A spectroscopic study of NGC 6251 and its companion galaxies
Abstract
Measurements of the velocities of galaxies thought to be associated with the giant radio galaxy NGC 6251 confirm the presence of a poor cluster with a systemic redshift of z= 0.0244 +/- 0.0004 and a line-of-sight velocity dispersion of sigmaz= 283 (+109, -52) km/s. This suggests a cluster atmosphere temperature of T = 0.7 (+0.6, -0.2) keV, which is not enough to confine the radio jet by gas pressure. The core of NGC 6251 shows strong emission lines of [O III] and H alpha + [N II], but there is no evidence for line emission from the jet (detected in optical continuum by Keel (1988)).
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