3,082 research outputs found
The outer filament of Centaurus A as seen by MUSE
We investigate signatures of a jet-interstellar medium (ISM) interaction
using optical integral-field observations of the so-called outer filament near
Centaurus A, expanding on previous results obtained on a more limited area.
Using the Multi Unit Spectroscopic Explorer (MUSE) on the VLT during science
verification, we observed a significant fraction of the brighter emitting gas
across the outer filament. The ionized gas shows complex morphology with
compact blobs, arc-like structures and diffuse emission. Based on the
kinematics, we identified three main components. The more collimated component
is oriented along the direction of the radio jet. The other two components
exhibit diffuse morphology together with arc-like structures also oriented
along the radio jet direction. Furthermore, the ionization level of the gas is
found to decrease from the more collimated component to the more diffuse
components. The morphology and velocities of the more collimated component
confirm our earlier results that the outer filament and the nearby HI cloud are
likely partially shaped by the lateral expansion of the jet. The arc-like
structures embedded within the two remaining components are the clearest
evidence of a smooth jet-ISM interaction along the jet direction. This suggests
that, although poorly collimated, the radio jet is still active and has an
impact on the surrounding gas. This result indicates that the effect on the ISM
of even low-power radio jets should be considered when studying the influence
Active Galactic Nuclei can have on their host galaxy.Comment: 5 pages, 3 figures, Accepted for publication by A&
A shrinking Compact Symmetric Object: J11584+2450?
We present multi-frequency multi-epoch Very Long Baseline Array (VLBA)
observations of J11584+2450. These observations clearly show this source,
previously classified as a core-jet, to be a compact symmetric object (CSO).
Comparisons between these new data and data taken over the last 9 years shows
the edge brightened hot spots retreating towards the core (and slightly to the
west) at approximately 0.3c. Whether this motion is strictly apparent or
actually physical in nature is discussed, as well as possible explanations, and
what implications a physical contraction of J11584+2450 would have for current
CSO models.Comment: 16 pages, 6 figures, 5 tables. Accepted for publication in Ap
Particular Integrability and (Quasi)-exact-solvability
A notion of a particular integrability is introduced when two operators
commute on a subspace of the space where they act. Particular integrals for
one-dimensional (quasi)-exactly-solvable Schroedinger operators and
Calogero-Sutherland Hamiltonians for all roots are found. In the classical case
some special trajectories for which the corresponding particular constants of
motion appear are indicated.Comment: 13 pages, typos correcte
Cross-sectional associations between sleep duration, sedentary time, physical activity, and adiposity indicators among Canadian preschool-aged children using compositional analyses
Abstract Background Sleep duration, sedentary behaviour, and physical activity are three co-dependent behaviours that fall on the movement/non-movement intensity continuum. Compositional data analyses provide an appropriate method for analyzing the association between co-dependent movement behaviour data and health indicators. The objectives of this study were to examine: (1) the combined associations of the composition of time spent in sleep, sedentary behaviour, light-intensity physical activity (LPA), and moderate- to vigorous-intensity physical activity (MVPA) with adiposity indicators; and (2) the association of the time spent in sleep, sedentary behaviour, LPA, or MVPA with adiposity indicators relative to the time spent in the other behaviours in a representative sample of Canadian preschool-aged children. Methods Participants were 552 children aged 3 to 4 years from cycles 2 and 3 of the Canadian Health Measures Survey. Sedentary time, LPA, and MVPA were measured with Actical accelerometers (Philips Respironics, Bend, OR USA), and sleep duration was parental reported. Adiposity indicators included waist circumference (WC) and body mass index (BMI) z-scores based on World Health Organization growth standards. Compositional data analyses were used to examine the cross-sectional associations. Results The composition of movement behaviours was significantly associated with BMI z-scores (p = 0.006) but not with WC (p = 0.718). Further, the time spent in sleep (BMI z-score: γ sleep = −0.72; p = 0.138; WC: γ sleep = −1.95; p = 0.285), sedentary behaviour (BMI z-score: γ SB = 0.19; p = 0.624; WC: γ SB = 0.87; p = 0.614), LPA (BMI z-score: γ LPA = 0.62; p = 0.213, WC: γ LPA = 0.23; p = 0.902), or MVPA (BMI z-score: γ MVPA = −0.09; p = 0.733, WC: γ MVPA = 0.08; p = 0.288) relative to the other behaviours was not significantly associated with the adiposity indicators. Conclusions This study is the first to use compositional analyses when examining associations of co-dependent sleep duration, sedentary time, and physical activity behaviours with adiposity indicators in preschool-aged children. The overall composition of movement behaviours appears important for healthy BMI z-scores in preschool-aged children. Future research is needed to determine the optimal movement behaviour composition that should be promoted in this age group
A Comprehensive Spectroscopic Analysis of DB White Dwarfs
We present a detailed analysis of 108 helium-line (DB) white dwarfs based on
model atmosphere fits to high signal-to-noise optical spectroscopy. We derive a
mean mass of 0.67 Mo for our sample, with a dispersion of only 0.09 Mo. White
dwarfs also showing hydrogen lines, the DBA stars, comprise 44% of our sample,
and their mass distribution appears similar to that of DB stars. As in our
previous investigation, we find no evidence for the existence of low-mass (M <
0.5 Mo) DB white dwarfs. We derive a luminosity function based on a subset of
DB white dwarfs identified in the Palomar-Green survey. We show that 20% of all
white dwarfs in the temperature range of interest are DB stars, although the
fraction drops to half this value above Teff ~ 20,000 K. We also show that the
persistence of DB stars with no hydrogen features at low temperatures is
difficult to reconcile with a scenario involving accretion from the
interstellar medium, often invoked to account for the observed hydrogen
abundances in DBA stars. We present evidence for the existence of two different
evolutionary channels that produce DB white dwarfs: the standard model where DA
stars are transformed into DB stars through the convective dilution of a thin
hydrogen layer, and a second channel where DB stars retain a helium-atmosphere
throughout their evolution. We finally demonstrate that the instability strip
of pulsating V777 Her white dwarfs contains no nonvariables, if the hydrogen
content of these stars is properly accounted for.Comment: 74 pages including 30 figures, accepted for publication in the
Astrophysical Journa
Characteristics of EGRET Blazars in the VLBA Imaging and Polarimetry Survey (VIPS)
We examine the radio properties of EGRET-detected blazars observed as part of
the VLBA Imaging and Polarimetry Survey (VIPS). VIPS has a flux limit roughly
an order of magnitude below the MOJAVE survey and most other samples that have
been used to study the properties of EGRET blazars. At lower flux levels, radio
flux density does not directly correlate with gamma-ray flux density. We do
find that the EGRET-detected blazars tend to have higher brightness
temperatures, greater core fractions, and possibly larger than average jet
opening angles. A weak correlation is also found with jet length and with
polarization. All of the well-established trends can be explained by
systematically larger Doppler factors in the gamma-ray loud blazars, consistent
with the measurements of higher apparent velocities found in monitoring
programs carried out at radio frequencies above 10 GHz.Comment: 20 pages, 7 figures, accepted to Ap
Higher order effective low-energy theories
Three well-known perturbative approaches to deriving low-energy effective
theories, the degenerate Brillouin-Wigner perturbation theory (projection
method), the canonical transformation, and the resolvent methods are compared.
We use the Hubbard model as an example to show how, to fourth order in hopping
t, all methods lead to the same effective theory, namely the t-J model with
ring exchange and various correlated hoppings. We emphasize subtle technical
difficulties that make such a derivation less trivial to carry out for orders
higher than second. We also show that in higher orders, different approaches
can lead to seemingly different forms for the low-energy Hamiltonian. All of
these forms are equivalent since they are connected by an additional unitary
transformation whose generator is given explicitly. The importance of
transforming the operators is emphasized and the equivalence of their
transformed structure within the different approaches is also demonstrated.Comment: 14 pages, no figure
The puzzling case of the radio-loud QSO 3C 186: a gravitational wave recoiling black hole in a young radio source?
Context. Radio-loud AGNs with powerful relativistic jets are thought to be
associated with rapidly spinning black holes (BHs). BH spin-up may result from
a number of processes, including accretion of matter onto the BH itself, and
catastrophic events such as BH-BH mergers. Aims. We study the intriguing
properties of the powerful (L_bol ~ 10^47 erg s^-1) radio-loud quasar 3C 186.
This object shows peculiar features both in the images and in the spectra.
Methods. We utilize near-IR Hubble Space Telescope (HST) images to study the
properties of the host galaxy, and HST UV and Sloan Digital Sky Survey optical
spectra to study the kinematics of the source. Chandra X-ray data are also used
to better constrain the physical interpretation. Results. HST imaging shows
that the active nucleus is offset by 1.3 +- 0.1 arcsec (i.e. ~11 kpc) with
respect to the center of the host galaxy. Spectroscopic data show that the
broad emission lines are offset by -2140 +-390 km/s with respect to the narrow
lines. Velocity shifts are often seen in QSO spectra, in particular in
high-ionization broad emission lines. The host galaxy of the quasar displays a
distorted morphology with possible tidal features that are typical of the late
stages of a galaxy merger. Conclusions. A number of scenarios can be envisaged
to account for the observed features. While the presence of a peculiar outflow
cannot be completely ruled out, all of the observed features are consistent
with those expected if the QSO is associated with a gravitational wave (GW)
recoiling BH. Future detailed studies of this object will allow us to confirm
this type of scenario and will enable a better understanding of both the
physics of BH-BH mergers and the phenomena associated with the emission of GW
from astrophysical sources.Comment: 16 pages, 8 figures. Accepted for publication in Astronomy &
Astrophysics. New appendix adde
Conductance Distributions in Random Resistor Networks: Self Averaging and Disorder Lengths
The self averaging properties of conductance are explored in random
resistor networks with a broad distribution of bond strengths
P(g)\simg^{\mu-1}. Distributions of equivalent conductances are estimated
numerically on hierarchical lattices as a function of size and distribution
tail parameter . For networks above the percolation threshold, convergence
to a Gaussian basin is always the case, except in the limit --> 0. A {\it
disorder length} is identified beyond which the system is effectively
homogeneous. This length diverges as ( is the
regular percolation correlation length exponent) as -->0. This suggest
that exactly the same critical behavior can be induced by geometrical disorder
and bu strong bond disorder with the bond occupation probability .
Only lattices at the percolation threshold have renormalized probability
distribution in a {\it Levy-like} basin. At the threshold the disorder length
diverges at a vritical tail strength as , with
, a new exponent. Critical path analysis is used in a generalized
form to give form to give the macroscopic conductance for lattice above .Comment: 16 pages plain TeX file, 6 figures available upon
request.IBC-1603-01
An infinite family of solvable and integrable quantum systems on a plane
An infinite family of exactly-solvable and integrable potentials on a plane
is introduced. It is shown that all already known rational potentials with the
above properties allowing separation of variables in polar coordinates are
particular cases of this family. The underlying algebraic structure of the new
potentials is revealed as well as its hidden algebra. We conjecture that all
members of the family are also superintegrable and demonstrate this for the
first few cases. A quasi-exactly-solvable and integrable generalization of the
family is found.Comment: 30 pages, Introduction extended, description of known integrals
given, some statements clarified, one reference added, will be published in J
Phys A (FTC
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