2,340 research outputs found
The Phoenix Deep Survey: The 1.4 GHz microJansky catalogue
The initial Phoenix Deep Survey (PDS) observations with the Australia
Telescope Compact Array have been supplemented by additional 1.4 GHz
observations over the past few years. Here we present details of the
construction of a new mosaic image covering an area of 4.56 square degrees, an
investigation of the reliability of the source measurements, and the 1.4 GHz
source counts for the compiled radio catalogue. The mosaic achieves a 1-sigma
rms noise of 12 microJy at its most sensitive, and a homogeneous radio-selected
catalogue of over 2000 sources reaching flux densities as faint as 60 microJy
has been compiled. The source parameter measurements are found to be consistent
with the expected uncertainties from the image noise levels and the Gaussian
source fitting procedure. A radio-selected sample avoids the complications of
obscuration associated with optically-selected samples, and by utilising
complementary PDS observations including multicolour optical, near-infrared and
spectroscopic data, this radio catalogue will be used in a detailed
investigation of the evolution in star-formation spanning the redshift range 0
< z < 1. The homogeneity of the catalogue ensures a consistent picture of
galaxy evolution can be developed over the full cosmologically significant
redshift range of interest. The 1.4 GHz mosaic image and the source catalogue
are available on the web at http://www.atnf.csiro.au/~ahopkins/phoenix/ or from
the authors by request.Comment: 16 pages, 11 figures, 4 tables. Accepted for publication by A
Mapping nonlinear gravity into General Relativity with nonlinear electrodynamics
We show that families of nonlinear gravity theories formulated in a
metric-affine approach and coupled to a nonlinear theory of electrodynamics can
be mapped into General Relativity (GR) coupled to another nonlinear theory of
electrodynamics. This allows to generate solutions of the former from those of
the latter using purely algebraic transformations. This correspondence is
explicitly illustrated with the Eddington-inspired Born-Infeld theory of
gravity, for which we consider a family of nonlinear electrodynamics and show
that, under the map, preserve their algebraic structure. For the particular
case of Maxwell electrodynamics coupled to Born-Infeld gravity we find, via
this correspondence, a Born-Infeld-type nonlinear electrodynamics on the GR
side. Solving the spherically symmetric electrovacuum case for the latter, we
show how the map provides directly the right solutions for the former. This
procedure opens a new door to explore astrophysical and cosmological scenarios
in nonlinear gravity theories by exploiting the full power of the analytical
and numerical methods developed within the framework of GR.Comment: 11 pages. v2: next discussions inserted, refs added; matches the
version accepted for publication in EPJ
A correspondence between modified gravity and General Relativity with scalar fields
We describe a novel procedure to map the field equations of nonlinear
Ricci-based metric-affine theories of gravity, coupled to scalar matter
described by a given Lagrangian, into the field equations of General Relativity
coupled to a different scalar field Lagrangian. Our analysis considers examples
with a single and real scalar fields, described either by canonical
Lagrangians or by generalized functions of the kinetic and potential terms. In
particular, we consider several explicit examples involving theories and
the Eddington-inspired Born-Infeld gravity model, coupled to different scalar
field Lagrangians. We show how the nonlinearities of the gravitational sector
of these theories can be traded to nonlinearities in the matter fields, and how
the procedure allows to find new solutions on both sides of the correspondence.
The potential of this procedure for applications of scalar field models in
astrophysical and cosmological scenarios is highlighted.Comment: 14 pages; v2: section IIID extended, some minor corrections,
references update
Constructing networks of defects with scalar fields
We propose a new way to build networks of defects. The idea takes advantage
of the deformation procedure recently employed to describe defect structures,
which we use to construct networks, spread from small rudimentary networks that
appear in simple models of scalar fields.Comment: 5 pages, 4 figures, version with new title, motivations and
references, to appear in PL
Radio observations of the CDF-South: a possible link between radio emission and star formation in X-ray selected AGN
We explore the nature of the radio emission of X-ray selected AGN by
combining deep radio (1.4GHz; 60micro-Jy) and X-ray data with multiwavelength
(optical, mid-infrared) observations in the Extended Chandra Deep Field South
(E-CDFS). The fraction of radio detected X-ray sources increases from 9% in the
E-CDFS to 14% in the central region of this field, which has deeper X-ray
coverage from the 1Ms CDFS. We find evidence that the radio emission of up to
60% of the hard X-ray/radio matched AGN is likely associated with
star-formation in the host galaxy. Firstly, the mid-IR (24micron) properties of
these sources are consistent with the infrared/radio correlation of starbursts.
Secondly, most of them are found in galaxies with blue rest-frame optical
colours (U-V), suggesting a young stellar population. On the contrary,
X-ray/radio matched AGN which are not detected in the mid-infrared have red U-V
colours suggesting their radio emission is associated with AGN activity. We
also find no evidence for a population of heavily obscured radio-selected AGN
that are not detected in X-rays. Finally, we do no confirm previous claims for
a correlation between radio emission and X-ray obscuration. Assuming that the
radio continuum measures star-formation, this finding is against models where
the dust and gas clouds associated with circumnuclear starbursts are
spherically blocking our view to the central engine.Comment: Accepted by A&
The Phoenix Deep Survey: X-ray properties of faint radio sources
In this paper we use a 50ks XMM-Newton pointing overlapping with the Phoenix
Deep Survey, a homogeneous radio survey reaching muJy sensitivities, to explore
the X-ray properties and the evolution of star-forming galaxies. UV, optical
and NIR photometry is available and is used to estimate photometric redshifts
and spectral types for radio sources brighter than R=21.5mag (total of 82).
Sources with R<21.5mag and spiral galaxy SEDs (34) are grouped into two
redshift bins with a median of z=0.240 and 0.455 respectively. Stacking
analysis for both the 0.5-2 and 2-8keV bands is performed on these subsamples.
A high confidence level signal (>3.5sigma) is detected in the 0.5-2keV band
corresponding to a mean flux of ~3e-16cgs for both subsamples. This flux
translates to mean luminosities of ~5e40 and 1.5e41cgs for the z=0.240 and
0.455 subsamples respectively. Only a marginally significant signal (2.6sigma)
is detected in the 2-8keV band for the z=0.455 subsample. We argue that the
stacked signal above is dominated by star-formation. The mean L_X/L_B ratio and
the mean L_X of the two subsamples are found to be higher than optically
selected spirals and similar to starbursts. We also find that the mean L_X and
L_1.4 of the faint radio sources studied here are consistent with the L_X-L_1.4
correlation of local star-forming galaxies. Moreover, the X-ray emissivity of
sub-mJy sources to z~0.3 is found to be elevated compared to local HII
galaxies. The observed increase is consistent with L_X evolution of the form
(1+z)^3. Assuming that our sample is indeed dominated by starbursts this is
direct evidence for evolution of such systems at X-ray wavelengths. Using an
empirical L_X to SFR conversion we estimate a global SFR density at z~0.3 of
\~0.029M_o/yr/Mpc in agreement with previous studies.Comment: 12 pages, 6 figures, accepted for publication in MNRA
Technological diffusion between different environmental countries
Using an endogenous Schumpeterian R&D growth model, this paper intends to analyse how international trade of
intermediate goods can affect the structure and diffusion of technological knowledge between ecological and dirty
countries. Each country is assumed to have different environmental quality levels and different available technological knowledge and to be able of conducting R&D activities (innovative in ecological-country and imitative in dirty-country). We concluded that under international trade, there is a higher probability of successful imitation that improves the Dirty-country ability to benefit from Ecological-country innovations. This induces an efficient allocation of production in the Dirty-country, where marginal cost is lower, and increases the ecological goods production. Furthermore, subsidies, by promoting technological knowledge progress, lead to a permanent increase in the world
steady-state growth rate.info:eu-repo/semantics/acceptedVersio
From an individual approach to a Cluster strategy
Portuguese agri-food sector, as well as in Europe, is characterized by being dispersed and pulverized. Nevertheless, in Portugal, the Food and Beverage Industry (F&BI) has the highest rates in terms of turnover of the manufacturing industry - corresponding to 20% (INE - 2009). This sector is a key vector of the economy, contributing the most to the Gross Domestic Product (GDP). Due to the relative small dimension of the domestic market, and its subsequent small scale, companies are obliged to turn to international markets in order to be more competitive
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