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Astron. Astrophys. 333, 13-16 (1998)

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2. Observations

We observed Mkn 6 with the 8-element MERLIN array (Wilkinson 1992), including the Lovell telescope; the results are summarised in Fig. 1. The observations were tuned to the 1420 MHz hyperfine transition of H I centered near the Doppler velocity [FORMULA]  km s-1 (heliocentric, optical convention). The systemic velocity of the host galaxy is actually [FORMULA]  km s-1 (Meaburn et al. 1989), well within the observed bandwidth. The velocity resolution of the observations is 26.4 km s-1, and, after removing end channels with poor frequency response, the effective bandwidth is [FORMULA] 6.6 MHz (1400 km s-1).

[FIGURE] Fig. 1. Results of the H I absorption experiment. The uniformly weighted, 21 cm continuum image is displayed as contours over greyscale. The white circle indicates the location of the AGN according to the alignment of Capetti et al. (1995). The naturally weighted spectra towards each bright component of the radio jet are displayed as overlays. H I absorption is clearly detected towards component 6, but a search over the data cube reveals no other significant absorption. The continuum contour levels, in mJy beam-1, are: [FORMULA] ([FORMULA]), 1.2, 2.9, 6.8, 15.9, and 37.3 (logarithmic scaling). The restoring beam dimensions are: natural weight, [FORMULA], P.A. [FORMULA] ; and uniform weight, [FORMULA], P.A. [FORMULA].

Data reduction followed standard techniques employed for MERLIN data, including initial calibration and processing with software local to Jodrell Bank. Further data processing, including self-calibration against line-free continuum channels, was performed within the AIPS data reduction package. Channel maps and line-free continuum images were produced following standard numerical Fourier transform techniques and deconvolution using the CLEAN algorithm (Högbom 1974). A more detailed description of the MERLIN data reduction techniques employed can be found in Mundell et al. (1995).

We constructed both naturally and uniformly weighted spectral line cubes. Continuum images were generated by averaging over channels with no significant line detections. For the naturally weighted images, the restoring beam dimensions (FWHM) are [FORMULA], P.A. [FORMULA], and the respective continuum and spectral line sensitivities are 0.13 mJy beam-1 and 0.68 mJy beam-1 ([FORMULA]). The resolution of the uniformly weighted images is [FORMULA], P.A. [FORMULA], and the continuum and spectral line sensitivities are 0.19 mJy beam-1 and 1.2 mJy beam-1.

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© European Southern Observatory (ESO) 1998

Online publication: April 15, 1998