198 research outputs found
An interactive learning environment in geographical information systems
The Unigis Learning Station is a computer‐based learning management tool for the Postgraduate Diploma in Geographical Information Systems by distance learning (correspondence). Unigis is an international network of universities co‐operating in the delivery of such courses. The students on Unigis courses are mature mid‐career professionals who study in addition to undertaking full time jobs. The Learning Station offers these students information about the course, resources for independent study, a structured set of exercises, assessments and feedback opportunities, and an integrated and easy way to interact with other course software. Following a brief introduction to the Unigis curriculum, this paper discusses the design of the Learning Station. The roles the Learning Station adopts are outlined, and the range of multimedia and communications tools used discussed. Evaluation of the Learning Station is presented and the issued raised by this provide useful lessons for other computer‐based learning management tools, and the adaptation of the Learning Station to other teaching and learning situations
Evolution of the Milky Way in Semi-Analytic Models: Detecting Cold Gas at z=3 with ALMA and SKA
We forecast the abilities of the Atacama Large Millimeter/submillimeter Array
(ALMA) and the Square Kilometer Array (SKA) to detect CO and HI emission lines
in galaxies at redshift z=3. A particular focus is set on Milky Way (MW)
progenitors at z=3 for their detection within 24 h constitutes a key science
goal of ALMA. The analysis relies on a semi-analytic model, which permits the
construction of a MW progenitor sample by backtracking the cosmic history of
all simulated present-day galaxies similar to the real MW. Results: (i) ALMA
can best observe a MW at z=3 by looking at CO(3-2) emission. The probability of
detecting a random model MW at 3-sigma in 24 h using 75 km/s channels is
roughly 50%, and these odds can be increased by co-adding the CO(3-2) and
CO(4-3) lines. These lines fall into ALMA band 3, which therefore represents
the optimal choice towards MW detections at z=3. (ii) Higher CO transitions
contained in the ALMA bands geq6 will be invisible, unless the considered MW
progenitor coincidentally hosts a major starburst or an active black hole.
(iii) The high-frequency array of SKA, fitted with 28.8 GHz receivers, would be
a powerful instrument for observing CO(1-0) at z=3, able to detect nearly all
simulated MWs in 24 h. (iv) HI detections in MWs at z=3 using the low-frequency
array of SKA will be impossible in any reasonable observing time. (v) SKA will
nonetheless be a supreme ha survey instrument through its enormous
instantaneous field-of-view (FoV). A one year pointed HI survey with an assumed
FoV of 410 sqdeg would reveal at least 10^5 galaxies at z=2.95-3.05. (vi) If
the positions and redshifts of those galaxies are known from an
optical/infrared spectroscopic survey, stacking allows the detection of HI at
z=3 in less than 24 h.Comment: 14 pages, 5 figures, 5 table
Paula Kane Studio Wall
Paula Kane Studio Wall was produced as part of 'How Art Thinks', a collaborative project engaging with artists' practice and process.
It brings together notes and images relating to the artist’s
Studio Wall project, in which Kane exhibited a wall-mounted assemblage of evidence that also functioned as an artwork in its own right. It has been designed as a visual record of the artist’s process, enabling the readerviewer to find a path through the work, supplemented by responsive essays from painter Mikey Cuddihy and critic Ian Heywood. The book is the first in a series produced by the International Centre for Fine Art Research at UAL as part of the research project How Art Thinks. The project takes artist’s publication as one of several sites of creative and critical enquiry, providing insight into the visual, material and intellectual processes of making. It aims to find creative ways to document artists’ decision-making
processes, as well as listening and responding to artists’ narratives
The closest black holes
Starting from the assumption that there is a large population (> 10^8) of
isolated, stellar-mass black holes (IBH) distributed throughout our galaxy, we
consider the detectable signatures of accretion from the interstellar medium
(ISM) that may be associated with such a population. We simulate the nearby
(radius 250 pc) part of this population, corresponding to the closest ~35 000
black holes, using current best estimates of the mass distribution of stellar
mass black holes combined with two models for the velocity distribution of
stellar-mass IBH which bracket likely possibilities. We distribute this
population of objects appropriately within the different phases of the ISM and
calculate the Bondi-Hoyle accretion rate, modified by a further dimensionless
efficiency parameter \lambda. Assuming a simple prescription for radiatively
inefficient accretion at low Eddington ratios, we calculate the X-ray
luminosity of these objects, and similarly estimate the radio luminosity from
relations found empirically for black holes accreting at low rates. The latter
assumption depends crucially on whether or not the IBH accrete from the ISM in
a manner which is axisymmetric enough to produce jets. Comparing the predicted
X-ray fluxes with limits from hard X-ray surveys, we conclude that either the
Bondi-Hoyle efficiency parameter \lambda, is rather small (< 0.01), the
velocities of the IBH are rather high, or some combination of both. The
predicted radio flux densities correspond to a population of objects which,
while below current survey limits, should be detectable with the Square
Kilometre Array (SKA). Converting the simulated space velocities into proper
motions, we further demonstrate that such IBH could be identified as faint high
proper motion radio sources in SKA surveys.Comment: Accepted for publication in MNRA
Gravitationally Lensed HI with MeerKAT
The SKA era is set to revolutionize our understanding of neutral hydrogen
(HI) in individual galaxies out to redshifts of z~0.8; and in the z > 6
intergalactic medium through the detection and imaging of cosmic reionization.
Direct HI number density constraints will, nonetheless, remain relatively weak
out to cosmic noon (z~2) - the epoch of peak star formation and black hole
accretion - and beyond. However, as was demonstrated from the 1990s with
molecular line observations, this can be overcome by utilising the natural
amplification afforded by strong gravitational lensing, which results in an
effective increase in integration time by the square of the total magnification
(\mu^2) for an unresolved source. Here we outline how a dedicated lensed HI
survey will leverage MeerKAT's high sensitivity, frequency coverage, large
instantaneous bandwidth, and high dynamic range imaging to enable a lasting
legacy of high-redshift HI emission detections well into the SKA era. This
survey will not only provide high-impact, rapid-turnaround MeerKAT science
commissioning results, but also unveil Milky Way-like systems towards cosmic
noon which is not possible with any other SKA precursors/pathfinders. An
ambitious lensed HI survey will therefore make a significant impact from
MeerKAT commissioning all the way through to the full SKA era, and provide a
more complete picture of the HI history of the Universe.Comment: 15 pages, 3 figures, accepted for publication, Proceedings of
Science, workshop on "MeerKAT Science: On the Pathway to the SKA", held in
Stellenbosch 25-27 May 2016. Comments welcom
A new pulsar candidate in 47 Tucanae discovered with MeerKAT imaging
MeerKAT imaging of the globular cluster 47 Tucanae (47 Tuc) reveals 1.28 GHz
continuum emission at the locations of 20 known millisecond pulsars (MSPs). We
use time series and spectral imaging to investigate the image-domain
characteristics of the MSPs, and search for previously unknown sources of
interest. The MSPs exhibit a range of differences in their temporal and
spectral properties compared the general background radio source population.
Temporal variability differs strongly from pulsar to pulsar, some appearing to
vary randomly on 15 min timescales, others varying coherently by factors of >10
on timescales of hours. The error in the typical power law fit to the spectrum
emerges as a powerful parameter for indentifying the MSPs. This behaviour is
likely due to differing diffractive scintillation conditions along the sight
lines to the MSPs. One MSP exhibits tentative periodic variations that are
consistent with modulation due the orbit of an eclipsing binary system. One
radio source has spectro-temporal properites closely resembling those of the
MSP population in the cluster, and we report its position as a candidate new
MSP, or alternatively an interferometric localisation of one of six MSPs which
do not yet have an accurate position from the timing solutions.Comment: 6 pages, 2 figures, accepted for publication in MNRAS Letter
Towards the first detection of strongly lensed HI emission
We report interferometric observations tuned to the redshifted neutral
hydrogen (HI) 21cm emission line in three strongly lensed galaxies at with the Giant Metrewave Radio Telescope (GMRT). One galaxy spectrum
(J1106+5228 at z=0.407) shows evidence of a marginal detection with an
integrated signal-to-noise ratio of 3.8, which, if confirmed by follow-up
observations, would represent the first strongly lensed and most distant
individual galaxy detected in HI emission. Two steps are performed to
transcribe the lensed integrated flux measurements into HI mass measurements
for all three target galaxies. First, we calculate the HI magnification factor
by applying general relativistic ray-tracing to a physical model of the
source-lens system. The HI magnification generally differs from the optical
magnification and depends largely on the intrinsic HI mass due to
the HI mass-size relation. Second, we employ a Bayesian formalism to convert
the integrated flux, amplified by the -dependent magnification
factor , into a probability density for , accounting for the
asymmetric uncertainty due to the declining HI mass function (Eddington bias).
In this way, we determine a value of for J1106+5228, consistent with the estimate of
from the optical properties of this galaxy. The HI mass of the other two
sources are consistent with zero within a 95 per cent confidence interval
however we still provide upper limits for both sources and a lower
limit for J1250-0135 using the same formalism.Comment: Accepted by MNRAS, no changes made. 12 pages, 7 figure
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
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