arXiv subjects

Clive N. Tadhunter

Publications and source records attributed to Clive N. Tadhunter.

At least 19 recordsLinked to original sources

arXiv2026

Dust destruction signals shock-accelerated outflows in the nearby active galaxy NGC 1068

Massive gas outflows driven by active galactic nuclei (AGN) are a key ingredient in models of galaxy evolution, in which they are required to regulate star formation and thus explain the observed properties of the galaxy population. However, it remains uncertain how such outflows are accelerated. Here, we use deep spectroscopic observations of the nearby active galaxy NGC 1068 to directly address this issue. Based on the flux ratios of high-ionisation [NeV]$λ$3425 and [FeVII]$λ$6087 coronal forbidden lines, we show that the non-outflowing gas in the disk of the galaxy is characterised by high levels of depletion of refractory elements onto dust grains, but the outflowing gas just above the disk is largely dust-free. Consistent results are also found for the ratios of lower-ionisation forbidden lines of refractory and non-refractory elements. Moreover, a range of diagnostic ratios demonstrate that the density of outflowing gas is a factor 19-110 times higher than that of the non-outflowing gas. Together, these results imply that the outflows in NGC 1068 are accelerated by fast shocks that both compress the gas and destroy much of the dust. Consistent with the idea that AGN-driven shocks play an important role in heating and accelerating the near-nuclear gas in galaxies, this study demonstrates that coronal emission lines are a key diagnostic of the destructive impact of AGN activity.

astro-ph.GA↗

arXiv2026

The dependence of triggering mechanisms on radio AGN sub-types: the role of galaxy mergers

Powerful, radio-loud active galactic nuclei (AGN) are associated with one of the most important forms of AGN feedback, and understanding how they are triggered is key to properly incorporating them into models of galaxy evolution. Here, we present the results of a deep Isaac Newton Telescope/Wide Field Camera imaging survey which, when combined with Gemini/Gemini Multi-Object Spectrograph South images, gives a 98 per cent complete sample of 112 3CR radio galaxies with redshifts $z$ < 0.3, alongside a stellar mass matched control sample. Our results provide strong evidence for significant differences ($\sim$3$σ$) between the triggering mechanisms of the different sub-types of powerful radio AGN. The high-excitation radio galaxies (HERGs) show a high rate of morphological disturbance (62$^{+6}_{-7}$ per cent) -- an excess of $\sim$4$σ$ compared with the control sample -- consistent with them being predominantly triggered in galaxy mergers and interactions. In contrast, the low-excitation radio galaxies (LERGs) show a much lower rate of morphological disturbance (36$^{+7}_{-6}$ per cent), consistent with the control sample, and suggesting a different dominant triggering mechanism, such as the accretion of gas from the hot X-ray haloes of the host galaxies or galaxy clusters. We also demonstrate that, when considering the radio morphology, the FRII HERG sources preferentially reside in disturbed morphologies, a difference of $\sim$3$σ$ to the FRII LERG objects. This suggests that the FRII LERG sources do not solely represent a `switched-off' phase in the HERG lifecycle of the same parent galaxy population as the FRII HERGs.

astro-ph.GA↗

arXiv2024

No evidence for fast, galaxy-wide ionised outflows in a nearby quasar -- the importance of accounting for beam smearing

To test the scenario that outflows accelerated by active galactic nuclei (AGN) have a major impact on galaxy-wide scales, we have analysed deep VLT/MUSE data for the type-2 quasar/ultraluminous infrared galaxy F13451+1232 - an object that represents the major mergers considered in models of galaxy evolution. After carefully accounting for the effects of atmospheric seeing that had smeared the emission from known compact nuclear outflows across the MUSE field of view, we find that the large-scale kinematics in F13451+1232 are consistent with gravitational motions that are expected in a galaxy merger. Therefore, the fast ($\mathrm{W_{80}}>500$ km s$^{-1}$) warm-ionised AGN-driven outflows in this object are limited to the central $\sim$100 pc of the galaxy, although we cannot rule out larger-scale, lower-velocity outflows. Moreover, we directly demonstrate that failure to account for the beam-smearing effects of atmospheric seeing would have led to the mass outflow rates and kinetic powers of spatially-extended emission being overestimated by orders of magnitude. We also show that beam-smeared compact-outflow emission can be significant beyond radial distances of 3.5 arcseconds (more than eight times the radius of the seeing disk), and support the argument that some previous claims of large-scale outflows in active galaxies were likely the result of this effect rather than genuine galaxy-wide ($r>5$ kpc) outflows. Our study therefore provides further evidence that warm-ionised AGN-driven outflows are limited to the central kiloparsecs of galaxies and highlights the critical importance of accounting for atmospheric seeing in ground-based observational studies of active galaxies.

astro-ph.GA↗

arXiv2024

QSOFEED: The relationship between star formation and AGN Feedback

Large-scale cosmological simulations suggest that feedback from active galactic nuclei (AGN) plays a crucial role in galaxy evolution. In this study, we directly test this hypothesis utilising SDSS spectra of a sample of 48 low redshift (z<0.14) type 2 quasars (QSO2s). We characterised the kinematics of the warm ionised gas by performing a non-parametric analysis of the [OIII]$λ5007$ emission line, as well as constrain the properties of the young stellar populations (YSP) of their host galaxies through spectral synthesis modelling. These analyses revealed that 85% of the QSO2s display gas velocity dispersions larger than that of the stellar component of their host galaxies, indicating the presence of AGN-driven outflows. Comparing the gas kinematics to the AGN properties, we found a positive correlation between gas velocity dispersion and 1.4 GHz radio luminosity but not with AGN bolometric luminosity or Eddington ratio, suggesting that, either the radio luminosity is the key factor in driving outflows or that the outflows themselves are shocking the ISM and producing synchrotron emission. We found that 98% of the sample host YSPs to varying degrees, with star formation rates (SFR) $0 \le SFR \le 92 \mbox{ M}_{\odot} \mbox{yr}^{-1}$, averaged over 100 Myr. We compared the gas kinematics and outflow properties to the SFRs to establish possible correlations which may suggest that the presence of the outflowing gas is impacting SF and find that none exists, leading to the conclusion that, on the scales probed by the SDSS fibre, AGN-driven outflows do not impact SF on the timescales probed in this study. However, we found a positive correlation between the light-weighted stellar ages of the QSO2s and the black hole mass, which may indicate that successive AGN episodes lead to the suppression of SF over the course of galaxy evolution.

astro-ph.GA↗

arXiv2024

ALMA reveals a compact and massive molecular outflow driven by the young AGN in a nearby ULIRG

The ultra luminous infrared galaxy (ULIRG) F13451+1232 is an excellent example of a galaxy merger in the early stages of active galactic nucleus (AGN) activity, a phase in which AGN-driven outflows are expected to be particularly important. However, previous observations have determined that the mass outflow rates of the warm ionised and neutral gas phases in F13451+1232 are relatively modest, and there has been no robust detection of molecular outflows. Using high spatial resolution ALMA CO(1-0) observations, we detect a kiloparsec-scale circumnuclear disk, as well as extended ($r\sim440$ pc), intermediate-velocity (300<|$v$|<400 km s$^{-1}$) cold molecular gas emission that cannot be explained by rotational disk motions. If interpreted as AGN-driven outflows, the mass outflow rates associated with this intermediate-velocity gas are relatively modest ($\dot{M}_\mathrm{out}=22$-$27$ M$_\odot$ yr$^{-1}$); however, we also detect a compact ($r_\mathrm{out}$<120 pc), high velocity (400<$v$<680 km s$^{-1}$) cold molecular outflow near the primary nucleus of F13451+1232, which carries an order of magnitude more mass ($\dot{M}_\mathrm{out}\sim230$ M$_\odot$ yr$^{-1}$) than (and several times the kinetic power of) the previously-detected warmer phases. Moreover, the similar spatial scales of this compact outflow and the radio structure indicate that it is likely accelerated by the small-scale ($r\sim130$ pc) AGN jet in the primary nucleus of F13451+1232. Considering the compactness of the nuclear outflow and intermediate-velocity non-rotating gas that we detect, we argue that high spatial-resolution observations are necessary to properly quantify the properties of AGN-driven outflows and their impacts on host galaxies.

astro-ph.GA↗

arXiv2023

Outflow densities and ionisation mechanisms in the NLRs of the prototypical Seyfert galaxies NGC 1068 and NGC 4151

Despite being thought to play an important role in galaxy evolution, the true impact of outflows driven by active galactic nuclei (AGN) on their host galaxies is unclear. In part, this may be because electron densities of outflowing gas are often underestimated: recent studies that use alternative diagnostics have measured much higher densities than those from commonly used techniques, and consequently find modest outflow masses and kinetic powers. Furthermore, outflow ionisation mechanisms - which are often used to probe acceleration mechanisms - are also uncertain. To address these issues, we have analysed archival HST/STIS spectra of the inner regions (r<160pc) of the nearby prototypical Seyfert galaxies NGC 1068 and NGC 4151, which show evidence of warm-ionised outflows driven by the central AGN. We derive high electron densities ($10^{3.6}$<$n_e$<$10^{4.8}$cm$^{-3}$) using the transauroral [OII] and [SII] emission lines ratios for the first time with spatially-resolved observations. Moreover, we find evidence that the gas along the radio axis in NGC 1068 has a significant AGN-photoionised matter-bounded component, and there is evidence for shock-ionisation and/or radiation-bounded AGN-photoionisation along the radio axis in NGC 4151. We also note that the outflow extents are similar to those of the radio structures, consistent with acceleration by jet-induced shocks. Taken together, our investigation demonstrates the diversity of physical and ionisation conditions in the narrow line regions of Seyfert galaxies, and hence reinforces the need for robust diagnostics of outflowing gas densities and ionisation mechanisms.

astro-ph.GA↗

arXiv2023

Precise physical conditions for the warm gas outflows in the nearby active galaxy IC 5063

AGN-driven outflows are now routinely used in models of galaxy evolution as a feedback mechanism, however many of their properties remain highly uncertain. Perhaps the greatest source of uncertainty is the electron density of the outflowing gas, which directly affects derived kinetic powers and mass outflow rates. Here we present spatially-resolved, wide spectral-coverage Xshooter observations of the nearby active galaxy IC 5063 (z=0.001131), which shows clear signatures of outflows being driven by shocks induced by a radio jet interacting with the ISM. For the first time, we use the higher critical-density transauroral [SII] and [OII] lines to derive electron densities in spatially-resolved observations of an active galaxy, and present evidence that the lines are emitted in the same spatial regions as other key diagnostic lines. In addition, we find that the post-shock gas is denser than the pre-shock gas, possibly due to shock compression effects. We derive kinetic powers for the warm ionised outflow phase and find them to be below those required by galaxy evolution models; however, other studies of different gas phases in IC 5063 allow us to place our results in a wider context in which the cooler gas phases constitute most of the outflowing mass. We investigate the dominant ionisation and excitation mechanisms and find that the warm ionised outflow phase is dominated by AGN-photoionisation, while the warm molecular phase has composite AGN-shock excitation. Overall, our results highlight the importance of robust outflow diagnostics and reinforce the utility of the transauroral lines for future studies of outflows in active galaxies.

astro-ph.GA↗

arXiv2021

HI absorption at z~0.7 against the lobe of the powerful radio galaxy PKS 0409-75

We present results from a search for the HI 21-cm line in absorption towards 16 bright radio sources with the 6-antenna commissioning array of the Australian Square Kilometre Array Pathfinder (ASKAP). Our targets were selected from the 2-Jy sample, a flux-limited survey of the southern radio sky with extensive multi-wavelength follow-up. Two sources were detected in HI absorption including a new detection towards the bright FRII radio galaxy PKS 0409-75 at a redshift of z=0.674. The HI absorption line is blueshifted by ~3300 km/s compared to the optical redshift of the host galaxy of PKS 0409-75 at z=0.693. Deep optical imaging and spectroscopic follow-up with the GMOS instrument on the Gemini-South telescope reveal that the HI absorption is associated with a galaxy in front of the southern radio lobe with a stellar mass of $3.2 - 6.8 \times 10^{11}M_\odot$, a star-formation rate of $\sim 1.24 M_\odot$ yr$^{-1}$ and an estimated HI column density of $2.16\times10^{21}$ cm$^{-2}$, assuming a spin temperature of $T_{\rm spin}=500$ K and source covering factor of $C_{\rm f}=0.3$. Using polarisation measurements of PKS 0409-75 from the literature we estimate the magnetic field of the absorbing galaxy to be ~14.5$μ$G, consistent with field strengths observed in nearby spiral galaxies, but larger than expected for an elliptical galaxy. Results from this pilot study can inform future surveys as new wide-field telescopes allow us to search for 21-cm HI absorption towards all bright radio sources as opposed to smaller targeted samples.

astro-ph.GA↗

arXiv2020

Taking snapshots of the jet-ISM interplay with ALMA

We present an update of our on-going project to characterise the impact of radio jets on the ISM by tracing molecular gas at high spatial resolution using ALMA. The radio active galactic nuclei (AGN) studied show recently born radio jets. In this stage, the plasma jets can have the largest impact on the ISM, as also predicted by state-of-the-art simulations. The two targets have quite different ages, allowing us to get snapshots of the effects of radio jets as they grow. Interestingly, both also host powerful quasar emission. The largest mass outflow rate of molecular gas is found in a radio galaxy hosting a newly born radio jet emerging from an obscuring cocoon of gas and dust. Although the mass outflow rate is high (few hundred Msun/yr), the outflow is limited to the inner few hundred pc region. In a second object, the jet is larger (a few kpc) and is in a more advanced evolutionary phase. In this object, the distribution of the molecular gas is reminiscent of what is seen, on larger scales, in cool-core clusters hosting radio galaxies. Gas deviating from quiescent kinematics is not very prominent, limited only to the very inner region, and has a low mass outflow rate. Instead, on kpc scales, the radio lobes appear associated with depressions in the distribution of the molecular gas, suggesting they have broken out from the dense nuclear region. The AGN does not appear to be able at present to stop the star formation observed in this galaxy. These results suggest that the effects of the radio source start in the first phases by producing outflows which, however, tend to be limited to the kpc region. After that, the effects turn into producing large-scale bubbles which could, in the long term, prevent the surrounding gas from cooling. Our results characterise the effect of radio jets in different phases of their evolution, bridging the studies done for radio galaxies in clusters.

astro-ph.HE↗

arXiv2020

The radio properties of HERGs with intermediate radio powers

In the past decade, high sensitivity radio surveys have revealed that the local radio AGN population is dominated by moderate-to-low power sources with emission that is compact on galaxy scales. High-excitation radio galaxies (HERGs) with intermediate radio powers (22.5 $<$ log(L$_{\rm 1.4GHz}$) $<$ 25.0 W Hz$^{-1}$) form an important sub-group of this population, since there is strong evidence that they also drive multi-phase outflows on the scales of galaxy bulges. Here, we present high-resolution VLA observations at 1.5, 4.5 and 7.5 GHz of a sample of 16 such HERGs in the local universe ($z<0.1$), conducted in order to investigate the morphology, extent and spectra of their radio emission in detail, down to sub-kpc scales. We find that the majority (56 per cent) have unresolved structures at the limiting angular resolution of the observations ($\sim$0.3"). Although similar in the compactness of their radio structures, these sources have steep radio spectra and host galaxy properties that distinguish them from local low-excitation radio galaxies (LERGs) that are unresolved on similar scales. The remaining sources exhibit extended radio structures with projected diameters $\sim$1.4$-$19.0 kpc and a variety of morphologies: three double-lobed; two large-scale diffuse; one jetted and `S-shaped'; one undetermined. Only 19 per cent of the sample therefore exhibit the double-lobed/edge-brightened structures often associated with their counterparts at high and low radio powers: radio-powerful HERGs and Seyfert galaxies, respectively. Additional high-resolution observations are required to investigate this further, and to probe the $\lesssim$300 pc scales on which some Seyfert galaxies show extended structures.

astro-ph.GA↗

arXiv2019

A near-infrared study of the multi-phase outflow in the type-2 quasar J1509+0434

Based on new near-infrared spectroscopic data from the instrument EMIR on the 10.4 m Gran Telescopio Canarias (GTC) 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$\pm$0.18 kpc and 1.46$\pm$0.20 kpc respectively). We use these radii, the broad emission-line luminosities and in the case of the ionized outflow, the density calculated from the trans-auroral [OII] and [SII] lines, to derive mass outflow rates and kinetic coupling efficiencies. Whilst the ionized and warm molecular outflows represent a small fraction of the AGN power ($\leq$0.033% and 0.0001% of L$_{bol}$ respectively), the total molecular outflow, whose mass is estimated from an assumed warm-to-cold gas mass ratio of 6$\times10^{-5}$, has a kinetic coupling efficiency of $\sim$1.7%L$_{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 Pa$α$ emission extending out to 4 arcsec (8 kpc) South-East and North-West from the active nucleus.

astro-ph.GA↗

arXiv2019

Do AGN triggering mechanisms vary with radio power? I.Optical morphologies of radio-intermediate HERGs

Radio AGNs with intermediate radio powers are capable of driving multi-phase outflows in galaxy bulges, and are also more common than their high-radio-power counterparts. In-depth characterisation 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 WHz$^{-1}$). The fraction of hosts with morphological signatures of mergers and interactions is greatly reduced compared to the 2 Jy radio-powerful galaxies (log(L$_{\rm 1.4GHz}$) $>$ 25.0 WHz$^{-1}$) with strong optical emission lines: 53 $\pm$ 9 per cent and 94 $\pm$ 4 per cent, respectively. In addition, the most radio-powerful half of the sample has a higher frequency of morphological disturbance than the least radio-powerful half (67 $\pm$ 12 per cent and 40 $\pm$ 13 per cent, respectively), including the eight most highly-disturbed galaxies. This suggests that the importance of triggering nuclear activity in 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, disk-based processes has increased importance for HERGs with lower radio powers (e.g. disk instabilities, large scale bars).

astro-ph.GA↗

arXiv2014

Extended Warm Gas in the ULIRG Mrk273: Galactic Outflows and Tidal Debris

We present new HST ACS medium- and narrow-band images and long-slit, optical (4000 - 7200A) spectra obtained using the Isaac Newton Telescope (INT) on La Palma, of the merging system Mrk273. The HST observations sample the [OIII]4959,5007 emission from the galaxy and the nearby continuum. The 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 extending ~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 [OIII] emission. Kinematic disturbance, in the form of broad (FWHM > 500 km s-1) and/or strongly shifted (abs(\DeltaV) >150 km s-1) emission line components, is found at almost all locations within a radius of ~4 kpc to the east and west of the northern nucleus. We fit the profiles of all the emission lines of different ionisation with a kinematic model using up to 3 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, in general, the line ratios are consistent with photoionization by an AGN as the main ionisation mechanism. Finally, the highest surface brightness [OIII] 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.

astro-ph.GA↗

arXiv2013

Clear evidence for the early triggering of a luminous quasar-like AGN in a major, gas rich merger

We present deep, intermediate resolution, long slit Gemini GMOS-S optical spectra of the 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 (YSP) 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 AGN 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) X 10^10 solar masses, lower than typically found for quasar host galaxies.

astro-ph.CO↗

arXiv2012

The importance of galaxy interactions in triggering type II quasar activity

We present deep Gemini GMOS-S optical broad-band images for a complete sample of 20 SDSS selected type II quasars with redshifts 0.3 < z < 0.41 and [OIII] emission line luminosities greater than 10^8.5 solar luminosities. We use these images to determine the significance of galaxy interactions in triggering nuclear activity, finding that 15 (75%) show evidence for interaction in the form of tails, shells, double nuclei etc. The median surface brightness of the features is 23.4 mag arcsec sq and the range is 20.9-24.7 mag arcsec sq. We find a similar rate of interaction in the type II quasars as in a comparison sample of quiescent early-type galaxies at similar redshift (67 +/- 14%). However the surface brightness of the detected features is up to 2 magnitudes brighter for the type II quasars than for the quiescent early-types, which have surface brightnesses in the range 22.1-26.1 mag arcsec sq and a median surface brightness 24.3 mag arcsec sq. This may indicate that the mergers witnessed in the comparison sample galaxies could have different progenitors, or we may be viewing the interactions at different stages. We also compare our results with a sample of radio-loud AGN and find a higher rate of interaction signatures (95 +/- 21%) than in the type II quasars, but a very similar range of surface brightnesses for the morphological features (20.9-24.8 mag arcsec sq), possibly indicating a similarity in the types of triggering interactions. The range of features detected in the type II quasars suggests that AGN activity can be triggered before, during or after the coalescence of the black holes. Overall, our results are consistent with the idea that galaxy interaction plays an important role in the triggering of quasar activity.

astro-ph.CO↗

arXiv2010

The optical morphologies of the 2Jy sample of radio galaxies: evidence for galaxy interactions

We present deep GMOS-S/Gemini optical broad-band images for a complete sample of 46 southern 2Jy radio galaxies at intermediate redshifts (0.05<z<0.7). The high-quality observations show for the first time that the overall majority of PRGs at intermediate redshifts (78-85%) show peculiarities in their optical morphologies at relatively high levels of surface brightness ($μ$v=23.6 and Δ$μ$v~[21,26] mag arcsec-2) including tails, fans, bridges, shells, dust lanes, irregular features, amorphous haloes, and multiple nuclei. While the results for many of the galaxies are consistent with them being observed at, or after, the time of coalescence of the nuclei in a galaxy merger, we find that more than 1/3 of the sample are observed in a pre-coalescence phase of the merger, or following a close encounter between galaxies. By dividing the sample into Weak-Line Radio Galaxies (WLRGs; 11 objects) and Strong-Line Radio Galaxies (SLRGs; 35 objects) we find that only 27% of the former show clear evidence for interactions in their optical morphologies, in contrast to the SLRGs, of which at least 94% appear interacting. This is consistent with the idea that many WLRGs are fuelled/triggered by Bondi accretion of hot gas. Of the 28% of the sample that display evidence for significant starburst activity, we find that 92% present disturbed morphologies, following the same general trend as the total and SLRG samples. By comparing our PRGs with various samples of quiescent ellipticals from the literature, we conclude that the percentage of morphological disturbance that we find here exceeds that found for quiescent ellipticals when similar surface brightnesses are considered. Overall, our study indicates that galaxy interactions are likely to play a key role in the triggering of AGN/jet activity.

astro-ph.CO↗

arXiv2010

A near-IR study of the host galaxies of 2Jy radio sources at 0.03 < z < 0.5: I - the data

We present the results of a program of K- and Ks-band imaging of a sample of 2Jy radio galaxies with redshifts 0.03 < z < 0.5, for which the host galaxy morphologies and structural parameters (effective radius, Sersic index and unresolved nuclear point source contribution) have been determined using GALFIT. Two-thirds of our sample are best modelled as being hosted by massive elliptical galaxies with Sersic indices of n=4-6, with the remainder being better suited either by a mixture of morphological components (usually a bulge plus a small, less luminous, disk component) or by more disky galaxy models with n=1-2. 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 HST-based programs. This is due to our inability to separate the AGN 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.

astro-ph.CO↗

arXiv2002

The Ionization of the Emission Line Gas in Nearby Powerful Radio Galaxies

In this article I review the dominant physical mechanisms in the extended emission line regions (EELR) of powerful radio galaxies at low redshifts and, in particular, the balance between jet-induced shocks and AGN photoionization. I consider the evidence for jet-induced shocks based on morphological, kinematical and ionization (diagnostic diagram) information. Although each of these three types of information separately provides some evidence for the effects of jet-induced shocks, this evidence is often ambiguous. The major advance in recent years has been to combine morphological, kinematical and diagnostic diagram approaches. In this way it has been possible to show that jet-induced shocks dominate the ionization and acceleration of the EELR along the radio axes of many powerful radio galaxies. However, AGN photoionization is likely to remain the dominant mechanism in the nuclear regions of radio galaxies in which the radio sources extend well beyond the emission line regions.

astro-ph↗