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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]

We present the first systematic search for UV signatures from radio source-driven active galactic nuclei (AGN) feedback in Compact Steep Spectrum (CSS) radio galaxies. Owing to their characteristic sub-galactic jets (1–20 kpc projected linear sizes), CSS hosts are excellent laboratories for probing galaxy scale feedback via jet-triggered star formation. The sample consists of seven powerful CSS galaxies, and two galaxies host to radio sources >20 kpc as the control, at low to intermediate redshifts (z < 0.6). Our new Hubble Space Telescope images show extended UV continuum emission in six out of seven CSS galaxies, with five CSS hosts exhibiting UV knots cospatial and aligned along the radio-jet axis. Young (≲ 10 Myr), massive (≳ 5 M ⊙) stellar populations are likely to be the dominant source of the blue excess emission in radio galaxies at these redshifts. Hence, the radio-aligned UV regions could be attributed to jet-induced starbursts. Lower near-UV star formation rates compared to other indicators suggest low scattered AGN light contribution to the observed UV. Dust attenuation of UV emission appears unlikely from high internal extinction correction estimates in most sources. Comparison with evolutionary synthesis models shows that our observations are consistent with recent (∼1−8 Myr old) star-forming activity likely triggered by current or an earlier episode of radio emission, or by a confined radio source that has frustrated growth, due to a dense environment. While follow-up spectroscopic and polarized light observations are needed to constrain the activity-related components in the observed UV, the detection of jet-induced star formation is a confirmation of an important prediction of the jet feedback paradigm. [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]

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]

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]

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 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 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]

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 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]

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 understand how radio sources may regulate the star formation in their host galaxies. We present deep Spitzer Infrared 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 [Ne II] 12.8μm) 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 [Ne II] 12.8μm line, and to a lesser extent the [Ne III] 15.5μm and [Ne V] 14.3μm 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. [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]

ABSTRACT We present long-slit spectroscopy and imaging data obtained with the Focal Reducer and Low Dispersion Spectrograph (FORS2) on the Very Large Telescope of 13 optically selected type 2 quasars at z ∼ 0.3-0.6 from the original sample of . The sample is likely to be affected by different selection biases. We investigate the evidence for (i) mergers/interactions (ii) star formation activity in the neighbourhood of the quasars and (iii) extended emission-line regions (EELRs) and their nature. Evidence for mergers/interactions is found in 5/13 objects. This is a lower limit for our sample, given the shallowness of most of our continuum images. Although active galactic nucleus (AGN) photoionization cannot be totally discarded, line ratios consistent with stellar photoionization are found in general in companion galaxies/knots/nuclei near these same objects. On the contrary, the gas in the neighbourhood of the quasar nucleus shows line ratios inconsistent with H ii galaxies and typical of AGN photoionized nebulae. A natural scenario to explain the observations is that star formation is ongoing in companion galaxies/knots/nuclei, possibly triggered by the interactions. These systems are, therefore, composite in their emission-line properties showing a combination of AGN and star formation features. EELRs have been found in 7/13 objects, although this fraction might be higher if a complete spatial coverage around the quasars was performed. The sizes vary between a few and up to 64 kpc. In general, the EELR apparently consists of an extended nebula associated with the quasar. In at least one case, the EELR is associated with ionized tidal features. [ABSTRACT FROM AUTHOR]

BSTRACT [ABSTRACT FROM AUTHOR]

ABSTRACT We present new deep Very Large Telescope (VLT)/FORS optical spectra with intermediate resolution and large wavelength coverage of the compact radio source and ultra-luminous IR galaxy (ULIRG) PKS 1345+12 (4C 12.50; z= 0.122), taken with the aim of investigating the impact of the nuclear activity on the circumnuclear interstellar medium (ISM). PKS 1345+12 is a powerful quasar [ L(Hβ)NLR∼ 1042 erg s−1] and is also the best studied case of an emission line outflow in a ULIRG. Using the density-sensitive transauroral emission lines [S ii]4068,4076 and [O ii]7318,7319,7330,7331, we pilot a new technique to accurately model the electron density for cases in which it is not possible to use the traditional diagnostic [S ii]6716/6731, namely sources with highly broadened complex emission line profiles and/or high ( Ne≳ 104 cm −3) electron densities. We measure electron densities of Ne= (2.94+0.71−1.03) × 103 cm −3, Ne= (1.47+0.60−0.47) × 104 cm −3 and Ne= (3.16+1.66−1.01) × 105 cm −3 for the regions emitting the narrow, broad and very broad components, respectively. We therefore calculate a total mass outflow rate of M ⊙ yr −1, similar to the range estimated for another compact radio source, PKS 1549−79. We estimate the total mass in the warm gas outflow is Mtotal= (8+3−3) × 105 M ⊙ with filling factors of ε= (4.4+1.8−1.5) × 10−4 and ε= (1.6+0.7−0.5) × 10−7 for the regions emitting the broad and very broad components, respectively. The total kinetic power in the warm outflow is erg s −1. Taking the black hole properties published by Dasyra et al., we find that only a small fraction [] of the available accretion power is driving the warm outflow in PKS 1345+12, which is significantly less than that currently required by the majority of quasar feedback models ( ∼5-10 per cent of Lbol), but similar to the recent suggestion of Hopkins & Elvis if a two-stage feedback model is implemented ( ∼0.5 per cent of Lbol). The models also predict that active galactic nuclei (AGN)-driven outflows will eventually remove the gas from the bulge of the host galaxy. Our observations show that the visible warm outflow in PKS 1345+12 is not currently capable of doing so. However, it is entirely possible that much of the outflow is either obscured by a dense and dusty natal cocoon and/or in cooler or hotter phases of the ISM. This result is important not just for studies of young Gigahertz-Peaked Spectrum/Compact Steep Spectrum radio sources, but for AGN in general. [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]

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 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), massiveand 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. [ABSTRACT FROM AUTHOR]

It remains uncertain which continuum and emission line diagnostics best indicate the bolometric powers of active galactic nuclei (AGNs), especially given the attenuation caused by the circumnuclear material and the possible contamination by components related to star formation. Here we use mid-IR spectra along with multiwavelength data to investigate the merit of various diagnostics of AGN radiative power, including the mid-IR [Ne III] λ25.89 μm and [O IV] λ25.89 μm fine-structure lines, the optical [O III] λ5007 forbidden line, and mid-IR 24 μm, 5 GHz radio, and X-ray continuum emission, for complete samples of 46 2Jy radio galaxies (0.05 < z < 0.7) and 17 3CRR FRII radio galaxies (z < 0.1). We find that the mid-IR [O IV] line is the most reliable indicator of AGN power for powerful radio-loud AGNs. By assuming that the [O IV] is emitted isotropically, and comparing the [O III] and 24 μm luminosities of the broad- and narrow-line AGNs in our samples at fixed [O IV] luminosity, we show that the [O III] and 24 μm emission are both mildly attenuated in the narrow-line compared to the broad-line objects by a factor of ≈2. However, despite this attenuation, the [O III] and 24 μm luminosities are better AGN power indicators for our sample than either the 5 GHz radio or the X-ray continuum luminosities. We also detect the mid-IR 9.7 μm silicate feature in the spectra of many objects but not ubiquitously: at least 40% of the sample shows no clear evidence for these features. We conclude that, for the majority of powerful radio galaxies, the mid-IR lines are powered by AGN photoionization. [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]