619 research outputs found
The X-ray Spectrum of the z=6.30 QSO SDSS J1030+0524
We present a deep XMM-Newton observation of the z=6.30 QSO SDSS J1030+0524,
the second most distant quasar currently known. The data contain sufficient
counts for spectral analysis, demonstrating the ability of XMM-Newton to
measure X-ray spectral shapes of z~6 QSOs with integration times >100ks. The
X-ray spectrum is well fit by a power law with index Gamma=2.12 +/- 0.11, an
optical-X-ray spectral slope of a_{ox}=-1.80, and no absorption excess to the
Galactic value, though our data are also consistent with a power law index in
the range 2.02 < Gamma < 2.5 and excess absorption in the range 0 < N_H(cm^-2)
< 8x10^22. There is also a possible detection (2 sigma) of FeKa emission. The
X-ray properties of this QSO are, overall, similar to those of lower-redshift
radio-quiet QSOs. This is consistent with the statement that the X-ray
properties of radio-quiet QSOs show no evolution over 0<z<6.3. Combined with
previous results, this QSO appears indistinguishable in any way from lower
redshift QSOs, indicating that QSOs comparable to those seen locally existed
less than one Gyr after the Big Bang.Comment: ApJ Letters, accepte
THE STRUCTURE OF 5-AMINO-4-METHYL-1-ISOQUINOLINECARBALDEHYDE THIOSEMICARBAZONE HYDROCHLORIDE, C12H14N5S+.CL-
Mr=295.80 , P21/n , a=8.284(1), b=
13.906 (1), c= 12.040 (2) A, fl= 92.95 (1) °, V=
1385.0 (5) ,/k 3, Z = 4, D m = 1.42, D x = 1.418 Mg m -3,
2(Cu K~t) = 1.54178 A,, g = 3.8134 mm -~, F(000) =
616, R =0.061 for 628 unique significant reflections
measured at 298 K. The structure was compared with
that of other active/inactive thiosemicarbazone
derivatives, in the search for a structure-activity
relationship. It was also compared with the structure of
a related metal complex
Application of a Bayesian Method to Absorption Spectral-Line Finding in Simulated ASKAP Data
The large spectral bandwidth and wide field of view of the Australian SKA
Pathfinder radio telescope will open up a completely new parameter space for
large extragalactic HI surveys. Here we focus on identifying and parametrising
HI absorption lines which occur in the line of sight towards strong radio
continuum sources. We have developed a method for simultaneously finding and
fitting HI absorption lines in radio data by using multi-nested sampling, a
Bayesian Monte Carlo algorithm. The method is tested on a simulated ASKAP data
cube, and is shown to be reliable at detecting absorption lines in low
signal-to-noise data without the need to smooth or alter the data. Estimation
of the local Bayesian evidence statistic provides a quantitative criterion for
assigning significance to a detection and selecting between competing
analytical line-profile models.Comment: 8 pages, 5 figures and 1 table; accepted for publication in PAS
Fragmentation dynamics of the ethyl bromide and ethyl iodide cations: a velocity-map imaging study
The photodissociation dynamics of ethyl bromide and ethyl iodide cations (C2H5Br+ and C2H5I+) have been studied. Ethyl halide cations were formed through vacuum ultraviolet (VUV) photoionization of the respective neutral parent molecules at 118.2 nm, and were photolysed at a number of ultraviolet (UV) photolysis wavelengths, including 355 nm and wavelengths in the range from 236 to 266 nm. Time-of-flight mass spectra and velocity-map images have been acquired for all fragment ions and for ground (Br) and spin–orbit excited (Br*) bromine atom products, allowing multiple fragmentation pathways to be investigated. The experimental studies are complemented by spin–orbit resolved ab initio calculations of cuts through the potential energy surfaces (along the RC–Br/I stretch coordinate) for the ground and first few excited states of the respective cations. Analysis of the velocity-map images indicates that photoexcited C2H5Br+ cations undergo prompt C–Br bond fission to form predominantly C2H5+ + Br* products with a near-limiting ‘parallel’ recoil velocity distribution. The observed C2H3+ + H2 + Br product channel is thought to arise via unimolecular decay of highly internally excited C2H5+ products formed following radiationless transfer from the initial excited state populated by photon absorption. Broadly similar behaviour is observed in the case of C2H5I+, along with an additional energetically accessible C–I bond fission channel to form C2H5 + I+ products. HX (X = Br, I) elimination from the highly internally excited C2H5X+ cation is deemed the most probable route to forming the C2H4+ fragment ions observed from both cations. Finally, both ethyl halide cations also show evidence of a minor C–C bond fission process to form CH2X+ + CH3 products
\u27Stay-Green\u27 and Non-\u27Stay-Green\u27 Perennial Ryegrass in Field Swards with Different Intervals between Cuts
The purpose of this study was to investigate the effect of the \u27stay-green\u27 character, originally introduced into perennial ryegrass (Lolium perenne L.) for amenity purposes, on herbage yield, N concentration and colour in field swards of \u27stay-green\u27 forage ryegrass managed in different ways for agricultural use. The conclusions were that the introduction of the \u27stay-green\u27 character (1) confers greater greenness only at some times of year and only when there has been a sufficiently long period of regrowth, (2) is expressed only in older, as distinct from young, tillers, (3) reduces herbage yield, particularly when a long interval is allowed between defoliations, and (4) reduces the decline in the concentration of N in herbage during the latter part of a long period of regrowth
The completeness and reliability of threshold and false-discovery-rate source extraction algorithms for compact continuum sources
The process of determining the number and characteristics of sources in
astronomical images is so fundamental to a large range of astronomical problems
that it is perhaps surprising that no standard procedure has ever been defined
that has well understood properties with a high degree of statistical rigour on
completeness and reliability. There are now a large number of commonly used
software tools for accomplishing this task, typically with different tools
being used for images acquired using different technologies. Despite this,
there have been relatively few quantitative analyses of the robustness or
reliability of individual tools, or the details of the techniques they
implement. We have an opportunity to redress this omission in the context of
surveys planned with the Australian Square Kilometre Array Pathfinder (ASKAP).
The Evolutionary Map of the Universe (EMU) survey with ASKAP, a continuum
survey of the Southern Hemisphere up to declination +30 deg, aims to utilise an
automated source identification and measurement approach that is demonstrably
optimal, to maximise the reliability, utility and robustness of the resulting
radio source catalogues. A key stage in source extraction methods is the
background estimation (background level and noise level) and the choice of a
threshold high enough to reject false sources yet not so high that the
catalogues are significantly incomplete. In this analysis we present results
from testing such algorithms as implemented in the SExtractor, Selavy
(Duchamp), and sfind tools on simulated data. In particular the effects of
background estimation, threshold and false-discovery rate settings are
explored. For parameters that give similar completeness, the false-discovery
rate method employed by sfind results in a more reliable catalogue compared to
the peak threshold methods of SExtractor and Selavy.Comment: 17 pages, 13 figures, accepted by PAS
Genome-wide and Mendelian randomisation studies of liver MRI yield insights into the pathogenesis of steatohepatitis
Background
A non-invasive method to grade the severity of steatohepatitis and liver fibrosis is magnetic resonance imaging (MRI) based corrected T1 (cT1). We aimed to identify genetic variants influencing liver cT1 and use genetics to understand mechanisms underlying liver fibroinflammatory disease and its link with other metabolic traits and diseases.
Methods
First, we performed a genome-wide association study (GWAS) in 14,440 Europeans in UK Biobank with liver cT1 measures. Second, we explored the effects of the cT1 variants on liver blood tests, and a range of metabolic traits and diseases. Third, we used Mendelian randomisation to test the causal effects of 24 predominantly metabolic traits on liver cT1 measures.
Results
We identified six independent genetic variants associated with liver cT1 that reached GWAS significance threshold (p<5x10-8). Four of the variants (rs75935921 in SLC30A10, rs13107325 in SLC39A8, rs58542926 in TM6SF2, rs738409 in PNPLA3) were also associated with elevated transaminases and had variable effects on liver fat and other metabolic traits. Insulin resistance, type 2 diabetes, non-alcoholic fatty liver and BMI were causally associated with elevated cT1 whilst favourable adiposity (instrumented by variants associated with higher adiposity but lower risk of cardiometabolic disease and lower liver fat) was found to be protective.
Conclusion
The association between two metal ion transporters and cT1 indicates an important new mechanism in steatohepatitis. Future studies are needed to determine whether interventions targeting the identified transporters might prevent liver disease in at risk individuals
The Distribution and Condition of the Warm Molecular Gas in Abell 2597 and Sersic 159-03
We have used the SINFONI integral field spectrograph to map the near-infrared
K-band emission lines of molecular and ionised hydrogen in the central regions
of two cool core galaxy clusters, Abell 2597 and Sersic 159-03. Gas is detected
out to 20 kpc from the nuclei of the brightest cluster galaxies and found to be
distributed in clumps and filaments around it. The ionised and molecular gas
phases trace each other closely in extent and dynamical state. Both gas phases
show signs of interaction with the active nucleus. Within the nuclear regions
the kinetic luminosity of this gas is found to be somewhat smaller than the
current radio luminosity. Outside the nuclear region the gas has a low velocity
dispersion and shows smooth velocity gradients. There is no strong correlation
between the intensity of the molecular and ionised gas emission and either the
radio or X-ray emission. The molecular gas in Abell 2597 and Sersic 159-03 is
well described by a gas in local thermal equilibrium (LTE) with a single
excitation temperature T_exc ~ 2300 K. The emission line ratios do not vary
strongly as function of position, with the exception of the nuclear regions
where the ionised to molecular gas ratio is found decrease. These constant line
ratios imply a single source of heating and excitation for both gas phases.Comment: 44 pages, 32 figures, accepted for publication in MNRA
The Integrated Polarization of Spiral Galaxy Disks
We present integrated polarization properties of nearby spiral galaxies at
4.8 GHz, and models for the integrated polarization of spiral galaxy disks as a
function of inclination. Spiral galaxies in our sample have observed integrated
fractional polarization in the range < 1% to 17.6%. At inclinations less than
50 degrees, the fractional polarization depends mostly on the ratio of random
to regular magnetic field strength. At higher inclinations, Faraday
depolarization associated with the regular magnetic field becomes more
important. The observed degree of polarization is lower (<4%) for more luminous
galaxies, in particular those with L_{4.8} > 2 x 10^{21} W/Hz. The polarization
angle of the integrated emission is aligned with the apparent minor axis of the
disk for galaxies without a bar. In our axially symmetric models, the
polarization angle of the integrated emission is independent of wavelength.
Simulated distributions of fractional polarization for randomly oriented spiral
galaxies at 4.8 GHz and 1.4 GHz are presented. We conclude that polarization
measurements, e.g. with the SKA, of unresolved spiral galaxies allow
statistical studies of the magnetic field in disk galaxies using large samples
in the local universe and at high redshift. As these galaxies behave as
idealized background sources without internal Faraday rotation, they can be
used to detect large-scale magnetic fields in the intergalactic medium.Comment: 13 pages, 6 figures; Accepted for publication in The Astrophysical
Journa
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