A B S T R A C TWe present spectroscopic and polarimetric observations of a complete, optically unbiased sample of 2-Jy radio galaxies at intermediate redshifts ð0:15 , z , 0:7Þ. These data -which cover the nuclear regions of the target galaxies -allow us to quantify for the first time the various components that contribute to the UV excess in the population of powerful, intermediate-redshift radio galaxies. We find that, contrary to the results of previous surveys -which have tended to be biased towards the most luminous and spectacular objects in any redshift range -the contribution of scattered quasar light to the UV excess is relatively minor in most of the objects in our sample. Only seven objects (32 per cent of the complete sample) show significant polarization in the rest-frame UV, and none of the objects in our sample is polarized in the near-UV at the P . 10 per cent level. Careful measurement and modelling of our spectra have allowed us to quantify the contributions of other components to the UV excess. We show that nebular continuum (present in all objects at the 3 -40 per cent level), direct active galactic nucleus (AGN) light (significant in 40 per cent of objects) and young stellar populations (significant in 15 -50 per cent of objects) all make important contributions to the UV continuum in the population of powerful radio galaxies. These results serve to emphasize the multicomponent nature of the UV continuum in radio galaxies. The results also point to an interesting link between the optical/UV and far-IR properties of our sample objects, in the sense that the objects with the clearest evidence for optical/UV starburst activity are also the most luminous at far-IR wavelengths. This supports the idea that the cooler dust components in radio galaxies are heated by starbursts rather than by AGN.

We present high‐quality long‐slit spectra for three nearby powerful radio galaxies – 3C 293, 3C 305 and PKS 1345+12. These were taken with the aim of characterizing the young stellar populations (YSP), and thereby investigating the evolution of the host galaxies, as well as the events that triggered the activity. Isochrone spectral synthesis modelling of the wide wavelength coverage spectra of nuclear and off‐nuclear continuum‐emitting regions have been used to estimate the ages, masses and luminosities of the YSP component, taking full account of reddening effects and potential contamination by activity‐related components. We find that the YSP make a substantial contribution to the continuum flux in the off‐nuclear regions on a radial scale of 1–20 kpc in all three objects. Moreover, in two objects we find evidence for reddened post‐starburst stellar populations in the near‐nuclear regions of the host galaxies. The YSP are relatively old (0.1–2 Gyr), massive (109 < MYSP < 2 × 1010 M⊙) and make up a large proportion (∼1–50 per cent) of the total stellar mass in the regions of the galaxies sampled by the observations. Overall, these results are consistent with the idea that the nuclear activity of active galactic nuclei in some radio galaxies is triggered by major gas‐rich mergers. Therefore, these radio galaxies form part of the subset of early‐type galaxies that is evolving most rapidly in the local Universe. Intriguingly, the results also suggest that the radio jets are triggered relatively late in the merger sequence, and that there is an evolutionary link between radio galaxies and luminous/ultraluminous infrared galaxies.

We use a combination of high spatial resolution optical and near‐infrared spectroscopic data to make a detailed study of the kinematics of the narrow‐line region (NLR) gas in the near‐nuclear regions of the powerful, FRII radio galaxy Cygnus A (z= 0.0560), with the overall goal of placing limits on the mass of any supermassive black hole in the core. Our K‐band infrared observations (0.75‐arcsec seeing) – taken with NIRSPEC on the Keck II telescope – show a smooth rotation pattern across the nucleus in the Paα and H2 emission lines along a slit position (PA180°) close to perpendicular to the radio axis, however, there is no evidence for such rotation along the radio axis (PA105°). Higher spatial resolution observations of the [O iii]λ5007 emission line – taken with STIS on the Hubble Space Telescope (HST) – confirm the general rotation pattern of the gas in the direction perpendicular to the radio axis, and provide evidence for steep velocity gradients within a radius of 0.1 arcsec of the core – corresponding to the high surface brightness structure visible in high‐resolution narrow‐band images. The [O iii] line remains broad throughout the core region (FWHM ∼ 300–900 km s−1), but the spatial distribution of [O iii] provides no evidence for an unresolved inner narrow‐line region (INLR). Assuming that the ionized gas is circularly rotating in a thin disc and that the large linewidths are due to activity‐induced turbulence, the circular velocities measured from both the Keck and HST data lead to an estimate of the mass of the supermassive black hole of 2.5 ± 0.7 × 109 M⊙. For the host galaxy properties of Cygnus A, this mass is consistent with the global correlations between black hole mass and host galaxy properties deduced for non‐active galaxies. Therefore, despite the extreme power of its radio source and the quasar‐like luminosity of its active galactic nucleus (AGN), the black hole in Cygnus A is not unusually massive considering the luminosity of its host galaxy. Indeed, the estimated mass of the black hole in Cygnus A is similar to that inferred for the supermassive black hole in the FRI radio galaxy M87, despite the fact that the AGN and radio jets of Cygnus A are two to three orders of magnitude more powerful. Overall, these results are consistent with the idea that the properties and powers of the AGN in radio galaxies are determined as much by the mass accretion rates as by the absolute masses of their supermassive black holes. As well as providing evidence for a supermassive black hole in the core of Cygnus A, our data also demonstrate that nuclear activity has an important effect on the kinematics of the circumnuclear gas on a subkiloparsec scale. Most notably, the velocity offsets measured in the two outer HST/STIS slit positions are consistent with the presence of an activity‐induced outflow in the NW cone.

We present spectroscopic observations of a complete sub-sample of 13 low-luminosity radio galaxies selected from the 2Jy sample. The underlying continuum in these sources is carefully modelled in order to make a much-needed comparison between the emission line and continuum properties of FRIs with those of other classes of radio sources. We find that 5 galaxies in the sample show a measurable UV excess: 2 of the these sources are BL Lacs and in the remaining 3 galaxies we argue that the most likely contributor to the UV excess is a young stellar component. Excluding the BL Lacs, we therefore find that \~30% of the sample show evidence for young stars, which is similar to the results obtained for higher luminosity samples. We compare our results with far-infrared measurements in order to investigate the far-infrared-starburst link. The nature of the optical-radio correlations is investigated in light of this new available data and, in contrast to previous studies, we find that the FRI sources follow the correlations with a similar slope to that found for the FRIIs. Finally, we compare the luminosity of the emission lines in the FRI and BL Lac sources and find a significant difference in the [OIII] line luminosities of the two groups. Our results are discussed in the context of the unified schemes.Comment: 18 pages, 31 figures, MNRAS in press, (all enquiries to Clive Tadhunter (c.tadhunter@sheffield.ac.uk)

A B S T R A C TWe present VLA A-array 21-cm atomic hydrogen (H i) absorption observed against the central region of the starburst galaxy M82 with an angular resolution of ,1.3 arcsec (.20 pc). These observations, together with MERLIN H i absorption measurements, are compared with the molecular (CO) and ionized ([Ne ii]) gas distributions and are used to constrain the dynamics and structure of the ionized, neutral and molecular gas in this starburst.A position±velocity diagram of the H i distribution reveals an unusual`hole' feature which, when previously observed in CO, has been interpreted as an expanding superbubble contained within a ring of gas in solid body rotation. However, we interpret this feature as a signature of a nearly edge-on barred galaxy. In addition, we note that the CO, H i and [Ne ii] position±velocity diagrams reveal two main velocity gradients, and we interpret these as gas moving on x 1 -and x 2 -orbits within a bar potential. We find the best fit to the data to be produced using a bar potential with a flat rotation curve velocity v b 140 km s 21 and a total length of 1 kpc, a non-axisymmetry parameter q 0X9Y an angular velocity of the bar V b 217 km s 21 arcsec 21 Y a core radius R c 25 pcY an inclination angle i 808 and a projected angle between the bar and the major axis of the galaxy f H 48X We also discuss the orientation of the disc and bar in M82.