NGC 6251


Basic Data
S178 Alpha FR Class ID Spectrum Best z mag. LAS lg P178 D
10.90.72IWB+HP Gal0.024R = 11.663940.0023.981758.0


Size: 5100.0 × 5100.0 arcsec²
LUT: Logarithmic
Beam: 55 arcsec
Frequency: 327 MHz
Method: CLEAN ՘>55
Telescope: WSRT
Credits: Mack et al. (1996)

At just over one degree across, NGC 6251 is the largest known DRAGN in the northern sky. It was missed in 3CR and other early radio surveys because its radio emission was too spread out to be identified as a single object. Our Westerbork image shows dozens of background radio sources within and around the twin lobes of NGC 6251 itself. Most of these are distant DRAGNs at much higher redshift.

The brightest part of NGC 6251 is its one-sided jet, which has been studied in detail at much higher resolution by Perley, Bridle & Willis (1984). The host galaxy, NGC 6251 proper, is located at the eastern end of the jet. A very faint counterjet is also just visible.

This relatively nearby and very bright example provides a useful test of our understanding of how radio jets work. Perley et al. concluded that the jet is confined into its narrow channel by the pressure of the hot interstellar gas of the galaxy. Recently a deep X-ray observation by Birkinshaw & Worrall (1993) showed that there is much less gas present than is needed, so we still have work to do on this point!

The structure is intermediate between tailed and bridged twin-jets, which the western lobe surrounding the jet (i.e. a bridge) but the eastern lobe apparently beginning at the "warmspot" which marks the end of the eastern jet. The northern lobe also contains a relatively compact "warmspot" so this object also seems to be an "almost" classical double.

The apparent faint emission in the top left and bottom right corner of this image is an artifact due to imperfect deconvolution.

A higher-resolution 608 MHz image is on the Other Images page; it suffers from the same artifacts as the main image, as well as striping paralled to the jet.

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Page created: 2009 Apr 2 14:16:43
J. P. Leahy