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The jets of radio AGN provide one of the most important forms of active galactic nuclei (AGN) feedback, yet considerable uncertainties remain about how they are triggered. Since the molecular gas reservoirs of the host galaxies can supply key information about the dominant triggering mechanism(s), here we present Atacama Large Millimeter/sub-millimeter Array CO(1-0) observations of a complete sample of 29 powerful radio AGN (⁠|$P_{1.4\,{\rm GHz}} \gt 10^{25}$|  W Hz |$^{-1}$| and |$0.05 \lt z \lt 0.3$|⁠) with an angular resolution of about 2–3 arcsec (corresponding to 2–8 kpc). We detect molecular gas with masses in the range |$10^{8.9} \lt M_{{\rm H}_2} \lt 10^{10.2}$| M |$_\odot$| in the early-type host galaxies of ten targets, while for the other 19 sources, we derive upper limits. The detection rate of objects with such large molecular masses – |$34\pm 9$|  per cent – is higher than in the general population of non-active early-type galaxies (ETGs: |$\lt $| 10 per cent). The kinematics of the molecular gas are dominated in most cases by rotating disc-like structures, with diameters up to 25 kpc. Compared with the results for samples of quiescent ETG in the literature, we find a larger fraction of more massive, more extended and less settled molecular gas structures. In most of the CO-detected sources, the results are consistent with triggering of the AGN as the gas settles following a merger or close encounter with a gas-rich companion. However, in a minority of objects at the centres of rich clusters of galaxies, the accretion of gas cooling from the hot X-ray haloes is a plausible alternative to galaxy interactions as a triggering mechanism. [ABSTRACT FROM AUTHOR]

The triggering mechanism for the most luminous, quasar-like active galactic nuclei (AGN) remains a source of debate, with some studies favouring triggering via galaxy mergers, but others finding little evidence to support this mechanism. Here, we present deep Isaac Newton Telescope/Wide Field Camera imaging observations of a complete sample of 48 optically selected type 2 quasars – the QSOFEED sample (⁠|$L_{\rm [O\, \small {III}]}\gt 10^{8.5}\, \mathrm{L}_{\odot }$|⁠ ; z < 0.14). Based on visual inspection by eight classifiers, we find clear evidence that galaxy interactions are the dominant triggering mechanism for quasar activity in the local universe, with 65 |$^{+6}_{-7}$|  per cent of the type 2 quasar hosts showing morphological features consistent with galaxy mergers or encounters, compared with only 22 |$^{+5}_{-4}$|  per cent of a stellar-mass- and redshift-matched comparison sample of non-AGN galaxies – a 5σ difference. The type 2 quasar hosts are a factor of 3.0 |$^{+0.5}_{-0.8}$| more likely to be morphologically disturbed than their matched non-AGN counterparts, similar to our previous results for powerful 3CR radio AGN of comparable [O  iii ] emission-line luminosity and redshift. In contrast to the idea that quasars are triggered at the peaks of galaxy mergers as the two nuclei coalesce, and only become visible post-coalescence, the majority of morphologically disturbed type 2 quasar sources in our sample are observed in the pre-coalescence phase (61 |$^{+8}_{-9}$|  per cent). We argue that much of the apparent ambiguity that surrounds observational results in this field is a result of differences in the surface brightness depths of the observations, combined with the effects of cosmological surface brightness dimming. [ABSTRACT FROM AUTHOR]

The far-IR/sub-mm wavelength range contains a wealth of diagnostic information that is important for understanding the role of active galactic nuclei (AGN) in galaxy evolution. Here we present the results of Herschel PACS and SPIRE observations of a complete sample of 46 powerful 2 Jy radio AGN at intermediate redshifts (0.05 < z < 0.7), which represent the deepest pointed observations of a major sample of radio AGN undertaken by Herschel. In order to assess the importance of non-thermal synchrotron emission at far-IR wavelengths, we also present new APEX sub-mm and ALMA mm data. We find that the overall incidence of non-thermal contamination in the PACS bands (<200  μ m) is in the range 28–43 per cent; however, this rises to 30–72 per cent for wavelengths (>200  μ m) sampled by the SPIRE instrument. Non-thermal contamination is strongest in objects with compact CSS/GPS or extended FRI radio morphologies, and in those with type 1 optical spectra. Considering thermal dust emission, we find strong correlations between the 100 and 160  μ m monochromatic luminosities and AGN power indicators, providing further evidence that radiation from the AGN may be an important heating source for the far-IR emitting dust. Clearly, AGN contamination – whether by the direct emission from synchrotron-emitting lobes and cores, or via radiative heating of the cool dust – needs to be carefully considered when using the far-IR continuum to measure the star formation rates in the host galaxies of radio AGN. [ABSTRACT FROM AUTHOR]

We use deep Herschel observations of the complete 2Jy sample of powerful radio active galactic nuclei (AGNs) in the local Universe (0.05 <  z  < 0.7) to probe their cool interstellar medium (ISM) contents and star-forming properties, comparing them against other samples of nearby luminous AGNs and quiescent galaxies. This allows us to investigate triggering and feedback mechanisms. We find that the dust masses of the strong-line radio galaxies (SLRGs) in our sample are similar to those of radio-quiet quasars, and that their median dust mass (M dust = 2 × 107 M⊙) is enhanced by a factor of ∼200 compared to that of non-AGN ellipticals, but lower by a factor of ∼16 relative to that of local ultraluminous infrared galaxies (ULIRGs). Along with compelling evidence for merger signatures in optical images, the SLRGs in our sample also show relatively high star formation efficiencies, despite the fact that many of them fall below the main sequence for star-forming galaxies. Together, these results suggest that most of our SLRGs have been retriggered by late-time mergers that are relatively minor in terms of their gas contents. In comparison with the SLRGs, the radio AGNs with weak optical emission lines (weak-line radio galaxies – WLRGs) and edge-darkened radio jets (Fanaroff–Riley Class I radio sources – FRIs) have both lower cool ISM masses and star formation rates (by a factor of >30), consistent with being fuelled by a different mechanism (e.g. the direct accretion of hot gas). [ABSTRACT FROM AUTHOR]

Investigation of the triggering mechanisms of radio active galactic nuclei (radio AGN) is important for improving our general understanding of galaxy evolution. In the first paper in this series, detailed morphological analysis of high-excitation radio galaxies (HERGs) with intermediate radio powers suggested that the importance of triggering via galaxy mergers and interactions increases strongly with AGN radio power and weakly with optical emission-line luminosity. Here, we use an online classification interface to expand our morphological analysis to a much larger sample of 155 active galaxies (3CR radio galaxies, radio-intermediate HERGs, and Type 2 quasars) that covers a broad range in both 1.4 GHz radio power and [O  iii ] λ5007 emission-line luminosity. All active galaxy samples are found to exhibit excesses in their rates of morphological disturbance relative to 378 stellar-mass- and redshift-matched non-active control galaxies classified randomly and blindly alongside them. These excesses are highest for the 3CR HERGs (4.7σ) and Type 2 quasar hosts (3.9σ), supporting the idea that galaxy mergers provide the dominant triggering mechanism for these subgroups. When the full active galaxy sample is considered, there is clear evidence to suggest that the enhancement in the rate of disturbance relative to the controls increases strongly with [O  iii ] λ5007 emission-line luminosity but not with 1.4 GHz radio power. Evidence that the dominant AGN host types change from early-type galaxies at high radio powers to late-type galaxies at low radio powers is also found, suggesting that triggering by secular, disc-based processes holds more importance for lower-power radio AGN. [ABSTRACT FROM AUTHOR]

Measuring the star-forming properties of active galactic nucleus (AGN) hosts is key to our understanding of galaxy formation and evolution. However, this topic remains debated, partly due to the difficulties in separating the infrared (i.e. 1–1000  |${\rm \mu m}$|⁠) emission into AGN and star-forming components. Taking advantage of archival far-infrared data from Herschel , we present a new set of AGN and galaxy infrared templates and introduce the spectral energy distribution fitting code iragnsep. Both can be used to measure infrared host galaxy properties, free of AGN contamination. To build these, we used a sample of 100 local (z  < 0.3), low-to-high luminosity AGNs (i.e. L bol |$\ \sim \ 10^{42-46}$|  erg s−1), selected from the 105-month Swift –BAT X-ray survey, which have archival Spitzer –IRS spectra and Herschel photometry. We first built a set of seven galaxy templates using a sample of 55 star-forming galaxies selected via infrared diagnostics. Using these templates, combined with a flexible model for the AGN contribution, we extracted the intrinsic infrared emission of our AGN sample. We further demonstrate that we can reduce the diversity in the intrinsic shapes of AGN spectral energy distributions down to a set of three AGN templates, of which two represent AGN continuum, and one represents silicate emission. Our results indicate that, on average, the contribution of AGNs to the far-infrared (λ ≳ 50  |${\rm \mu m}$|⁠) is not as high as suggested by some recent work. We further show that the need for two infrared AGN continuum templates could be related to nuclear obscuration, where one of our templates appears dominated by the emission of the extended polar dust. [ABSTRACT FROM AUTHOR]

Considerable uncertainties remain about the nature of warm, AGN-driven outflows and their impact on the evolution of galaxies. This is because the outflows are often unresolved in ground-based observations. As part of a project to study the AGN outflows in some of the most rapidly evolving galaxies in the local Universe, here we present Hubble Space Telescope (HST)/ Space Telescope Imaging Spectrograph (STIS) observations of F14394+5332E that resolve the sub-kpc warm outflow for the first time in an ultra-luminous infrared galaxy. The observations reveal a compact, high-ionization outflow region (r max ∼ 0.9 kpc) set in a more extensive (r max ∼ 1.4 kpc) halo that is kinematically quiescent and has a lower ionization state. A large line width (600 < FWHM < 1500 km s−1) is measured throughout the outflow region, and the outflowing gas shows a steep velocity gradient with radius, with the magnitude of the blueshifted velocities increasing from ∼500 to 1800 km s−1 from the inner to the outer part of the outflow. We interpret the observations in terms of the local acceleration, and hydrodynamic destruction, of dense clouds as they are swept up in a hot, low-density wind driven by the AGN. We discuss the implications for measuring the mass outflow rates and kinetic powers for the AGN-driven outflows in such objects. [ABSTRACT FROM AUTHOR]

Active galactic nuclei (AGNs) with intermediate radio powers are capable of driving multiphase outflows in galaxy bulges, and are also more common than their high-radio-power counterparts. In-depth characterization of the typical host galaxies and likely triggering mechanisms for this population is therefore required in order to better understand the role of radio AGN feedback in galaxy evolution. Here, we use deep optical imaging data to study the detailed host morphologies of a complete sample of 30 local radio AGNs with high-excitation optical emission (HERG) spectra and intermediate radio powers [ z < 0.1; 22.5 < log(⁠|$L_{\rm 1.4GHz}$|⁠) < 24.0 W Hz-1]. The fraction of hosts with morphological signatures of mergers and interactions is greatly reduced compared to the 2Jy radio-powerful galaxies [log(⁠|$L_{\rm 1.4GHz}$|⁠) > 25.0 W Hz-1] with strong optical emission lines: 53 ± 9 per cent compared with 94 ± 4 per cent. In addition, the most radio-powerful half of the sample has a higher frequency of morphological disturbance than the least radio-powerful half (67 ± 12 per cent and 40 ± 13 per cent, respectively), including the eight most highly disturbed galaxies. This suggests that the importance of triggering nuclear activity in high-excitation radio galaxies (HERGs) through mergers and interactions reduces with radio power. Both visual inspection and detailed light profile modelling reveal a mixed population of early-type and late-type morphologies, contrary to the massive elliptical galaxy hosts of radio-powerful AGNs. The prevalence of late-type hosts could suggest that triggering via secular, disc-based processes has increased importance for HERGs with lower radio powers (e.g. disc instabilities and large-scale bars). [ABSTRACT FROM AUTHOR]

Based on new near-infrared spectroscopic data from the instrument Espectrógrafo Multiobjeto Infra-Rojo (EMIR) on the 10.4 m Gran Telescopio Canarias, we report the presence of an ionized and warm molecular outflow in the luminous type-2 quasar J150904.22+043441.8 (z = 0.1118). The ionized outflow is faster than its molecular counterpart, although the outflow sizes that we derive for them are consistent within the errors (1.34 ± 0.18 and 1.46 ± 0.20 kpc, respectively). We use these radii, the broad emission-line luminosities and in the case of the ionized outflow, the density calculated from the trans-auroral [O  ii ] and [S  ii ] lines, to derive mass outflow rates and kinetic coupling efficiencies. While the ionized and warm molecular outflows represent a small fraction of the AGN power (≤0.033 and 0.0001 per cent of L bol, respectively), the total molecular outflow, whose mass is estimated from an assumed warm-to-cold gas mass ratio of 6 × 10−5, has a kinetic coupling efficiency of ∼1.7 per cent L bol. Despite the large uncertainty, this molecular outflow represents a significant fraction of L bol and it could potentially have a significant impact on the host galaxy. In addition, the quasar spectrum reveals bright and patchy narrow Paα emission extending out to 4 arcsec (8 kpc) south-east and north-west from the active nucleus. [ABSTRACT FROM AUTHOR]

We study the morphological and structural properties of the host galaxies associated with 57 optically selected luminous type 2 active galactic nuclei (AGNs) at |$z$| ∼ 0.3–0.4: 16 high-luminosity Seyfert 2 [HLSy2, 8.0 ≤ log(⁠|$L_{\rm [O\,{\small III}]}/L_{\odot })\,\lt\,$| 8.3] and 41 obscured [QSO2, log(⁠|$L_{\rm [O\,{\small III}]}/L_{\odot })\ge$| 8.3] quasars. With this work, the total number of QSO2s at |$z$| < 1 with parametrized galaxies increases from ∼35 to 76. Our analysis is based on Hubble Space Telescope WFPC2 and ACS images that we fit with galfit. HLSy2s and QSO2s show a wide diversity of galaxy hosts. The main difference lies in the higher incidence of highly disturbed systems among QSO2s. This is consistent with a scenario in which galaxy interactions are the dominant mechanism triggering nuclear activity at the highest AGN power. There is a strong dependence of galaxy properties with AGN power (assuming |$L_ {\rm [O\,{\small III}]}$| is an adequate proxy). The relative contribution of the spheroidal component to the total galaxy light (B/T) increases with |$L_ {\rm [O\,{\small III}]}$|⁠. While systems dominated by the spheroidal component spread across the total range of |$L_ {\rm [O\,{\small III}]}$|⁠, most disc-dominated galaxies concentrate at log(⁠|$L_{\rm [O\,{\small III}]}/L_{\odot })\lt$| 8.6. This is expected if more powerful AGNs are powered by more massive black holes which are hosted by more massive bulges or spheroids. The average galaxy sizes (〈 r e〉) are 5.0 ± 1.5 kpc for HLSy2s and 3.9 ± 0.6 kpc for HLSy2s and QSO2s, respectively. These are significantly smaller than those found for QSO1s and narrow-line radio galaxies at similar |$z$|⁠. We put the results of our work in the context of related studies of AGNs with quasar-like luminosities. [ABSTRACT FROM AUTHOR]

We explore the distribution of R MS ≡ SFR/SFRMS (where SFRMS is the star formation rate of 'main-sequence' star-forming galaxies) for AGN hosts at |$z$|  = 1. We split our sample into two bins of X-ray luminosity divided at L X  = 2 × 1043 erg s−1 to investigate whether the R MS distribution changes as a function of AGN power. Our main results suggest that, when the R MS distribution of AGN hosts is modelled as a log-normal distribution (i.e. the same shape as that of MS galaxies), galaxies hosting more powerful X-ray AGNs (i.e. L X  > 2 × 1043 erg s−1) display a narrower R MS distribution that is shifted to higher values compared to their lower L X counterparts. In addition, we find that more powerful X-ray AGNs have SFRs that are more consistent with that of MS galaxies compared to lower L X AGNs. Despite this, the mean SFRs (as opposed to R MS) measured from these distributions are consistent with the previously observed flat relationship between SFR and L X . Our results suggest that the typical star-forming properties of AGN hosts change with L X , and that more powerful AGNs typically reside in more MS-like star-forming galaxies compared to lower L X AGNs. [ABSTRACT FROM AUTHOR]

Young radio AGN are pivotal for our understanding of many of the still-debated aspects of AGN feedback. In this paper we present a study of the interstellar medium (ISM) in the compact, peaked-spectrum radio galaxy PKS B1934-63 using X-shooter observations. Most of the warm ionized gas resides within a circum-nuclear disk with a radius of about 200 pc that is likely to constitute the gas reservoir from which the central black hole feeds. On the other hand, we find a biconical outflow of warm ionized gas with an estimated radius of 59 ± 12 pc. This matches the radial extent of the radio source and suggests that the outflow is jet driven. Thanks to the superior wavelength coverage of the data, we can estimate the density of the warm ionized gas using the trans-auroral line technique, and we find that the outflowing gas has remarkably high density, up to log ne (cm−3) ≃ 5.5. The estimated mass outflow rate is low (Ṁ = 10−3 −10−1M⊙ yr−1), and the AGN feedback operates at relatively low efficiency (Ė/Lbol ∼ 10−4−10−3%). In addition, optical and near-IR line ratios show that the expansion of the radio source drives fast shocks (with velocities vs ≳ 500 km s−1) that ionize and accelerate the outflowing gas. At odds with the properties of other compact, peaked-spectrum radio sources hosting warm ionized gas outflows, we do not find signs of kinematically disturbed or outflowing gas in phases colder than the warm ionized gas. We argue that this is due to the young age of our source and thus to the recent nature of the AGN-ISM interaction, and suggest that cold gas forms within the outflowing material and the shock-ionized outflowing gas of PKS B1934-63 did not have enough time to cool down and accumulate in a colder phase. This scenario is also supported by the multi-phase outflows of other compact and young radio sources in the literature. [ABSTRACT FROM AUTHOR]

The true importance of the warm, AGN-driven outflows for the evolution of galaxies remains uncertain. Measurements of the radial extents of the outflows are key for quantifying their masses and kinetic powers, and also establishing whether the AGN outflows are galaxy-wide. Therefore, as part of a larger project to investigate the significance of warm, AGN-driven outflows in the most rapidly evolving galaxies in the local universe, here we present deep Hubble Space Telescope (HST) narrow-band [O iii] λ5007 observations of a complete sample of eight nearby ULIRGs with optical AGN nuclei. Combined with the complementary information provided by our ground-based spectroscopy, the HST images show that the warm gas outflows are relatively compact for most of the objects in the sample: in three objects, the outflow regions are barely resolved at the resolution of HST ( $0.065 \lt R_{\rm [O\,{\small III}]} \lt 0.12$ kpc); in a further four cases, the outflows are spatially resolved but with flux-weighted mean radii in the range $0.65 \lt R_{\rm [O\,{\small III}]} \lt 1.2$ kpc; and in only one object (Mrk273) is there clear evidence for a more extended outflow, with a maximum extent of $R_{\rm [O\,{\small III}]}\sim 5$  kpc. Overall, our observations show little evidence for the galaxy-wide outflows predicted by some models of AGN feedback. [ABSTRACT FROM AUTHOR]

We report the discovery of a radio-quiet type 2 quasar (SDSS J165315.06+234943.0 nicknamed the 'Beetle' at z=0.103) with unambiguous evidence for active galactic nucleus (AGN) radio-induced feedback acting across a total extension of ~46 kpc and up to ~26 kpc from the AGN. To the best of our knowledge, this is the first radio-quiet system where radio-induced feedback has been securely identified at ⪢several kpc from the AGN. The morphological, ionization and kinematic properties of the extended ionized gas are correlated with the radio structures. We find along the radio axis (a) enhancement of the optical line emission at the location of the radio hotspots (b) turbulent gas kinematics (FWHM ~ 380-470 km s-1) across the entire spatial range circumscribed by them (c) ionization minima for the turbulent gas at the location of the hot spots, (d) high temperature Te≳ 1.9 × 104 K at the NE hotspot. Turbulent gas is also found far from the radio axis, ~25 kpc in the perpendicular direction.We propose a scenario in which the radio structures have perforated the interstellar medium of the galaxy and escaped into the circumgalactic medium. While advancing, they have interacted with in situ gas modifying its properties. Our results show that jets of modest power can be the dominant feedback mechanism acting across huge volumes in radio-quiet systems, including highly accreting luminous AGNs, where radiative mode feedback may be expected. [ABSTRACT FROM AUTHOR]

The 2 Jy sample is a survey of radio galaxies with flux densities above 2 Jy at 2.7 GHz. As part of our ongoing work on the southern subset of 2 Jy sources, in paper I of this series we analysed the X-ray cores of the complete 2 Jy sample with redshifts 0.05 < z < 0.7. For this work we focus on the X-ray emission associated with the extended structures (jets, lobes and environments) of the complete subset of 2 Jy sources with 0.05 < z < 0.2 that we have observed with Chandra. We find that hotspots and jet knots are ubiquitous in Fanaroff-Riley class II (FRII) sources, which also inhabit systematically poorer environments than the Fanaroff-Riley class I (FRI) sources in our sample. Spectral fits of the hotspots with good X-ray statistics invariably show properties consistent with synchrotron emission and we show that inverse-Compton mechanisms underpredict the X-ray emission we observe by 1-2 orders of magnitude. Inverse-Compton emission is detected from many of the lobes in our sample and we find that the lobes of the FRII sources show magnetic fields lower by up to an order of magnitude than expected from equipartition extrapolations. This is consistent with previous results, which show that most FRII sources have electron energy densities higher than minimum energy requirements. [ABSTRACT FROM AUTHOR]

The origin of the unification model for Active Galactic Nuclei (AGN) was the detection of broad hydrogen recombination lines in the optical polarized spectrum of the Seyfert 2 galaxy (Sy2) NGC 1068. Since then, a search for the hidden broad-line region (HBLR) of nearby Sy2s started, but polarized broad lines have only been detected in ~30-40% of the nearby Sy2s observed to date. Here we present new VLT/FORS2 optical spectropolarimetry of a sample of 15 Sy2s, including Compton-thin and Compton-thick sources. The sample includes six galaxies without previously published spectropolarimetry, some of them normally treated as non-hidden BLR (NHBLR) objects in the literature, four classified as NHBLR, and five as HBLR based on previous data. We report ≥4σ detections of a HBLR in 11 of these galaxies (73% of the sample) and a tentative detection in NGC 5793, which is Compton-thick according to the analysis of X-ray data performed here. Our results confirm that at least some NHBLRs are misclassified, bringing previous publications reporting differences between HBLR and NHBLR objects into question. We detect broad Ha and Hβ components in polarized light for 10 targets, and just broad Hα for NGC 5793 and NGC 6300, with line widths ranging between 2100 and 9600 km s-1. High bolometric luminosities and low column densities are associated with higher polarization degrees, but not necessarily with the detection of the scattered broad components. [ABSTRACT FROM AUTHOR]

We investigate the presence of extended ionized outflows in 18 luminous type 2 AGNs (11 quasars and 7 high-luminosity Seyfert 2s) at 0.3o ≲ several × 100 pc and upper limits Ro ☉1-2 kpc. Our results are inconsistent with related studies which suggest that large scale (Ro ≲ several-15 kpc) are ubiquitous in QSO2. We study the possible causes of discrepancy and propose that seeing smearing is the cause of the large inferred sizes. The implications in our understanding of the feedback phenomenon are important since the mass Mo (through the density), mass injection M˙o and energy injection E˙o rates of the outflows become highly uncertain. One conclusion seems unavoidable: Eo, M˙o and E˙o are modest or low compared with previous estimations. We obtain typically Eo ☉ (0.4-22) × 106 M⊙ (median 1.1 × 106 M⊙) assuming n = 1000 cm-3. These are -102-104 times lower than values reported in the literature. Even under the most favourable assumptions, we obtain M˙o ☉ 10 M⊙ yr-1 in general, 100-1000 times lower than claimed in related studies. Although the uncertainties are large, it is probable that these are lower than typical star-forming rates. In conclusion, no evidence is found supporting that typical outflows can affect the interstellar medium of the host galaxies across spatial scales -1-2 kpc. [ABSTRACT FROM AUTHOR]

I review the observational evidence that CSS/GPS radio sources have a significant impact on the evolution of their host galaxies, particularly on the kpc-scales of the galaxy bulges. Starting with an overview of the observational evidence for jet-cloud interactions and warm ionised outflows in CSS/GPS sources, I then consider the challenges involved in quantifying the feedback effect of the warm outflows in terms of their mass outflow rates and kinetic powers. For the best-observed cases it is shown that the warm outflows may have a major negative feedback effect in the very central regions, but probably lack the power to heat and eject the full cool ISM contents of the host galaxies. In contrast, the recently-discovered neutral and molecular outflows are more massive and powerful and therefore carry more destructive potential. However, the feedback effect of such outflows is not necessarily negative: there is now clear observational evidence that the molecular outflows are formed as the hot, compressed gas cools behind fast shocks driven into the ISM by the relativistic jets. The natural endpoint of this process is the formation of stars. Therefore, jet-induced star formation may be a significant process in CSS/GPS radio galaxies. Finally, I discuss whether CSS/GPS sources are 'imposters' in flux-limited radio samples, due the flux boosting of the radio sources by strong jet-cloud interactions in the early stages of radio source evolution. (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Newly born and young radio sources are in a delicate phase of their life. Their jets are fighting their way through the surrounding gaseous medium, strongly experiencing this interaction while, at the same time, impacting and affecting the interstellar medium (ISM). Quantifying this interplay has far reaching implications: the rate of occurrence and the magnitude of the interaction between radio jets and ISM can have consequences for the evolution of the host galaxy. Despite the hostile conditions, cold gas - neutral atomic hydrogen and molecular - has been often found in these objects and can be also associated to fast outflows. Here we present the results from two studies of H I and molecular gas illustrating what can be learned from these phases of the gas. We first describe a statistical study of the occurrence and kinematics of H I observed in absorption with the Westerbork Synthesis Radio telescope. This allows a comparison between the properties of the gas in extended and in compact/young radio sources. The study shows that the young radio sources not only have an higher detection rate of H I, but also systematically broader and more asymmetric H I profiles, most of them blueshifted. This supports the idea that we are looking at young radio jets making their way through the surrounding ISM, which also appears to be, on average, richer in gas than in evolved radio sources. Signatures of the impact of the jet are seen in the kinematics of the gas, but the resulting outflows may be characteristic of only the initial phase of the radio source evolution. However, even among the young sources, we identify a population that remains undetected in H I even after stacking their profiles. Orientation effects can only partly explain the result. These objects either are genuinely gas-poor or have different conditions of the medium, e.g. higher spin temperature. The upcoming blind H I surveys which are about to start with large-field-of-view radio facilities (i.e. Apertif at the WSRT and ASKAP) will allow us to expand the statistics and reach even higher sensitivity with stacking techniques. We further present the case of the radio source IC 5063 where we have used the molecular gas observed with ALMA to trace in detail the jet impacting the ISM. The kinematics of the cold, molecular gas co-spatial with the radio plasma shows this process in action. The ALMA data reveal a fast outflow of molecular gas extending along the entire radio jet (∼1 kpc), with the highest outflow velocities at the location of the brighter hot-spot. The results can be described by a scenario of a radio plasma jet expanding into a clumpy medium, interacting directly with the clouds and inflating a cocoon that drives a lateral outflow into the ISM. This is consistent with the scenario proposed by numerical simulations for the expansion of a young radio jet, confirming the disruptive effect the radio plasma jet can have. Following this case, more ALMA observations of nearby young radio sources will be able to confirm if this process is common, as expected, in the initial phase of the evolution of the radio source. (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

We present optical imaging and long slit spectroscopic observations of nine luminous type 2 active galactic nuclei (AGN) within the redshift range 0.3

We study the physical and kinematic properties of the narrow-line region (NLR) of the nearest obscured quasar MRK 477 (z = 0.037), using optical and near-infrared (NIR) spectroscopy. About 100 emission lines are identified in the optical+NIR spectrum (90 in the optical), including several narrow optical Fe+ lines. To our knowledge, this is the first type 2 active galactic nucleus (AGN) with such a detection. The Fe+ lines can be explained as the natural emission from theNLRphotoionized by theAGN. Coronal line emission can only be confirmed in the NIR spectrum. As in many other AGNs, a significant correlation is found between the lines' full width at half-maximum and the critical density log(ncrit).We propose that it is caused by the outflow. This could be the case in other AGNs. The nuclear jet-induced ionized outflow has been kinematically isolated in many emission lines covering a broad range of ionization potentials and critical densities. It is concentrated within R ˜few×100 pc from the central engine. The outflowing gas is denser (n ≳ 8000 cm-3) than the ambient non-perturbed gas (n ˜400-630 cm-3). This could be due to the compression effect of the jet-induced shocks. Alternatively, we propose that the outflow has been triggered by the jet at R ≲220 pc (possibly at ≲30 pc), and we trace how the impact weakens as it propagates outwards following the radiation-pressure-dominated density gradient. The different kinematic behaviour of [Fe Π] λ1.644 µm suggests that its emission is enhanced by shocks induced by the nuclear outflow/jet and is preferentially emitted at a different, less reddened spatial location. [ABSTRACT FROM AUTHOR]

We present new HST/ACS medium- and narrow-band images and optical Isaac Newton Telescope long-slit spectra of the merging system Mrk273. The HST observations sample the [Oш]λλ4959,5007 emission from the galaxy and the nearby continuum. These data were taken as a part of a larger study of ultra-luminous infrared galaxies (ULIRGs) with the aim of investigating the importance of the warm, AGN induced outflows in such objects. The HST images show that the morphologies of the extended continuum and the ionised gas emission from the galaxy are decoupled, extending almost perpendicular to each other. In particular, we detect for the first time a spectacular structure of ionised gas in the form of filaments and clumps that extend ∼23 kpc to the east of the nuclear region. The quiescent ionised gas kinematics at these locations suggests that these filaments are tidal debris left over from a secondary merger event that are illuminated by an AGN in the nuclear regions. The images also reveal a complex morphology in the nuclear region of the galaxy for both the continuum and the [Oш] emission. Consistent with this complexity, we find a wide diversity of emission line profiles in these regions. Kinematic disturbance in the form of broad (FWHM > 500 km s-1) and/or strongly shifted (ǀΔVǀ > 150 km s-1 ) emission line components is found at almost all locations in the nuclear regions, but confined to a radius of ∼4 kpc to the east and west of the northern nucleus. In most cases, we are able to fit the profiles of all the emission lines of different ionisation with a kinematic model using two or three Gaussian components. From these fits, we derive diagnostic line ratios that are used to investigate the ionisation mechanisms at the different locations in the galaxy. We show that these line ratios are generally consistent with photoionisation by an AGN as the main ionisation mechanism. Finally, the highest surface brightness [Oш] emission is found in a compact region that is coincident with the so-called SE nuclear component. The compactness, kinematics, and emission line ratios of this component suggest that it is a separate nucleus with its own AGN. At this stage, further observations are required to confirm the dual (or multiple?) AGN nature of Mrk273. [ABSTRACT FROM AUTHOR]

We present an analysis of 2.05 μm Hubble Space Telescope polarimetric data for a sample of 13 nearby Fanaroff–Riley type II (FRII) 3CR radio sources (0.03 < z < 0.11) that are classified as narrow-line radio galaxies (NLRG) at optical wavelengths. We find that the compact cores of the NLRG in our sample are intrinsically highly polarized in the near-infrared (near-IR) (6 < P2.05 μm < 60 per cent), with the electric vector (E-vector) perpendicular to the radio axis in 54 per cent of the sources. The levels of extinction required to produce near-IR polarization by the dichroic extinction mechanism are consistent with the measured values recently reported in Ramírez et al., provided that this mechanism has its maximum efficiency. This consistency suggests that the nuclear polarization could be due to dichroic extinction. In this case, toroidal magnetic fields that are highly coherent would be required in the circumnuclear tori to align the elongated dust grains responsible for the dichroic extinction. However, it is not entirely possible to rule out other polarization mechanisms (e.g. scattering, synchrotron emission) with our observations at only one near-IR wavelength. Therefore, further polarimetry observations at mid-IR and radio wavelengths will be required to test whether all the near-IR polarization is due to dichroic extinction. [ABSTRACT FROM PUBLISHER]

The tight correlations observed between galaxies and their SMBH provides compelling evidence that the evolution of the galaxy and its central black hole are strongly linked. This is generally attributed to feedback mechanisms which, according to simulations, often take the form of outflows of gas, quenching star formation in the host galaxy and halting accretion onto the central black hole. While there are a number of plausible ways that outflows could be produced, recent results have shown that in some cases radio jets could be responsible for driving fast outflows of gas. One such example is seen in the nearby radio galaxy 3C293. In this talk I will present results from JVLA radio observations where we detect fast outflows (~1200 km/s) of neutral gas which are being driven by the radio-jet approximately 0.5 kpc from the central core, providing direct evidence for jet-ISM interaction. This is accompanied with recent IFU observations showing that ionised gas outflows are also being driven by the radio jet. Pinpointing the location of these outflows enables us to derive crucial parameters, such as the mass outflow rates and kinetic energy involved, which we can compare to predictions from galaxy evolution simulations. [ABSTRACT FROM PUBLISHER]

We present deep, intermediate resolution, long-slit Gemini GMOS-S optical spectra of the Sloan Digital Sky Survey (SDSS) type II quasar J002531−104022, which is a highly disturbed system currently undergoing a major merger event. We use these data to model the ages and reddenings of the stellar populations in three distinct spatial regions and find a remarkable uniformity in the properties of the young stellar populations (YSPs) that dominate the optical spectra. The YSPs are all found to have relatively young ages (tysp < 40 Myr), strongly implying that the latest episode of star formation and quasar activity have been triggered quasi-simultaneously. The lack of reddening deduced from both continuum modelling and the measured Balmer decrements (E(B − V) < 0.3) suggests that starburst and/or active galactic nuclei-induced outflows have already effectively removed a substantial proportion of the gas and dust from the central region. These findings starkly contrast with model predictions which suggest an offset of a few 100 Myr between the peak of merger-induced star formation and the emergence of the optically visible quasar activity. Based on our stellar population fits, we also show that the total stellar mass is in the range (4–17) × 1010 M⊙, lower than typically found for quasar host galaxies. [ABSTRACT FROM AUTHOR]

We present an optical spectroscopic study of a 90 per cent complete sample of nearby ULIRGs (z < 0.175) with optical Seyfert nuclei, with the aim of investigating the nature of the near-nuclear (r ≲ 3.5 kpc) warm gas outflows. A high proportion (94 per cent) of our sample show disturbed emission line kinematics in the form of broad (FWHM > 500 km s−1) and/or strongly blueshifted (ΔV < −150 km s−1) emission line components. This proportion is significantly higher than found in a comparison sample of nearby ultraluminous infrared galaxies (ULIRGs) that lack optical Seyfert nuclei (19 per cent). We also find evidence that the emission line kinematics of the Sy-ULIRGs are more highly disturbed than those of samples of non-ULIRG Seyferts and Palomar–Green quasars in the sense that, on average, their [O iii] λλ5007, 4959 emission lines are broader and more asymmetric.The Sy-ULIRG sample encompasses a wide diversity of emission line profiles. In most individual objects, we are able to fit the profiles of all the emission lines of different ionization with a kinematic model derived from the strong [O iii] λλ4959, 5007 lines, using between two and five Gaussian components. From these fits, we derive diagnostic line ratios that are used to investigate the ionization mechanisms for the different kinematic components. We show that, in general, the line ratios are consistent with gas of supersolar abundance photoionized by a combination of AGN and starburst activity, with an increasing contribution from the AGN with increasing FWHM of the individual kinematic components, and the AGN contribution dominating for the broadest components. However, shock ionization cannot be ruled out in some cases. Our derived upper limits on the mass outflows rates and kinetic powers of the emission line outflows show that they can be as energetically significant as the neutral and molecular outflows in ULIRGs – consistent with the requirements of the hydrodynamic simulations that include AGN feedback. However, the uncertainties are large, and more accurate estimates of the radii, densities and reddening of the outflows are required to put these results on a firmer footing. [ABSTRACT FROM AUTHOR]

We report the discovery with the Atacama Pathfinder EXperiment (APEX) of an outflow of molecular gas in the radio-loud Seyfert galaxy IC 5063 (z = 0.0110). In addition to the emission of the large-scale CO disk, a prominent blueshifted wing is observed in the CO(2-1) spectrum. IC 5063 represents one of the best cases of a fast jet-driven HI (and ionized gas) outflow, which is located at the site of a radio-bright feature about 0.5 kpc from the nucleus. It is possible that the blueshifted part of the molecular gas is associated with this outflow and is accelerated by the interaction with the radio jet. The outflow of molecular gas is characterized by an H2 mass of the outflowing component of between 2.25±0.70×107 M☉ and 1.29±0.40×108 M☉ and a mass outflow rate between 22 and 129 M☉ yr-1 depending on the assumption for αX and assuming a luminosity ratio L'CO(2-1)/L'CO(1-0) = 1. This confirms that this may indeed be the dominant component in outflows driven by the nuclear activity as also found in other objects. However, this high mass outflow rate cannot easily be supported for a long time, suggesting that the gas outflow in IC 5063 happens in bursts and is in a particularly strong phase at present. Owing to its proximity, IC 5063 serves as an excellent laboratory for understanding the impact of radio jets on the gas-rich inter-stellar medium. [ABSTRACT FROM AUTHOR]

ABSTRACT We present optical, infrared (IR) and radio observations of the powerful Fanaroff-Riley type II (FR II) radio source PKS 0347+05 ( z = 0.3390), and demonstrate that it is a rare example of a radio-loud/radio-quiet double active galactic nucleus (AGN) system, comprising a weak-line radio galaxy (WLRG) separated by 25 kpc (in projection) from a Seyfert 1 nucleus at the same redshift. Our deep Gemini optical images show a highly disturbed morphology, with a warped dust lane crossing through the halo and nuclear regions of the radio galaxy host, tidal tails and a bridge connecting the radio galaxy to the Seyfert 1 nucleus. Spectral synthesis modelling of our Gemini optical spectrum of the radio galaxy shows evidence for a reddened young stellar population of age ≤100 Myr. Further evidence for recent star formation activity in this source is provided by the detection of strong polycyclic aromatic hydrocarbon features in mid-IR Spitzer/IRS spectra. Together, these observations support a model in which both AGN have been triggered simultaneously in a major galaxy merger. However, despite the presence of a powerful FR II radio source, and the apparently plentiful supply of fuel provided by the merger, the nucleus of the radio galaxy shows only weak, low-ionization emission-line activity. We speculate that the fuel supply to nuclear regions of the radio galaxy has recently switched off (within the last ∼106 yr), but the information about the resulting decrease in nuclear AGN activity has yet to reach the extended lobes and hotspots of the FR II radio source. Based on this scenario, we derive a lower limit on the typical lifetimes of powerful, intermediate-redshift FR II radio sources of [ABSTRACT FROM AUTHOR]

ABSTRACT We present deep Gemini Multi-Object Spectrograph-South optical broad-band images for a complete sample of 20 Sloan Digital Sky Survey selected type II quasars taken from Zakamska et al., with redshifts in the range 0.3 < z < 0.41 and [O iii]λ5007 emission-line luminosities [ABSTRACT FROM AUTHOR]

ABSTRACT PKS B2152−699, which has radio power characteristic of sources that dominate radio feedback, is exceptional in showing a wide range of features associated with radio-galaxy/gas interactions. We present new deep radio (Australia Telescope Compact Array), X-ray ( Chandra) and ground-based optical observations, and test the energetics of the feedback model. We report the first high-resolution observations of the radio jet, finding that the inner jet extends ∼8.5 kpc (10° viewing angle) in the direction of an optical emission-line high-ionization cloud (HIC) before taking a zigzag path to a position offset from the HIC. Jet synchrotron radiation to X-ray energies is seen. The HIC is associated with cool, kT∼ 0.3 keV, X-ray gas of anomalously low metallicity. On larger scales, the radio galaxy displays all three X-ray features that together confirm supersonic expansion of the lobes into the external medium: gas cavities, inverse Compton emission showing excess internal lobe pressure, and high-contrast arms of temperature above the kT∼ 1 keV ambient medium. The well-formed southern lobe on the counterjet side is expanding with a Mach number between 2.2 and 3. The lobe energy appears to be more gently dissipated in the north. We estimate a cavity power ∼3 × 1043 erg s−1, which falls well below previously reported correlations with radio power. The total inferred time-averaged jet power, ∼4 × 1044 erg s−1, is dominated by the kinetic and thermal energy of shocked gas, and if used instead would bring the source into better agreement with the correlations. The southern hotspot is the more complex, with a spiral polarization structure. Its bright peak emits synchrotron X-rays. The fainter northern hotspot is particularly interesting, with X-rays offset in the direction of the incoming jet by ∼1 arcsec relative to the radio peak. Here modest (δ∼ 6) relativistic beaming and a steep radio spectrum cause the jet to be X-ray bright through inverse Compton scattering before it decelerates. With such beaming, a modest proton content or small departure from minimum energy in the jet will align estimates of the instantaneous and time-averaged jet power. The hotspots suggest acceleration of electrons to a maximum energy ∼1013 eV in the jet termination shocks. [ABSTRACT FROM AUTHOR]

ABSTRACT We present a compilation of Hubble Space Telescope ( HST) images of 58 luminous Sloan Digital Sky Survey (SDSS) type 2 active galactic nuclei (AGNs) at . Of these, 42 are type 2 quasars, which is a good representation of all optically selected SDSS type 2 quasars in this z range. We find that the majority of the host galaxies are ellipticals (30/42 or 71 per cent). This is consistent with studies of radio-loud and radio-quiet type 1 quasars, which show that their host galaxies are, in general, ellipticals. A significant fraction of type 2 quasars (≥25/42 or ≥59 per cent) show clear signatures of morphological disturbance. In most cases, these are clearly identified with merger/interaction processes. We discuss this in the context of related works on type 2 quasars and powerful radio galaxies. We study in detail the particular case of the radio-quiet type 2 quasar SDSS J143027.66-005614.8 at z= 0.318 based on imaging and spectroscopic data from the Very Large Telescope, HST and SDSS. The system shows highly complex morphology, similar to that found in many ultraluminous infrared galaxies, which suggests that it is in the late pre-coalescence stage of a major galaxy merger. The optical continuum spectrum is dominated by a young stellar population of age <80 Myr, probably formed as a consequence of the merger-induced starburst. Ionized gas is confirmed up to a maximum total extension of r∼ 13 kpc from the quasar, although gas is also possibly detected at up to r∼ 32 kpc. The ionizing mechanism, AGN versus stellar photoionization, varies depending on the spatial location. There is a nuclear ( r≤ few kpc) ionized outflow, which is blueshifted by ∼520 km s−1 relative to the systemic redshift and has FWHM ∼ 1600 km s−1. Several × 105 M⊙ at most are expected to participate in the outflow. We discuss the global properties of the object in the context of theoretical and observational studies of galaxy mergers/interactions and their role in the triggering of the nuclear and star formation activities in the most luminous active galaxies. [ABSTRACT FROM AUTHOR]

We present deep Spitzer/Infrared Spectrograph (IRS) spectra for complete samples of 46 2 Jy radio galaxies (0.05 < z < 0.7) and 19 3CRR FRII radio galaxies (z < 0.1), and use the detection of polycyclic aromatic hydrocarbon (PAH) features to examine the incidence of contemporaneous star formation and radio-loud active galactic nucleus (AGN) activity. Our analysis reveals PAH features in only a minority (30%) of the objects with good IRS spectra. Using the wealth of complementary data available for the 2 Jy and 3CRR samples we make detailed comparisons between a range of star formation diagnostics: optical continuum spectroscopy, mid- to far-IR (MFIR) color, far-IR excess and PAH detection. There is good agreement between the various diagnostic techniques: most candidates identified to have star formation activity on the basis of PAH detection are also identified using at least two of the other techniques. We find that only 35% of the combined 2 Jy and 3CRR sample show evidence for recent star formation activity (RSFA) at optical and/or MFIR wavelengths. This result argues strongly against the idea of a close link between starburst and powerful radio-loud AGN activity, reinforcing the view that, although a large fraction of powerful radio galaxies may be triggered in galaxy interactions, only a minority are triggered at the peaks of star formation activity in major, gas-rich mergers. However, we find that compact radio sources (D < 15 kpc) show a significantly higher incidence of RSFA (>75%) than their more extended counterparts (≈ 15%-25%). We discuss this result in the context of a possible bias toward the selection of compact radio sources triggered in gas-rich environments. [ABSTRACT FROM AUTHOR]

We present and analyse integral-field observations of six type II QSOs with , selected from the Sloan Digital Sky Survey (SDSS). Two of our sample are found to be surrounded by a nebula of warm ionized gas, with the largest nebula extending across 8 arcsec (40 kpc). Some regions of the extended nebulae show kinematics that are consistent with gravitational motion, while other regions show relatively perturbed kinematics: velocity shifts and linewidths too large to be readily explained by gravitational motion. We propose that a outflow is present in one of the galaxies. Possible mechanisms for triggering the outflow are discussed. In this object, we also find evidence for ionization both by shocks and by the radiation field of the AGN. [ABSTRACT FROM AUTHOR]

We present the results of a program of K- and -band imaging of a sample of 2 Jy radio galaxies with redshifts , for which the host galaxy morphologies and structural parameters (effective radius, Sérsic index and unresolved nuclear point source contribution) have been determined usinggalfit. Two-thirds of our sample are best modelled as being hosted by massive elliptical galaxies with Sérsic indices of , with the remainder being better suited either by a mixture of morphological components (usually a bulge plus a small, less luminous, disc component) or by more discy galaxy models with . Our measured galaxy sizes are generally in very good agreement with other imaging programs, both space- and ground-based. We also determine a slightly higher average nuclear point source contribution than similar Hubble Space Telescope based programs. This is due to our inability to separate the active galactic nuclei emission from compact circum-nuclear stellar emission, but does not bias our modelling of the remainder of the host galaxies and our results remain robust. We also observe that roughly half of the objects in our sample are either undergoing major or minor merger activity or are clearly morphologically disturbed. [ABSTRACT FROM AUTHOR]

An important aspect of solving the long-standing question as to what triggers various types of active galactic nuclei (AGN) involves a thorough understanding of the overall properties and formation history of their host galaxies. This is the second in a series of papers that systematically study the large-scale properties of cold neutral hydrogen (H i) gas in nearby radio galaxies. The main goal is to investigate the importance of gas-rich galaxy mergers and interactions among radio-loud AGN. In this paper, we present results of a complete sample of classical low-power radio galaxies. We find that extended Fanaroff & Riley type-I radio sources are generally not associated with gas-rich galaxy mergers or ongoing violent interactions, but occur in early-type galaxies without large amounts of extended neutral hydrogen gas. In contrast, enormous discs/rings of H i gas (with sizes up to 190 kpc and masses up to ) are detected around the host galaxies of a significant fraction of the compact radio sources in our sample. This segregation in H i mass with radio-source size likely indicates that either these compact radio sources are confined by large amounts of gas in the central region or that their fuelling is inefficient and different from the fuelling process of classical FR I radio sources. To first order, the overall H i properties of our complete sample (detection rate, mass and morphology) appear similar to those of radio-quiet early-type galaxies. If confirmed by better statistics, this would imply that low-power radio-AGN activity may be a short and recurrent phase that occurs at some point during the lifetime of many early-type galaxies. [ABSTRACT FROM AUTHOR]

This paper is the second in a series in which 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. In the first paper (Holt, Tadhunter & Morganti), we presented the kinematic results from the nuclear emission-line modelling and reported fast outflows in the circumnuclear gas. In this paper, we use the line fluxes to investigate the physical conditions and dominant ionization mechanisms of the emission-line gas. We find evidence for large electron densities and high reddening in the nuclear regions, particularly in the broader, blueshifted components. These results are consistent with the idea that the young, recently triggered radio sources still reside in dense and dusty cocoons deposited by the recent activity triggering event (merger/interaction). In addition, we find that the quiescent nuclear and extended narrow components are consistent with active galactic nucleus (AGN) photoionization, split between simple-slab AGN photoionization and mixed-medium photoionization models. For the nuclear broader and shifted components, the results are less clear. Whilst there are suggestions that the broader components may be closer to shock plus precursor models on the diagnostic diagrams, and that the electron temperatures and densities are high, we are unable to unambiguously distinguish the dominant ionization mechanism using the optical emission-line ratios. This is surprising given the strong evidence for jet–cloud interactions (broad emission lines, large outflow velocities and strong radio-optical alignments), which favours the idea that the warm gas has been accelerated in shocks driven by the radio lobes expanding through a dense cocoon of gas deposited during the triggering event. [ABSTRACT FROM AUTHOR]

We report the analysis of near-infrared (near-IR) imaging, polarimetric and spectroscopic observations of the powerful radio galaxy 3C 433 , obtained with the Hubble Space Telescope ( HST) and the United Kingdom Infrared Telescope. The high spatial resolution of HST allows us to study the near-nuclear regions of the galaxy (<1 kpc). In line with previous observations, we find that 3C 433 has an unresolved core source that is detected in all near-IR bands, but dominates over the host galaxy emission at m. Our analysis reveals (1) the presence of a dust lane aligned close to the perpendicular [position angle ] to the inner radio jet axis , (2) a steep slope to the near-IR spectral energy distribution (SED; ), (3) an apparent lack of broad permitted emission lines at near-IR wavelengths, in particular the absence of a broad Paα emission line and (4) high intrinsic polarization for the unresolved core nuclear source , with an E-vector perpendicular to the inner radio jet. Using five independent techniques, we determine an extinction to the compact core source in the range mag. An analysis of the long wavelength SED rules out a synchrotron origin for the high near-IR polarization of the compact core source. Therefore, scattering and dichroic extinction are plausible polarizing mechanisms, although in both of these cases the broad permitted lines from the active galactic nuclei are required to have a width (full width at half-maximum) to escape detection in our near-IR spectrum. Dichroic extinction is the most likely polarization mechanism because it is consistent with the various available extinction estimates. In this case, a highly ordered, coherent toroidal magnetic field must be present in the obscuring structure close to the nucleus. [ABSTRACT FROM AUTHOR]

We present new observational results that conclude that the nearby radio galaxy B2 0722+30 is one of the very few known disc galaxies in the low-redshift Universe that host a classical double-lobed radio source. In this paper, we use H i observations, deep optical imaging, stellar population synthesis modelling and emission-line diagnostics to study the host galaxy, classify the active galactic nucleus (AGN) and investigate environmental properties under which a radio-loud AGN can occur in this system. Typical for spiral galaxies, B2 0722+30 has a regularly rotating gaseous disc throughout which star formation occurs. Dust heating by the ongoing star formation is likely responsible for the high infrared luminosity of the system. The optical emission-line properties of the central region identify a Low Ionization Nuclear Emission-line Region (LINER)-type nucleus with a relatively low [O iii] luminosity, in particular when compared with the total power of the Fanaroff & Riley type-I radio source that is present in this system. This classifies B2 0722+30 as a classical radio galaxy rather than a typical Seyfert galaxy. The environment of B2 0722+30 is extremely H i-rich, with several nearby interacting galaxies. We argue that a gas-rich interaction involving B2 0722+30 is a likely cause for the triggering of the radio AGN and/or the fact that the radio source managed to escape the optical boundaries of the host galaxy. [ABSTRACT FROM AUTHOR]

We present an investigation into the absorber in front of the radio galaxy MRC 2025−218, using integral field spectroscopy obtained at the Very Large Telescope, and long-slit spectroscopy obtained at the Keck II telescope. The properties of MRC 2025−218 are particularly conducive to study the nature of the absorbing gas, i.e. this galaxy shows bright and spatially extended Lyα emission, along with bright continuum emission from the active nucleus. Lyα absorption is detected across , has a covering factor of ∼1, and shows remarkably little variation in its properties across its entire spatial extent. This absorber is kinematically detached from the extended emission line region (EELR). Its properties suggest that the absorber is outside of the EELR. We derive lower limits to the H i, H ii and H column densities for this absorber of and , respectively. Moreover, the relatively bright emission from the active nucleus has allowed us to measure a number of metal absorption lines: C i, C ii, C iv, N v, O i, Si ii, Si iv, Al ii and Al iii. The column density ratios are most naturally explained using photoionization by a hard continuum, with an ionization parameter . Shocks or photoionization by young stars cannot reproduce satisfactorily the measured column ratios. Using the ratio between the Si ii* and Si ii column densities, we derive a lower limit of for the electron density of the absorber. The data do not allow useful constraints to be placed on the metallicity of the absorber. We consider two possibilities for the nature of this absorber: the cosmological infall of gas, and an outflow driven by supernovae or the radio jets. We find it plausible that the absorber around 2025−218 is in outflow. We also find good agreement between the observed properties of the H i absorber and the properties of the H i absorption expected from the cosmological infall model of Barkana & Loeb. [ABSTRACT FROM AUTHOR]

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 half-maximum (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. [ABSTRACT FROM AUTHOR]

We present the detection of an enormous disc of cool neutral hydrogen (H i) gas surrounding the S0 galaxy NGC 612, which hosts one of the nearest powerful radio sources (PKS 0131−36). Using the Australia Telescope Compact Array, we detect of H i emission-line gas that is distributed in a 140-kpc wide disc-like structure along the optical disc and dust lane of NGC 612. The bulk of the gas in the disc appears to be settled in regular rotation with a total velocity range of 850 km s−1, although asymmetries in this disc indicate that perturbations are being exerted on part of the gas, possibly by a number of nearby companions. The H i disc in NGC 612 suggests that the total mass enclosed by the system is , implying that this early-type galaxy contains a massive dark matter halo. We also discuss an earlier study by Holt et al. that revealed the presence of a prominent young stellar population at various locations throughout the disc of NGC 612, indicating that this is a rare example of an extended radio source that is hosted by a galaxy with a large-scale star-forming disc. In addition, we map a faint H i bridge along a distance of 400 kpc in between NGC 612 and the gas-rich barred galaxy NGC 619, indicating that likely an interaction between both systems occurred. From the unusual amounts of H i gas and young stars in this early-type galaxy, in combination with the detection of a faint optical shell and the system's high infrared luminosity, we argue that either ongoing or past galaxy interactions or a major merger event are a likely mechanism for the triggering of the radio source in NGC 612. This paper is part of an ongoing study to map the large-scale neutral hydrogen properties of nearby radio galaxies and it presents the first example of large-scale H i detected around a powerful Fanaroff–Riley type II (FR-II) radio galaxy. The H i properties of the FR-II radio galaxy NGC 612 are very similar to those found for low-power compact radio sources, but different from those of extended Fanaroff–Riley type I (FR-I) sources. [ABSTRACT FROM AUTHOR]

We present the results of a multiwavelength study of the z= 0.31 radio source PKS2250−41. Integral field unit and long-slit spectroscopy obtained using VIMOS and FORS1 on the VLT, and archival Hubble Space Telescope optical imaging observations are used to study the morphology, kinematics and ionization state of the extended emission-line region (EELR) surrounding this source, and also a companion galaxy at a similar redshift. Near-infrared imaging observations obtained using the New Technology Telescope are used to analyse the underlying galaxy morphologies. The EELR displays a complex variety of different gas kinematics and ionization states, consistent with a mixture of radio source shocks and active galactic nucleus (AGN) photoionization. The radio galaxy is likely to lie within a group environment, and is plausibly undergoing interactions with one or more other objects. The disc-like galaxy to the north-east of the radio source lies at a similar redshift to the radio galaxy itself, and has its major axis position angle aligned with the filamentary continuum and line emission extending outwards from the radio galaxy. This filamentary structure is most plausibly interpreted as a tidal structure associated with an interaction involving the radio source host galaxy and the aligned companion galaxy to the north-east; this encounter may have potentially triggered the current epoch of radio source activity. Overall, PKS2250−41 displays some of the best evidence that radio source activity can be triggered in this manner. While the environment and recent interactions of a radio galaxy can have some bearing on its subsequent evolution, our data also highlight the varied means by which the radio source can effect changes in adjacent objects. Our IFU and long-slit spectroscopy confirm the presence of radio source shocks within the western radio lobe, and, together with our continuum observations, add further weight to the presence of a faint continuum source coincident with the secondary hotspot in the western radio lobe. On the basis of our multiwavelength observations of this object, we suggest that the radio source has indeed triggered recent star formation within this faint companion. [ABSTRACT FROM AUTHOR]

We present European Southern Observatory Very Large Telescope (ESO VLT) and William Herschel Telescope (WHT) spectroscopic observations of two powerful radio galaxies at intermediate redshifts (3C 213.1 and 3C 459), obtained with the aim of establishing the nature and evolutionary status of the host galaxies. Spectral synthesis modelling has been used to demonstrate that young stellar populations (YSP) make a major contribution to the integrated optical light in both sources, contributing at least 37 and 80 per cent of the integrated B-band light in 3C 213.1 and 3C 459, respectively. While in the case of 3C 213.1 the YSP has an intermediate age (0.4–0.8 Gyr) and comprises 3–30 per cent of the total stellar mass, adequate fits to the spectra of 3C 459 require a combination of younger (<0.1 Gyr) and intermediate (0.2–1.2 Gyr) age YSP components that together comprise 5–100 per cent of the total stellar mass. Both the optical and far-IR properties of 3C 459 are consistent with its status as an ultraluminous infrared galaxy (ULIRG), and a scenario in which the observed radio source has been triggered close to the peak of star formation activity in a major gas-rich merger. On the other hand, in 3C 213.1 it is likely that the radio source has been triggered (or re-triggered) a significant period after the starburst peak, and the far-IR luminosity of the source is substantially lower. Following correction for the contributions of the YSP, the absolute magnitudes of the host galaxies of both sources are relatively modest (≤2 L*), thus demonstrating that powerful radio activity is not always associated with the most massive and luminous elliptical galaxies. These results serve to emphasize that the radio source population is diverse, in terms of both the host galaxy properties and the triggering mechanism(s) for the radio source activity. [ABSTRACT FROM AUTHOR]

We present the results of a multiwavelength study of the radio source PKS1932−46. Integral field unit spectroscopy using the Visible Multi-object Spectrograph (VIMOS) on the Very Large Telescope (VLT) is used to study the morphology, kinematics and ionization state of the extended emission-line region (EELR) surrounding this source, and also a companion galaxy at a similar redshift. Near- and far-infrared imaging observations obtained using the New Technology Telescope and Spitzer are used to analyse the underlying galaxy morphologies and the nature of the active galactic nucleus (AGN). The host galaxy is identified as an elliptical. Combining Spitzer mid-infrared (mid-IR) with X-ray, optical and near-IR imaging observations of this source, we conclude that its AGN is underluminous for a radio source of this type, despite its status as a broad-line object. However, given its relatively large [O iii] luminosity it is likely that the AGN was substantially more luminous in the recent past ( ago). The EELR is remarkably extensive and complex, reminiscent of the systems observed around sources at higher redshifts/radio powers, and the gas is predominantly ionized by a mixture of AGN photoionization and emission from young stars. We confirm the presence of a series of star-forming knots extending north–south from the host galaxy, with more prodigious star formation occurring in the merging companion galaxy to the north-east, which has sufficient luminosity at mid- to far-IR (MFIR) wavelengths to be classified as a luminous infrared galaxy (LIRG). The most plausible explanation of our observations is that PKS1932−46 is a member of an interacting galaxy group, and that the impressive EELR is populated by star-forming, tidal debris. We suggest that the AGN itself may currently be fuelled by material associated either with the current interaction or with a previous merger event. Surprisingly, it is the companion object, rather than the radio source host galaxy, which is undergoing the bulk of the star formation activity within the group. [ABSTRACT FROM AUTHOR]