3.1. X-ray and optical morphology
Our HRI X-ray contour levels - smoothed with a Gaussian filter of 5 arcsec FWHM - are plotted over the V-band image of Mrk 266 in Fig. 1. One can distinguish four components in the X-ray image: two compact nuclei separated by 10 arcsec, a diffuse component of the merging system ( box) and a northern jet component ( box). During our 40 ksec observing run we obtained the following count rates: 66 8 counts (north-eastern component, 10 arcsec ring), 78 9 counts (south-western component, 10 arcsec ring), 311 18 counts ( box, integrated system without the jet) and 120 11 counts (northern jet, box). The individual HRI components are not resolved with the ROSAT PSPC detector (30 arcsec spatial resolution). Tests with single component models gave unsatisfactory fits to the observed PSPC spectrum (Wang et al., 1997). The integrated PSPC X-ray luminosity of Mrk 266 comes to 1.1 (7.-2.6) erg/s. Assuming the relative number of HRI counts is directly proportional to their share of the integrated X-ray flux we work out the following X-ray luminosities of the individual components (in units of 1041 erg/s): north-eastern nucleus: 1.65, south-western nucleus: 2.0, diffuse component without the nuclei and the jet region: 4.3, northern jet: 3.1.
The dominating X-ray jet structure begins 15 arcsec north of the SW-nucleus and extends as far as 24 arcsec in north-east direction. This corresponds to a projected length of 13.2 kpc for the galactic radial velocity = 8280 km ( = 75 km ). An even more striking similarity can be found between the X-ray structure of the northern jet and the B-V, B-R and V-R images (Fig. 2). The V-R colour is quite homogeneous over the merging galaxy system (V-R = 0.50.1) but exceptionally blue in the northern jet region (V-R = -0.250.2). The correspondence between the optical and X-ray jet morphology indicates their same physical origin. One can recognise a bubble like structure in the jet of 14 arcsec length (7.7 kpc) and 7 arcsec width (4. kpc) in the optical due to the better spatial resolution. While the V-R colour of this northern jet component is exceptionally blue due to the intensive [OIII] 5007 line emission the B-V colour (B-V=1.20.1) is very red on the other hand.
The two nuclei have a distance of 10.3 arcsec in the HST image as well as in our VLA radio image. This corresponds to a projected distance of 5.67 kpc. The north-eastern Liner component is more compact in all frequencies from radio (VLA), opt.(HST, ground based), UV (IUE) to X-ray (ROSAT) in comparison to the south-western Seyfert nucleus.
It has been mentioned by Mazzarella et al.(1988) and Hutchings et al.(1988) that a third VLA radio component is located in between the optical nuclei nearly exactly on the connecting line between the outer components (see Fig. 3). No counterpart of the central radio component can be detected in the X-ray image and in the HST image within a 1 arcsec radio error-box. This central radio component is located at a huge s-shaped bipolar jet-like structure extending 13.5 arcsec (7.7 kpc) to the south-east and 12.5 arcsec (7.1 kpc) to the north-west where it leads into the extended X-ray jet. The s-shaped structure is to be seen in the HST image (Fig. 3) and in the ground based [OIII]5007 image (e.g. Hutchings et al., 1988). This double structure can be recognised partly in the V-R image (Fig. 2), too. The inner jet draws to a helical structure considering the white filaments (Fig. 3).
3.2. Spectral Diagnostics and Kinematics
We took spectra with the slit in north-south direction passing the south-western nucleus and the northern jet region. Fig. 4 shows spatially resolved intensity tracings of the [OIII] 5007 line (4991-5023 Å) and the neighbouring continuum (5042-5074 Å). This pattern is typical for all emission line and continua tracings: the northern jet structure seen in the broad band images originates only from line emission; it is not present in the stellar continuum.
An integrated optical spectrum over the X-ray jet region is shown in Fig. 5. The excitation degree - derived from the line ratios HeII 4686/H and [NeIII] 3869/[OII] 3727 - is highest in the jet region (0.33 resp. 0.41) in comparison to other internal galaxy spectra (0.17 resp. 0.11). Furthermore, the intensities of the [OIII] 5007,4959 lines are exceptionally strong with respect to H and H.
Earlier observations have shown that the velocity field of Mrk 266 is highly disturbed due to the merging process (e.g. Hutchings et al., 1988; Kollatschny,1990).In Fig. 6 we present the projected gaseous velocities in north-south direction derived from the [OIII] 5007 line.
The velocities have been normalized to = 0 km s-1 at the south-western Seyfert nucleus. The velocity field in the northern jet region is decoupled from the rest of the interacting galaxy system. Furthermore, at the border of the filamentary structures (enhanced [OIII]-intensities) the velocities show a constant gradient in the same direction on both sides.
© European Southern Observatory (ESO) 1998
Online publication: July 20, 1998