4,458 research outputs found
The final two redshifts for radio sources from the equatorial BRL sample
Best, Rottgering and Lehnert (1999, 2000a) defined a new sample of powerful
radio sources from the Molonglo Reference Catalogue, for which redshifts were
compiled or measured for 177 of the 178 objects. For the final object,
MRC1059-010 (3C249), the host galaxy is here identified using near-infrared
imaging, and the redshift is determined from VLT spectroscopy. For one other
object in the sample, MRC0320+053 (4C05.14), the literature redshift has been
questioned: new spectroscopic observations of this object are presented,
deriving a corrected redshift. With these two results, the spectroscopic
completeness of this sample is now 100%.
New redshifts are also presented for PKS0742+10 from the Wall & Peacock 2.7
GHz catalogue, and PKS1336+003 from the Parkes Selected Regions. PKS0742+10
shows a strong neutral hydrogen absorption feature in its Lyman-alpha emission
profile.Comment: 4 pages. LaTeX. Accepted for publication in MNRA
HST and UKIRT imaging observations of z~1 6C radio galaxies - II. Galaxy morphologies and the alignment effect
(abridged) Powerful radio galaxies often display enhanced optical/UV emission
regions, elongated and aligned with the radio jet axis. The aim of this series
of papers is to separately investigate the effects of radio power and redshift
on the alignment effect, together with other radio galaxy properties. In this
second paper, we present a deeper analysis of the morphological properties of
these systems, including both the host galaxies and their surrounding aligned
emission. The host galaxies of our 6C subsample are well described as de
Vaucouleurs ellipticals, with typical scale sizes of ~10kpc. This is comparable
to the host galaxies of low-z radio sources of similar powers, and also the
more powerful 3CR sources at the same redshift. The contribution of nuclear
point source emission is also comparable, regardless of radio power. The 6C
alignment effect is remarkably similar to that seen around more powerful 3CR
sources at the same redshift in terms of extent and degree of alignment with
the radio source axis, although it is generally less luminous. The bright,
knotty features observed in the case of the z~1 3CR sources are far less
frequent in our 6C subsample; neither do we observe such strong evidence for
evolution in the strength of the alignment effect with radio source size/age.
However, we do find a very strong link between the most extreme alignment
effects and emission line region properties indicative of shocks, regardless of
source size/age or power. In general, the 6C alignment effect is still
considerably stronger than that seen around lower redshift galaxies of similar
radio powers. (abridged)Comment: 23 pages, 15 figures, accepted for publication in MNRAS. See
http://www.mrao.cam.ac.uk/~kji/MorphPaper/ for version of paper with full
resolution images of Figs 1-1
The black holes of radio galaxies during the "Quasar Era": Masses, accretion rates, and evolutionary stage
We present an analysis of the AGN broad-line regions of 6 powerful radio
galaxies at z>~2 (HzRGs) with rest-frame optical imaging spectroscopy obtained
at the VLT. All galaxies have luminous (L(H-alpha)=few x 10^44 erg s^-1),
spatially unresolved H-alpha line emission with FWHM>= 10,000 km s^-1 at the
position of the nucleus, suggesting their AGN are powered by supermassive black
holes with masses of few x 10^9 M_sun and accretion luminosities of a few
percent of the Eddington luminosity. In two galaxies we also detect the BLRs in
H-beta, suggesting relatively low extinction of A_V~1 mag, which agrees with
constraints from X-ray observations. By relating black hole and bulge mass, we
find a possible offset towards higher black-hole masses of at most ~0.6 dex
relative to nearby galaxies at a given host mass, although each individual
galaxy is within the scatter of the local relationship. If not entirely from
systematic effects, this would then suggest that the masses of the host
galaxies have increased by at most a factor ~4 since z~2 relative to the
black-hole masses, perhaps through accretion of satellite galaxies or because
of a time lag between star formation in the host galaxy and AGN fueling. We
also compare the radiative and mechanical energy output (from jets) of our
targets with predictions of recent models of "synthesis" or "grand unified" AGN
feedback, which postulate that AGN with similar radiative and mechanical energy
output rates to those found in our HzRGs may be nearing the end of their period
of active growth. We discuss evidence that they may reach this stage at the
same time as their host galaxies.Comment: A&A in pres
Defying jet-gas alignment in two radio galaxies at z~2 with extended light profiles: Similarities to brightest cluster galaxies
We report the detection of extended warm ionized gas in two powerful
high-redshift radio galaxies, NVSS J210626-314003 at z=2.10 and TXS 2353-003 at
z=1.49, that does not appear to be associated with the radio jets. This is
contrary to what would be expected from the alignment effect, a characteristic
feature of distant, powerful radio galaxies at z> 0.6. The gas also has smaller
velocity gradients and line widths than most other high-z radio galaxies with
similar data. Both galaxies are part of a systematic study of 50 high-redshift
radio galaxies with SINFONI, and are the only two that are characterized by the
presence of high surface-brightness gas not associated with the jet axis and by
the absence of such gas aligned with the jet. Both galaxies are spatially
resolved with ISAAC broadband imaging covering the rest-frame R band, and have
extended wings that cannot be attributed to line contamination. We argue that
the gas and stellar properties of these galaxies are more akin to gas-rich
brightest cluster galaxies in cool-core clusters than the general population of
high-redshift radio galaxies at z>2. In support of this interpretation, one of
our sources, TXS 2353-003, for which we have H\alpha\ narrowband imaging, is
associated with an overdensity of candidate H\alpha\ emitters by a factor of 8
relative to the field at z=1.5. We discuss possible scenarios of the
evolutionary state of these galaxies and the nature of their emission line gas
within the context of cyclical AGN feedback.Comment: A&A in pres
Testing Black Hole Jet Scaling Relations in Low Luminosity AGN
We present the results of the analysis of a sample of 17 low-luminosity (L_x
< 1e42 erg/s), radio loud AGNs in massive galaxies. The sample is extracted
from the SDSS database and it spans uniformly a wide range in optical [OIII]
emission line and radio luminosity, but within a narrow redshift range (0.05 <
z < 0.11) and a narrow super massive black hole mass range (~ 1e8 M_sun). For
these sources we measured core X-ray emission with the Chandra X-ray telescope
and radio emission with the VLA. Our main goal is to establish which emission
component, if any, can be regarded as the most reliable accretion/jet-power
estimator at these regimes. In order to do so, we studied the correlation
between emission line properties, radio luminosity, radio spectral slopes and
X-ray luminosity, as well as more complex multi-variate relations involving
black hole mass, such as the fundamental plane of black hole activity. We find
that 15 out of 17 sources of our sample can be classified as Low-Excitation
Galaxies (LEG) and their observed properties suggest X-ray and radio emission
to originate from the jet basis. We also find that X-ray emission does not
appear to be affected by nuclear obscuration and can be used as a reliable
jet-power estimator. More generally, X-ray, radio and optical emission appear
to be related, although no tight correlation is found. In accordance with a
number of recent studies of this class of objects these findings may be
explained by a lack of cold (molecular) gaseous structures in the innermost
region of these massive galaxies.Comment: 11 pages, 6 figures, published in MNRA
CENSORS: A Combined EIS-NVSS Survey Of Radio Sources. I. Sample definition, radio data and optical identifications
A new sample of radio sources, with the designated name CENSORS (A Combined
EIS-NVSS Survey Of Radio Sources), has been defined by combining the NRAO VLA
Sky Survey (NVSS) at 1.4 GHz with the ESO Imaging Survey (EIS) Patch D, a 3 by
2 degree region of sky centred at 09 51 36.0, -21 00 00 (J2000). New radio
observations of 199 NVSS radio sources with NVSS flux densities S(1.4GHz) >
7.8mJy are presented, and compared with the EIS I-band imaging observations
which reach a depth of I~23; optical identifications are obtained for over
two-thirds of the ~150 confirmed radio sources within the EIS field. The radio
sources have a median linear size of 6 arcseconds, consistent with the trend
for lower flux density radio sources to be less extended. Other radio source
properties, such as the lobe flux density ratios, are consistent with those of
brighter radio source samples. From the optical information, 30-40% of the
sources are expected to lie at redshifts z >~ 1.5.
One of the key goals of this survey is to accurately determine the high
redshift evolution of the radio luminosity function. These radio sources are at
the ideal flux density level to achieve this goal; at redshifts z~2 they have
luminosities which are around the break of the luminosity function and so
provide a much more accurate census of the radio source population at those
redshifts than the existing studies of extreme, high radio power sources. Other
survey goals include investigating the dual--population unification schemes for
radio sources, studying the radio luminosity dependence of the evolution of
radio source environments, and understanding the radio power dependence of the
K-z relation for radio galaxies.Comment: Accepted for publication in MNRAS. 28 pages plus 36 reduced
resolution jpeg figures. A postscript version with full resolution figures
included in the text is available from
http://www.roe.ac.uk/~pnb/censors.ps.g
Celebrity advocacy and public engagement: the divergent uses of celebrity
This article sounds a cautionary note about the instrumental use of celebrity advocacy to (re)engage audiences in public life. It begins by setting out the steps necessary to achieve public recognition of a social problem requiring a response. It then presents empirical evidence which suggests that those most interested in celebrity, while also paying attention to the main stories of the day, are also least likely to participate in any form of politics. However, this does not rule out the possibility of forging a link between celebrity and public engagement, raising questions about what would potentially sustain such an articulation. After discussing the broader cultural context of celebrity advocacy in which perceived authenticity functions valorised form of symbolic capital, the article outlines a phenomenological approach to understanding the uses audiences make of celebrity advocacy, using the example of a Ewan McGregor UNICEF appeal for illustration. It concludes that while media encounters with celebrities can underpin a viewerâs sense of self, this is as likely to lead to the rationalisation of inaction as a positive response to a charity appeal
Double Lobed Radio Quasars from the Sloan Digital Sky Survey
We have combined a sample of 44984 quasars, selected from the Sloan Digital
Sky Survey (SDSS) Data Release 3, with the FIRST radio survey. Using a novel
technique where the optical quasar position is matched to the complete radio
environment within 450", we are able to characterize the radio morphological
make-up of what is essentially an optically selected quasar sample, regardless
of whether the quasar (nucleus) itself has been detected in the radio. About
10% of the quasar population have radio cores brighter than 0.75 mJy at 1.4
GHz, and 1.7% have double lobed FR2-like radio morphologies. About 75% of the
FR2 sources have a radio core (> 0.75 mJy). A significant fraction (~40%) of
the FR2 quasars are bent by more than 10 degrees, indicating either
interactions of the radio plasma with the ICM or IGM. We found no evidence for
correlations with redshift among our FR2 quasars: radio lobe flux densities and
radio source diameters of the quasars have similar distributions at low (mean
0.77) and high (mean 2.09) redshifts. Using a smaller high reliability FR2
sample of 422 quasars and two comparison samples of radio-quiet and non-FR2
radio-loud quasars, matched in their redshift distributions, we constructed
composite optical spectra from the SDSS spectroscopic data. Based on these
spectra we can conclude that the FR2 quasars have stronger high-ionization
emission lines compared to both the radio quiet and non-FR2 radio loud sources.
This is consistent with the notion that the emission lines are brightened by
ongoing shock ionization of ambient gas in the quasar host as the radio source
expands.Comment: 20 pages, 10 figures - some of which have been reduced in quality /
size. Accepted for publication in the Astronomical Journa
HST, radio and infrared observations of 28 3CR radio galaxies at redshift z ~ 1: I. Old stellar populations in central cluster galaxies
Hubble Space Telescope images of 3CR radio galaxies at redshifts 0.6 < z <
1.8 have shown a remarkable variety of structures, generally aligned along the
radio axis, indicating that the radio source strongly influences the optical
appearance of these galaxies. In this paper we investigate the host galaxies
underlying this aligned emission, combining the HST data with ground-based
infrared images. An investigation of the spectral energy distributions of the
galaxies shows that the contribution of the aligned blue component to the
K--band light is generally small (about 10%). The radial intensity profiles of
the galaxies are well matched at radii <~ 35 kpc by de Vaucouleurs' law,
demonstrating that the K--band light is dominated by that of an elliptical
galaxy. There is no evidence for a nuclear point source, in addition to the de
Vaucouleurs profile, with a contribution >~15% of the total K--band flux
density, except in two cases, 3C22 and 3C41. Large characteristic radii are
derived, indicating that the 3CR galaxies must be highly evolved dynamically,
even at a redshift of one. At radii > 35 kpc, a combined galaxy profile clearly
shows an excess of emission reminiscent of cD--type halos. This supports other
independent evidence for the hypothesis that the distant 3CR galaxies lie in
moderately rich (proto--)clusters. Since the nearby FR II galaxies in the 3CR
catalogue lie in more diffuse environments and do not possess cD halos, the
galactic environments of the 3CR galaxies must change with redshift. The K-z
relation of the 3CR galaxies cannot, therefore, be interpreted using a standard
`closed-box, passive stellar evolution' model. We offer a new interpretation,
and compare the model with the K-z relations of lower power radio galaxies and
brightest cluster galaxies. (abridged)Comment: 21 pages including 13 figures, LaTeX. To appear in MNRA
Recovery identity and wellbeing: is it better to be 'recovered' or 'in recovery'?
While there has been debate about the meaning of recovery, there has been little discussion about how people characterise their own recovery experience, in particular whether people describe themselves as 'recovered' (as with a therapeutic community (TC) philosophy) or as 'in recovery' (typically those engaged in 12-step). The paper assesses differences in wellbeing as a function of recovery self-ascriptions, based on the UK Life in Recovery survey. Those who described themselves as 'recovered' or 'ex-addicts' reported better psychological health and lower identification with addicts and recovery, and showed stronger recovery functioning. There are clearly multiple pathways to recovery, and philosophy may impact on both trajectory of recovery and the social identity mechanisms underpinning change
- âŠ