2,538 research outputs found
The preferentially magnified active nucleus in IRAS F10214+4724 - II. Spatially resolved cold molecular gas
We present JVLA observations of the cold (CO (1-0)) molecular gas in IRAS
F10214+4724, a lensed ULIRG at z=2.3 with an obscured active nucleus. The
galaxy is spatially and spectrally well-resolved in the CO (1-0) emission line.
A CO (1-0) counter-image is detected at the 3-sigma level. Five of the 42 km/s
channels (with >5-sigma detections) are mapped back into the source plane and
their total magnification posterior PDFs sampled. This reveals a roughly linear
arrangement, tentatively a rotating disk. We derive a molecular gas mass of
M_gas = 1.2 +- 0.2 x 10^10 M_sun, assuming a ULIRG L_{CO}-to-M_{gas} conversion
ratio of \alpha = 0.8 M_sun / (K km/s pc^2) that agrees well with the derived
range of \alpha = 0.3 - 1.3 for separate dynamical mass estimates at assumed
inclinations of i = 90 - 30 degrees. Based on the AGN and CO (1-0) peak
emission positions and the lens model, we predict a distortion of the CO
Spectral Line Energy Distribution (SLED) where higher order J lines that may be
partially excited by AGN heating will be preferentially lensed owing to their
smaller solid angles and closer proximity to the AGN and therefore the cusp of
the caustic. Comparison with other lensing inversion results shows that the
narrow line region and AGN radio core in IRAS F10214+4724 are preferentially
lensed by a factor >~ 3 and 11 respectively, relative to the molecular gas
emission. This distorts the global continuum emission Spectral Energy
Distribution (SED) and suggests caution in unsophisticated uses of IRAS
F10214+4724 as an archetype high-redshift ULIRG. We explore two Large Velocity
Gradient (LVG) models, incorporating spatial CO (1-0) and (3-2) information and
present tentative evidence for an extended, low excitation cold gas component
that implies that the total molecular gas mass in IRAS F10214+4724 is a factor
>~2 greater than that calculated using spatially unresolved CO observations.Comment: Dedicated to Steve Rawlings. Accepted for publication in MNRAS. 16
pages, 11 figure
SKA HI end2end simulation
The current status of the HI simulation efforts is presented, in which a self
consistent simulation path is described and basic equations to calculate array
sensitivities are given. There is a summary of the SKA Design Study (SKADS) sky
simulation and a method for implementing it into the array simulator is
presented. A short overview of HI sensitivity requirements is discussed and
expected results for a simulated HI survey are presented.Comment: 7 pages, 6 figues, need skads2009.cls file to late
A submillimetre survey of the star-formation history of radio galaxies
We present the results of the first major systematic submillimetre survey of
radio galaxies spanning the redshift range 1 < z < 5. The primary aim of this
work is to elucidate the star-formation history of this sub-class of elliptical
galaxies by tracing the cosmological evolution of dust mass. Using SCUBA on the
JCMT we have obtained 850-micron photometry of 47 radio galaxies to a
consistent rms depth of 1 mJy, and have detected dust emission in 14 cases. The
radio galaxy targets have been selected from a series of low-frequency radio
surveys of increasing depth (3CRR, 6CE, etc), in order to allow us to separate
the effects of increasing redshift and increasing radio power on submillimetre
luminosity. Although the dynamic range of our study is inevitably small, we
find clear evidence that the typical submillimetre luminosity (and hence dust
mass) of a powerful radio galaxy is a strongly increasing function of redshift;
the detection rate rises from 15 per cent at z 2.5,
and the average submillimetre luminosity rises as (1+z)^3 out to z~4. Moreover
our extensive sample allows us to argue that this behaviour is not driven by
underlying correlations with other radio galaxy properties such as radio power,
radio spectral index, or radio source size/age. Although radio selection may
introduce other more subtle biases, the redshift distribution of our detected
objects is in fact consistent with the most recent estimates of the redshift
distribution of comparably bright submillimetre sources discovered in blank
field surveys. The evolution of submillimetre luminosity found here for radio
galaxies may thus be representative of massive ellipticals in general.Comment: 31 pages - 10 figures in main text, 3 pages of figures in appendix.
This revised version has been re-structured, but the analysis and conclusions
have not changed. Accepted for publication in MNRA
The Evolution of the Stellar Hosts of Radio Galaxies
We present new near-infrared images of z>0.8 radio galaxies from the
flux-limited 7C-III sample of radio sources for which we have recently obtained
almost complete spectroscopic redshifts. The 7C objects have radio luminosities
about 20 times fainter than 3C radio galaxies at a given redshift. The absolute
magnitudes of the underlying host galaxies and their scale sizes are only
weakly dependent on radio luminosity. Radio galaxy hosts at z~2 are
significantly brighter than the hosts of radio-quiet quasars at similar
redshifts and the model AGN hosts of Kauffmann & Haehnelt (2000). There is no
evidence for strong evolution in scale size, which shows a large scatter at all
redshifts. The hosts brighten significantly with redshift, consistent with the
passive evolution of a stellar population that formed at z>~3. This scenario is
consistent with studies of host galaxy morphology and submillimeter continuum
emission, both of which show strong evolution at z>~2.5. The lack of a strong
``redshift cutoff'' in the radio luminosity function to z>4 suggests that the
formation epoch of the radio galaxy host population lasts >~1Gyr from z>~5 to
z~3. We suggest these facts are best explained by models in which the most
massive galaxies and their associated AGN form early due to high baryon
densities in the centres of their dark matter haloes.Comment: To appear in A
Living Walls in The City: Community Values and Expectations
There is an increasing interest in living walls in the urban environment, particularly when linked into green infrastructure for urban heat island mitigation. However, the social acceptance of such systems in Australia is largely untested. To address this knowledge gap, a survey of nineteen local government authorities and twenty living wall owners and managers was conducted. The survey participants included commercial and residential buildings. The survey was used to study living wall owners’ motivations and expectations of living walls as well as the social values attached to the installed infrastructure. This study related the experiences of living wall owners to the current technical knowledge of living walls and contextualised the benefits and costs of living walls for Australian homes and buildings within the public attitudes and motivations for installing such infrastructure. The survey found that social acceptance and the aesthetic values placed on living walls and greenery more broadly represented a substantial advantage for living walls
Living Walls in The City: Community Values and Expectations
There is an increasing interest in living walls in the urban environment, particularly when linked into green infrastructure for urban heat island mitigation. However, the social acceptance of such systems in Australia is largely untested. To address this knowledge gap, a survey of nineteen local government authorities and twenty living wall owners and managers was conducted. The survey participants included commercial and residential buildings. The survey was used to study living wall owners’ motivations and expectations of living walls as well as the social values attached to the installed infrastructure. This study related the experiences of living wall owners to the current technical knowledge of living walls and contextualised the benefits and costs of living walls for Australian homes and buildings within the public attitudes and motivations for installing such infrastructure. The survey found that social acceptance and the aesthetic values placed on living walls and greenery more broadly represented a substantial advantage for living walls
A complete sample of quasars from the 7C redshift survey
We present details of a new sample of radio-loud quasars drawn from 0.013 sr
of the 7C Redshift Survey. This sample is small (21 quasars) but complete in
that every object with an unresolved nucleus and/or broad emission lines with
S(151MHz) > 0.5 Jy has been discovered. The dependence of the quasar fraction
with redshift and radio luminosity is investigated, providing new evidence
supporting the unification of radio-loud quasars and powerful radio galaxies.
This 7C sample is compared with optically-selected quasars, in order to
determine whether there are systematic biases in the different selection
techniques. There are no lightly reddened (Av approx. 1) quasars in our sample
amongst the 14 with z < 2. The discovery of a reddened quasar at z = 2.034 and
its implications are discussed. A tight correlation between radio luminosity
and optical/near infrared continuum luminosity for a subset of the sample is
also found.Comment: 6 pages Latex, To appear in the "Cosmology with the New Radio
Surveys" Conference - Tenerife 13-15 January 199
Expanding e-MERLIN with the Goonhilly Earth Station
A consortium of universities has recently been formed with the goal of using
the decommissioned telecommunications infrastructure at the Goonhilly Earth
Station in Cornwall, UK, for astronomical purposes. One particular goal is the
introduction of one or more of the ~30-metre parabolic antennas into the
existing e-MERLIN radio interferometer. This article introduces this scheme and
presents some simulations which quantify the improvements that would be brought
to the e-MERLIN system. These include an approximate doubling of the spatial
resolution of the array, an increase in its N-S extent with strong implications
for imaging the most well-studied equatorial fields, accessible to ESO
facilities including ALMA. It also increases the overlap between the e-MERLIN
array and the European VLBI Network. We also discuss briefly some niche science
areas in which an e-MERLIN array which included a receptor at Goonhilly would
be potentially world-leading, in addition to enhancing the existing potential
of e-MERLIN in its role as a Square Kilometer Array pathfinder instrument.Comment: 7 pages, 3 figures, to appear in the proceedings of "Astronomy with
megastructures: Joint science with the E-ELT and SKA", 10-14 May 2010, Crete,
Greece (Eds: Isobel Hook, Dimitra Rigopoulou, Steve Rawlings and Aris
Karastergiou
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