201 research outputs found
Understanding the escape of LyC and Lyα photons from turbulent clouds
Understanding the escape of Lyman continuum (LyC) and Lyman alpha (Lya)
photons from molecular clouds is one of the keys to constraining the
reionization history of the Universe and the evolution of galaxies at high
redshift. Using a set of radiation-hydrodynamic simulations with adaptive mesh
refinement, we investigate how photons propagate and escape from turbulent
clouds with different masses, star formation efficiencies (SFEs), and
metallicities, as well as with different models of stellar spectra and
supernova feedback. We find that the escape fractions in both LyC and Lya are
generally increasing with time if the cloud is efficiently dispersed by
radiation and supernova feedback. When the total SFE is low (1% of the cloud
mass), 0.1-5% of LyC photons leave the metal-poor cloud, whereas the fractions
increase to 20-70% in clouds with a 10% SFE. LyC photons escape more
efficiently if gas metallicity is lower, if the upper mass limit in the stellar
initial mass function is higher, if binary interactions are allowed in the
evolution of stars, or if additional strong radiation pressure, such as Lya
pressure, is present. As a result, the number of escaping LyC photons can
easily vary by a factor of on cloud scales. The escape fractions of Lya
photons are systemically higher (60-80%) than those of LyC photons despite
large optical depths at line centre (). Scattering of Lya
photons is already significant on cloud scales, leading to double-peaked
profiles with peak separations of during
the initial stage of the cloud evolution, while it becomes narrower than
in the LyC bright phase. Comparisons
with observations of low-redshift galaxies suggest that Lya photons require
further interactions with neutral hydrogen to reproduce their velocity offset
for a given LyC escape fraction
The SPHINX cosmological simulations of the first billion years: The impact of binary stars on reionization
We present the SPHINX suite of cosmological adaptive mesh refinement
simulations, the first radiation-hydrodynamical simulations to simultaneously
capture large-scale reionization and the escape of ionizing radiation from
thousands of resolved galaxies. Our and co-moving Mpc volumes resolve
haloes down to the atomic cooling limit and model the inter-stellar medium with
better than pc resolution. The project has numerous goals in
improving our understanding of reionization and making predictions for future
observations. In this first paper we study how the inclusion of binary stars in
computing stellar luminosities impacts reionization, compared to a model that
includes only single stars. Owing to the suppression of galaxy growth via
strong feedback, our galaxies are in good agreement with observational
estimates of the galaxy luminosity function. We find that binaries have a
significant impact on the timing of reionization: with binaries, our boxes are
percent ionized by volume at , while without them our
volumes fail to reionize by . These results are robust to changes in
volume size, resolution, and feedback efficiency. The escape of ionizing
radiation from individual galaxies varies strongly and frequently. On average,
binaries lead to escape fractions of percent, about times
higher than with single stars only. The higher escape fraction is a result of a
shallower decline in ionizing luminosity with age, and is the primary reason
for earlier reionization, although the higher integrated luminosity with
binaries also plays a sub-dominant role
Probing cosmic dawn with emission lines: predicting infrared and nebular line emission for ALMA and JWST
Infrared and nebular lines provide some of our best probes of the physics
regulating the properties of the interstellar medium (ISM) at high-redshift.
However, interpreting the physical conditions of high-redshift galaxies
directly from emission lines remains complicated due to inhomogeneities in
temperature, density, metallicity, ionisation parameter, and spectral hardness.
We present a new suite of cosmological, radiation-hydrodynamics simulations,
each centred on a massive Lyman-break galaxy that resolves such properties in
an inhomogeneous ISM. Many of the simulated systems exhibit transient but well
defined gaseous disks that appear as velocity gradients in [CII]~158.6m
emission. Spatial and spectral offsets between [CII]~158.6m and
[OIII]~88.33m are common, but not ubiquitous, as each line probes a
different phase of the ISM. These systems fall on the local [CII]-SFR relation,
consistent with newer observations that question previously observed
[CII]~158.6m deficits. Our galaxies are consistent with the nebular line
properties of observed galaxies and reproduce offsets on the BPT and
mass-excitation diagrams compared to local galaxies due to higher star
formation rate (SFR), excitation, and specific-SFR, as well as harder spectra
from young, metal-poor binaries. We predict that local calibrations between
H and [OII]~3727 luminosity and galaxy SFR apply up to , as
do the local relations between certain strong line diagnostics (R23 and
[OIII]~5007/H) and galaxy metallicity. Our new simulations are well
suited to interpret the observations of line emission from current (ALMA and
HST) and upcoming facilities (JWST and ngVLA)
New Methods for Identifying Lyman Continuum Leakers and Reionization-Epoch Analogues
Identifying low-redshift galaxies that emit Lyman continuum radiation (LyC leakers) is one of the primary, indirect methods of studying galaxy formation in the epoch of reionization. However, not only has it proved challenging to identify such systems, it also remains uncertain whether the low-redshift LyC leakers are truly ‘analogues’ of the sources that reionized the Universe. Here, we use high-resolution cosmological radiation hydrodynamics simulations to examine whether simulated galaxies in the epoch of reionization share similar emission line properties to observed LyC leakers at z ∼ 3 and z ∼ 0. We find that the simulated galaxies with high LyC escape fractions (fesc) often exhibit high O32 and populate the same regions of the R23–O32 plane as z ∼ 3 LyC leakers. However, we show that viewing angle, metallicity, and ionization parameter can all impact where a galaxy resides on the O32–fesc plane. Based on emission line diagnostics and how they correlate with fesc, lower metallicity LyC leakers at z ∼ 3 appear to be good analogues of reionization-era galaxies. In contrast, local [S II]-deficient galaxies do not overlap with the simulated high-redshift LyC leakers on the S II Baldwin–Phillips–Terlevich (BPT) diagram; however, this diagnostic may still be useful for identifying leakers. We use our simulated galaxies to develop multiple new diagnostics to identify LyC leakers using infrared and nebular emission lines. We show that our model using only [C II]158 μm and [O III]88 μm can identify potential leakers from non-leakers from the local Dwarf Galaxy Survey. Finally, we apply this diagnostic to known high-redshift galaxies and find that MACS 1149_JD1 at z = 9.1 is the most likely galaxy to be actively contributing to the reionization of the Universe
New methods for identifying Lyman continuum leakers and reionization-epoch analogues
Identifying low-redshift galaxies that emit Lyman Continuum radiation (LyC
leakers) is one of the primary, indirect methods of studying galaxy formation
in the epoch of reionization. However, not only has it proved challenging to
identify such systems, it also remains uncertain whether the low-redshift LyC
leakers are truly "analogues" of the sources that reionized the Universe. Here,
we use high-resolution cosmological radiation hydrodynamics simulations to
examine whether simulated galaxies in the epoch of reionization share similar
emission line properties to observed LyC leakers at and . We
find that the simulated galaxies with high LyC escape fractions ()
often exhibit high O32 and populate the same regions of the R23-O32 plane as
LyC leakers. However, we show that viewing angle, metallicity, and
ionisation parameter can all impact where a galaxy resides on the O32- plane. Based on emission line diagnostics and how they correlate with
, lower-metallicity LyC leakers at appear to be good
analogues of reionization-era galaxies. In contrast, local [SII]-deficient
galaxies do not overlap with the simulated high-redshift LyC leakers on the
SII-BPT diagram; however, this diagnostic may still be useful for identifying
leakers. We use our simulated galaxies to develop multiple new diagnostics to
identify LyC leakers using IR and nebular emission lines. We show that our
model using only [CII] and [OIII] can identify
potential leakers from non-leakers from the local Dwarf Galaxy Survey. Finally,
we apply this diagnostic to known high-redshift galaxies and find that
MACS1149_JD1 at is the most likely galaxy to be actively contributing
to the reionization of the Universe
Metabolism during anaesthesia and recovery in colic and healthy horses: a microdialysis study
<p>Abstract</p> <p>Background</p> <p>Muscle metabolism in horses has been studied mainly by analysis of substances in blood or plasma and muscle biopsy specimens. By using microdialysis, real-time monitoring of the metabolic events in local tissue with a minimum of trauma is possible. There is limited information about muscle metabolism in the early recovery period after anaesthesia in horses and especially in the colic horse. The aims were to evaluate the microdialysis technique as a complement to plasma analysis and to study the concentration changes in lactate, pyruvate, glucose, glycerol, and urea during anaesthesia and in the recovery period in colic horses undergoing abdominal surgery and in healthy horses not subjected to surgery.</p> <p>Methods</p> <p>Ten healthy university-owned horses given anaesthesia alone and ten client-owned colic horses subjected to emergency abdominal surgery were anaesthetised for a mean (range) of 230 min (193–273) and 208 min (145–300) respectively. Venous blood samples were taken before anaesthesia. Venous blood sampling and microdialysis in the gluteal muscle were performed during anaesthesia and until 24 h after anaesthesia. Temporal changes and differences between groups were analysed with an ANOVA for repeated measures followed by Tukey Post Hoc test or Planned Comparisons.</p> <p>Results</p> <p>Lactate, glucose and urea, in both dialysate and plasma, were higher in the colic horses than in the healthy horses for several hours after recovery to standing. In the colic horses, lactate, glucose, and urea in dialysate, and lactate in plasma increased during the attempts to stand. The lactate-to-pyruvate ratio was initially high in sampled colic horses but decreased over time. In the colic horses, dialysate glycerol concentrations varied considerably whereas in the healthy horses, dialysate glycerol was elevated during anaesthesia but decreased after standing. In both groups, lactate concentration was higher in dialysate than in plasma. The correspondence between dialysate and plasma concentrations of glucose, urea and glycerol varied.</p> <p>Conclusion</p> <p>Microdialysis proved to be suitable in the clinical setting for monitoring of the metabolic events during anaesthesia and recovery. It was possible with this technique to show greater muscle metabolic alterations in the colic horses compared to the healthy horses in response to regaining the standing position.</p
Feedback-regulated star formation and escape of LyC photons from mini-haloes during reionization
Reionization in the early Universe is likely driven by dwarf galaxies. Using cosmological radiation-hydrodynamic simulations, we study star formation and the escape of Lyman continuum (LyC) photons from mini-haloes with 10 M. Our simulations include a new thermo-turbulent star formation model, non-equilibrium chemistry and relevant stellar feedback processes (photoionization by young massive stars, radiation pressure and mechanical supernova explosions). We find that feedback reduces star formation very efficiently in mini-haloes, resulting in the stellar mass consistent with the slope and normalization reported in Kimm & Cen and the empirical stellar mass-to-halo mass relation derived in the local Universe. Because star formation is stochastic and dominated by a few gas clumps, the escape fraction in mini-haloes is generally determined by radiation feedback (heating due to photoionization), rather than supernova explosions. We also find that the photon number-weighted mean escape fraction in mini-haloes is higher (~ 20–40 per cent) than that in atomic-cooling haloes, although the instantaneous fraction in individual haloes varies significantly. The escape fraction from Pop III stars is found to be significant ( 10 per cent) only when the mass is greater than ~100 M. Based on simple analytic calculations, we show that LyC photons from mini-haloes are, despite their high escape fractions, of minor importance for reionization due to inefficient star formation. We confirm previous claims that stars in atomic-cooling haloes with masses 10 M 10 M are likely to be the most important source of reionization.This work was supported by the ERC Advanced Grant 320596 ‘The Emergence of Structure during the Epoch of Reionization’ and the Spin(e) grants ANR-13-BS05-0005 of the French Agence Nationale de la Recherche (http://cosmicorigin.org). HK is supported by Foundation Boustany, the Isaac Newton Studentship and the Cambridge Overseas Trust. JR was funded by the European Research Council under the European Unions Seventh Framework Programme (FP7/2007-2013)/ERC Grant agreement 278594-GasAroundGalaxies, and the Marie Curie Training Network CosmoComp (PITN- GA-2009-238356). JD and AS's research is supported by the funding from Adrian Beecroft, the Oxford Martin School and the STFC. This work used the DiRAC Complexity system, operated by the University of Leicester IT Services, which forms part of the STFC DiRAC HPC Facility (www.dirac.ac.uk). This equipment is funded by BIS National E-Infrastructure capital grant ST/K000373/1 and STFC DiRAC Operations grant ST/K0003259/1. DiRAC is part of the National E-Infrastructure
Tracing the sources of reionization in cosmological radiation hydrodynamics simulations
We use the photon flux and absorption tracer algorithm presented in Katz et
al.~2018, to characterise the contribution of haloes of different mass and
stars of different age and metallicity to the reionization of the Universe. We
employ a suite of cosmological multifrequency radiation hydrodynamics AMR
simulations that are carefully calibrated to reproduce a realistic reionization
history and galaxy properties at . In our simulations, haloes with
mass , stars with
metallicity , and stars with age
dominate reionization by both mass and
volume. We show that the sources that reionize most of the volume of the
Universe by are not necessarily the same sources that dominate the
meta-galactic UV background at the same redshift. We further show that in our
simulations, the contribution of each type of source to reionization is not
uniform across different gas phases. The IGM, CGM, filaments, ISM, and rarefied
supernova heated gas have all been photoionized by different classes of
sources. Collisional ionisation contributes at both the lowest and highest
densities. In the early stages of the formation of individual HII bubbles,
reionization proceeds with the formation of concentric shells of gas ionised by
different classes of sources, leading to large temperature variations as a
function of galacto-centric radius. The temperature structure of individual HII
bubbles may thus give insight into the star formation history of the galaxies
acting as the first ionising sources. Our explorative simulations highlight how
the complex nature of reionization can be better understood by using our photon
tracer algorithm
Local metabolic changes in subcutaneous adipose tissue during intravenous and epidural analgesia.
BACKGROUND: This clinical study aimed at investigating the impact of postoperative thoracic epidural analgesia on extracellular glycerol concentration and glucose metabolism in subcutaneous adipose tissue, using the microdialysis technique. The sympathetic nervous activity, which can be attenuated by epidural anesthesia, influences lipolysis and the release of glycerol. METHODS: Fourteen patients who underwent major abdominal or thoraco-abdominal surgery were studied postoperatively over 3 days. For postoperative analgesia the patients were prospectively randomized to receive either thoracic epidural analgesia with a bupivacaine/morphine infusion (EPI-group, n=6) or a continuous i.v. infusion of morphine (MO-group, n=8). The concentration of glycerol, glucose and lactate in the abdominal and deltoid subcutaneous adipose tissue were measured using a microdialysis technique. RESULTS: The abdominal glycerol levels were equal in both groups. In the deltoid region of the EPI-group, glycerol concentrations started to increase on Day 2, and reached significantly higher levels on Day 3 compared with the MO-group. The glucose and lactate levels showed no differences between groups in the two regions. CONCLUSION: The uniform glycerol levels in abdominal subcutaneous adipose tissue in conjunction with the difference in glycerol levels in the deltoid area indicate that the local lipolysis is different in the two study groups. This might be explained by a regional metabolic influence of thoracic epidural analgesia, possibly via the sympathetic nervous system
The nature of high [O III]88 μ m/[C II]158 μm galaxies in the epoch of reionization: Low carbon abundance and a top-heavy IMF?
ALMA observations of z > 6 galaxies have revealed abnormally high [O III]88 μm/[C II]158 μm ratios and [C II]158 μm deficits compared to local galaxies. The origin of this behaviour is unknown. Numerous solutions have been proposed including differences in C and O abundance ratios, observational bias, and differences in ISM properties, including ionization parameter, gas density, or photodissociation region (PDR) covering fraction. In order to elucidate the underlying physics that drives this high-redshift phenomenon, we employ SPHINX20, a state-of-the-art, cosmological radiation–hydrodynamics simulation, that resolves detailed ISM properties of thousands of galaxies in the epoch of reionization which has been post-processed with CLOUDY to predict emission lines. We find that the observed z > 6 [O III]88 μm–SFR and [C II]158 μm–SFR relations can only be reproduced when the C/O abundance ratio is ∼8 × lower than Solar and the total metal production is ∼4 × higher than that of a Kroupa IMF. This implies that high-redshift galaxies are potentially primarily enriched by low-metallicity core–collapse supernovae with a more top-heavy IMF. As AGB stars and type-Ia supernova begin to contribute to the galaxy metallicity, both the [C II]158 μm–SFR and [C II]158 μm luminosity functions are predicted to converge to observed values at z ∼ 4.5. While we demonstrate that ionization parameter, LyC escape fraction, ISM gas density, and CMB attenuation all drive galaxies towards higher [O III]88 μm/[C II]158 μm, observed values at z > 6 can only be reproduced with substantially lower C/O abundances compared to Solar. The combination of [C II]158 μm and [O III]88 μm can be used to predict the values of ionization parameter, ISM gas density, and LyC escape fraction and we provide estimates of these quantities for nine observed z > 6 galaxies. Finally, we demonstrate that [O I]63 μm can be used as a replacement for [C II]158 μ m in high-redshift galaxies where [C II]158 μ m is unobserved and argue that more observation time should be used to target [O I]63 μm at z > 6. Future simulations will be needed to self-consistently address the numerous uncertainties surrounding a varying IMF at high redshift and the associated metal returns
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