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Astron. Astrophys. 340, 351-370 (1998)

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5. Summary

We have reported the results of the first detailed analysis of ROSAT data of the NGC 3079 field. We have paid special emphasis on the best attitude solution to achieve optimal HRI point spread function and positional accuracy. With HRI and PSPC we detected 23 and 34 sources within [FORMULA] diameter and a box of [FORMULA], respectively, apart from complex emission from the inner [FORMULA] around NGC 3079. We have identified possible counterparts for several of the sources outside NGC 3079 by comparison with optical plates and catalogues.

The LINER/Seyfert 2 galaxy NGC 3079 manifests itself as a complex X-ray source with a luminosity of [FORMULA]erg s-1 and could be resolved into three components:

(1) Extended emission in the inner [FORMULA] with a luminosity of [FORMULA]erg s-1 can be resolved with the HRI and is coincident with the super-bubble seen in optical images. The active nucleus may contribute to the emission as a point source. We, however, prefer an explanation of this emission as the brightest and hottest part of the out-flowing material similar to the slightly extended emission emission close to the galaxy nucleus within the plume of NGC 253 (Pietsch et al. 1998).

(2) Emission from the disk of the galaxy has a luminosity of [FORMULA]erg s-1 and can be partly resolved by the HRI in 3 point sources with luminosities of [FORMULA]erg s-1 each. The soft spectrum of the disk can be explained by a mixture of X-ray binaries and over-luminous H II regions.

(3) Emission from the halo has a luminosity of [FORMULA]erg s-1 and is rather soft (temperature of 0.3 keV). It extends to nuclear distances of more than 13 kpc and has a X-shaped appearance. Using simplifying assumptions we derived parameters for this halo gas.

The X-ray luminosity of NGC 3079 is higher by a factor of 10 compared to other galaxies of similar optical luminosity. It also exceeds the luminosity seen in starburst galaxies like NGC 253. We argue that this may be caused by the presence of an AGN in NGC 3079 rather then by starburst activity. Investigations of the other galaxies in the NGC 3079 group, NGC 3073 and MCG 9-17-9, showed that the X-ray emission is not extraordinary for their type as might have been expected from the disturbance by the galactic super-wind emanating from the active companion NGC 3079.

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© European Southern Observatory (ESO) 1998

Online publication: November 9, 1998