3C 319


Basic Data
S178 Alpha FR Class ID Spectrum Best z mag. LAS lg P178 D
16.70.90IIR+HB Gal0.192R = 18.07 109.3026.00 298.8


Size: 256.0 × 256.0 arcsec²
LUT: Linear
Beam: 4.0 arcsec
Frequency: 1646 MHz
Method: CLEAN ՘>4.0
Telescope: VLA B+C
Credits: Leahy, Pooley & Riley (1986)

3C 319 is identified with the brightest galaxy of a cluster or group: a dozen or so other members are visible in the deep optical images of Crane, Tyson & Saslaw (1983) and Keel & Martini (1995). No quantitative measures of clustering are available but this is unlikely to be a rich cluster as there is no evidence for Faraday rotation caused by an intra-cluster medium: Leahy et al. (1986) found that the Rotation Measure was constant to better than ±4 rad m-2, around two orders of magnitude below the typical RM fluctuations found in central radio sources in Abell clusters; there is also negligible depolarization at wavelengths shorter than 21 cm (Leahy, unpublished, and compare the polarization maps at 18 cm in Leahy et al. and at 3.6 cm in Hardcastle et al 1997a). The depolarization wavelength of 20 cm listed by Tabara & Inoue (1980) is therefore in error.

Apart from the host, three other galaxies are projected within the radio lobes, but there is no sign that either the total intensity or polarization structure of the DRAGN is affected by them, so they are probably behind the lobes.

The radio structure is unusual in that although the north-east lobe has a normal hotspot at its end (seen at high resolution in the maps of Hardcastle et al), there is no sign of a hotspot or even "warmspot" at the end of the south-west lobe (which we therefore classify as relaxed). There is also no sign of a radio core. Since one of the other galaxies is projected close to the northern hotspot, it has been suggested that that is the true identification, making this a head-tail DRAGN. However, the identification with the central galaxy seems secure, based on the clear division into two lobes with a central brightness minimum (first shown by Bridle & Fomalont 1979), and the spectral index maps (Macklin 1983, Alexander & Leahy 1987) which show that both ends of the DRAGN have relatively flat spectra, with the spectrum steepening towards the centre as in typical classical doubles.

It has also been suggested (e.g. by Crane et al. 1983) that the northern optical object is not a galaxy, but synchrotron emission from the hotspot; however it is not exactly coincident with the hotspot and in any case a spectrum by Keel & Martini shows that almost certainly it is a galaxy.

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