314 research outputs found
A search for distant radio galaxies from SUMSS and NVSS: III. radio spectral energy distributions and the z-alpha correlation
This is the third in a series of papers that present observations and results
for a sample of 76 ultra-steep-spectrum radio sources designed to find galaxies
at high redshift. Here we present multi-frequency radio observations, from the
Australia Telescope Compact Array, for a subset of 37 galaxies from the sample.
Matched resolution observations at 2.3, 4.8 and 6.2GHz are presented for all
galaxies, with the z<2 galaxies additionally observed at 8.6 and 18GHz. New
angular size constraints are reported for 19 sources based on high resolution
4.8 and 6.2GHz observations. Functional forms for the rest-frame spectral
energy distributions are derived: 89% of the sample is well characterised by a
single power law, whilst the remaining 11% show some flattening toward higher
frequencies: not one source shows any evidence for high frequency steepening.
We discuss the implications of this result in light of the empirical
correlation between redshift and spectral index seen in flux limited samples of
radio galaxies. Finally, a new physical mechanism to explain the redshift --
spectral index correlation is posited: extremely steep spectrum radio galaxies
in the local universe usually reside at the centres of rich galaxy clusters. We
argue that if a higher fraction of radio galaxies, as a function of redshift,
are located in environments with densities similar to nearby rich clusters,
then this could be a natural interpretation for the correlation. We briefly
outline our plans to pursue this line of investigation.Comment: MNRAS in pres
International capital mobility in an era of globalisation: adding a political dimension to the 'Feldstein–Horioka Puzzle'
The debate about the scope of feasible policy-making in an era of globalisation continues to be set within the context of an assumption that national capital markets are now perfectly integrated at the international level. However, the empirical evidence on international capital mobility contradicts such an assumption. As a consequence, a significant puzzle remains. Why is it, in a world in which the observed pattern of capital flows is indicative of a far from globalised reality, that public policy continues to be constructed in line with more extreme variants of the globalisation hypothesis? I attempt to solve this puzzle by arguing that ideas about global capital market integration have an independent causal impact on political outcomes which extends beyond that which can be attributed to the extent of their actual integration
L-lysine as adjunctive treatment in patients with schizophrenia: a single-blinded, randomized, cross-over pilot study
<p>Abstract</p> <p>Background</p> <p>Accumulating evidence suggests that the brain's nitric oxide (NO) signalling system may be involved in the pathophysiology of schizophrenia and could thus constitute a novel treatment target. The study was designed to investigate the benefit of L-lysine, an amino acid that interferes with NO production, as an add-on treatment for schizophrenia.</p> <p>Methods</p> <p>L-lysine, 6 g/day, was administered to 10 patients with schizophrenia as an adjunctive to their conventional antipsychotic medication. The study was designed as a single-blinded, cross-over study where patients were randomly assigned to initial treatment with either L-lysine or placebo and screened at baseline, after four weeks when treatment was crossed over, and after eight weeks.</p> <p>Results</p> <p>L-lysine treatment caused a significant increase in blood concentration of L-lysine and was well tolerated. A significant decrease in positive symptom severity, measured by the Positive And Negative Syndrome Scale (PANSS), was detected. A certain decrease in score was also observed during placebo treatment and the effects on PANSS could not unequivocally be assigned to the L-lysine treatment. Furthermore, performance on the Wisconsin Card Sorting Test was significantly improved compared to baseline, an effect probably biased by training. Subjective reports from three of the patients indicated decreased symptom severity and enhanced cognitive functioning.</p> <p>Conclusions</p> <p>Four-week L-lysine treatment of 6 g/day caused a significant increase in blood concentration of L-lysine that was well tolerated. Patients showed a significant decrease in positive symptoms as assessed by PANSS in addition to self-reported symptom improvement by three patients. The NO-signalling pathway is an interesting, potentially new treatment target for schizophrenia; however, the effects of L-lysine need further evaluation to decide the amino acid's potentially beneficial effects on symptom severity in schizophrenia.</p> <p>Trial registration</p> <p><a href="http://www.clinicaltrials.gov/ct2/show/NCT00996242">NCT00996242</a></p
The ATLAS 5.5 GHz survey of the Extended Chandra Deep Field South: Catalogue, Source Counts and Spectral Indices
Star forming galaxies are thought to dominate the sub-mJy radio population,
but recent work has shown that low luminosity AGN can still make a significant
contribution to the faint radio source population. Spectral indices are an
important tool for understanding the emission mechanism of the faint radio
sources. We have observed the extended Chandra Deep Field South at 5.5 GHz
using a mosaic of 42 pointings with the Australia Telescope Compact Array
(ATCA). Our image reaches an almost uniform sensitivity of ~12 microJy rms over
0.25 deg^2 with a restoring beam of 4.9 x 2.0 arcsec, making it one of the
deepest 6cm surveys to date. We present the 5.5 GHz catalogue and source counts
from this field. We take advantage of the large amounts of ancillary data in
this field to study the 1.4 to 5.5 GHz spectral indices of the sub-mJy
population. For the full 5.5 GHz selected sample we find a flat median spectral
index, alpha_med = -0.40, which is consistent with previous results. However,
the spectral index appears to steepen at the faintest flux density levels
(S_{5.5 GHz} < 0.1 mJy), where alpha_med = -0.68. We performed stacking
analysis of the faint 1.4 GHz selected sample (40 < S_{1.4 GHz} < 200 microJy)
and also find a steep average spectral index, alpha = -0.8, consistent with
synchrotron emission. We find a weak trend of steepening spectral index with
redshift. Several young AGN candidates are identified using spectral indices,
suggesting Gigahertz Peaked Spectrum (GPS) sources are as common in the mJy
population as they are at Jy levels.Comment: 18 pages, 16 figures, accepted for publication in MNRA
The star catalogues of Ptolemaios and Ulugh Beg: Machine-readable versions and comparison with the modern Hipparcos Catalogue
In late antiquity and throughout the middle ages, the positions of stars on
the celestial sphere were obtained from the star catalogue of Ptolemaios. A
catalogue based on new measurements appeared in 1437, with positions by Ulugh
Beg, and magnitudes from the 10th-century astronomer al-Sufi. We provide
machine-readable versions of these two star catalogues, based on the editions
by Toomer (1998) and Knobel (1917), and determine their accuracies by
comparison with the modern Hipparcos Catalogue. The magnitudes in the
catalogues correlate well with modern visual magnitudes; the indication `faint'
by Ptolemaios is found to correspond to his magnitudes 5 and 6. Gaussian fits
to the error distributions in longitude / latitude give widths sigma ~ 27
arcmin / 23 arcmin in the range |Delta lambda, Delta beta|<50 arcmin for
Ptolemaios and sigma ~ 22 arcmin /18 arcmin in Ulugh Beg. Fits to the range
|Delta lambda, Delta beta|<100 arcmin gives 10-15 per cent larger widths,
showing that the error distributions are broader than gaussians. The fraction
of stars with positions wrong by more than 150 arcmin is about 2 per cent for
Ptolemaios and 0.1 per cent in Ulugh Beg; the numbers of unidentified stars are
1 in Ptolemaios and 3 in Ulugh Beg. These numbers testify to the excellent
quality of both star catalogues (as edited by Toomer and Knobel).Comment: to be published in Astronomy and Astrophysics; 34 pages with 57
Figures. Note changed address and email address of first autho
A new search for distant radio galaxies in the southern hemisphere - I. Sample definition and radio properties
This paper introduces a new program to find high-redshift radio galaxies in
the southern hemisphere through ultra-steep spectrum (USS) selection. We define
a sample of 234 USS radio sources with spectral indices alpha_408^843 < -1.0
and flux densities S_408 > 200 mJy in a region of 0.35 sr, chosen by
cross-correlating the revised 408 MHz Molonglo Reference Catalogue, the 843 MHz
Sydney University Molonglo Sky Survey and the 1400 MHz NRAO VLA Sky Survey in
the overlap region -40 deg < delta < -30 deg. We present Australia Telescope
Compact Array (ATCA) high-resolution 1384 and 2368 MHz radio data for each
source, which we use to analyse the morphological, spectral index and
polarization properties of our sample. We find that 85 per cent of the sources
have observed-frame spectral energy distributions that are straight over the
frequency range 408-2368 MHz, and that, on average, sources with smaller
angular sizes have slightly steeper spectral indices and lower fractional
linear polarization. Fractional polarization is anti-correlated with flux
density at both 1400 and 2368 MHz. We also use the ATCA data to determine
observed-frame Faraday rotation measures for half of the sample.Comment: 28 pages, 9 figures, 10 tables, accepted for publication in MNRAS.
Correct version of SUMSS catalogue now noted in Section 2.1.2; analysis and
conclusions unchanged. A higher-resolution version of Figure 1 is available
at http://www.physics.usyd.edu.au/~jess/papers.htm
Measuring space-time variation of the fundamental constants with redshifted submillimetre transitions of neutral carbon
We compare the redshifts of neutral carbon and carbon monoxide in the
redshifted sources in which the fine structure transition of neutral carbon,
[CI], has been detected, in order to measure space-time variation of the
fundamental constants. Comparison with the CO rotational lines measures gives
the same combination of constants obtained from the comparison fine structure
line of singly ionised carbon, [CII]. However, neutral carbon has the distinct
advantage that it may be spatially coincident with the carbon monoxide, whereas
[CII] could be located in the diffuse medium between molecular clouds, and so
any comparison with CO could be dominated by intrinsic velocity differences.
Using [CI], we obtain a mean variation of dF/F = (-3.6 +/- 8.5) x 10^-5, over z
= 2.3 - 4.1, for the eight [CI] systems, which degrades to (-1.5+/- 11) x
10^-5, over z = 2.3 - 6.4 when the two [CII] systems are included. That is,
zero variation over look-back times of 10.8-12.8 Gyr. However, the latest
optical results indicate a spatial variation in alpha, which describes a dipole
and we see the same direction in dF/F. This trend is, however, due to a single
source for which the [CI] spectrum is of poor quality. This also applies to one
of the two [CII] spectra previously used to find a zero variation in
alpha^2/mu. Quantifying this, we find an anti-correlation between |dF/F| and
the quality of the carbon detection, as measured by the spectral resolution,
indicating that the typical values of >50 km/s, used to obtain a detection, are
too coarse to reliably measure changes in the constants. From the fluxes of the
known z > 1 CO systems, we predict that current instruments are incapable of
the sensitivities required to measure changes in the constants through the
comparison of CO and carbon lines. We therefore discuss in detail the use of
ALMA for such an undertaking ... ABRIDGEDComment: Accepted for publication in Section 3 - Cosmology (including clusters
of galaxies) of Astronomy and Astrophysic
The ATLAS 5.5 GHz survey of the extended Chandra Deep Field South: The second data release
We present a new image of the 5.5 GHz radio emission from the extended Chandra Deep Field South. Deep radio observations at 5.5 GHz were obtained in 2010 and presented in the first data release. A further 76 h of integration has since been obtained, nearly doubling the integration time. This paper presents a new analysis of all the data. The new image reaches 8.6 µJy rms, an improvement of about 40 per cent in sensitivity. We present a new catalogue of 5.5 GHz sources, identifying 212 source components, roughly 50 per cent more than were detected in the first data release. Source counts derived from this sample are consistent with those reported in the literature for S5.5 GHz > 0.1 mJy but significantly lower than published values in the lowest flux density bins (S5.5 GHz < 0.1 mJy), where we have more detected sources and improved statistical reliability. The 5.5 GHz radio sources were matched to 1.4 GHz sources in the literature and we find a mean spectral index of -0.35 ± 0.10 for S5.5 GHz > 0.5 mJy, consistent with the flattening of the spectral index observed in 5 GHz sub-mJy samples. The median spectral index of the whole sample is amed =-0.58, indicating that these observations may be starting to probe the star-forming population. However, even at the faintest levels (0.05 < S5.5 GHz < 0.1 mJy), 39 per cent of the 5.5 GHz sources have flat or inverted radio spectra. Four flux density measurements from our data, across the full 4.5-6.5 GHz bandwidth, are combined with those from literature and we find 10 per cent of sources (S5.5 GHz ? 0.1 mJy) show significant curvature in their radio spectral energy distribution spanning 1.4-9 GHz. © 2015 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society
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