43,172 research outputs found
Impact of an AGN featureless continuum on estimation of stellar population properties
The effect of the featureless power-law (PL) continuum of an active galactic
nucleus (AGN) on the estimation of physical properties of galaxies with optical
population spectral synthesis (PSS) remains largely unknown. With this in mind,
we fit synthetic galaxy spectra representing a wide range of galaxy star
formation histories (SFHs) and including distinct PL contributions of the form
with the PSS code STARLIGHT to study to which
extent various inferred quantities (e.g. stellar mass, mean age, and mean
metallicity) match the input. The synthetic spectral energy distributions
(SEDs) computed with our evolutionary spectral synthesis code include an AGN PL
component with and a fractional contribution to the monochromatic flux at 4020 \AA. At the
empirical AGN detection threshold that we
previously inferred in a pilot study on this subject, our results show that the
neglect of a PL component in spectral fitting can lead to an overestimation by
2 dex in stellar mass and by up to 1 and 4 dex in the light-
and mass-weighted mean stellar age, respectively, whereas the light- and
mass-weighted mean stellar metallicity are underestimated by up to 0.3
and 0.6 dex, respectively. Other fitting set-ups including either a
single PL or multiple PLs in the base reveal, on average, much lower
unsystematic uncertainties of the order of those typically found when fitting
purely stellar SEDs with stellar templates, however, reaching locally up to
1, 3 and 0.4 dex in mass, age and metallicity, respectively. Our results
underscore the importance of an accurate modelling of the AGN spectral
contribution in PSS fits as a minimum requirement for the recovery of the
physical and evolutionary properties of stellar populations in active galaxies.Comment: 18 pages, 22 figures, accepted for publication in A&
Dense Molecular Filaments Feeding a Starburst: ALMA Maps of CO(3-2) in Henize 2-10
We present ALMA CO(3-2) observations at 0.3 arcsec resolution of He2-10, a
starburst dwarf galaxy and possible high-z galaxy analogue. The warm dense gas
traced by CO(3--2) is found in clumpy filaments that are kinematically and
spatially distinct. The filaments have no preferred orientation or direction;
this may indicate that the galaxy is not evolving into a disk galaxy. Filaments
appear to be feeding the active starburst; the velocity field in one filament
suggests acceleration onto an embedded star cluster. The relative strengths of
CO(3-2) and radio continuum vary strongly on decaparsec scales in the
starburst. There is no CO(3--2) clump coincident with the non-thermal radio
source that has been suggested to be an AGN, nor unusual kinematics.
The kinematics of the molecular gas show significant activity apparently
unrelated to the current starburst. The longest filament, east of the
starburst, has a pronounced shear of FWHM ~\kms\ across its 50~pc
width over its entire kpc length. The cause of the shear is not
clear. This filament is close in projection to a `dynamically distinct' CO
feature previously seen in CO(1--0). The most complex region and the most
highly disturbed gas velocities are in a region 200~pc south of the starburst.
The CO(3--2) emission there reveals a molecular outflow, of linewidth FWZI
120-140 \kms, requiring an energy . There is
at present {\it no} candidate for the driving source of this outflow.Comment: This was revised 31 October to correct some typos and to replace
Figure
Resolving Structure in Human Brain Organization: Identifying Mesoscale Organization in Weighted Network Representations
Human brain anatomy and function display a combination of modular and
hierarchical organization, suggesting the importance of both cohesive
structures and variable resolutions in the facilitation of healthy cognitive
processes. However, tools to simultaneously probe these features of brain
architecture require further development. We propose and apply a set of methods
to extract cohesive structures in network representations of brain connectivity
using multi-resolution techniques. We employ a combination of soft
thresholding, windowed thresholding, and resolution in community detection,
that enable us to identify and isolate structures associated with different
weights. One such mesoscale structure is bipartivity, which quantifies the
extent to which the brain is divided into two partitions with high connectivity
between partitions and low connectivity within partitions. A second,
complementary mesoscale structure is modularity, which quantifies the extent to
which the brain is divided into multiple communities with strong connectivity
within each community and weak connectivity between communities. Our methods
lead to multi-resolution curves of these network diagnostics over a range of
spatial, geometric, and structural scales. For statistical comparison, we
contrast our results with those obtained for several benchmark null models. Our
work demonstrates that multi-resolution diagnostic curves capture complex
organizational profiles in weighted graphs. We apply these methods to the
identification of resolution-specific characteristics of healthy weighted graph
architecture and altered connectivity profiles in psychiatric disease.Comment: Comments welcom
High field electro-thermal transport in metallic carbon nanotubes
We describe the electro-thermal transport in metallic carbon nanotubes
(m-CNTs) by a semi-classical approach that takes into account the high-field
dynamical interdependence between charge carrier and phonon populations. Our
model is based on the self-consistent solution of the Boltzmann transport
equation and the heat equation mediated by a phonon rate equation that accounts
for the onset of non-equilibrium (optical) phonons in the high-field regime.
Given the metallic nature of the nanostructures, a key ingredient of the model
is the assumption of local thermalization of charge carriers. Our theory
remarkably reproduces the room temperature electrical characteristics of m-CNTs
on substrate and free standing (suspended), shedding light on charge-heat
transport in these one dimensional nanostructures. In particular, the negative
differential resistance observed in suspended m-CNTs under electric stress is
attributed to inhomogeneous field profile induced by self-heating rather than
the presence of hot phonons.Comment: 10 pages, 10 figure
Brans-Dicke gravity and the capture of stars by black holes: some asymptotic results
In the context of star capture by a black hole, a new noticeable difference
between Brans-Dicke theory and general relativity gravitational radiation is
pointed out. This feature stems from the non-stationarity of the black hole
state, barring Hawking's theorem.Comment: 4 pages. Submitted to Classical and Quantum Gravit
Bouncing trimer: a random self-propelled particle, chaos and periodical motions
A trimer is an object composed of three centimetrical stainless steel beads
equally distant and is predestined to show richer behaviours than the bouncing
ball or the bouncing dimer. The rigid trimer has been placed on a plate of a
electromagnetic shaker and has been vertically vibrated according to a
sinusoidal signal. The horizontal translational and rotational motions of the
trimer have been recorded for a range of frequencies between 25 and 100 Hz
while the amplitude of the forcing vibration was tuned for obtaining maximal
acceleration of the plate up to 10 times the gravity. Several modes have been
detected like e.g. rotational and pure translational motions. These modes are
found at determined accelerations of the plate and do not depend on the
frequency. By recording the time delays between two successive contacts when
the frequency and the amplitude are fixed, a mapping of the bouncing regime has
been constructed and compared to that of the dimer and the bouncing ball.
Period-2 and period-3 orbits have been experimentally observed. In these modes,
according to observations, the contact between the trimer and the plate is
persistent between two successive jumps. This persistence erases the memory of
the jump preceding the contact. A model is proposed and allows to explain the
values of the particular accelerations for which period-2 and period-3 modes
are observed. Finally, numerical simulations allow to reproduce the
experimental results. That allows to conclude that the friction between the
beads and the plate is the major dissipative process.Comment: 22 pages, 10 figure
Local Symmetries and Order-Disorder Transitions in Small Macroscopic Wigner Islands
The influence of local order on the disordering scenario of small Wigner
islands is discussed. A first disordering step is put in evidence by the time
correlation functions and is linked to individual excitations resulting in
configuration transitions, which are very sensitive to the local symmetries.
This is followed by two other transitions, corresponding to orthoradial and
radial diffusion, for which both individual and collective excitations play a
significant role. Finally, we show that, contrary to large systems, the focus
that is commonly made on collective excitations for such small systems through
the Lindemann criterion has to be made carefully in order to clearly identify
the relative contributions in the whole disordering process.Comment: 14 pages, 10 figure
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