907 research outputs found
Probing the Radio Loud/Quiet AGN dichotomy with quasar clustering
We investigate the clustering properties of 45441 radio-quiet quasars (RQQs)
and 3493 radio-loud quasars (RLQs) drawn from a joint use of the Sloan Digital
Sky Survey (SDSS) and Faint Images of the Radio Sky at 20 cm (FIRST) surveys in
the range . This large spectroscopic quasar sample allow us to
investigate the clustering signal dependence on radio-loudness and black hole
(BH) virial mass. We find that RLQs are clustered more strongly than RQQs in
all the redshift bins considered. We find a real-space correlation length of
and
{\normalsize{}for} RQQs and
RLQs, respectively, for the full redshift range. This implies that RLQs are
found in more massive host haloes than RQQs in our samples, with mean host halo
masses of and
, respectively. Comparison with
clustering studies of different radio source samples indicates that this mass
scale of is characteristic for the
bright radio-population, which corresponds to the typical mass of galaxy groups
and galaxy clusters. The similarity we find in correlation lengths and host
halo masses for RLQs, radio galaxies and flat-spectrum radio quasars agrees
with orientation-driven unification models. Additionally, the clustering signal
shows a dependence on black hole (BH) mass, with the quasars powered by the
most massive BHs clustering more strongly than quasars having less massive BHs.
We suggest that the current virial BH mass estimates may be a valid BH proxies
for studying quasar clustering. We compare our results to a previous
theoretical model that assumes that quasar activityComment: 15 pages, 13 figures, A&A in pres
Metric of a Slow Rotating Body with Quadrupole Moment from the Erez-Rosen Metric
A metric representing a slowly rotating object with quadrupole moment is
obtained using a perturbation method to include rotation into the weak limit of
the Erez-Rosen metric. This metric is intended to tackle relativistic
astrometry and gravitational lensing problems in which a quadrupole moment has
to be taken into account
Efficient Shortest Paths in Scale-Free Networks with Underlying Hyperbolic Geometry
A common way to accelerate shortest path algorithms on graphs is the use of a bidirectional search, which simultaneously explores the graph from the start and the destination. It has been observed recently that this strategy performs particularly well on scale-free real-world networks. Such networks typically have a heterogeneous degree distribution (e.g., a power-law distribution) and high clustering (i.e., vertices with a common neighbor are likely to be connected themselves). These two properties can be obtained by assuming an underlying hyperbolic geometry.
To explain the observed behavior of the bidirectional search, we analyze its running time on hyperbolic random graphs and prove that it is {O~}(n^{2 - 1/alpha} + n^{1/(2 alpha)} + delta_{max}) with high probability, where alpha in (0.5, 1) controls the power-law exponent of the degree distribution, and delta_{max} is the maximum degree. This bound is sublinear, improving the obvious worst-case linear bound. Although our analysis depends on the underlying geometry, the algorithm itself is oblivious to it
PROPIEDADES DEL EFECTO LENTE PARA EL PERFIL DE EINASTO EN TÉRMINOS DE LA FUNCIÓN G DE MEIJER
In N-body simulations of cold dark matter, it has been found that three-parameter models, particularly the Einasto profile, yield better fits to a wide range of dark matter haloes than two parameter models like the Navarro-Frenk-White profile. Recently, the analytical properties of the Einasto profile has been studied, allowing closed expressions for its surface mass density and lensing properties in terms of the Fox H and Meijer G functions, using a Mellin transform formalism. These expressions are valid for all values of the Einasto index in terms of the Fox H function, and valid for integer and half-integer values of Einasto index in terms of the Meijer G function. In this paper, we derive expressions for lensing properties of the Einasto profile for all rational values of the Einasto index in terms of the Meijer G function. Equivalency between these expressions and other recent results is also discussed En simulaciones de N-cuerpos de materia oscura fría, se ha encontrado que modelos de tres parámetros, particularmente el perfil de Einasto, ofrece mejores ajustes para un amplio rango de halos de materia oscura que los modelos de dos parámetros como el perfil Navarro-Frenk-White. Recientemente, las propiedades analíticas del perfil de Einasto han sido estudiadas, lográdose expresiones cerradas para su densidad de masa superficial y propiedades de lente gravitational en términos de la función H de Fox, usando el formalismo de la transformada de Mellin. Estas expresiones son válidas para todos los valores del índice de Einasto en términos de la función H de Fox, y válidos para valores enteros y semi-enteros del índice de Einasto en términos de la función G de Meijer. En este artículo, se determinan expresiones para las propiedades de lente gravitational del perfil de Einasto para todos los valores racionales del índice de Einasto en términos de la función G de Meijer. La equivalencia entre estas expre- siones y otros resultados recientes también es discutida
Deep LOFAR 150 MHz imaging of the Bo\"otes field: Unveiling the faint low-frequency sky
We have conducted a deep survey (with a central rms of )
with the LOw Frequency ARray (LOFAR) at 120-168 MHz of the Bo\"otes field, with
an angular resolution of , and obtained a sample of
10091 radio sources ( limit) over an area of .
The astrometry and flux scale accuracy of our source catalog is investigated.
The resolution bias, incompleteness and other systematic effects that could
affect our source counts are discussed and accounted for. The derived 150 MHz
source counts present a flattening below sub-mJy flux densities, that is in
agreement with previous results from high- and low- frequency surveys. This
flattening has been argued to be due to an increasing contribution of
star-forming galaxies and faint active galactic nuclei. Additionally, we use
our observations to evaluate the contribution of cosmic variance to the scatter
in source counts measurements. The latter is achieved by dividing our Bo\"otes
mosaic into 10 non-overlapping circular sectors, each one with an approximate
area of The counts in each sector are computed in the
same way as done for the entire mosaic. By comparing the induced scatter with
that of counts obtained from depth observations scaled to 150MHz, we find that
the scatter due to cosmic variance is larger than the Poissonian
errors of the source counts, and it may explain the dispersion from previously
reported depth source counts at flux densities . This work
demonstrates the feasibility of achieving deep radio imaging at low-frequencies
with LOFAR.Comment: A\&A in press. 15 pages, 16 figure
Efficient Shortest Paths in Scale-Free Networks with Underlying Hyperbolic Geometry
A common way to accelerate shortest path algorithms on graphs is the use of a
bidirectional search, which simultaneously explores the graph from the start
and the destination. It has been observed recently that this strategy performs
particularly well on scale-free real-world networks. Such networks typically
have a heterogeneous degree distribution (e.g., a power-law distribution) and
high clustering (i.e., vertices with a common neighbor are likely to be
connected themselves). These two properties can be obtained by assuming an
underlying hyperbolic geometry.
To explain the observed behavior of the bidirectional search, we analyze its
running time on hyperbolic random graphs and prove that it is with high probability,
where controls the power-law exponent of the degree
distribution, and is the maximum degree. This bound is
sublinear, improving the obvious worst-case linear bound. Although our analysis
depends on the underlying geometry, the algorithm itself is oblivious to it
Extreme conditions in the molecular gas of lensed star-forming galaxies at z~3
Atomic Carbon can be an efficient tracer of the molecular gas mass, and when
combined to the detection of high-J and low-J CO lines it yields also a
sensitive probe of the power sources in the molecular gas of high redshift
galaxies. The recently installed SEPIA5 receiver at the focus of the APEX
telescope has opened up a new window at frequencies 159 - 211 GHz allowing the
exploration of the Atomic Carbon in high-z galaxies, at previously inaccessible
frequencies from the ground. We have targeted three gravitationally lensed
galaxies at redshift of about 3 and conducted a comparative study of the
observed high-J CO/CI ~ratios with well-studied nearby galaxies. Atomic Carbon
(CI(2-1)) was detected in one of the three targets and marginally in a second,
while in all three targets the CO line is detected. The
CO(7-6)/CI(2-1), CO(7-6)/CO(1-0) line ratios and the CO(7-6)/(far-IR continuum)
luminosity ratio are compared to those of nearby objects. A large excitation
status in the ISM of these high-z objects is seen, unless differential lensing
unevenly boosts the CO line fluxes from the warm and dense gas more than the
CO(1-0), CI(2-1), tracing a more widely distributed cold gas phase. We provide
estimates of total molecular gas masses derived from the atomic Carbon and the
Carbon monoxide CO(1-0), which within the uncertainties turn out to be equal.Comment: A&A, in pres
Analytical shear and flexion of Einasto dark matter haloes
N-body simulations predict that dark matter haloes are described by specific
density profiles on both galactic- and cluster-sized scales. Weak gravitational
lensing through the measurements of their first and second order properties,
shear and flexion, is a powerful observational tool for investigating the true
shape of these profiles. One of the three-parameter density profiles recently
favoured in the description of dark matter haloes is the Einasto profile. We
present exact expressions for the shear and the first and second flexions of
Einasto dark matter haloes derived using a Mellin-transform formalism in terms
of the Fox H and Meijer G functions, that are valid for general values of the
Einasto index. The resulting expressions can be written as series expansions
that permit us to investigate the asymptotic behaviour of these quantities.
Moreover, we compare the shear and flexion of the Einasto profile with those of
different mass profiles including the singular isothermal sphere, the
Navarro-Frenk-White profile, and the S\'ersic profile. We investigate the
concentration and index dependences of the Einasto profile, finding that the
shear and second flexion could be used to determine the halo concentration,
whilst for the Einasto index the shear and first and second flexions may be
employed. We also provide simplified expressions for the weak lensing
properties and other lensing quantities in terms of the generalized
hypergeometric function.Comment: 14 pages, 3 figures. Accepted for publication in Astronomy and
Astrophysic
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