364 research outputs found
Accurately predicting the escape fraction of ionizing photons using restframe ultraviolet absorption lines
The fraction of ionizing photons that escape high-redshift galaxies
sensitively determines whether galaxies reionized the early universe. However,
this escape fraction cannot be measured from high-redshift galaxies because the
opacity of the intergalactic medium is large at high redshifts. Without methods
to indirectly measure the escape fraction of high-redshift galaxies, it is
unlikely that we will know what reionized the universe. Here, we analyze the
far-ultraviolet (UV) H I (Lyman series) and low-ionization metal absorption
lines of nine low-redshift, confirmed Lyman continuum emitting galaxies. We use
the H I covering fractions, column densities, and dust attenuations measured in
a companion paper to predict the escape fraction of ionizing photons. We find
good agreement between the predicted and observed Lyman continuum escape
fractions (within ) using both the H I and ISM absorption lines. The
ionizing photons escape through holes in the H I, but we show that dust
attenuation reduces the fraction of photons that escape galaxies. This means
that the average high-redshift galaxy likely emits more ionizing photons than
low-redshift galaxies. Two other indirect methods accurately predict the escape
fractions: the Ly escape fraction and the optical [O III]/[O II] flux
ratio. We use these indirect methods to predict the escape fraction of a sample
of 21 galaxies with rest-frame UV spectra but without Lyman continuum
observations. Many of these galaxies have low escape fractions (\%), but 11 have escape fractions \%. The methods presented here will
measure the escape fractions of high-redshift galaxies, enabling future
telescopes to determine whether star-forming galaxies reionized the early
universe.Comment: Accepted for publication in A&A. 12 pages, 5 figure
Hypertension in older patients, a retrospective cohort study
Background: It is unknown to what extent General Practitioners (GPs) manage hypertension (HT) differently in older patients, as compared to younger age groups. The purpose of our study was to compare HT management in older patients to younger age groups. Methods: We performed a retrospective cohort study of patients of 159 GP's practices in the Integrated Primary Care Information (IPCI) database. The study period lasted from September 2010 through December 2012. The study population consisted of all patients aged 60 years or older with at least one blood pressure (BP) measurement during the inclusion period, without pre-existent HT, diabetes mellitus (DM) or atherosclerotic cardiovascular disease at time of study start. Study outcomes were a diagnosis of HT within one month after cohort entry and the use of antihypertensive medication within 4 months after cohort entry in HT diagnosed patients. We compared the incidence of outcomes between the age groups, stratified by systolic blood pressure (SBP). Logistic regression analysis was used to assess the influence of age-adjusted SBP Z-scores, age and gender on the outcomes. Results: We included 19,500 patients from 159 GP's practices of whom 1,181 (6.1 %) were newly diagnosed with HT. Corrected for age-adjusted SBP, older patients were less likely to be diagnosed with HT (odds ratio per year age increase 0.98, p < 0.001). Corrected for age-adjusted SBP, no significant effect of age on the probability of treatment in newly diagnosed HT patients was observed (p = 0.82). Conclusions: This study showed that GPs are less inclined to diagnose HT with increasing patient age, but do not withhold treatment when they diagnose HT in older patients
The properties of the brightest Lyα emitters at z ∼ 5.7
We use deep Very Large Telescope (VLT) optical and near-infrared spectroscopy and deep Spitzer/IRAC imaging to examine the properties of two of the most luminous Lyα emitters at z= 5.7. The continuum redward of the Lyα line is clearly detected in both objects, thus facilitating a relatively accurate measurement (10-20 per cent uncertainties) of the observed rest-frame equivalent widths, which are around 160 Å for both objects. Through detailed modelling of the profile of the Lyα line with a 3D Monte Carlo radiative transfer code, we estimate the intrinsic rest-frame equivalent width of Lyα and find values that are around 300 Å, which is at the upper end of the range allowed for very young, moderately metal-poor star-forming galaxies. However, the uncertainties are large and values as high as 700 Å are permitted by the data. Both Lyα emitters are detected at 3.6 m in deep images taken with the Spitzer Space Telescope. We use these measurements, the measurement of the continuum redward of Lyα and other photometry to constrain the spectral energy distributions of these very luminous Lyα emitters and to compare them with three similar Lyα emitters from the literature. The contribution from nebular emission is included in our models: excluding it results in significantly higher masses. Four of the five Lyα emitters have masses of the order of ∼109 M⊙ and fairly high specific star formation rates (≳10-100 Gyr−1). While our two Lyα emitters appear similar in terms of the observed Lyα rest-frame equivalent width, they are quite distinct from each other in terms of age, mass and star formation history. Evidence for dust is found in all objects, and emission from nebular lines often makes a dominant contribution to the rest-frame 3.6 m flux. Rich in emission lines, these objects are prime targets for the next generation of extremely large telescopes, the James Webb Space Telescope (JWST) and the Atacama Large Millimeter Array (ALMA
High-resolution spectroscopy of a young, low-metallicity optically-thin L=0.02L* star-forming galaxy at z=3.12
We present VLT/X-Shooter and MUSE spectroscopy of an faint F814W=28.60+/-0.33
(Muv=-17.0), low mass (~<10^7 Msun) and compact (Reff=62pc) freshly
star-forming galaxy at z=3.1169 magnified (16x) by the Hubble Frontier Fields
galaxy cluster Abell S1063. Gravitational lensing allows for a significant jump
toward low-luminosity regimes, in moderately high resolution spectroscopy
(R=lambda/dlambda ~ 3000-7400). We measured CIV1548,1550, HeII1640,
OIII]1661,1666, CIII]1907,1909, Hbeta, [OIII]4959,5007, emission lines with
FWHM< 50 km/s and (de-lensed) fluxes spanning the interval 1.0x10^-19 -
2.0x10^-18 erg/s/cm2 at S/N=4-30. The double peaked Lya emission with
Delta_v(red-blue) = 280(+/-7)km/s and de-lensed fluxes
2.4_(blue)|8.5_(red)x10^-18 erg/s/cm2 (S/N=38_(blue)|110_(red)) indicate a low
column density of neutral hydrogen gas consistent with a highly ionized
interstellar medium as also inferred from the large [OIII]5007/[OII]3727>10
ratio. We detect CIV1548,1550 resonant doublet in emission, each component with
FWHM ~< 45 km/s, and redshifted by +51(+/-10)km/s relative to the systemic
redshift. We interpret this as nebular emission tracing an expanding
optically-thin interstellar medium. Both CIV1548,1550 and HeII1640 suggest the
presence of hot and massive stars (with a possible faint AGN). The ultraviolet
slope is remarkably blue, beta =-2.95 +/- 0.20 (F_lambda=lambda^beta),
consistent with a dust-free and young ~<20 Myr galaxy. Line ratios suggest an
oxygen abundance 12+log(O/H)<7.8. We are witnessing an early episode of
star-formation in which a relatively low NHI and negligible dust attenuation
might favor a leakage of ionizing radiation. This galaxy currently represents a
unique low-luminosity reference object for future studies of the reionization
epoch with JWST.Comment: 7 pages, 4 figures and 1 table; ApJL, accepted for publicatio
Galaxy Counterparts of metal-rich Damped Lyman-alpha Absorbers - I: The case of the z=2.35 DLA towards Q2222-0946
We have initiated a survey using the newly commissioned X-shooter
spectrograph to target candidate relatively metal-rich damped Lyman-alpha
absorbers (DLAs). The spectral coverage of X-shooter allows us to search for
not only Lyman-alpha emission, but also rest-frame optical emission lines. We
have chosen DLAs where the strongest rest-frame optical lines ([OII], [OIII],
Hbeta and Halpha) fall in the NIR atmospheric transmission bands. In this first
paper resulting from the survey, we report on the discovery of the galaxy
counterpart of the z_abs = 2.354 DLA towards the z=2.926 quasar Q2222$-0946.
This DLA is amongst the most metal-rich z>2 DLAs studied so far at comparable
redshifts and there is evidence for substantial depletion of refractory
elements onto dust grains. We measure metallicities from ZnII, SiII, NiII, MnII
and FeII of -0.46+/-0.07, -0.51+/-0.06, -0.85+/-0.06, -1.23+/-0.06, and
-0.99+/-0.06, respectively. The galaxy is detected in the Lyman-alpha, [OIII]
lambda4959,5007 Halpha emission lines at an impact parameter of about 0.8
arcsec (6 kpc at z_abs = 2.354). We infer a star-formation rate of 10 M_sun
yr^-1, which is a lower limit due to the possibility of slit-loss. Compared to
the recently determined Halpha luminosity function for z=2.2 galaxies the
DLA-galaxy counterpart has a luminosity of L~0.1L^*_Halpha. The emission-line
ratios are 4.0 (Lyalpha/Halpha) and 1.2 ([OIII]/Halpha). The Lyalpha line shows
clear evidence for resonant scattering effects, namely an asymmetric,
redshifted (relative to the systemic redshift) component and a much weaker
blueshifted component. The fact that the blueshifted component is relatively
weak indicates the presence of a galactic wind. The properties of the galaxy
counterpart of this DLA is consistent with the prediction that metal-rich DLAs
are associated with the most luminous of the DLA-galaxy counterparts.Comment: 9 pages, 7 figures. Accepted for publication in MNRA
Belgian clinical guidance on anticoagulation management in hospitalised and ambulatory patients with COVID-19
Objectives COVID-19 predisposes patients to thrombotic disease. The aim of this guidance document is to provide Belgian health-care workers with recommendations on anticoagulation management in COVID-19 positive patients. Methods These recommendations were based on current knowledge and a limited level of evidence. Results We formulated recommendations for the prophylaxis and treatment of COVID-related venous thromboembolism in ambulatory and hospitalised patients, as well as recommendations for the use of antithrombotic drugs in patients with prior indication for anticoagulation who develop COVID-19. Conclusions These recommendations represent an easy-to-use practical guidance that can be implemented in every Belgian hospital and be used by primary care physicians and gynaecologists. Of note, they are likely to evolve with increased knowledge of the disease and availability of data from ongoing clinical trials
Equivalent widths of Lyman emitters in MUSE-Wide and MUSE-Deep
The aim of this study is to better understand the connection between the
Lyman rest-frame equivalent width (EW) and spectral properties as
well as ultraviolet (UV) continuum morphology by obtaining reliable EW
histograms for a statistical sample of galaxies and by assessing the fraction
of objects with large equivalent widths. We used integral field spectroscopy
from MUSE combined with broad-band data from the Hubble Space Telescope (HST)
to measure EW. We analysed the emission lines of Lyman
emitters (LAEs) detected in the full MUSE-Wide (one hour exposure time) and
MUSE-Deep (ten hour exposure time) surveys and found UV continuum counterparts
in archival HST data. We fitted the UV continuum photometric images using the
Galfit software to gain morphological information on the rest-UV emission and
fitted the spectra obtained from MUSE to determine the double peak fraction,
asymmetry, full-width at half maximum, and flux of the Lyman line. The
two surveys show different histograms of Lyman EW. In MUSE-Wide,
of objects have EW \r{A}, while this fraction is only
in MUSE-Deep and for the full sample. This includes objects
without HST continuum counterparts (one-third of our sample), for which we give
lower limits for EW. The object with the highest securely measured EW
has EW \r{A} (the highest lower limit being EW \r{A}).
We investigate the connection between EW and Lyman spectral or UV
continuum morphological properties. The survey depth has to be taken into
account when studying EW distributions. We find that in general, high
EW objects can have a wide range of spectral and UV morphological
properties, which might reflect that the underlying causes for high EW
values are equally varied. (abridged)Comment: 28 pages, 21 + 1 figures, 7 + 1 tables, accepted for publication in
A&
Reduced-Dose Intravenous Thrombolysis for Acute Intermediate-High-risk Pulmonary Embolism: Rationale and Design of the Pulmonary Embolism International THrOmbolysis (PEITHO)-3 trial
Intermediate-high-risk pulmonary embolism (PE) is characterized by right ventricular (RV) dysfunction and elevated circulating cardiac troponin levels despite apparent hemodynamic stability at presentation. In these patients, full-dose systemic thrombolysis reduced the risk of hemodynamic decompensation or death but increased the risk of life-threatening bleeding. Reduced-dose thrombolysis may be capable of improving safety while maintaining reperfusion efficacy. The Pulmonary Embolism International THrOmbolysis (PEITHO)-3 study (ClinicalTrials.gov Identifier: NCT04430569) is a randomized, placebo-controlled, double-blind, multicenter, multinational trial with long-term follow-up. We will compare the efficacy and safety of a reduced-dose alteplase regimen with standard heparin anticoagulation. Patients with intermediate-high-risk PE will also fulfill at least one clinical criterion of severity: systolic blood pressure ≤110 mm Hg, respiratory rate >20 breaths/min, or history of heart failure. The primary efficacy outcome is the composite of all-cause death, hemodynamic decompensation, or PE recurrence within 30 days of randomization. Key secondary outcomes, to be included in hierarchical analysis, are fatal or GUSTO severe or life-threatening bleeding; net clinical benefit (primary efficacy outcome plus severe or life-threatening bleeding); and all-cause death, all within 30 days. All outcomes will be adjudicated by an independent committee. Further outcomes include PE-related death, hemodynamic decompensation, or stroke within 30 days; dyspnea, functional limitation, or RV dysfunction at 6 months and 2 years; and utilization of health care resources within 30 days and 2 years. The study is planned to enroll 650 patients. The results are expected to have a major impact on risk-adjusted treatment of acute PE and inform guideline recommendations
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