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Astron. Astrophys. 322, 89-97 (1997)

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X-ray emission components from Stephan's Quintet resolved with the ROSAT HRI

W. Pietsch 1, G. Trinchieri 1, 2, H. Arp 3 and J.W. Sulentic 4

1 Max-Planck-Institut für extraterrestrische Physik, Giessenbachstraße, D-85740 Garching bei München, Germany
2 on leave from Osservatorio Astronomico di Brera, via Brera 28, Milano, Italy
3 Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Straße 1, D-85740 Garching bei München, Germany
4 Department of Physics and Astronomy, University of Alabama, Tuscaloosa, 35487, USA

Received 21 October 1996 / Accepted 20 November 1996


We obtained a high spatial resolution image of Stephan's Quintet with the ROSAT HRI detector. The observations reveal that the extended X-ray emission from the compact group originates from several distinct components. The total X-ray luminosity in the 0.1 - 2 keV band within a circle of [FORMULA] diameter is [FORMULA] erg s-1. This measure is consistent with previous ROSAT PSPC observations. The new results indicate that only a fraction of the detected emission can be attributed to a diffuse, hot intergalactic medium and/or to individual members of the group. One third of the detected photons are concentrated in an intergalactic feature that closely matches one previously observed in the radio continuum. This structure is likely a manifestation of shocks resulting from the strong interactions or collisions occuring in the group. Individual galaxies are also detected: 1) coincident with the Seyfert 2 galaxy NGC 7319 and 2) with NGC 7318a. They contribute [FORMULA] 20 % of the total emission. A residual component with [FORMULA] erg s-1 is also detected which may be due to emission from more diffuse hot gas.

The present observation reduces the X-ray luminosity that can be attributed to a diffuse intergalactic medium in this system. It limits the mass of any diffuse component to [FORMULA] [FORMULA] [FORMULA]. These results raise the possibility of the existance of two quite different intergalactic X-ray components in spiral-dominated compact groups.

Key words: galaxies: interaction – intergalactic medium – X-rays: galaxies – galaxies: Stephan's Quintet; NGC 7319; NGC 7318A

Send offprint requests to: W. Pietsch, e-mail address wnp@mpe-garching.mpg.de

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© European Southern Observatory (ESO) 1997

Online publication: June 30, 1998