613 research outputs found
Luminosity function, sizes and FR dichotomy of radio-loud AGN
The radio luminosity function (RLF) of radio galaxies and radio-loud quasars
is often modelled as a broken power-law. The break luminosity is close to the
dividing line between the two Fanaroff-Riley (FR) morphological classes for the
large-scale radio structure of these objects. We use an analytical model for
the luminosity and size evolution of FRII-type objects together with a simple
prescription for FRI-type sources to construct the RLF. We postulate that all
sources start out with an FRII-type morphology. Weaker jets subsequently
disrupt within the quasi-constant density cores of their host galaxies and
develop turbulent lobes of type FRI. With this model we recover the slopes of
the power laws and the break luminosity of the RLF determined from
observations. The rate at which AGN with jets of jet power appear in the
universe is found to be proportional to . The model also roughly
predicts the distribution of the radio lobe sizes for FRII-type objects, if the
radio luminosity of the turbulent jets drops significantly at the point of
disruption. We show that our model is consistent with recent ideas of two
distinct accretion modes in jet-producing AGN, if radiative efficiency of the
accretion process is correlated with jet power.Comment: 13 pages, 1 figure, accepted by MNRA
6C radio galaxies at z~1: The influence of radio power on the alignment effect
Powerful radio galaxies often display enhanced optical/UV continuum emission
and extended emission line regions, elongated and aligned with the radio jet
axis. The expansion of the radio source strongly affects the gas clouds in the
surrounding IGM, and the kinematic and ionization properties of the extended
emission line regions display considerable variation over the lifetime of
individual sources, as well as with cosmic epoch. We present the results of
deep rest-frame UV and optical imaging and UV spectroscopy of high redshift 6C
radio galaxies. The interdependence of the host galaxy and radio source
properties are discussed, considering: (i) the relative contribution of shocks
associated with the expanding radio source to the observed emission line gas
kinematics, and their effect on the ionization state of the gas; (ii) the
similarities and differences between the morphologies of the host galaxies and
aligned emission for a range of radio source powers; and (iii) the influence of
radio power on the strength of the observed alignment effect.Comment: LaTeX, 6 pages, 5 figures, Elsevier Science format. To appear in
"Radio galaxies: past, present & future". eds. M. Jarvis et al., Leiden, Nov
200
Evolution of AGN Space Densities and the FR Dichotomy
We focus on a comparison of the space densities of FRI and FRII extended
radio sources at different epochs, and find that FRI and FRII sources show
similar space density enhancements in various redshift ranges, possibly
implying a common evolution.Comment: IAU Symposium 267 Proceeding - 1 pag
Apocalypticisim in the fiction of William S. Burroughs, J.G. Ballard, and Thomas Pynchon.
Apocalypse should not be thought of as merely a synonym for chaos or disaster or cataclysmic upheaval; more properly we should think of disclosure, unveiling and revelation. The exact status of literary apocalyptic is the subject of some debate, and in an attempt to help clarify matters an introductory historical survey examines both the formal characteristics of apocalypse and the various critical positions taken in regard to the genre's social influence. Texts considered in the chapter include the Revelation of John and Thomas Pynchon's short story Entropy (1959); theoretical works by Frank Kermode, John Barth, and Jean Baudrillard (amongst others) are also discussed. Chapter One traces the development of William S. Burroughs's apocalyptic sensibility through readings of his correspondence with Allen Ginsberg and the novel The Naked Lunch (1959); the latter's apocalyptic title referring to the "frozen moment when everyone sees what is on the end of every fork". Chapter Two considers Burroughs's experiments with the "cut-ups" and their application in a number of texts, most notably Nova Express (1964). Chapter Three is concerned with Burroughs's work in the 1970s and 80s, and specifically his concept of Here to Go, a theory of mutability presented as a transcendental antidote to the threat of nuclear annihilation (the author's alleged misogyny and the views of radical US feminists are also taken into account). Chapters Four and Five explore the apocalyptic fiction of J. G. Ballard; topics covered include Ballard's concept of inner space, his debt to Surrealism, and the coded landscapes of his more experimental texts; in particular the "condensed novels" which comprise The Atrocity Exhibition (1970). A concluding chapter returns to the work of Thomas Pynchon, offering a reading of Gravity's Rainbow (1973) which allows us to consider his treatment of such related themes as Paranoia, Holocaust, Apocalypse, and finally, Counterforce
Clustering around radio galaxies at z~1.5
The importance of studying old elliptical galaxies at redshift z ~ 1.5 is
reviewed, considering both what can be learned by extending studies of the
evolution of cluster galaxy scaling relations to earlier cosmic epochs, and the
age-dating of old elliptical galaxies at high redshifts. Following this, the
first results are provided of an on-going project to find such distant
elliptical galaxies, through an investigation of the cluster environments of
powerful radio sources with redshifts 1.44 < z < 1.7. These studies show a
considerable excess of red galaxies in the radio sources fields, with the
magnitudes (K >~ 17.5) and colours (R-K > 4) expected of old passively evolving
galaxies at the radio source redshift. The red galaxy overdensities are found
on two different scales around the radio sources; a pronounced small-scale peak
at radial distances of <~ 150 kpc, and a weaker large-scale excess extending
out to 1 - 1.5 Mpc. The presence and richness of these red galaxy excesses
varies considerably from source to source. An interpretation of these results
is provided.Comment: LaTeX, 6 pages, Elsevier Science format. To appear in "Radio
galaxies: past, present & future". eds. M. Jarvis et al., Leiden, Nov 200
Māori values for Māori business: Cultural Capital in Indigenous Organisations
Cultural capital holds much prospect as a theoretical concept for engaging core Indigenous Māori values in capitalistic endeavours, yet it still awaits satisfactory interpretation by Indigenous Māori management theorists researching in Aotearoa New Zealand. Particularly, little is known about how Māori values, beliefs and perspectives impact managerial decision-making to create competitive advantage locally, nationally and internationally. Kaupapa Māori Research has been cited in the research literature as an ideal method for exploring the little known experiences of Māori managers employing the concept of cultural capital. This paper argues that a particular variation of Kaupapa Māori Research be employed to collect and interpret empirical material collected in face-to-face interviews with managers in Māori-centred (tribal and family -based) organisations operating in Aotearoa New Zealand
Erratum: Luminosity function, sizes and FR dichotomy of radio-loud AGN
This erratum corrects a number of formulae containing mistakes in the paper
'Luminosity function, sizes and FR dichotomy of radio-loud AGN', 2007, MNRAS,
v. 381, p.1548. The corrections do not alter any of the conclusions in the
original paper.Comment: single page, no figures, erratum to MNRAS, 2007, v. 381, p. 154
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