4,694 research outputs found
Reionization history constraints from neural network based predictions of high-redshift quasar continua
Observations of the early Universe suggest that reionization was complete by
, however, the exact history of this process is still unknown. One
method for measuring the evolution of the neutral fraction throughout this
epoch is via observing the Ly damping wings of high-redshift quasars.
In order to constrain the neutral fraction from quasar observations, one needs
an accurate model of the quasar spectrum around Ly, after the spectrum
has been processed by its host galaxy but before it is altered by absorption
and damping in the intervening IGM. In this paper, we present a novel machine
learning approach, using artificial neural networks, to reconstruct quasar
continua around Ly. Our QSANNdRA algorithm improves the error in this
reconstruction compared to the state-of-the-art PCA-based model in the
literature by 14.2% on average, and provides an improvement of 6.1% on average
when compared to an extension thereof. In comparison with the extended PCA
model, QSANNdRA further achieves an improvement of 22.1% and 16.8% when
evaluated on low-redshift quasars most similar to the two high-redshift quasars
under consideration, ULAS J1120+0641 at and ULAS J1342+0928 at
, respectively. Using our more accurate reconstructions of these two
quasars, we estimate the neutral fraction of the IGM using a homogeneous
reionization model and find at
and at . Our
results are consistent with the literature and favour a rapid end to
reionization
Reionization and galaxy inference from the high-redshift Ly α forest
The transmission of Lyman α (Ly α) in the spectra of distant quasars depends on the density, temperature, and ionization state of the intergalactic medium. Therefore, high-redshift (z > 5) Ly α forests could be invaluable in studying the late stages of the epoch of reionization (EoR), as well as properties of the sources that drive it. Indeed, high-quality quasar spectra have now firmly established the existence of large-scale opacity fluctuations at z > 5, whose physical origins are still debated. Here, we introduce a Bayesian framework capable of constraining the EoR and galaxy properties by forward-modelling the high-z Ly α forest. Using priors from galaxy and cosmic microwave background observations, we demonstrate that the final overlap stages of the EoR (when >95 per cent of the volume was ionized) should occur at z < 5.6, in order to reproduce the large-scale opacity fluctuations seen in forest spectra. However, it is the combination of patchy reionization and the inhomogeneous ultraviolet background that produces the longest Gunn-Peterson troughs. Ly α forest observations tighten existing constraints on the characteristic ionizing escape fraction of galaxies, with the combined observations suggesting fesc ≈ 7+4-3} per cent, and disfavouring a strong evolution with the galaxy's halo (or stellar) mass
Observing Carbon & Oxygen Carriers in Protoplanetary Disks at Mid-infrared Wavelengths
Infrared observations probe the warm gas in the inner regions of
planet-forming disks around young sun-like, T Tauri stars. In these systems,
HO, OH, CO, CO, CH, and HCN have been widely observed. However,
the potentially abundant carbon carrier CH remains largely unconstrained.
The James Webb Space Telescope (JWST) will be able to characterize mid-infrared
fluxes of CH along with several other carriers of carbon and oxygen. In
anticipation of the JWST mission, we model the physical and chemical structure
of a T Tauri disk to predict the abundances and mid-infrared fluxes of
observable molecules. A range of compositional scenarios are explored involving
the destruction of refractory carbon materials and alterations to the total
elemental (volatile and refractory) C/O ratio. Photon-driven chemistry in the
inner disk surface layers largely destroys the initial carbon and oxygen
carriers. This causes models with the same physical structure and C/O ratio to
have similar steady state surface compositions, regardless of the initial
chemical abundances. Initial disk compositions are better preserved in the
shielded inner disk midplane. The degree of similarity between the surface and
midplane compositions in the inner disk will depend on the characteristics of
vertical mixing at these radii. Our modeled fluxes of observable molecules
respond sensitively to changes in the disk gas temperature, inner radius, and
the total elemental C/O ratio. As a result, mid-infrared observations of disks
will be useful probes of these fundamental disk parameters, including the C/O
ratio, which can be compared to values determined for planetary atmospheres.Comment: Accepted for publication in The Astrophysical Journa
Sound localization with bilateral bone conduction devices
Purpose To investigate sound localization in patients bilaterally fitted with bone conduction devices (BCDs). Additionally, clinically applicable methods to improve localization accuracy were explored. Methods Fifteen adults with bilaterally fitted percutaneous BCDs were included. At baseline, sound localization, (un)aided pure-tone thresholds, device use, speech, spatial and qualities of hearing scale (SSQ) and York hearing-related quality of life (YHRQL) questionnaire were measured. Settings to optimize sound localizing were added to the BCDs. At 1 month, sound localization was assessed again and localization was practiced with a series of sounds with visual feedback. At 3 months, localization performance, device use and questionnaire scores were determined again. Results At baseline, one patient with congenital hearing loss demonstrated near excellent localization performance and four other patients (three with congenital hearing loss) localized sounds (quite) accurately. Seven patients with acquired hearing loss were able to lateralize sounds, i.e. identify whether sounds were coming from the left or right side, but could not localize sounds accurately. Three patients (one with congenital hearing loss) could not even lateralize sounds correctly. SSQ scores were significantly higher at 3 months. Localization performance, device use and YHRQL scores were not significantly different between visits. Conclusion In this study, the majority of experienced bilateral BCD users could lateralize sounds and one third was able to localize sounds (quite) accurately. The localization performance was robust and stable over time. Although SSQ scores were increased at the last visit, optimizing device settings and a short practice session did not improve sound localization
Off hour admission to an intensivist-led ICU is not associated with increased mortality
Introduction: Caring for the critically ill is a 24-hour-a-day responsibility, but not all resources and staff are available during off hours. We evaluated whether intensive care unit (ICU) admission during off hours affects hospital mortality. Methods: This retrospective multicentre cohort study was carried out in three non-academic teaching hospitals in the Netherlands. All consecutive patients admitted to the three ICUs between 2004 and 2007 were included in the study, except for patients who did not fulfil APACHE II criteria (readmissions, burns, cardiac surgery, younger than 16 years, length of stay less than 8 hours). Data were collected prospectively in the ICU databases. Hospital mortality was the primary endpoint of the study. Off hours was defined as the interval between 10 pm and 8 am during weekdays and between 6 pm and 9 am during weekends. Intensivists, with no responsibilities outside the ICU, were present in the ICU during daytime and available for either consultation or assistance on site during off hours. Residents were available 24 hours a day 7 days a week in two and fellows in one of the ICUs. Results: A total of 6725 patients were included in the study, 4553 (67.7%) admitted during daytime and 2172 (32.3%) admitted during off hours. Baseline characteristics of patients admitted during daytime were significantly different from those of patients admitted during off hours. Hospital mortality was 767 (16.8%) in patients admitted during daytime and 469 (21.6%) in patients admitted during off hours (P < 0.001, unadjusted odds ratio 1.36, 95%CI 1.20-1.55). Standardized mortality ratios were similar for patients admitted during off hours and patients admitted during daytime. In a logistic regression model APACHE II expected mortality, age and admission type were all significant confounders but off-hours admission was not significantly associated with a higher mortality (P = 0.121, adjusted odds ratio 1.125, 95%CI 0.969-1.306). Conclusions: The increased mortality after ICU admission during off hours is explained by a higher illness severity in patients admitted during off hours
Photometric IGM tomography with Subaru/HSC: the large-scale structure of Lyα emitters and IGM transmission in the COSMOS field at z ∼ 5
We present a novel technique called “photometric IGM tomography” to map the intergalactic medium (IGM) at z ≃ 4.9 in the COSMOS field. It utilizes deep narrow-band (NB) imaging to photometrically detect faint Lyα forest transmission in background galaxies across the Subaru/Hyper-Suprime Cam (HSC)’s 1.8sq.deg
field of view and locate Lyα emitters (LAEs) in the same cosmic volume. Using ultra-deep HSC images and Bayesian spectral energy distribution fitting, we measure the Lyα forest transmission at z ≃ 4.9 along a large number (140) of background galaxies selected from the DEIMOS10k spectroscopic catalogue at 4.98 < z < 5.89 and the SILVERRUSH LAEs at z ≃ 5.7. We photometrically measure the mean Lyα forest transmission and achieve a result consistent with previous measurements based on quasar spectra. We also measure the angular LAE-Lyα forest cross-correlation and Lyα forest auto-correlation functions and place an observational constraint on the large-scale fluctuations of the IGM around LAEs at z ≃ 4.9. Finally, we present the reconstructed 2D tomographic map of the IGM, co-spatial with the large-scale structure of LAEs, at a transverse resolution of 11h−1cMpc
across 140h−1cMpc
in the COSMOS field at z ≃ 4.9. We discuss the observational requirements and the potential applications of this new technique for understanding the sources of reionization, quasar radiative history, and galaxy-IGM correlations across z ∼ 3 − 6. Our results represent the first proof-of-concept of photometric IGM tomography, offering a new route to examining early galaxy evolution in the context of the large-scale cosmic web from the epoch of reionization to cosmic noon
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