452 research outputs found
High redshift radio galaxies
There is considerable evidence that powerful radio quasars and radio galaxies
are orientation-dependent manifestations of the same parent population: massive
spheroids containing correspondingly massive black holes. Following the
recognition of this unification, research is directed to the task of
elucidating the structure and composition of the active nuclei and their hosts
to understand the formation and evolution of what we expect to become the most
massive of galaxies. In contrast to the quasars, where the nucleus can outshine
the galaxy at optical/near infrared wavelengths by a large factor, the radio
galaxies contain a 'built-in coronograph' that obscures our direct view to the
nucleus. These objects present our best opportunity to study the host galaxy in
detail. Of particular interest are those sources with redshifts greater than
about 2 that represent an epoch when nuclear activity was much more common that
it is now and when we believe these objects were in the process of assembly. In
combination with high resolution imaging from space (HST), optical
spectropolarimetry with Keck II allows us to clearly separate the scattered
nuclear radiation from the stellar and gaseous emission from the host galaxy.
The rest-frame ultraviolet emission line spectra suggest that rapid chemical
evolution is occurring at this epoch. Near infrared spectroscopy with the VLT
is giving us access to both the lines and continuum in the rest-frame optical
spectrum, allowing investigations of the evolved stellar population and
extending the composition analysis with measurements of the familiar
forbidden-line spectrum.Comment: 7 pages including 2 figures. Paper no. 4005-10 in the proceedings of
the SPIE International Symposium on 'Astronomical Telescopes and
Instrumentation' held in Munich, Germany from 27-31 March 200
Polarized Broad H-alpha Emission from the LINER Nucleus of NGC 1052
Optical spectropolarimetry of the nucleus of the LINER NGC 1052, obtained at
the Keck Observatory, reveals a rise in polarization in the wings of the
H-alpha line profile. The polarization vector of H-alpha is offset by 67
degrees from the parsec-scale radio axis and by 83 degrees from the
kiloparsec-scale radio axis, roughly in accord with expectations for scattering
within the opening cone of an obscuring torus. The broad component of H-alpha
has FWHM ~ 2100 km/s in total flux and FWHM ~ 5000 km/s in polarized light.
Scattering by electrons is the mechanism most likely responsible for this
broadening, and we find T_e ~ 10^5 K for the scattering medium, similar to
values observed in Seyfert 2 nuclei. This is the first detection of a polarized
broad emission line in a LINER, demonstrating that unified models of active
galactic nuclei are applicable to at least some LINERs.Comment: 6 pages, 2 figures, prepared using the emulateapj style file,
accepted for publication in The Astrophysical Journal Letter
Studies of acquired and inherited coagulopathy using the thrombin generation assay
In order to survive, an individual’s haemostatic system has to have the capacity to respond promptly to injury and thrombus formation has to occur in a highly regulated fashion. Over the past two hundred years, our understanding of this complex system has increased dramatically. It is perhaps surprising, therefore, that clinicians rely predominantly on assays to assess coagulation that were developed over 50 years ago and that only assess the time to initial clot formation. This reflects the challenge of truly understanding the complex dynamic contributions of platelets, vascular endothelium and coagulation factors under shear force and replicating this in a test-tube. There has therefore been a drive to develop better methods of detecting disordered haemostasis that can be accurately correlated with bleeding or thrombotic risk and that can be utilised to guide treatment. The thrombin generation assay is currently a research tool that is able to chart the different phases of thrombin generation, recognising that the majority of this occurs after the end-point of traditional coagulation assays. Thrombin is key to effective haemostasis and the thrombin generation assay has been shown to correlate with a range of bleeding and thrombotic states. Although it is recognised to produce valuable information, it is hampered by the impact of pre-analytical variables, lack of standardisation and inter-operator and inter-laboratory variability. Optimisation of the assay as well as development of normal reference ranges is key. This is in addition to further phenotyping of dysfunctional haemostasis and providing evidence of clinical relevance. This thesis sets out to address these different areas with studies including the generation of normal reference ranges in addition to examining the sensitivity of the assay to anticoagulation (and its reversal) as well as exploring potential factors contributing to the variable bleeding phenotype seen in patients with severe haemophilia
Jet-gas interactions in z~2.5 radio galaxies: evolution of the ultraviolet line and continuum emission with radio morphology
We present an investigation into the nature of the jet-gas interactions in a
sample of 10 radio galaxies at 2.3<z<2.9 using deep spectroscopy of the UV line
and continuum emission obtained at Keck II and the Very Large Telescope.
Kinematically perturbed gas, which we have shown to be within the radio
structure in previous publications, is always blueshifted with respect to the
kinematically quiescent gas, is usually spatially extended, and is usually
detected on both sides of the nucleus. In the three objects from this sample
for which we are able to measure line ratios for both the perturbed and
quiescent gases, we suggest that the former has a lower ionization state than
the latter.
We propose that the perturbed gas is part of a jet-induced outflow, with dust
obscuring the outflowing gas that lies on the far side of the object. The
spatial extent of the blueshifted perturbed gas, typically ~35 kpc, implies
that the dust is spatially extended at least on similar spatial scales.
We also find interesting interrelationships between UV line, UV continuum and
radio continuum properties of this sample.Comment: Accepted for publication in MNRA
The centre-to-limb variations of solar Fraunhofer lines imprinted upon lunar eclipse spectra - Implications for exoplanet transit observations
The atmospheres of exoplanets are commonly studied by observing the transit
of the planet passing in front of its parent star. The obscuration of part of
the stellar disk during a transit will reveal aspects of its surface structure
resulting from general centre-to-limb variations (CLVs). These become apparent
when forming the ratio between the stellar light in and out of transit. These
phenomena can be seen particularly clearly during the progress of a penumbral
lunar eclipse, where the Earth transits the solar disk and masks different
regions of the solar disk as the eclipse progresses. When inferring the
properties of the planetary atmosphere, it is essential that this effect
originating at the star is properly accounted for. Using the data observed from
the 2014-April-15 lunar eclipse with the ESPaDOnS spectrograph mounted on the
Canada France Hawaii Telescope (CFHT), we have obtained for the first time a
time sequence of the penumbral spectra. These penumbral spectra enable us to
study the centre-to-limb variations of solar Fraunhofer lines when the Earth is
transiting Sun. The Na i and Ca ii absorption features reported from previous
lunar eclipse observations are demonstrated to be CLV features, which dominate
the corresponding line profiles and mask possible planetary signal. Detecting
atmospheric species in exoplanets via transit spectroscopy must account for the
CLV effect.Comment: 9 pages, 11 figures, accepted, A&
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