keV) is observed in all galaxies. In NGC 1553 the BeppoSAX data show that this component is extended, and suggest an origin for the emission in the evolved stellar population. In NGC 3115, a point-like source appears embedded in an extended component morphologically similar to the stellar body, suggesting an almost equal contribution from the nuclear region and the binary population. A large central mass concentration and low level optical activity in NGC 3379 argue for a contribution from the nucleus also in this object. However, for both NGC 3115 and NGC 3379, the nuclear emission is at a level well below that observed in other galaxies who host similar nuclear black holes. A second soft (kT [FORMULA]0.3- 0.7 keV) spectral component is needed to fit the data of NGC 1407, NGC 1553 and NGC 4125 over the entire energy range probed ([FORMULA] 0.2-10 keV), best represented by a thermal component with line emission. We discuss possible interpretations of the origin of this component, which however will be better defined only with higher quality data.

Key words: galaxies: elliptical and lenticular, cD – galaxies: individual: NGC 1407 – galaxies: individual: NGC 1553 – galaxies: individual: NGC 3115 – galaxies: individual: NGC 3379 – galaxies: individual: NGC 4125

Send offprint requests to: G. Trinchieri

Correspondence to: ginevra@brera.mi.astro.it

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© European Southern Observatory (ESO) 2000

Online publication: December 15, 2000