C. N. Tadhunter

Fast neutral outflows in powerful radio galaxies : a major source of feedback in massive galaxies

We report the detection of fast (similar to 1000 km s(-1)), massive outflows of neutral gas observed - using the WSRT - as 21- cm H), Hi absorption against the strong radio continuum of seven radio sources. The neutral outflows occur, in at least somes cases, at kpc distance from the nucleus, and they are most likely driven by the interactions between the expanding radio jets and the gaseous medium enshrouding the central regions. We estimate that the associated mass outflow rates are up to similar to 50 M(circle dot)yr(-1), comparable ( although at the lower end of the distribution) to the outflow, rates found for starburst- driven superwinds in Ultra Luminous IR Galaxies ( ULIRG). This suggests that massive, jet- driven outflows of neutral gas in radio- loud AGN can have as large an impact on the evolution of the host galaxies as the outflows associated with starbursts. A radio- loud phase of the AGN is likely a relatively common, albeit short, phase in the life of many ( or even all) massive ellipticals. Jet- driven neutral outflows may represent one of the main feedback mechanisms in these galaxies.

Fast outflows in compact radio sources: evidence for AGN-induced feedback in the early stages of radio source evolution

We present intermediate-resolution, wide-wavelength coverage spectra for a complete sample of 14 compact radio sources taken with the aim of investigating the impact of the nuclear activity on the circumnuclear interstellar medium (ISM) in the early stages of radio source evolution. We observe spatially extended line emission (up to ∼20 kpc) in the majority of sources which is consistent with a quiescent halo. In the nuclear apertures we observe broad, highly complex emission-line profiles. Multiple Gaussian modelling of the [O III]λ5007 line reveals between two and four components which can have velocity widths [full width at halfmaximum (FWHM)] and blueshifts relative to the halo of up to ∼2000 km s −1 . We interpret these broad, blueshifted components as material in outflow and discuss the kinematical evidence for jet-driven outflows as previously proposed for PKS 1549−79 and PKS 1345+12. Comparisons with samples in the literature show that compact radio sources harbour more extreme nuclear kinematics than their extended counterparts, a trend seen within our sample with larger velocities in the smaller sources. The observed velocities are also likely to be influenced by source orientation with respect to the observer’s line of sight. Nine sources have associated H I absorption. In common with the optical emission-line gas, the H I profiles are often highly complex with the majority of the detected components significantly blueshifted, tracing outflows in the neutral gas. The sample has been tested for stratification in the ISM (FWHM/ionization potential/critical density) as suggested by Holt, Tadhunter & Morganti for PKS 1345+12 but we find no significant trends within the sample using a Spearman rank analysis. This study supports the idea that compact radio sources are young radio-loud active galactic nuclei observed during the early stages of their evolution and currently shedding their natal cocoons through extreme circumnuclear outflows.

Starbursts and the triggering of the activity in nearby powerful radio galaxies

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.

The origin of the UV excess in powerful radio galaxies: spectroscopy and polarimetry of a complete sample of intermediate-redshift radio galaxies

We present spectroscopic and polarimetric observations of a complete, optically unbiased sample of 2-Jy radio galaxies at intermediate redshifts (0.15 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.

Spectroscopy of the near-nuclear regions of Cygnus A: estimating the mass of the supermassive black hole

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, FRIIradio 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 Paa and H 2 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 IH] 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 x 10 9 M O .. 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.

Highly extinguished emission line outflows in the young radio source PKS 1345+12

We present intermediate resolution, large wavelength coverage spectra for the compact radio source PKS 1345+12 (4C 12.50, z = 0.122) that were taken with the aim of investigating the impact of the nuclear activity on thecircumnuclear interstellar medium (ISM). Our spectra show extended line emission up to ∼20 kpc from the nucleus, consistent with the asymmetric halo of diffuse emission observed in optical and infrared images. At the position of the nucleus we observe complex emission line profiles and Gaussian fits to the [O III] emission lines require three components (narrow, intermediate and broad), the broadest of which has width ∼2000 km s - 1 (FWHM) and is blueshifted by ∼2000 km s - 1 with respect to the halo of the galaxy and HI absorption. We interpret this latter component as material in outflow. We also find evidence for large reddening [0.92 4200 cm - 3 ) for the most kinematically disturbed component. The corresponding total mass of line-emitting gas in the kinematically disturbed components is M g a s < 10 6 M O .. Not all emission line profiles can be reproduced by the same model: [OI]λλ6300, 6363 and [SII]λλ6716, 6731 require separate, unique models. We argue that PKS 1345+12 is a young radio source with nuclear regions that are enshrouded in a dense cocoon of gas and dust. The radio jets are expanding through this cocoon, sweeping material out of the nuclear regions. Emission originates from three kinematically distinct regions, though gradients (e.g. in density, ionization potential, velocity) must exist across the regions responsible for the emission of the intermediate and broad components.

PKS 2250—41 and the role of jet-cloud interactions in powerful radio galaxies

We have studied the effects of the interaction between the radio jet and the ambient gas in the powerful radio galaxy PKS2250-41 (z = 0.31). Our results show that the gas has been accelerated, compressed, heated and collisionally ionized by the shock. This study helps us to understand the processes which determine the observed properties of many high redshift radio galaxies.

The co-evolution of the obscured quasar PKS 1549−79 and its host galaxy: evidence for a high accretion rate and warm outflow

We use deep optical, infrared and radio observations to explore the symbiosis between nuclear activity and galaxy evolution in the southern compact radio source PKS 1549-79 (z = 0.1523). The optical imaging observations reveal the presence of tidal tail features which provide strong evidence that the host galaxy has undergone a major merger in the recent past. The merger hypothesis is further supported by the detection of a young stellar population (YSP), which, on the basis of spectral synthesis modelling of our deep Very Large Telescope (VLT) optical spectra, was formed 50-250 Myr ago and makes up a significant fraction of the total stellar mass (1-30 per cent). Despite the core-jet structure of the radio source, which is consistent with the idea that the jet is pointing close to our line of sight, our HI 21-cm observations reveal significant HI absorption associated with both the core and the jet. Moreover, the luminous, quasar-like active galactic nucleus (AGN) (MV 6.4) at optical wavelengths and show many properties in common with narrow-line Seyfert 1 galaxies (NLS1), including relatively narrow permitted lines [ full width at half-maximum (FWHM) similar to 1940 km s(-1)], highly blueshifted [O III]lambda lambda 5007,4959 lines (Delta V similar to 680 km s(-1)) and evidence that the putative supermassive black hole is accreting at a high Eddington ratio (0.3 3000 K.

The location of the broad HI absorption in 3C 305: clear evidence for a jet-accelerated neutral outflow

We present high-spatial resolution 21-cm HI VLA observations of the radio galaxy 3C 305 ( z = 0.041). These new high-resolution data show that the similar to 1000 km s(-1) broad H. absorption, earlier detected in low-resolution WSRT observations, is occurring against the bright, eastern radio lobe, about 1.6 kpc from the nucleus. We use new optical spectra taken with the WHT to make a detailed comparison of the kinematics of the neutral hydrogen with that of the ionised gas. The striking similarity between the complex kinematics of the two gas phases suggests that both the ionised gas and the neutral gas are part of the same outflow. Earlier studies of the ionised gas had already found evidence for a strong interaction between the radio jet and the interstellar medium at the location of the eastern radio lobe. Our results show that the fast outflow produced by this interaction also contains a component of neutral atomic hydrogen. The most likely interpretation is that the radio jet ionises the ISM and accelerates it to the high outflow velocities observed. Our observations demonstrate that, following this strong jet-cloud interaction, not all gas clouds are destroyed and that part of the gas can cool and become neutral. The mass outflow rate measured in 3C 305 is comparable, although at the lower end of the distribution, to that found in Ultra-Luminous IR galaxies. This suggests that AGN-driven outflows, and in particular jet-driven outflows, can have a similar impact on the evolution of a galaxy as starburst-driven superwinds.

STRONG MOLECULAR HYDROGEN EMISSION AND KINEMATICS OF THE MULTIPHASE GAS IN RADIO GALAXIES WITH FAST JET-DRIVEN OUTFLOWS

Observations of ionized and neutral gas outflows in radio galaxies (RGs) suggest that active galactic nucleus (AGN) radio jet feedback has a galaxy-scale impact on the host interstellar medium, but it is still unclear how the molecular gas is affected. Thus, it is crucial to determine the physical conditions of the molecular gas in powerful RGs to understandhowradiosourcesmayregulatethestarformationintheirhostgalaxies.WepresentdeepSpitzerInfrared Spectrograph (IRS) high-resolution spectroscopy of eight nearby RGs that show fast Hi outflows. Strikingly, all of these Hi-outflow RGs have bright H2 mid-IR lines that cannot be accounted for by UV or X-ray heating. This strongly suggests that the radio jet, which drives the Hi outflow, is also responsible for the shock excitation of the warm H2 gas. In addition, the warm H2 gas does not share the kinematics of the ionized/neutral gas. The mid-IR-ionized gas lines (with FWHM up to 1250 km s −1 for [Neii]12.8 μm) are systematically broader than the H2 lines, which are resolved by the IRS in ≈60% of the detected lines (with FWHM up to 900 km s −1 ). In five sources, 3C 236, 3C 293, 3C 459, 4C 12.50, and PKS 1549-79, the [Neii]12.8 μm line, and to a lesser extent the [Neiii]15.5 μm and [Nev]14.3 μm lines, clearly exhibits blueshifted wings (up to −900 km s −1 with respect to the systemic velocity) that match well the kinematics of the outflowing Hi or ionized gas. The H2 lines do not show these broad wings, except tentative detections in 4C 12.50, 3C 459, and PKS 1549-79. This shows that, contrary to the Hi gas, the H2 gas is inefficiently coupled to the AGN jet-driven outflow of ionized gas. While the dissipation of a small fraction (<10%) of the jet kinetic power can explain the turbulent heating of the molecular gas, our data show that the bulk of the warm molecular gas is not expelled from these galaxies.