619 research outputs found
Dust models post-Planck: constraining the far-infrared opacity of dust in the diffuse interstellar medium
We compare the performance of several dust models in reproducing the dust
spectral energy distribution (SED) per unit extinction in the diffuse
interstellar medium (ISM). We use our results to constrain the variability of
the optical properties of big grains in the diffuse ISM, as published by the
Planck collaboration.
We use two different techniques to compare the predictions of dust models to
data from the Planck HFI, IRAS and SDSS surveys. First, we fit the far-infrared
emission spectrum to recover the dust extinction and the intensity of the
interstellar radiation field (ISRF). Second, we infer the ISRF intensity from
the total power emitted by dust per unit extinction, and then predict the
emission spectrum. In both cases, we test the ability of the models to
reproduce dust emission and extinction at the same time.
We identify two issues. Not all models can reproduce the average dust
emission per unit extinction: there are differences of up to a factor
between models, and the best accord between model and observation is obtained
with the more emissive grains derived from recent laboratory data on silicates
and amorphous carbons. All models fail to reproduce the variations in the
emission per unit extinction if the only variable parameter is the ISRF
intensity: this confirms that the optical properties of dust are indeed
variable in the diffuse ISM.
Diffuse ISM observations are consistent with a scenario where both ISRF
intensity and dust optical properties vary. The ratio of the far-infrared
opacity to the band extinction cross-section presents variations of the
order of ( in extreme cases), while ISRF intensity varies
by ( in extreme cases). This must be accounted for in
future modelling.Comment: A&A, in pres
Statistical properties of dust far-infrared emission
The description of the statistical properties of dust emission gives
important constraints on the physics of the interstellar medium but it is also
a useful way to estimate the contamination of diffuse interstellar emission in
the cases where it is considered a nuisance. The main goals of this analysis of
the power spectrum and non-Gaussian properties of 100 micron dust emission are
1) to estimate the power spectrum of interstellar matter density in three
dimensions, 2) to review and extend previous estimates of the cirrus noise due
to dust emission and 3) to produce simulated dust emission maps that reproduce
the observed statistical properties. The main results are the following. 1) The
cirrus noise level as a function of brightness has been previously
overestimated. It is found to be proportional to instead of ^1.5, where
is the local average brightness at 100 micron. This scaling is in
accordance with the fact that the brightness fluctuation level observed at a
given angular scale on the sky is the sum of fluctuations of increasing
amplitude with distance on the line of sight. 2) The spectral index of dust
emission at scales between 5 arcmin and 12.5 degrees is =-2.9 on average
but shows significant variations over the sky. Bright regions have
systematically steeper power spectra than diffuse regions. 3) The skewness and
kurtosis of brightness fluctuations is high, indicative of strong
non-Gaussianity. 4) Based on our characterization of the 100 micron power
spectrum we provide a prescription of the cirrus confusion noise as a function
of wavelength and scale. 5) Finally we present a method based on a modification
of Gaussian random fields to produce simulations of dust maps which reproduce
the power spectrum and non-Gaussian properties of interstellar dust emission.Comment: 13 pages, 13 figures. Accepted for publication in A&
An Imprint of Molecular Cloud Magnetization in the Morphology of the Dust Polarized Emission
We describe a morphological imprint of magnetization found when considering
the relative orientation of the magnetic field direction with respect to the
density structures in simulated turbulent molecular clouds. This imprint was
found using the Histogram of Relative Orientations (HRO): a new technique that
utilizes the gradient to characterize the directionality of density and column
density structures on multiple scales. We present results of the HRO analysis
in three models of molecular clouds in which the initial magnetic field
strength is varied, but an identical initial turbulent velocity field is
introduced, which subsequently decays. The HRO analysis was applied to the
simulated data cubes and mock-observations of the simulations produced by
integrating the data cube along particular lines of sight. In the 3D analysis
we describe the relative orientation of the magnetic field with
respect to the density structures, showing that: 1.The magnetic field shows a
preferential orientation parallel to most of the density structures in the
three simulated cubes. 2.The relative orientation changes from parallel to
perpendicular in regions with density over a critical density in the
highest magnetization case. 3.The change of relative orientation is largest for
the highest magnetization and decreases in lower magnetization cases. This
change in the relative orientation is also present in the projected maps. In
conjunction with simulations HROs can be used to establish a link between the
observed morphology in polarization maps and the physics included in
simulations of molecular clouds.Comment: (16 pages, 11 figures, submitted to ApJ 05MAR2013, accepted
07JUL2013
Direct Estimate of Cirrus Noise in Herschel Hi-GAL Images
In Herschel images of the Galactic plane and many star forming regions, a
major factor limiting our ability to extract faint compact sources is cirrus
confusion noise, operationally defined as the "statistical error to be expected
in photometric measurements due to confusion in a background of fluctuating
surface brightness". The histogram of the flux densities of extracted sources
shows a distinctive faint-end cutoff below which the catalog suffers from
incompleteness and the flux densities become unreliable. This empirical cutoff
should be closely related to the estimated cirrus noise and we show that this
is the case. We compute the cirrus noise directly, both on Herschel images from
which the bright sources have been removed and on simulated images of cirrus
with statistically similar fluctuations. We connect these direct estimates with
those from power spectrum analysis, which has been used extensively to predict
the cirrus noise and provides insight into how it depends on various
statistical properties and photometric operational parameters. We report
multi-wavelength power spectra of diffuse Galactic dust emission from Hi-GAL
observations at 70 to 500 microns within Galactic plane fields at l= 30 degrees
and l= 59 degrees. We find that the exponent of the power spectrum is about -3.
At 250 microns, the amplitude of the power spectrum increases roughly as the
square of the median brightness of the map and so the expected cirrus noise
scales linearly with the median brightness. Generally, the confusion noise will
be a worse problem at longer wavelengths, because of the combination of lower
angular resolution and the rising power spectrum of cirrus toward lower spatial
frequencies, but the photometric signal to noise will also depend on the
relative spectral energy distribution of the source compared to the cirrus.Comment: 4 pages (in journal), 3 figures, Astronomy and Astrophysics, accepted
for publication 13 May 201
Correlated Anisotropies in the Cosmic Far-Infrared Background Detected by MIPS/Spitzer: Constraint on the Bias
We report the detection of correlated anisotropies in the Cosmic Far-Infrared
Background at 160 microns. We measure the power spectrum in the Spitzer/SWIRE
Lockman Hole field. It reveals unambiguously a strong excess above cirrus and
Poisson contributions, at spatial scales between 5 and 30 arcminutes,
interpreted as the signature of infrared galaxy clustering. Using our model of
infrared galaxy evolution we derive a linear bias b=1.74 \pm 0.16. It is a
factor 2 higher than the bias measured for the local IRAS galaxies. Our model
indicates that galaxies dominating the 160 microns correlated anisotropies are
at z~1. This implies that infrared galaxies at high redshifts are biased
tracers of mass, unlike in the local Universe.Comment: ApJ Letters, in pres
Altered Trafficking of Mutant Connexin32
We examined the cellular localization of nine different connexin32 (Cx32) mutants associated with X-linked Charcot–Marie–Tooth disease (CMTX) in communication-incompetent mammalian cells. Cx32 mRNA was made, but little or no protein was detected in one class of mutants. In another class of mutants, Cx32 protein was detectable in the cytoplasm and at the cell surface, where it appeared as plaques and punctate staining. Cx32 immunoreactivity in a third class of mutants was restricted to the cytoplasm, where it often colocalized with the Golgi apparatus. Our studies suggest that CMTX mutations have a predominant effect on the trafficking of Cx32 protein, resulting in a potentially toxic cytoplasmic accumulation of Cx32 in these cells. These results and evidence of cytoplasmic accumulation of other mutated myelin proteins suggest that diseases affecting myelinating cells may share a common pathophysiology
Evidence for dust evolution within the Taurus Complex from Spitzer images
We present Spitzer images of the Taurus Complex (TC) and take advantage of
the sensitivity and spatial resolution of the observations to characterize the
diffuse IR emission across the cloud. This work highlights evidence of dust
evolution within the translucent sections of the archetype reference for
studies of quiescent molecular clouds. We combine Spitzer 160 um and IRAS 100
um observations to produce a dust temperature map and a far-IR dust opacity map
at 5' resolution. The average dust temperature is about 14.5K with a dispersion
of +/-1K across the cloud. The far-IR dust opacity is a factor 2 larger than
the average value for the diffuse ISM. This opacity increase and the
attenuation of the radiation field (RF) both contribute to account for the
lower emission temperature of the large grains. The structure of the TC
significantly changes in the mid-IR images that trace emission from PAHs and
VSGs. We focus our analysis of the mid-IR emission to a range of ecliptic
latitudes where the zodiacal light residuals are small. Within this cloud area,
there are no 8 and 24 um counterparts to the brightest 160 um emission
features. Conversely, the 8 and 24 um images reveal filamentary structure that
is strikingly inconspicuous in the 160 um and extinction maps. The IR colors
vary over sub-parsec distances across this filamentary structure. We compare
the observed colors with model calculations quantifying the impact of the RF
intensity and the abundance of stochastically heated particles on the dust SED.
To match the range of observed colors, we have to invoke variations by a factor
of a few of both the interstellar RF and the abundance of PAHs and VSGs. We
conclude that within this filamentary structure a significant fraction of the
dust mass cycles in and out the small size end of the dust size distribution.Comment: 43 pages, 13 figures, accepted for publication in Ap
Dust-Gas Scaling Relations and OH Abundance in the Galactic ISM
Observations of interstellar dust are often used as a proxy for total gas
column density . By comparing thermal dust data
(Release 1.2) and new dust reddening maps from Pan-STARRS 1 and 2MASS (Green et
al. 2018), with accurate (opacity-corrected) HI column densities and
newly-published OH data from the Arecibo Millennium survey and 21-SPONGE, we
confirm linear correlations between dust optical depth , reddening
and the total proton column density in the range
(130)10cm, along sightlines with no molecular gas
detections in emission. We derive an / ratio of
(9.41.6)10cmmag for purely atomic sightlines
at 5, which is 60 higher than the canonical value of
Bohlin et al. (1978). We report a 40 increase in opacity
=/, when moving from the low column
density (510cm) to moderate column
density (510cm) regime, and suggest that
this rise is due to the evolution of dust grains in the atomic ISM. Failure to
account for HI opacity can cause an additional apparent rise in ,
of the order of a further 20. We estimate molecular hydrogen column
densities from our derived linear relations, and hence
derive the OH/H abundance ratio of 110
for all molecular sightlines. Our results show no evidence of systematic trends
in OH abundance with in the range
(0.110)10cm. This suggests
that OH may be used as a reliable proxy for H in this range, which includes
sightlines with both CO-dark and CO-bright gas.Comment: The revised manuscript is accepted for publication in The
Astrophysical Journa
Broadband dual-comb hyperspectral imaging and adaptable spectroscopy with programmable frequency combs
We explore the advantages of a free-form dual-comb spectroscopy (DCS)
platform based on time-programmable frequency combs for real-time, penalty-free
apodized scanning. In traditional DCS, the fundamental spectral resolution,
which equals the comb repetition rate, can be excessively fine for many
applications. While the fine resolution is not itself problematic, it comes
with the penalty of excess acquisition time. Post-processing apodization
(windowing) can be applied to tailor the resolution to the sample, but only
with a deadtime penalty proportional to the degree of apodization. The excess
acquisition time remains. With free-form DCS, this deadtime is avoided by
programming a real-time apodization pattern that dynamically reverses the pulse
periods between the dual frequency combs. In this way, one can tailor the
spectrometer's resolution and update rate to different applications without
penalty. We show operation of a free-form DCS system where the spectral
resolution is varied from the intrinsic fine resolution of 160 MHz up to 822
GHz by applying tailored real-time apodization. Because there is no deadtime
penalty, the spectral signal-to-noise ratio increases linearly with resolution
by 5000x over this range, as opposed to the square root increase observed for
postprocessing apodization in traditional DCS. We explore the flexibility to
change resolution and update rate to perform hyperspectral imaging at slow
camera frame rates, where the penalty-free apodization allows for optimal use
of each frame. We obtain dual-comb hyperspectral movies at a 20 Hz spectrum
update rate with broad optical spectral coverage of over 10 THz
Connexin32 is a Myelin-Related Protein in the PNS and CNS
We have examined the expression of a gap junction protein, connexin32 (Cx32), in Schwann cells and oligodendrocytes. In peripheral nerve, Cx32 is found in the paranodal myelin loops and Schmidt-Lanterman incisures of myelinating Schwann cells, and the levels of Cx32 protein and mRNA change in parallel with those of other myelin-related genes during development, Wallerian degeneration, and axonal regeneration. In the central nervous system, Cx32 is found in oligodendrocytes and their processes, but not in compact myelin, and the levels of Cx32 protein and mRNA increase during development in parallel with those of the other myelin genes. Thus, Cx32 is expressed as part of the myelinating phenotype of both Schwann cells and oligodendrocytes, indicating that this gap junction protein plays in important role in the biology of myelin-forming cells
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