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Astron. Astrophys. 334, 427-438 (1998)

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1. Introduction

Active galactic nuclei (AGN) in rich clusters of galaxies evolve faster than those in poor environments. The nearby clusters of galaxies usually contain radio weak galaxies of the Fanarroff- Riley I (FRI) type, while quasars at low redshifts ([FORMULA]) rarely, if ever, occur in rich clusters of galaxies (Stockton, 1980). On the other hand, the radio-loud quasars with [FORMULA] are often found in rich clusters. The time scales of evolution of AGN activity are similar to the dynamical ones of clusters of galaxies. Therefore, only the dynamical evolution of cluster cores may be responsible for the evolution of AGN at these time scales. The virialisation of cluster core increases the galaxy velocities in the core up to the values, where the galaxy-galaxy interactions are not effective enough to stop AGN activity. Then, the galaxy velocities in the vicinity of those AGNs (mainly quasars) are rather low.

The aim of the paper is to find the mechanism responsible for the non-collinearity of the radio structure of radio-loud quasar (RLQSO) 3C 275.1. Therefore, in Sect. 2 we shall discuss the dynamics of a group of galaxies around it to see if the drag force due to the motion of the host galaxy through the intracluster medium (ICM) could cause the bending of the radio jet .

On the other hand it is known that RLQSOs are stronger sources of X-ray emission than the radio-weak ones (Wilkes et al. 1994). Their X-ray emission, if spatially resolved, usually consists of the point-like emission of the QSO itself and of extended emission from the hot intra-cluster gas. It has been argued from both the theoretical and an observational standpoint that the X-ray gas in the cores of galaxy clusters or groups can cool and accrete onto the slow moving dominant galaxy. Thermal instabilities in the in-flowing gas are thought to cause cooling of dense knots, which are identified with the optical emission-line filaments seen around the dominant cluster galaxies. Since 3C 275.1 exhibits one of the largest and most luminous extended emission-line regions (Hintzen and Stocke, 1986) it lies in a cooling accretion flow. Its extended narrow-line emission nebulosity and the X-ray emission will also be discussed in Sect. 2. We shall derive the temperature of the gas emitting in X-rays and the accretion mass deposition rate as well as particle number density in narrow-emission line region.

In Sect. 3 we shall discuss the radio structure of 3C 275.1 and the oblique shocks to explain its non-collinearity. A 1.6 GHz European VLBI Network image of the quasar core will be presented in Appendix C. We assume the Hubble constant [FORMULA] and [FORMULA] throughout this paper. Then, at the distance of 3C 275.1 (z = 0.5549), 1 arcsec corresponds to [FORMULA] kpc and the luminosity distance is [FORMULA] Mpc.

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© European Southern Observatory (ESO) 1998

Online publication: May 15, 1998