The luminosity dependence of the Type 1 AGN fraction

Using a complete, magnitude-limited sample of active galaxies from the Sloan Digital Sky Survey (SDSS) we show that the fraction of broad-line (Type 1) active galactic nuclei increases with luminosity of the isotropically-emitted [O III] narrow emission line. Our results are quantitatively in agreement with, and far less uncertain than, similar trends found from studies of X-ray and radio-selected active galaxies. While the correlation between broad-line fraction and luminosity is qualitatively consistent with the receding torus model, its slope is shallower and we therefore propose a modification to this model where the height of the torus increases slowly with AGN luminosity. We demonstrate that the faint-end slope of the AGN luminosity function steepens significantly when a correction for `missing' Type 2 objects is made and that this can substantially affect the overall AGN luminosity density extrapolated from samples of more luminous objects.Comment: 8 pages, accepted for publication by MNRA

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

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

Vigorous star formation in a bulge-dominated ERO at z = 1.34

We present near-IR spectroscopy of three Extremely Red Objects (EROs) using the OHS/CISCO spectrograph at Subaru telescope. One target exhibits a strong emission line which we identify as H-alpha at z = 1.34. Using new and existing ground-based optical and near-IR imaging, and archival HST imaging, we argue that this target is essentially an elliptical galaxy, with an old stellar population of around 4E11 solar masses, but having a dust-enshrouded star-forming component with a SFR of some 50--100 solar masses per yr. There is no evidence that the galaxy contains an AGN. Analysis of a further two targets, which do not exhibit any features in our near-IR spectra, suggests that one is a quiescent galaxy in the redshift range 1.2 < z < 1.6, but that the other cannot be conclusively categorised as either star-forming or quiescent. Even though our first target has many of the properties of an old elliptical, the ongoing star formation means that it cannot have formed_all_ of its stellar population at high redshift. While we cannot infer any robust values for the star formation rate in ellipticals at z > 1 from this one object, we argue that the presence of an object with such a high SFR in such a small sample suggests that a non-negligible fraction of the elliptical galaxy population may have formed a component of their stellar population at redshifts z ~ 1--2. We suggest that this is evidence for ongoing star formation in the history of elliptical galaxies.Comment: Accepted by MNRAS 1 April 2005. Ten pages, six figure

Quasars are more luminous than radio galaxies - so what?

Surveys to find high-redshift radio galaxies deliberately exclude optically-bright objects, which may be distant radio-loud quasars. In order to properly determine the space density of supermassive black holes, the fraction of such objects missed must be determined within a quantitative framework for AGN unification. I briefly describe the receding torus model, which predicts that quasars should have more luminous ionizing continua than radio galaxies of similar radio luminosity, and present evidence to support it. I also suggest two further tests of the model which should constrain some of its parameters.Comment: 6 pages. To appear in "Radio galaxies: past, present and future", eds M. Jarvis et al., Leiden, Nov 200

Your Place or Mine: status and identity, space and place

This paper takes as its starting point an action research project which sought to reinvigorate a Research and Practice network whose members included both community-based practitioners and academic staff at a University College. It focuses particularly on one aspect of network functioning which emerged during the research process, that is the influence of the settings in which meetings were held; and uses Bourdieu's concept of habitus to discuss ways in which academic and community settings may have impacted on members' participation. The paper incorporates understandings of space and place taken from Massey (2005) alongside symbolic capital (Bourdieu 1989) in order to discuss some of the implications of socially relational space as experienced at meetings of this Research and Practice Network. It discusses network functioning in different settings (both face-to-face and virtual) and concludes with a consideration of the significance of academic spaces for members of the practitioner community

A new look at the isotropy of narrow line emission in extragalactic radio sources

We undertake a quantitative investigation, using Monte Carlo simulations, of the amount by which quasars are expected to exceed radio galaxies in optical luminosity in the context of the `receding torus' model. We compare these simulations with the known behaviour of the [O III] 5007 and [O II] 3727 emission lines and conclude that [O III] is the better indicator of the strength of the underlying non-stellar continuum.Comment: 4 pages, accepted by MNRA