Astron. Astrophys. 336, 855-877 (1998)

5. Summary

We have observed both the ROSAT HRI and PSPC data from fields centred on the edge-on, type 1 Seyfert galaxy IC 4329A and its nearby companion, the giant lenticular IC 4329. 17 and 22 sources are detected respectively in the full HRI and PSPC fields of view, the brightest being associated with the two central galaxies and a further source to the south-west. Many coincidences are seen in the two datasets and the nine most significant HRI sources all have equivalent PSPC counterparts. In addition to point source emission, unresolved residual emission is detected surrounding the IC 4329A/IC 4329 pair. This emission appears markedly two-component, with a smooth, circularly-distributed hard component, centred midway between the two central galaxies, and a more irregular, soft component, situated almost entirely to the south-east of IC 4329A. Our findings with regard to the observed point-source and unresolved emission can be summarized as follows:

1. An extremely bright ( erg s^-1) source is detected associated with the central Seyfert IC 4329A. Its spectral properties are compatible with a single power-law (), with a spectral break at 0.7 keV, in very good agreement with previous authors' work.

2. Two other very bright sources are detected associated with the nearby giant lenticular IC 4329 ( erg s^-1), and with a likely quasar to the south-west. Fitting of standard spectral models to these source spectra again result in fits that agree well with previous authors' work.

3. Many other bright sources are detected both in the HRI and PSPC fields of view, including three point-like sources, symmetrically positioned with respect to the disc of IC 4329A. Optical follow-up observations of these sources with the 2.2 m ESO/MPG telescope at La Silla, Chile, has established that they are nothing to do with the central Seyfert, being merely foreground and background objects.

4. None of the sources detected show any significant temporal variability.

5. In addition to the point sources, residual emission is detected, both in the HRI and in the PSPC, surrounding the IC 4329A/IC 4329 pair. This emission appears markedly two-component, comprising of a hard, smooth, circularly-distributed component, centred somewhere between IC 4329A and IC 4329, and a soft, irregular component, situated almost entirely to the south-east of the IC 4329A disc.

6. The hard component of the residual emission appears itself to be made up of two components. One of these is purely the `wings' of the extremely bright IC 4329A source, visible out to several arcminutes. The second component appears to be hot (1.5 keV) diffuse gas, with a luminosity of erg s^-1 and a mass of perhaps . The properties of this emission are very suggestive of it being due to hot gas within the galaxy group of which IC 4329A and IC 4329 are members.

7. The soft component of the residual emission, in terms of its temperature and one-sided nature, bears a good deal of resemblance to proposed starburst driven winds seen in some far-infrared ultraluminous systems. It is however much brighter ( erg s^-1), and larger. Another possibility discussed briefly, is that the soft emission may be a `wake' of stripped gas from the galaxy group.

8. A `bridge-like' feature is detected with the HRI between the two central galaxies, and is likely, as is seen in other similar systems, to be due to shocks resulting from the strong interaction taking place between the two systems.

© European Southern Observatory (ESO) 1998

Online publication: July 27, 1998
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