1,409 research outputs found
Observations of Dense Molecular Gas in a Quasar Host Galaxy at z=6.42: Further Evidence for a Non-Linear Dense Gas - Star Formation Relation at Early Cosmic Times
We report a sensitive search for the HCN(J=2-1) emission line towards SDSS
J1148+5251 at z=6.42 with the VLA. HCN emission is a star formation indicator,
tracing dense molecular hydrogen gas (n(H2) >= 10^4 cm^-3) within star-forming
molecular clouds. No emission was detected in the deep interferometer maps of
J1148+5251. We derive a limit for the HCN line luminosity of L'(HCN) < 3.3 x
10^9 K km/s pc^2, corresponding to a HCN/CO luminosity ratio of L'(HCN)/L'(CO)
< 0.13. This limit is consistent with a fraction of dense molecular gas in
J1148+5251 within the range of nearby ultraluminous infrared galaxies (ULIRGs;
median value: L'(HCN)/L'(CO) = 0.17 {+0.05/-0.08}) and HCN-detected z>2
galaxies (0.17 {+0.09/-0.08}). The relationship between L'(HCN) and L(FIR) is
considered to be a measure for the efficiency at which stars form out of dense
gas. In the nearby universe, these quantities show a linear correlation, and
thus, a practically constant average ratio. In J1148+5251, we find
L(FIR)/L'(HCN) > 6600. This is significantly higher than the average ratios for
normal nearby spiral galaxies (L(FIR)/L'(HCN) = 580 {+510/-270}) and ULIRGs
(740 {+505/-50}), but consistent with a rising trend as indicated by other z>2
galaxies (predominantly quasars; 1525 {+1300/-475}). It is unlikely that this
rising trend can be accounted for by a contribution of AGN heating to L(FIR)
alone, and may hint at a higher median gas density and/or elevated
star-formation efficiency toward the more luminous high-redshift systems. There
is marginal evidence that the L(FIR)/L'(HCN) ratio in J1148+5251 may even
exceed the rising trend set by other z>2 galaxies; however, only future
facilities with very large collecting areas such as the SKA will offer the
sensitivity required to further investigate this question.Comment: 5 pages, 2 figures, 2 tables, to appear in ApJL (accepted October 24,
2007
Atomic and Molecular Gas Components in Spiral Galaxies of the Virgo Cluster
Based on two models, we investigate the molecular-to-atomic gas ratio in
Virgo cluster galaxies in comparison with field galaxies. We show that the
enhanced metallicity for cluster members and the ram pressure stripping of
atomic gas from the disk periphery cannot fully explain the observed gas
component ratios. The additional environmental factors affecting the
interstellar medium and leading to an increase in the molecular gas fraction
should be taken into account for cluster galaxies.Comment: 11 pages, 4 figure
Outcomes in heart failure patients with preserved ejection fraction Mortality, readmission, and functional decline
AbstractObjectivesWe evaluated the six-month clinical trajectory of patients hospitalized for heart failure (HF) with preserved ejection fraction (EF), as the natural history of this condition has not been well established. We compared mortality, hospital readmission, and changes in functional status in patients with preserved versus depressed EF.BackgroundAlthough the poor prognosis of HF with depressed EF has been extensively documented, there are only limited and conflicting data concerning clinical outcomes for patients with preserved EF.MethodsWe prospectively evaluated 413 patients hospitalized for HF to determine whether EF ≥40% was an independent predictor of mortality, readmission, and the combined outcome of functional decline or death.ResultsAfter six months, 13% of patients with preserved EF died, compared with 21% of patients with depressed EF (p = 0.02). However, the rates of functional decline were similar among those with preserved and depressed EF (30% vs. 23%, respectively; p = 0.14). After adjusting for demographic and clinical covariates, preserved EF was associated with a lower risk of death (hazard ratio [HR] 0.49, 95% confidence interval [CI] 0.26 to 0.90; p = 0.02), but there was no difference in the risk of readmission (HR 1.01, 95% CI 0.72 to 1.43; p = 0.96) or the odds of functional decline or death (OR 1.01, 95% CI 0.59 to 1.72; p = 0.97).ConclusionsHeart failure with preserved EF confers a considerable burden on patients, with the risk of readmission, disability, and symptoms subsequent to hospital discharge, comparable to that of HF patients with depressed EF
CASTRO: A New Compressible Astrophysical Solver. II. Gray Radiation Hydrodynamics
We describe the development of a flux-limited gray radiation solver for the
compressible astrophysics code, CASTRO. CASTRO uses an Eulerian grid with
block-structured adaptive mesh refinement based on a nested hierarchy of
logically-rectangular variable-sized grids with simultaneous refinement in both
space and time. The gray radiation solver is based on a mixed-frame formulation
of radiation hydrodynamics. In our approach, the system is split into two
parts, one part that couples the radiation and fluid in a hyperbolic subsystem,
and another parabolic part that evolves radiation diffusion and source-sink
terms. The hyperbolic subsystem is solved explicitly with a high-order Godunov
scheme, whereas the parabolic part is solved implicitly with a first-order
backward Euler method.Comment: accepted for publication in ApJS, high-resolution version available
at https://ccse.lbl.gov/Publications/wqzhang/castro2.pd
Mapping the column density and dust temperature structure of IRDCs with Herschel
Infrared dark clouds (IRDCs) are cold and dense reservoirs of gas potentially
available to form stars. Many of these clouds are likely to be pristine
structures representing the initial conditions for star formation. The study
presented here aims to construct and analyze accurate column density and dust
temperature maps of IRDCs by using the first Herschel data from the Hi-GAL
galactic plane survey. These fundamental quantities, are essential for
understanding processes such as fragmentation in the early stages of the
formation of stars in molecular clouds. We have developed a simple
pixel-by-pixel SED fitting method, which accounts for the background emission.
By fitting a grey-body function at each position, we recover the spatial
variations in both the dust column density and temperature within the IRDCs.
This method is applied to a sample of 22 IRDCs exhibiting a range of angular
sizes and peak column densities. Our analysis shows that the dust temperature
decreases significantly within IRDCs, from background temperatures of 20-30 K
to minimum temperatures of 8-15 K within the clouds, showing that dense
molecular clouds are not isothermal. Temperature gradients have most likely an
important impact on the fragmentation of IRDCs. Local temperature minima are
strongly correlated with column density peaks, which in a few cases reach NH2 =
1 x 10^{23} cm^{-2}, identifying these clouds as candidate massive prestellar
cores. Applying this technique to the full Hi-GAL data set will provide
important constraints on the fragmentation and thermal properties of IRDCs, and
help identify hundreds of massive prestellar core candidates.Comment: Accepted for publication in A&A Herschel special issu
Randomized trial of an education and support intervention to preventreadmission of patients with heart failure
AbstractObjectivesWe determined the effect of a targeted education and support intervention on the rate of readmission or death and hospital costs in patients with heart failure (HF).BackgroundDisease management programs for patients with HF including medical components may reduce readmissions by 40% or more, but the value of an intervention focused on education and support is not known.MethodsWe conducted a prospective, randomized trial of a formal education and support intervention on one-year readmission or mortality and costs of care for patients hospitalized with HF.ResultsAmong the 88 patients (44 intervention and 44 control) in the study, 25 patients (56.8%) in the intervention group and 36 patients (81.8%) in the control group had at least one readmission or died during one-year follow-up (relative risk = 0.69, 95% confidence interval [CI]: 0.52, 0.92; p = 0.01). The intervention was associated with a 39% decrease in the total number of readmissions (intervention group: 49 readmissions; control group: 80 readmissions, p = 0.06). After adjusting for clinical and demographic characteristics, the intervention group had a significantly lower risk of readmission compared with the control group (hazard ratio = 0.56, 95% CI: 0.32, 0.96; p = 0.03) and hospital readmission costs of $7,515 less per patient.ConclusionsA formal education and support intervention substantially reduced adverse clinical outcomes and costs for patients with HF
VLT/SPHERE deep insight of NGC 3603's core: Segregation or confusion?
We present new near-infrared photometric measurements of the core of the
young massive cluster NGC 3603 obtained with extreme adaptive optics. The data
were obtained with the SPHERE instrument mounted on ESO Very Large Telescope,
and cover three fields in the core of this cluster. We applied a correction for
the effect of extinction to our data obtained in the J and K broadband filters
and estimated the mass of detected sources inside the field of view of
SPHERE/IRDIS, which is 13.5"x13.5". We derived the mass function (MF) slope for
each spectral band and field. The MF slope in the core is unusual compared to
previous results based on Hubble space telescope (HST) and very large telescope
(VLT) observations. The average slope in the core is estimated as
-1.06^{+0.26}_{-0.26} for the main sequence stars with 3.5 Msun < M < 120
Msun.Thanks to the SPHERE extreme adaptive optics, 814 low-mass stars were
detected to estimate the MF slope for the pre-main sequence stars with 0.6
Msun< M < 3.5 Msun , Gamma = -0.54^{+0.11}_{-0.11} in the K-band images in two
fields in the core of the cluster. For the first time, we derive the mass
function of the very core of the NGC 3603 young cluster for masses in the range
0.6 - 120 Msun. Previous studies were either limited by crowding, lack of
dynamic range, or a combination of both
Evolution of Stellar Feedback in HII Regions
Stellar feedback is needed to produce realistic giant molecular clouds (GMCs)
and galaxies in simulations, but due to limited numerical resolution, feedback
must be implemented using subgrid models. Observational work is an important
means to test and anchor these models, but limited studies have assessed the
relative dynamical role of multiple feedback modes, particularly at the
earliest stages of expansion when HII regions are still deeply embedded. In
this paper, we use multiwavelength (radio, infrared, and X-ray) data to measure
the pressures associated with direct radiation (), dust-processed
radiation (), photoionization heating (), and
shock-heating from stellar winds () in a sample of 106 young,
resolved HII regions with radii 0.5 pc to determine how stellar
feedback drives their expansion. We find that the dominates in 84%
of the regions and that the median and are smaller
than the median by factors of and ,
respectively. Based on the radial dependences of the pressure terms, we show
that HII regions transition from -dominated to -dominated at radii of 3 pc. We find a median trapping factor of
8 without any radial dependence for the sample, suggesting
this value can be adopted in sub-grid feedback models. Moreover, we show that
the total pressure is greater than the gravitational pressure in the majority
of our sample, indicating that the feedback is sufficient to expel gas from the
regions.Comment: 13 pages, 8 figures, ApJ, in pres
CASTRO: A New Compressible Astrophysical Solver. III. Multigroup Radiation Hydrodynamics
We present a formulation for multigroup radiation hydrodynamics that is
correct to order using the comoving-frame approach and the
flux-limited diffusion approximation. We describe a numerical algorithm for
solving the system, implemented in the compressible astrophysics code, CASTRO.
CASTRO uses an Eulerian grid with block-structured adaptive mesh refinement
based on a nested hierarchy of logically-rectangular variable-sized grids with
simultaneous refinement in both space and time. In our multigroup radiation
solver, the system is split into three parts, one part that couples the
radiation and fluid in a hyperbolic subsystem, another part that advects the
radiation in frequency space, and a parabolic part that evolves radiation
diffusion and source-sink terms. The hyperbolic subsystem and the frequency
space advection are solved explicitly with high-order Godunov schemes, whereas
the parabolic part is solved implicitly with a first-order backward Euler
method. Our multigroup radiation solver works for both neutrino and photon
radiation.Comment: accepted by ApJS, 27 pages, 20 figures, high-resolution version
available at https://ccse.lbl.gov/Publications/wqzhang/castro3.pd
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