3,543 research outputs found
Multiple Radial Cool Molecular Filaments in NGC 1275
We have extended our previous observation (Lim et al. 2008) of NGC1275
covering a central radius of ~10kpc to the entire main body of cool molecular
gas spanning ~14kpc east and west of center. We find no new features beyond the
region previously mapped, and show that all six spatially-resolved features on
both the eastern and western sides (three on each side) comprise radially
aligned filaments. Such radial filaments can be most naturally explained by a
model in which gas deposited "upstream" in localized regions experiencing an
X-ray cooling flow subsequently free falls along the gravitational potential of
PerA, as we previously showed can explain the observed kinematics of the two
longest filaments. All the detected filaments coincide with locally bright
Halpha features, and have a ratio in CO(2-1) to Halpha luminosity of ~1e-3; we
show that these filaments have lower star formation efficiencies than the
nearly constant value found for molecular gas in nearby normal spiral galaxies.
On the other hand, some at least equally luminous Halpha features, including a
previously identified giant HII region, show no detectable cool molecular gas
with a corresponding ratio at least a factor of ~5 lower; in the giant HII
region, essentially all the pre-existing molecular gas may have been converted
to stars. We demonstrate that all the cool molecular filaments are
gravitationally bound, and without any means of support beyond thermal pressure
should collapse on timescales ~< 1e6yrs. By comparison, as we showed previously
the two longest filaments have much longer dynamical ages of ~1e7yrs. Tidal
shear may help delay their collapse, but more likely turbulent velocities of at
least a few tens km/s or magnetic fields with strengths of at least several
~10uG are required to support these filaments.Comment: 52 pages, 11 figures. Accepted to Ap
Polarized X-rays from Magnetized Neutron Stars
We review the polarization properties of X-ray emission from highly
magnetized neutron stars, focusing on emission from the stellar surfaces. We
discuss how x-ray polarization can be used to constrain neutron star magnetic
field and emission geometry, and to probe strong-field quantum electrodynamics
and possibly constrain the properties of axions.Comment: to appear in "X-ray Polarimetry: A New Window in Astrophysics",
edited by R. Bellazzini, E. Costa, G. Matt and G. Tagliaferri (Cambridge
University Press
The adaptive nature of the bone-periodontal ligament-cementum complex in a ligature-induced periodontitis rat model.
The novel aspect of this study involves illustrating significant adaptation of a functionally loaded bone-PDL-cementum complex in a ligature-induced periodontitis rat model. Following 4, 8, and 15 days of ligation, proinflammatory cytokines (TNF- α and RANKL), a mineral resorption indicator (TRAP), and a cell migration and adhesion molecule for tissue regeneration (fibronectin) within the complex were localized and correlated with changes in PDL-space (functional space). At 4 days of ligation, the functional space of the distal complex was widened compared to controls and was positively correlated with an increased expression of TNF- α. At 8 and 15 days, the number of RANKL(+) cells decreased near the mesial alveolar bone crest (ABC) but increased at the distal ABC. TRAP(+) cells on both sides of the complex significantly increased at 8 days. A gradual change in fibronectin expression from the distal PDL-secondary cementum interfaces through precementum layers was observed when compared to increased and abrupt changes at the mesial PDL-cementum and PDL-bone interfaces in ligated and control groups. Based on our results, we hypothesize that compromised strain fields can be created in a diseased periodontium, which in response to prolonged function can significantly alter the original bone and apical cementum formations
Angular Momentum Exchange by Gravitational Torques and Infall in the Circumbinary Disk of the Protostellar System L1551 NE
We report the ALMA observation of the Class I binary protostellar system
L1551 NE in the 0.9-mm continuum, C18O (3-2), and 13CO (3-2) lines at a ~1.6
times higher resolution and a ~6 times higher sensitivity than those of our
previous SMA observations, which revealed a r ~300 AU-scale circumbinary disk
in Keplerian rotation. The 0.9-mm continuum shows two opposing U-shaped
brightenings in the circumbinary disk, and exhibits a depression between the
circumbinary disk and the circumstellar disk of the primary protostar. The
molecular lines trace non-axisymmetric deviations from Keplerian rotation in
the circumbinary disk at higher velocities relative to the systemic velocity,
where our previous SMA observations could not detect the lines. In addition, we
detect inward motion along the minor axis of the circumbinary disk. To explain
the newly-observed features, we performed a numerical simulation of gas orbits
in a Roche potential tailored to the inferred properties of L1551 NE. The
observed U-shaped dust features coincide with locations where gravitational
torques from the central binary system are predicted to impart angular momentum
to the circumbinary disk, producing shocks and hence density enhancements seen
as a pair of spiral arms. The observed inward gas motion coincides with
locations where angular momentum is predicted to be lowered by the
gravitational torques. The good agreement between our observation and model
indicates that gravitational torques from the binary stars constitute the
primary driver for exchanging angular momentum so as to permit infall through
the circumbinary disk of L1551 NE.Comment: 38 pages, 11 figures, accepted for publication in Ap
Temporomandibular Joint Pathology and Its Indication in Clinical Orthodontics
Temporomandibular joint (TMJ) pathology has been an area of study in dentistry specifically a research interest in clinical orthodontics in which treatment option has been a dilemma for practitioners. Discussion between ‘dos’ and ‘don’ts’ in growth modification has drawn spread however opposite opinions from different schools of thoughts in whether growth modification itself is working. To provide a better illustration of biological process within TMJ, this chapter discussed aspects including overall condylar growth; the histological structure of endochondral bone of condyle; extracellular factors that regulate proliferation, differentiation, hypertrophy, terminal maturation and apoptosis of chondrocytes; and molecular regulation of the entire process. An understanding of the pathology, histology, cellular and molecular events related to the morphology and growth of TMJ forms through reading over this chapter; the emphasis of the mechanotransduction mediators and the influence of mechanical strain on the level of expression of genes were presented in details. Novel studies using virus vector stimulating condylar growth through enhancing angiogenesis within a time limit were discussed; also clinical implications in treatment options in relation to mandibular advancement were briefly compared
The Taiwan ECDFS Near-Infrared Survey: Ultra-deep J and Ks Imaging in the Extended Chandra Deep Field-South
We present ultra-deep J and Ks imaging observations covering a 30' * 30' area
of the Extended Chandra Deep Field-South (ECDFS) carried out by our Taiwan
ECDFS Near-Infrared Survey (TENIS). The median 5-sigma limiting magnitudes for
all detected objects in the ECDFS reach 24.5 and 23.9 mag (AB) for J and Ks,
respectively. In the inner 400 arcmin^2 region where the sensitivity is more
uniform, objects as faint as 25.6 and 25.0 mag are detected at 5-sigma. So this
is by far the deepest J and Ks datasets available for the ECDFS. To combine the
TENIS with the Spitzer IRAC data for obtaining better spectral energy
distributions of high-redshift objects, we developed a novel deconvolution
technique (IRACLEAN) to accurately estimate the IRAC fluxes. IRACLEAN can
minimize the effect of blending in the IRAC images caused by the large
point-spread functions and reduce the confusion noise. We applied IRACLEAN to
the images from the Spitzer IRAC/MUSYC Public Legacy in the ECDFS survey
(SIMPLE) and generated a J+Ks selected multi-wavelength catalog including the
photometry of both the TENIS near-infrared and the SIMPLE IRAC data. We
publicly release the data products derived from this work, including the J and
Ks images and the J+Ks selected multiwavelength catalog.Comment: 25 pages, 25 figures, ApJS in pres
ALMA Observations of Circumnuclear Disks in Early Type Galaxies: 12CO(2-1) and Continuum Properties
We present results from an Atacama Large Millimeter/submillimeter Array
(ALMA) Cycle 2 program to map CO(2-1) emission in nearby early-type galaxies
(ETGs) that host circumnuclear gas disks. We obtained resolution
Band 6 observations of seven ETGs selected on the basis of dust disks in Hubble
Space Telescope images. We detect CO emission in five at high signal-to-noise
ratio with the remaining two only faintly detected. All CO emission is
coincident with the dust and is in dynamically cold rotation. Four ETGs show
evidence of rapid central rotation; these are prime candidates for
higher-resolution ALMA observations to measure the black hole masses. In this
paper we focus on the molecular gas and continuum properties. Total gas masses
and H column densities for our five CO-bright galaxies are on average
and cm over the kpc-scale
disks, and analysis suggests that these disks are stabilized against
gravitational fragmentation. The continuum emission of all seven galaxies is
dominated by a central, unresolved source, and in five we also detect a
spatially extended component. The 230 GHz nuclear continua are modeled as
power laws ranging from to within the
observed frequency band. The extended continuum profiles of the two
radio-bright (and CO-faint) galaxies are roughly aligned with their radio jet
and suggests resolved synchrotron jets. The extended continua of the CO-bright
disks are coincident with optically thick dust absorption and have spectral
slopes that are consistent with thermal dust emission.Comment: 20 pages, 10 figures; accepted for publication in Ap
Charting Galactic Accelerations with Stellar Streams and Machine Learning
We present a data-driven method for reconstructing the galactic acceleration
field from phase-space measurements of stellar streams. Our approach is based
on a flexible and differentiable fit to the stream in phase-space, enabling a
direct estimate of the acceleration vector along the stream. Reconstruction of
the local acceleration field can be applied independently to each of several
streams, allowing us to sample the acceleration field due to the underlying
galactic potential across a range of scales. Our approach is methodologically
different from previous works, since a model for the gravitational potential
does not need to be adopted beforehand. Instead, our flexible
neural-network-based model treats the stream as a collection of orbits with a
locally similar mixture of energies, rather than assuming that the stream
delineates a single stellar orbit. Accordingly, our approach allows for
distinct regions of the stream to have different mean energies, as is the case
for real stellar streams. Once the acceleration vector is sampled along the
stream, standard analytic models for the galactic potential can then be rapidly
constrained. We find our method recovers the correct parameters for a
ground-truth triaxial logarithmic halo potential when applied to simulated
stellar streams. Alternatively, we demonstrate that a flexible potential can be
constrained with a neural network, though standard multipole expansions can
also be constrained. Our approach is applicable to simple and complicated
gravitational potentials alike, and enables potential reconstruction from a
fully data-driven standpoint using measurements of slowly phase-mixing tidal
debris.Comment: 32 pages, 10 figures, Submitted for publication. Comments welcome.
Code will be made available upon publicatio
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