The environment and dynamics of the radio galaxy NGC 6251

This thesis is primarily a case study of the low-power radio galaxy NGC 6251. New radio (VLA), optical imaging (KPNO), optical spectroscopy (MMTO) and X-ray (Chandra) data are complemented with existing HST, ROSAT and ASCA results to give a comprehensive multi-wavelength overview of this spectacular source on different size scales. On the large scale, the gravity field is probed by measuring the velocity dispersion of the cluster members associated with NGC 6251 and relating this to the cluster's X-ray emission. The cluster is found to be a poor one, and the X-ray-emitting gas confined within is consequently cool. Potential optical and X-ray jet detections are discussed, and spectral distributions of three jet knots are modeled. The results suggest that synchrotron radiation most convincingly explains the radio to X-ray spectrum. The issue of the dynamics of the host galaxy and their relation to the radio structure is briefly discussed, but proves largely inconclusive, due to observational limitations. To probe the inner regions of NGC 6251, L-band spectral line radio observations are analysed, and show 21 cm neutral hydrogen absorption against the continuum of the galactic core. The HI spectrum shows a rare double-peaked absorption profile straddling the systemic velocity of the galaxy, suggesting the existence of both infalling and outflowing components. It is shown that the amount of infalling gas is more than enough to fuel the central engine of the AGN by accretion. Two models are proposed to account for the outflow, including an outflowing 'wind' that explains both the HI absorption component and the blue-shifted optical-line-emitting gas. The technique of using optical spectroscopic observations to probe cluster environments is also applied to the low-power radio galaxy NGC 326. The measured velocity dispersion is found to be consistent with the X-ray temperature of the cluster dominated by NGC 326. (author)