Thermal-infrared imaging of 3C radio galaxies at z~1

We present the results of a programme of thermal-IR imaging of nineteen z~1 radio galaxies from the 3CR and 3CRR samples. We detect emission at L' (3.8um) from four objects; in each case the emission is unresolved at 1" resolution. Fifteen radio galaxies remain undetected to sensitive limits of L'~15.5. Using these data in tandem with archived HST data and near-IR spectroscopy we show that 3 of the detected `radio galaxies' (3C22, 3C41, and 3C65) harbour quasars reddened by Av<5. Correcting for this reddening 3C22 and 3C41 are very similar to coeval 3C quasars, whilst 3C65 seems unusually underluminous. The fourth radio galaxy detection (3C265) is a more highly obscured (Av~15) but otherwise typical quasar which previously has been evident only in scattered light. We determine the fraction of dust-reddened quasars at z~1 to be 28(+25)(-13)% at 90% confidence. On the assumption that the undetected radio galaxies harbour quasars similar to those in 3C22, 3C41 and 3C265 (as seems reasonable given their similar narrow emission line luminosities) we deduce extinctions of Av>15 towards their nuclei. The contributions of reddened quasar nuclei to the total K-band light ranges from ~0 per cent for the non-detections, through ~10 per cent for 3C265 to ~80 per cent for 3C22 and 3C41. Correcting for these effects does not remove the previously reported differences between the K magnitudes of 3C and 6C radio galaxies, so contamination by reddened quasar nuclei is not a serious problem for drawing cosmological conclusions from the K-z relation for radio galaxies. We discuss these results in the context of the `receding torus' model which predicts a small fraction of lightly-reddened quasars in samples of high radio luminosity sources. We also examine the likely future importance of thermal-IR imaging in the study of distant powerful radio sources.Comment: 17 pages incl 14 figures, accepted by MNRA

The evolution of classical doubles: clues from complete samples

We describe the inter-dependence of four properties of classical double radio sources - spectral index, linear size, luminosity and redshift - from an extensive study based on spectroscopically-identified complete samples. We use these relationships to discuss aspects of strategies for searching for radio galaxies at extreme redshifts, in the context of possible capabilities of the new generation of proposed radio telescopes.Comment: To appear in `Perspectives in Radio Astronomy: scientific imperatives at cm and m wavelengths.' eds: M.P. van Haarlem and J.M. van der Hulst Version with colour figures available at http://www-astro.physics.ox.ac.uk/~km

Accretion indicators for the 37 brightest radio sources in the Subaru/XMM-Newton Deep Field

We study the 37 brightest radio sources in the Subaru/XMM-Newton Deep Field (SXDF). Using mid-IR (Spitzer MIPS 24 micron) data we expect to trace nuclear accretion activity, even if it is obscured at optical wavelengths, unless the obscuring column is extreme. Our results suggest that above the `FRI/FRII' radio luminosity break most of the radio sources are associated with objects that have excess mid-IR emission, only some of which are broad-line objects, although there is one clear low-accretion-rate FRI. The fraction of objects with mid-IR excess drops dramatically below the FRI/FRII break, although there exists at least one high-accretion-rate QSO. Investigation of mid-IR and blue excesses shows that they are correlated as predicted by a model in which a torus of dust absorbs ~30% of the light, and the dust above and below the torus scatters >~1% of the light.Comment: 4 pages, 2 figures, to appear in conference proceedings of 'A Century of Cosmology; Past, Present and Future', Venice 200

Extremely red galaxy counterparts to 7C radio sources

We present RIJHK imaging of seven radio galaxies from the 7C Redshift Survey (7CRS) which lack strong emission lines and we use these data to investigate their spectral energy distributions (SEDs) with models which constrain their redshifts. Six of these seven galaxies have extremely red colours (R-K>5.5) and we find that almost all of them lie in the redshift range 1<z<2. We also present near-infrared spectroscopy of these galaxies which demonstrate that their SEDs are not dominated by emission lines, although tentative lines, consistent with H-alpha at z=1.45 and z=1.61, are found in two objects. Although the red colours of the 7CRS galaxies can formally be explained by stellar populations which are either very old or young and heavily reddened, independent evidence favours the former hypothesis. At z~1.5 at least 1/4 of powerful radio jets are triggered in massive (>L*) galaxies which formed the bulk of their stars several Gyr earlier, that is at epochs corresponding to redshifts z>5. If a similar fraction of all z~1.5 radio galaxies are old, then extrapolation of the radio luminosity function shows that, depending on the radio source lifetimes, between 10-100% of the near-IR selected extremely red object (ERO) population undergo a radio outburst at epochs corresponding to 1<z<2. An ERO found serendipitously in the field of one of the 7CRS radio sources appears to be a radio-quiet analogue of the 7CRS EROs with an emission line likely to be [OII] at z=1.20. The implication is that some of the most massive elliptical galaxies formed the bulk of their stars at z>5 and these objects probably undergo at least two periods of AGN activity: one at high redshift during which the black hole forms and another one at an epoch corresponding to z~1.5.Comment: 20 pages, 10 figures, accepted for publication in MNRA

Cosmology with the Square Kilometre Array

We argue that the Square Kilometre Array has the potential to make both redshift (HI) surveys and radio continuum surveys that will revolutionize cosmological studies, provided that it has sufficient instantaneous field-of-view that these surveys can cover a hemisphere in a timescale ~1 yr. Adopting this assumption, we focus on two key experiments which will yield fundamental new measurements in cosmology, characterizing the properties of the mysterious dark energy which dominates the dynamics of today's Universe. Experiment I will map out ~10^9 HI galaxies to redshift z~1.5, providing the premier measurement of the clustering power spectrum of galaxies: accurately delineating the acoustic oscillations and the `turnover'. Experiment II will quantify the cosmic shear distortion of ~10^10 radio continuum sources, determining a precise power spectrum of the dark matter, and its growth as a function of cosmic epoch. We contrast the performance of the SKA in precision cosmology with that of other facilities which will, probably or possibly, be available on a similar timescale. We conclude that data from the SKA will yield transformational science as the direct result of four key features: (i) the immense cosmic volumes probed, exceeding future optical redshift surveys by more than an order of magnitude; (ii) well-controlled systematic effects such as the narrow `k-space window function' for Experiment I and the accurately-known `point-spread function' for Experiment II; (iii) the ability to measure with high precision large-scale modes in the clustering power spectra, for which nuisance effects such as non-linear structure growth, peculiar velocities and `galaxy bias' are minimised; and (iv) different degeneracies between key parameters to those which are inherent in the CMB.Comment: 20 pages, 8 figures. To appear in "Science with the Square Kilometer Array", eds. C.Carilli and S.Rawlings, New Astronomy Reviews (Elsevier: Amsterdam

The Nature and Evolution of Classical Double Radio Sources from Complete Samples

We present a study of the trends in luminosity, linear size, spectral index, and redshift of classical double radio sources from three complete samples selected at successively fainter low radio-frequency flux-limits. We have been able to decouple the effects of the tight correlation between redshift and luminosity (inherent in any single flux-limited sample) which have hitherto hindered interpretation of the relationships between these four source properties. The major trends found are that (i) spectral indices increase with linear size, (ii) rest-frame spectral indices have a stronger dependence on luminosity than on redshift except at high (GHz) frequencies, and that (iii) the linear sizes are smaller at higher redshifts. We reproduce the observed dependences in a model for radio sources (born throughout cosmic time according to a radio-source birth function) whose lobes are fed with a synchrotron-emitting population (whose energy distribution is governed by compact hotspots), and which suffer inverse Compton, synchrotron and adiabatic expansion losses. In simulating the basic observed dependences, we find that there is no need to invoke any systematic change in the environments of these objects with redshift if the consequences of imposing a survey flux-limit on our simulated datasets are properly included in the model. We present evidence that for a radio survey there is an unavoidable `youth--redshift degeneracy', even though radio sources are short-lived relative to the age of the Universe; it is imperative to take this into account in studies which seemingly reveal correlations of source properties with redshift such as the `alignment effect'.Comment: 48 pages, 19 figures, uses aas2pp4.sty. To appear in AJ. Also available at http://www-astro.physics.ox.ac.uk/~kmb References updated and minor typos correcte

Infrared photometry of z~1 3C quasars

We present JHKL' photometry of a complete sample of steep-spectrum radio-loud quasars from the revised 3CR catalogue in the redshift range 0.65 < z < 1.20. After correcting for contributions from emission lines and the host galaxies, we investigate their spectral energy distributions (SEDs) around 1 micron. About 75% of the quasars are tightly grouped in the plane of optical spectral index, alpha_lo, versus near-infrared spectral index, alpha_hi, with the median value of alpha_lo close to the canonical value, and the median alpha_hi slightly flatter. We conclude that the fraction of moderately-obscured, red quasars decreases with increasing radio power, in accordance with the `receding torus' model which can also explain the relatively flat median near-infrared spectra of the 3CR quasars. Two of the red quasars have inverted infrared spectral indices, and we suggest that their unusual SEDs might result from a combination of dust-scattered and transmitted quasar light.Comment: 6 pages, 3 figures, accepted by MNRAS Letter

Ground-state 12CO emission and a resolved jet at 115 GHz (rest-frame) in the radio loud quasar 3C318

An analysis of 44 GHz VLA observations of the z = 1.574 radio-loud quasar 3C318 has revealed emission from the redshifted J = 1 - 0 transition of the CO molecule and spatially resolved the 6.3 kpc radio jet associated with the quasar at 115 GHz rest-frame. The continuum-subtracted line emitter is spatially offset from the quasar nucleus by 0.33" (2.82 kpc in projection). This spatial offset has a significance of >8-sigma and, together with a previously published -400 km/s velocity offset measured in the J = 2 - 1 CO line relative to the systemic redshift of the quasar, rules out a circumnuclear starburst or molecular gas ring and suggests that the quasar host galaxy is either undergoing a major merger with a gas-rich galaxy or is otherwise a highly disrupted system. If the merger scenario is correct then the event may be in its early stages, acting as the trigger for both the young radio jets in the quasar and a starburst in the merging galaxy. The total molecular gas mass in the spatially offset line emitter as measured from the ground-state CO line M_H2 = 3.7 (+/-0.4) x 10^10 (alpha_CO/0.8) M_solar. Assuming that the line-emitter can be modelled as a rotating disk, an inclination-dependent upper limit is derived for its dynamical mass M_dyn sin^2(i) < 3.2 x 10^9 M_solar, suggesting that for M_H2 to remain less than M_dyn the inclination angle must be i < 16 degrees. The far infrared and CO luminosities of 246 extragalactic systems are collated from the literature for comparison. The high molecular gas content of 3C318 is consistent with that of the general population of high redshift quasars and sub-millimetre galaxies.Comment: 10 pages, 4 figures, 2 tables (additional table to appear online as supplementary material), accepted for publication in MNRA

The emission line - radio correlation for radio sources using the 7C Redshift Survey

We have used narrow emission line data from the new 7C Redshift Survey to investigate correlations between the narrow-line luminosities and the radio properties of radio galaxies and steep-spectrum quasars. The 7C Redshift Survey is a low-frequency (151 MHz) selected sample with a flux-density limit about 25-times fainter than the 3CRR sample. By combining these samples, we can for the first time distinguish whether the correlations present are controlled by 151 MHz radio luminosity L_151 or redshift z. We find unequivocal evidence that the dominant effect is a strong positive correlation between narrow line luminosity L_NLR and L_151, of the form L_NLR proportional to L_151 ^ 0.79 +/- 0.04. Correlations of L_NLR with redshift or radio properties, such as linear size or 151 MHz (rest-frame) spectral index, are either much weaker or absent. We use simple assumptions to estimate the total bulk kinetic power Q of the jets in FRII radio sources, and confirm the underlying proportionality between jet power and narrow line luminosity first discussed by Rawlings & Saunders (1991). We make the assumption that the main energy input to the narrow line region is photoionisation by the quasar accretion disc, and relate Q to the disc luminosity, Q_phot. We find that 0.05 < Q / Q_phot < 1 so that the jet power is within about an order of magnitude of the accretion disc luminosity. The most powerful radio sources are accreting at rates close to the Eddington limit of supermassive black holes (~ 10^9 - 10^10 solar masses), whilst lower power sources are accreting at sub-Eddington rates.Comment: 20 pages, 7 figures, to be published in MNRA

Analysis and visualisation of RDF resources in Ondex

An increasing number of biomedical resources provide their information on the Semantic Web and this creates the basis for a distributed knowledge base which has the potential to advance biomedical research [1]. This potential, however, cannot be realized until researchers from the life sciences can interact with information in the Semantic Web. In particular, there is a need for tools that provide data reduction, visualization and interactive analysis capabilities.&#xd;&#xa;Ondex is a data integration and visualization platform developed to support Systems Biology Research [2]. At its core is a data model based on two main principles: first, all information can be represented as a graph and, second, all elements of the graph can be annotated with ontologies. This data model conforms to the Semantic Web framework, in particular to RDF, and therefore Ondex is ideally positioned as a platform that can exploit the semantic web. &#xd;&#xa;The Ondex system offers a range of features and analysis methods of potential value to semantic web users, including:&#xd;&#xa;-&#x9;An interactive graph visualization interface (Ondex user client), which provides data reduction and representation methods that leverage the ontological annotation.&#xd;&#xa;-&#x9;A suite of importers from a variety of data sources to Ondex (http://ondex.org/formats.html)&#xd;&#xa;-&#x9;A collection of plug-ins which implement graph analysis, graph transformation and graph-matching functions.&#xd;&#xa;-&#x9;An integration toolkit (Ondex Integrator) which allows users to compose workflows from these modular components&#xd;&#xa;-&#x9;In addition, all importers and plug-ins are available as web-services which can be integrated in other tools, as for instance Taverna [3].&#xd;&#xa;The developments that will be presented in this demo have made this functionality interoperable with the Semantic Web framework. In particular we have developed an interactive importer, based on SPARQL that allows the query-driven construction of datasets which brings together information from different RDF data resources into Ondex.&#xd;&#xa;These datasets can then be further refined, analysed and annotated both interactively using the Ondex user client and via user-defined workflows. The results of these analyses can be exported in RDF, which can be used to enrich existent knowledge bases, or to provide application-specific views of the data. Both importer and exporter only focus on a subset of the Ondex and RDF data models, which are shared between these two data representations [4].&#xd;&#xa;In this demo we will show how Ondex can be used to query, analyse and visualize Semantic Web knowledge bases. In particular we will present real use cases focused, but not limited to, resources relevant to plant biology. &#xd;&#xa;We believe that Ondex can be a valid contribution to the adoption of the Semantic Web in Systems Biology research and in biomedical investigation more generally. We welcome feedback on our current import/export prototype and suggestions for the advancement of Ondex for the Semantic Web.&#xd;&#xa;&#xd;&#xa;References&#xd;&#xa;&#xd;&#xa;1.&#x9;Ruttenberg, A. et. al.: Advancing translational research with the Semantic Web, BMC Bioinformatics, 8 (Suppl. 3): S2 (2007).&#xd;&#xa;2.&#x9;K&#xf6;hler, J., Baumbach, J., Taubert, J., Specht, M., Skusa, A., Ruegg, A., Rawlings, C., Verrier, P., Philippi, S.: Graph-based analysis and visualization of experimental results with Ondex. Bioinformatics 22 (11):1383-1390 (2006).&#xd;&#xa;3.&#x9;Rawlings, C.: Semantic Data Integration for Systems Biology Research, Technology Track at ISMB&#x2019;09, http://www.iscb.org/uploaded/css/36/11846.pdf (2009).&#xd;&#xa;4.&#x9;Splendiani, A. et. al.: Ondex semantic definition, (Web document) http://ondex.svn.sourceforge.net/viewvc/ondex/trunk/doc/semantics/ (2009).&#xd;&#xa