87 research outputs found
Far-Infrared to Millimeter Astrophysical Dust Emission. II: Comparison of the Two-Level Systems (TLS) model with Astronomical Data
In a previous paper we proposed a new model for the emission by amorphous
astronomical dust grains, based on solid-state physics. The model uses a
description of the Disordered Charge Distribution (DCD) combined with the
presence of Two-Level Systems (TLS) defects in the amorphous solid composing
the grains. The goal of this paper is to confront this new model to
astronomical observations of different Galactic environments in the FIR/submm,
in order to derive a set of canonical model parameters to be used as a Galactic
reference to be compared to in future Galactic and extragalactic studies. We
confront the TLS model with existing astronomical data. We consider the average
emission spectrum at high latitudes in our Galaxy as measured with FIRAS and
WMAP, as well as the emission from Galactic compact sources observed with
Archeops, for which an inverse relationship between the dust temperature and
the emissivity spectral index has been evidenced. We show that, unlike models
previously proposed which often invoke two dust components at different
temperatures, the TLS model successfully reproduces both the shape of the
Galactic SED and its evolution with temperature as observed in the Archeops
data. The best TLS model parameters indicate a charge coherence length of
\simeq 13 nm and other model parameters in broad agreement with expectations
from laboratory studies of dust analogs. We conclude that the millimeter excess
emission, which is often attributed to the presence of very cold dust in the
diffuse ISM, is likely caused solely by TLS emission in disordered amorphous
dust grains. We discuss the implications of the new model, in terms of mass
determinations from millimeter continuum observations and the expected
variations of the emissivity spectral index with wavelength and dust
temperature. The implications for the analysis of the Herschel and Planck
satellite data are discussed.Comment: Accepted for publication in A&A (16 pages, 9 figures, 6 tables
Validity and responsiveness of the Clubfoot Assessment Protocol (CAP). A methodological study
BACKGROUND: The Clubfoot Assessment Protocol (CAP) is a multi dimensional instrument designed for longitudinal follow up of the clubfoot deformity during growth. Item reliability has shown to be sufficient. In this article the CAP's validity and responsiveness is studied using the Dimeglio classification scoring as a gold standard. METHODS: Thirty-two children with 45 congenital clubfeet were assessed prospectively and consecutively at ages of new-born, one, two, four months and two years of age. For convergent/divergent construct validity the Spearman's correlation coefficients were calculated. Discriminate validity was evaluated by studying the scores in bilateral clubfeet. The floor-ceiling effects at baseline (untreated clubfeet) and at two years of age (treated clubfeet) were evaluated. Responsiveness was evaluated by using effect sizes (ES) and by calculating if significant changes (Wilcoxons signed test) had occurred between the different measurement occasions. RESULTS: High to moderate significant correlation were found between CAP mobility I and morphology and the Dimeglio scores (r(s )= 0.77 and 0.44 respectively). Low correlation was found between CAP muscle function, mobility II and motion quality and the Dimeglio scoring system (r(s )= 0.20, 0.09 and 0.06 respectively). Of 13 children with bilateral clubfeet, 11 showed different CAP mobility I scores between right and left foot at baseline (untreated) compared with 5 with the Dimeglio score. At the other assessment occasions the CAP mobility I continued to show higher discrimination ability than the Dimeglio. No floor effects and low ceiling effects were found in the untreated clubfeet for both instruments. High ceiling effects were found in the CAP for the treated children and low for the Dimeglio. Responsiveness was good. ES from untreated to treated ranged from 0.80 to 4.35 for the CAP subgroups and was 4.68 for the Dimeglio. The first four treatment months, the CAP mobility I had generally higher ES compared with the Dimeglio. CONCLUSION: The Clubfoot Assessment Protocol shows in this study good validity and responsiveness. The CAP is more responsive when severity ranges between mild – moderate to severe, while the Dimeglio focuses more on the extremes. The ability to discriminate between different mobility status of the right and left foot in bilaterally affected children in this population was higher compared with the Dimeglio score implicating a better sensitivity for the CAP
Molecular velocity auto-correlation of simple liquids observed by NMR MGSE method
The velocity auto-correlation spectra of simple liquids obtained by the NMR
method of modulated gradient spin echo show features in the low frequency range
up to a few kHz, which can be explained reasonably well by a long
time tail decay only for non-polar liquid toluene, while the spectra of polar
liquids, such as ethanol, water and glycerol, are more congruent with the model
of diffusion of particles temporarily trapped in potential wells created by
their neighbors. As the method provides the spectrum averaged over ensemble of
particle trajectories, the initial non-exponential decay of spin echoes is
attributed to a spatial heterogeneity of molecular motion in a bulk of liquid,
reflected in distribution of the echo decays for short trajectories. While at
longer time intervals, and thus with longer trajectories, heterogeneity is
averaged out, giving rise to a spectrum which is explained as a combination of
molecular self-diffusion and eddy diffusion within the vortexes of hydrodynamic
fluctuations.Comment: 8 pages, 6 figur
Long-term disturbance dynamics and resilience of tropical peat swamp forests
Summary 1.The coastal peat swamp forests of Sarawak, Malaysian Borneo, are undergoing rapid conversion, predominantly into oil palm plantations. This wetland ecosystem is assumed to have experienced insignificant disturbance in the past, persisting under a single ecologically-stable regime. However, there is limited knowledge of the past disturbance regime, long-term functioning and fundamentally the resilience of this ecosystem to changing natural and anthropogenic perturbations through time. 2. In this study, long-term ecological data sets from three degraded peatlands in Sarawak were collected to shed light on peat swamp forest dynamics. Fossil pollen and charcoal were counted in each sedimentary sequence to reconstruct vegetation and investigate responses to past environmental disturbance, both natural and anthropogenic. 3. Results demonstrate that peat swamp forest taxa have dominated these vegetation profiles throughout the last c. 2000-year period despite the presence of various drivers of disturbance. Evidence for episodes of climatic variability, predominantly linked to ENSO events, and wildfires is present throughout. However, in the last c. 500 years, burning and indicators of human disturbance have elevated beyond past levels at these sites, concurrent with a reduction in peat swamp forest pollen. 4. Two key insights have been gained through this palaeoecological analysis: (i) peat swamp forest vegetation has demonstrated resilience to disturbance caused by burning and climatic variability in Sarawak in the late Holocene, however (ii) coincident with increased fire combined with human impact c. 500 years ago, these communities started to decline. 5. Synthesis. Sarawak's coastal peat swamps have demonstrated resilience to past natural disturbances, with forest vegetation persisting through episodes of fire and climatic variability. However, palaeoecological data presented here suggest that recent, anthropogenic disturbances are of a greater magnitude, causing the observed decline in the peat swamp forest communities in the last c. 500 years and challenging the ecosystem's persistence. This study greatly extends our knowledge of the ecological functioning of these understudied ecosystems, providing baseline information on the past vegetation and its response to disturbance. This understanding is central to developing management strategies that foster resilience in the remaining peat swamp forests and ensure continued provision of services, namely carbon storage, from this globally important ecosystem.</p
The DIRTY Model II: Self-Consistent Treatment of Dust Heating and Emission in a 3-D Radiative Transfer Code
In this paper and a companion paper we present the DIRTY model, a Monte Carlo
radiative transfer code, self-consistently including dust heating and emission,
and accounting for the effects of the transient heating of small grains. The
code is completely general; the density structure of the dust, the number and
type of heating sources, and their geometric configurations can be specified
arbitrarily within the model space. Source photons are tracked through the
scattering and absorbing medium using Monte Carlo techniques and the effects of
multiple scattering are included. The dust scattering, absorbing, and emitting
properties are calculated from realistic dust models derived by fitting
observed extinction curves in Local Group galaxies including the Magellanic
Clouds and the Milky Way. The dust temperature and the emitted dust spectrum
are calculated self consistently from the absorbed energy including the effects
of temperature fluctuations in small grains. Dust self-absorption is also
accounted for, allowing the treatment of high optical depths, by treating
photons emitted by the dust as an additional heating source and adopting an
iterative radiative transfer scheme. As an illustrative case, we apply the
DIRTY radiative transfer code to starburst galaxies wherein the heating sources
are derived from stellar evolutionary synthesis models. Within the context of
the starburst model, we examine the dependence of the UV to FIR SED, dust
temperatures, and dust masses predicted by DIRTY on variations of the input
parameters.Comment: 23 pages (emulateapj, single column), 17 figures. To appear in the
ApJ, in pres
Infrared Emission of Normal Galaxies from 2.5 to 12 Microns: ISO Spectra, Near-Infrared Continuum and Mid-Infrared Emission Features
We present ISO-PHOT spectra of the regions 2.5-4.9um and 5.8-11.6um for a
sample of 45 disk galaxies from the U.S. ISO Key Project on Normal Galaxies.
The spectra can be decomposed into three spectral components: (1) continuum
emission from stellar photospheres, which dominates the near-infrared (2.5-
4.9um; NIR) spectral region; (2) a weak NIR excess continuum, which has a color
temperature of ~ 1000K, carries a luminosity of a few percent of the total
far-infrared luminosity L(FIR), and most likely arises from the ISM; and (3)
the well-known broad emission features at 6.2, 7.7, 8.6 and 11.3 um, which are
generally attributed to aromatic carbon particles. These aromatic features in
emission (AFEs) dominate the mid-infrared (5.8-11.6 um; MIR) part of the
spectrum, and resemble the so-called Type-A spectra observed in many
non-stellar sources and the diffuse ISM in our own Galaxy. The relative
strengths of the AFEs vary by 15-25% among the galaxies. However, little
correlation is seen between these variations and either IRAS 60um-to-100um flux
density ratio R(60/100) or the FIR-to-blue luminosity ratio L(FIR)/L(B),
suggesting that the observed variations are not a direct consequence of the
radiation field differences among the galaxies. We demonstrate that the NIR
excess continuum and AFE emission are correlated, suggesting that they are
produced by similar mechanisms and similar (or the same) material. On the other
hand, as the current star-formation activity increases, the overall strengths
of the AFEs and the NIR excess continuum drop significantly with respect to
that of the far-infrared emission from large dust grains. This is likely a
consequence of the preferential destruction in intense radiation fields of the
small carriers responsible for the NIR/AFE emission.Comment: With 8 tables and 12 figures; to appear in the Astrophysical Journa
Infrared Emission from Interstellar Dust. I. Stochastic Heating of Small Grains
We present a method for calculating the infrared emission from a population
of dust grains heated by starlight, including very small grains for which
stochastic heating by starlight photons results in high temperature transients.
Because state-to-state transition rates are generally unavailable for complex
molecules, we consider model PAH, graphitic, and silicate grains with realistic
vibrational mode spectra and realistic radiative properties. The vibrational
density of states is used in a statistical-mechanical description of the
emission process. Unlike previous treatments, our approach fully incorporates
multiphoton heating effects, important for large grains or strong radiation
fields. We discuss how the "temperature" of the grain is related to its
vibrational energy. By comparing with an "exact" statistical calculation of the
emission process, we determine the conditions under which the "thermal" and the
"continuous cooling" approximations can be used to calculate the emission
spectrum.
We present results for the infrared emission spectra of PAH grains of various
sizes heated by starlight. We show how the relative strengths of the 6.2, 7.7,
and 11.3um features depend on grain size, starlight spectrum and intensity, and
grain charging conditions. We show results for grains in the "cold neutral
medium", "warm ionized medium", and representative conditions in
photodissociation regions. Our model results are compared to observed ratios of
emission features for reflection nebulae and photodissociation regions, the
Milky Way, normal spiral galaxies, and starburst galaxies.Comment: Submitted to ApJ. 42 pages, 18 figures, Late
Fitting the integrated Spectral Energy Distributions of Galaxies
Fitting the spectral energy distributions (SEDs) of galaxies is an almost
universally used technique that has matured significantly in the last decade.
Model predictions and fitting procedures have improved significantly over this
time, attempting to keep up with the vastly increased volume and quality of
available data. We review here the field of SED fitting, describing the
modelling of ultraviolet to infrared galaxy SEDs, the creation of
multiwavelength data sets, and the methods used to fit model SEDs to observed
galaxy data sets. We touch upon the achievements and challenges in the major
ingredients of SED fitting, with a special emphasis on describing the interplay
between the quality of the available data, the quality of the available models,
and the best fitting technique to use in order to obtain a realistic
measurement as well as realistic uncertainties. We conclude that SED fitting
can be used effectively to derive a range of physical properties of galaxies,
such as redshift, stellar masses, star formation rates, dust masses, and
metallicities, with care taken not to over-interpret the available data. Yet
there still exist many issues such as estimating the age of the oldest stars in
a galaxy, finer details ofdust properties and dust-star geometry, and the
influences of poorly understood, luminous stellar types and phases. The
challenge for the coming years will be to improve both the models and the
observational data sets to resolve these uncertainties. The present review will
be made available on an interactive, moderated web page (sedfitting.org), where
the community can access and change the text. The intention is to expand the
text and keep it up to date over the coming years.Comment: 54 pages, 26 figures, Accepted for publication in Astrophysics &
Space Scienc
Interstellar Grains -- The 75th Anniversary
The year of 2005 marks the 75th anniversary since Trumpler (1930) provided
the first definitive proof of interstellar grains by demonstrating the
existence of general absorption and reddening of starlight in the galactic
plane. This article reviews our progressive understanding of the nature of
interstellar dust.Comment: invited review article for the "Light, Dust and Chemical Evolution"
conference (Gerace, Italy, 26--30 September 2004), edited by F. Borghese and
R. Saija, 2005, in pres
The Bulk of the Cosmic Infrared Background Resolved by ISOCAM
We have computed the 15 microns integrated galaxy light produced by ISOCAM
galaxies above a sensitivity limit of 50 microJy. It sets a lower limit to the
15 microns extragalactic background light of (2.4+/-0.5) nW/m^2/Hz. The
redshift distribution of the ISOCAM galaxies is inferred from the
spectroscopically complete sample of galaxies in the Hubble Deep Field North
(HDFN). We demonstrate that mid (MIR) and far (FIR) infrared luminosities
correlate for local star forming galaxies and that this correlation is
consistent with the radio-FIR one up to z ~ 1. From these correlations, about
75 % of the ISOCAM galaxies are found to belong to the class of luminous
infrared galaxies (L[IR] >= 10^11 Lsol), with star formation rates of the order
of ~ 100 Msol/yr. The cross-correlation with the deepest X-ray surveys from the
Chandra and XMM-Newton observatories in the HDFN and Lockman Hole respectively,
indicates that at most 20 % of the 15 microns integrated galaxy light is due to
active galactic nuclei (AGNs) unless a large population of AGNs was missed by
Chandra and XMM-Newton. The contribution of ISOCAM galaxies to the peak of the
cosmic infrared background (CIRB) at 140 microns was computed from the MIR-FIR
correlations for star forming galaxies and from the spectral energy
distribution of the Seyfert 2, NGC 1068, for AGNs. We find that the galaxies
unveiled by ISOCAM surveys are responsible for the bulk of the CIRB, i.e
(16+/-5) nW/m^2/Hz as compared to the (25+/-7) nW/m^2/Hz measured with the COBE
satellite, with less than 10 % due to AGNs. Since the CIRB contains most of the
light radiated over the history of star formation in the universe, this means
that a large fraction of present-day stars must have formed during a dusty
starburst event similar to those revealed by ISOCAM.Comment: 19 pages, 10 figures, A&A accepte
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