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Astron. Astrophys. 349, 381-388 (1999)

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1. Introduction

Wide-angle tail radio galaxies are an interesting sub-class of the population of FRI (Fanaroff & Riley 1974) objects, which typically lie at the centres of clusters and show narrow, well-collimated jets which flare abruptly into broad, diffuse plumes. Their radio power is normally intermediate between the more typical jet-dominated FRI and the `classical double' FRII classes of extragalactic radio source, and an understanding of their dynamics is important to our knowledge of the relationships between these two classes and the possible evolution between them.

In an earlier paper (Hardcastle 1998, hereafter Paper I) I presented new radio maps of the wide-angle tail radio galaxy 3C 130 ([FORMULA]). Two-frequency spectral index mapping in that paper showed flat-spectrum jets (in this paper, the term is reserved for the narrow, well-collimated features seen in the inner 50 kpc of the sources) and a hotspot (a compact, sub-kpc feature at the end of the northern jet) together with steeper-spectrum material at the edges of the plumes (the broader, more diffuse features seen between 50 and [FORMULA] kpc from the nucleus). This steep-spectrum material is particularly clear in the southern plume, and is referred to here as a `sheath', although I emphasise that, unlike the sheaths seen in some twin-jet FRI radio galaxies, this region has no polarization properties to distinguish it from the rest of the plume. The sheath is the only feature of the two-point radio spectrum which is not obviously consistent with a fairly simple model for the source's dynamics, in which particles are accelerated at the base of the plumes and the spectral steepening along the plumes is a consequence of outflow of an ageing electron population. The additional data presented here show that the situation is more complicated than that simple model would imply.

B1950 co-ordinates are used throughout this paper, and spectral index [FORMULA] is defined in the sense [FORMULA].

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© European Southern Observatory (ESO) 1999

Online publication: September 2, 1999