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Astron. Astrophys. 332, 449-458 (1998)


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ROSAT HRI observations of six early-type galaxies

Michael Dahlemand Norbert Stuhrmann 1, 2

1 ESTEC, Astrophysics Division, Space Science Department, Postbus 299, 2200 AG Noordwijk, The Netherlands
2 Schwalbenweg 6, D-55765 Birkenfeld, Germany

Received 1 September 1997 / Accepted 20 November 1997

Abstract

High-resolution ROSAT HRI soft X-ray observations of four E/S0 galaxies were conducted by us. The data show no signs of Seyfert activity in the X-ray regime. The central emission peaks of the four galaxies, NGC 533, NGC 2832, NGC 4104 and NGC 6329, are associated with their cooling flows. The half intensity radii of the cooling flows range from 0.8 to 3.5 kpc. We find a trend (based up to now on only five objects) of the radio power of the cores in E/S0 galaxies to increase with the size and the accretion rates of their cooling flows.

In one galaxy, NGC 4921, no centrally peaked extended gaseous envelope was found, which is most likely due to the fact that it is not an E/S0 galaxy, but an early-type spiral.

NGC 2885, the sixth galaxy in our initial sample, shows signs of X-ray emission from an AGN. It has also been classified as a Sy-1 AGN by Bade et al. (1995). However, optical imaging suggests that this galaxy is probably not an E or S0 type system either, but rather an early-type spiral galaxy. Thus, in the context of accretion rate vs. galaxy type models of low-luminosity AGNs, the presence of an X-ray luminous Sy-1 nucleus in NGC 2885 is no surprise.

Key words: cooling flows – galaxies: elliptical and lenticular, cD – intergalactic medium – galaxies: nuclei – X-rays: galaxies

Send offprint requests to: M.Dahlem (mdahlem@astro.estec.esa.nl)

© European Southern Observatory (ESO) 1998

Online publication: March 23, 1998
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