FRII radio galaxies with z < 0.3 - I. Properties of jets, cores and hotspots

Abstract

In previous papers we have discussed high-resolution observations of a large sample of powerful radio galaxies with z < 0.3. Jets are detected in up to 80 per cent of the sample, and radio cores in nearly all the objects; in addition, we are able to resolve the hotspots in most sources. In this paper we present measurements of the radio properties of these components.The prominences of the jets detected do not appear to be a function of radio luminosity, providing the clearest evidence yet that the reported low detection rate of jets in radio galaxies has been an artefact of low-sensitivity observations. We find a positive correlation between the total source length and core prominence in the narrow-line radio galaxies. We have found evidence for a relationship between hotspot size and total source size, but few other significant relationships between hotspot properties and those of the jets or lobes. We compare our measurements with those of Bridle et al., based on observations of a sample of quasars, and argue that the results are consistent with a modification of the unified model in which the broad-line radio galaxies are the low-luminosity counterparts of quasars, although the situation is complicated by contamination with low-excitation radio galaxies which appear to have radio properties different from the high-excitation objects. We discuss the classes of empirical model that can be fitted to the data set.

Broad-line radio galaxies: Old and feeble?

“…In line with trends reported by Hardcastle et al (1998), some BLRGs such as superluminal, cool 3C 111 and optically variable, hot 3C 390.3 are undoubtedly low-power QSRs, observed at small inclination angles. Cohen et al (1999) and Dennett-Thorpe et al (2000) however point out that other BLRGs must be identified with critically inclined QSRs, i.e., radio sources observed close to or through their torus boundary.…”

The Bologna complete sample of nearby radio sources

“…On kiloparsec scales, 3C 98 shows a double-lobe FRII radio structure which spans 216 arcsec at 8.35 GHz, with a radio jet that crosses the northern lobe and terminates in a bright hotspot. There is little evidence of a southern jet, but a twin hotspot in the southern lobe is present (Hardcastle et al 1998). The core of this symmetric FRII radio galaxy is pointlike in our VLBI image, with the total flux density ∼2.2 mJy.…”

“…Because of the optical identification this source will not be considered in the following discussion. 0802+24 (3C 192) -On large scale, this radio source shows an "X" symmetric double-lobe structure which extends ∼200 arcsec at 8.35 GHz, showing bright hotspots at the end of the lobes (Baum et al 1988;Hardcastle et al 1998).…”

Dust tori in radio galaxies

“…High resolution radio images for all but one object, 3C 403.1, were available. All relevant optical spectroscopic classifications are extracted from Jackson & Rawlings (1997), Hardcastle et al (1998Hardcastle et al ( , 1999, and Morganti et al (1997). We note that BLRG 3C 120 differs from the rest of the selected BLRG subsample, since it is strongly core-dominated and has a FR-I morphology.…”