27 research outputs found
A few StePS forward in unveiling the complexity of galaxy evolution: Light-weighted stellar ages of intermediate-redshift galaxies with WEAVE
The upcoming new generation of optical spectrographs on four-meter-class
telescopes will provide invaluable information for reconstructing the history
of star formation in individual galaxies up to redshifts of about 0.7. We aim
at defining simple but robust and meaningful physical parameters that can be
used to trace the coexistence of widely diverse stellar components: younger
stellar populations superimposed on the bulk of older ones. We produce spectra
of galaxies closely mimicking data from the forthcoming Stellar Populations at
intermediate redshifts Survey (StePS), a survey that uses the WEAVE
spectrograph on the William Herschel Telescope. First, we assess our ability to
reliably measure both ultraviolet and optical spectral indices in galaxies of
different spectral types for typically expected signal-to-noise levels. Then,
we analyze such mock spectra with a Bayesian approach, deriving the probability
density function of r- and u-band light-weighted ages as well as of their
difference. We find that the ultraviolet indices significantly narrow the
uncertainties in estimating the r- and u-band light-weighted ages and their
difference in individual galaxies. These diagnostics, robustly retrievable for
large galaxy samples even when observed at moderate signal-to-noise ratios,
allow us to identify secondary episodes of star formation up to an age of ~0.1
Gyr for stellar populations older than ~1.5 Gyr, pushing up to an age of ~1 Gyr
for stellar populations older than ~5 Gyr. The difference between r-band and
u-band light-weighted ages is shown to be a powerful diagnostic to characterize
and constrain extended star-formation histories and the presence of young
stellar populations on top of older ones. This parameter can be used to explore
the interplay between different galaxy star-formation histories and physical
parameters such as galaxy mass, size, morphology, and environment
Astrodynamical Space Test of Relativity using Optical Devices I (ASTROD I) - A class-M fundamental physics mission proposal for Cosmic Vision 2015-2025: 2010 Update
This paper on ASTROD I is based on our 2010 proposal submitted for the ESA
call for class-M mission proposals, and is a sequel and an update to our
previous paper [Experimental Astronomy 23 (2009) 491-527; designated as Paper
I] which was based on our last proposal submitted for the 2007 ESA call. In
this paper, we present our orbit selection with one Venus swing-by together
with orbit simulation. In Paper I, our orbit choice is with two Venus
swing-bys. The present choice takes shorter time (about 250 days) to reach the
opposite side of the Sun. We also present a preliminary design of the optical
bench, and elaborate on the solar physics goals with the radiation monitor
payload. We discuss telescope size, trade-offs of drag-free sensitivities,
thermal issues and present an outlook. ASTROD I is a planned interplanetary
space mission with multiple goals. The primary aims are: to test General
Relativity with an improvement in sensitivity of over 3 orders of magnitude,
improving our understanding of gravity and aiding the development of a new
quantum gravity theory; to measure key solar system parameters with increased
accuracy, advancing solar physics and our knowledge of the solar system; and to
measure the time rate of change of the gravitational constant with an order of
magnitude improvement and the anomalous Pioneer acceleration, thereby probing
dark matter and dark energy gravitationally. It is envisaged as the first in a
series of ASTROD missions. ASTROD I will consist of one spacecraft carrying a
telescope, four lasers, two event timers and a clock. Two-way, two-wavelength
laser pulse ranging will be used between the spacecraft in a solar orbit and
deep space laser stations on Earth, to achieve the ASTROD I goals.Comment: 15 pages, 11 figures, 1 table, based on our 2010 proposal submitted
for the ESA call for class-M mission proposals, a sequel and an update to
previous paper [Experimental Astronomy 23 (2009) 491-527] which was based on
our last proposal submitted for the 2007 ESA call, submitted to Experimental
Astronom
The Gaia-ESO Public Spectroscopic Survey: Motivation, implementation, GIRAFFE data processing, analysis, and final data products
The Gaia-ESO Public Spectroscopic Survey is an ambitious project designed to
obtain astrophysical parameters and elemental abundances for 100,000 stars,
including large representative samples of the stellar populations in the
Galaxy, and a well-defined sample of 60 (plus 20 archive) open clusters. We
provide internally consistent results calibrated on benchmark stars and star
clusters, extending across a very wide range of abundances and ages. This
provides a legacy data set of intrinsic value, and equally a large wide-ranging
dataset that is of value for homogenisation of other and future stellar surveys
and Gaia's astrophysical parameters. This article provides an overview of the
survey methodology, the scientific aims, and the implementation, including a
description of the data processing for the GIRAFFE spectra. A companion paper
(arXiv:2206.02901) introduces the survey results. Gaia-ESO aspires to quantify
both random and systematic contributions to measurement uncertainties. Thus all
available spectroscopic analysis techniques are utilised, each spectrum being
analysed by up to several different analysis pipelines, with considerable
effort being made to homogenise and calibrate the resulting parameters. We
describe here the sequence of activities up to delivery of processed data
products to the ESO Science Archive Facility for open use. The Gaia-ESO Survey
obtained 202,000 spectra of 115,000 stars using 340 allocated VLT nights
between December 2011 and January 2018 from GIRAFFE and UVES. The full
consistently reduced final data set of spectra was released through the ESO
Science Archive Facility in late 2020, with the full astrophysical parameters
sets following in 2022
Pooled analysis of WHO Surgical Safety Checklist use and mortality after emergency laparotomy
Background The World Health Organization (WHO) Surgical Safety Checklist has fostered safe practice for 10 years, yet its place in emergency surgery has not been assessed on a global scale. The aim of this study was to evaluate reported checklist use in emergency settings and examine the relationship with perioperative mortality in patients who had emergency laparotomy. Methods In two multinational cohort studies, adults undergoing emergency laparotomy were compared with those having elective gastrointestinal surgery. Relationships between reported checklist use and mortality were determined using multivariable logistic regression and bootstrapped simulation. Results Of 12 296 patients included from 76 countries, 4843 underwent emergency laparotomy. After adjusting for patient and disease factors, checklist use before emergency laparotomy was more common in countries with a high Human Development Index (HDI) (2455 of 2741, 89.6 per cent) compared with that in countries with a middle (753 of 1242, 60.6 per cent; odds ratio (OR) 0.17, 95 per cent c.i. 0.14 to 0.21, P <0001) or low (363 of 860, 422 per cent; OR 008, 007 to 010, P <0.001) HDI. Checklist use was less common in elective surgery than for emergency laparotomy in high-HDI countries (risk difference -94 (95 per cent c.i. -11.9 to -6.9) per cent; P <0001), but the relationship was reversed in low-HDI countries (+121 (+7.0 to +173) per cent; P <0001). In multivariable models, checklist use was associated with a lower 30-day perioperative mortality (OR 0.60, 0.50 to 073; P <0.001). The greatest absolute benefit was seen for emergency surgery in low- and middle-HDI countries. Conclusion Checklist use in emergency laparotomy was associated with a significantly lower perioperative mortality rate. Checklist use in low-HDI countries was half that in high-HDI countries.Peer reviewe
WEAVE-StePS: A stellar population survey using WEAVE at WHT
Context. The upcoming new generation of optical spectrographs on four-meter-class telescopes will provide valuable opportunities for forthcoming galaxy surveys through their huge multiplexing capabilities, excellent spectral resolution, and unprecedented wavelength coverage. Aims. WEAVE is a new wide-field spectroscopic facility mounted on the 4.2 m William Herschel Telescope in La Palma. WEAVE-StePS is one of the five extragalactic surveys that will use WEAVE during its first five years of operations. It will observe galaxies using WEAVE MOS (∼950 fibres distributed across a field of view of ∼3 square degrees on the sky) in low-resolution mode (R ∼ 5000, spanning the wavelength range 3660-9590 Å). Methods. WEAVE-StePS will obtain high-quality spectra (S/N ∼ 10 Å -1 at R ∼ 5000) for a magnitude-limited (IAB = 20.5) sample of ∼25 000 galaxies, the majority selected at z ≥ 0.3. The survey goal is to provide precise spectral measurements in the crucial interval that bridges the gap between LEGA-C and SDSS data. The wide area coverage of ∼25 square degrees will enable us to observe galaxies in a variety of environments. The ancillary data available in each of the observed fields (including X-ray coverage, multi-narrow-band photometry and spectroscopic redshift information) will provide an environmental characterisation for each observed galaxy. Results. This paper presents the science case of WEAVE-StePS, the fields to be observed, the parent catalogues used to define the target sample, and the observing strategy that was chosen after a forecast of the expected performance of the instrument for our typical targets. Conclusions. WEAVE-StePS will go back further in cosmic time than SDSS, extending its reach to encompass more than ∼6 Gyr. This is nearly half of the age of the Universe. The spectral and redshift range covered by WEAVE-StePS will open a new observational window by continuously tracing the evolutionary path of galaxies in the largely unexplored intermediate-redshift range
Global variation in anastomosis and end colostomy formation following left-sided colorectal resection
Background
End colostomy rates following colorectal resection vary across institutions in high-income settings, being influenced by patient, disease, surgeon and system factors. This study aimed to assess global variation in end colostomy rates after left-sided colorectal resection.
Methods
This study comprised an analysis of GlobalSurg-1 and -2 international, prospective, observational cohort studies (2014, 2016), including consecutive adult patients undergoing elective or emergency left-sided colorectal resection within discrete 2-week windows. Countries were grouped into high-, middle- and low-income tertiles according to the United Nations Human Development Index (HDI). Factors associated with colostomy formation versus primary anastomosis were explored using a multilevel, multivariable logistic regression model.
Results
In total, 1635 patients from 242 hospitals in 57 countries undergoing left-sided colorectal resection were included: 113 (6·9 per cent) from low-HDI, 254 (15·5 per cent) from middle-HDI and 1268 (77·6 per cent) from high-HDI countries. There was a higher proportion of patients with perforated disease (57·5, 40·9 and 35·4 per cent; P < 0·001) and subsequent use of end colostomy (52·2, 24·8 and 18·9 per cent; P < 0·001) in low- compared with middle- and high-HDI settings. The association with colostomy use in low-HDI settings persisted (odds ratio (OR) 3·20, 95 per cent c.i. 1·35 to 7·57; P = 0·008) after risk adjustment for malignant disease (OR 2·34, 1·65 to 3·32; P < 0·001), emergency surgery (OR 4·08, 2·73 to 6·10; P < 0·001), time to operation at least 48 h (OR 1·99, 1·28 to 3·09; P = 0·002) and disease perforation (OR 4·00, 2·81 to 5·69; P < 0·001).
Conclusion
Global differences existed in the proportion of patients receiving end stomas after left-sided colorectal resection based on income, which went beyond case mix alone
The nature of sub-millimetre galaxies II: an ALMA comparison of SMG dust heating mechanisms
We compare the contribution of active galactic nuclei (AGNs) and star formation towards dust heating in sub-mm galaxies (SMGs). We have used ALMA at 0.1-arcsec resolution to image a complete flux-limited sample of seven sub-mm sources previously shown to have spectral energy distributions that were as well-fitted by obscured AGN as star-forming galaxy templates. Indeed, two sub-mm sources were known to be quasars from their absorbed X-ray emission. We find the sub-mm sizes of all SMGs to be small (≈1−2 kpc) and generally ∼3 times smaller than any host detected in the near-infrared (NIR). In all cases, the five SMGs are comparable in sub-mm size to the two known quasars and four z ≈ 6 quasars, also observed with ALMA. We detect no evidence of diffuse spiral arms in this complete sample. We then convert the far-infrared (FIR) luminosities to star formation rate (SFR) surface densities and find that the SMGs occupy the same range as the known quasars in our sample. We conclude that in terms of sub-mm size, extent relative to host and SFR density as well as luminosity and mid-IR (MIR) colour, there is little distinction between the SMGs and sub-mm bright quasars. Finally, we present preliminary evidence that SMGs with higher MIR luminosities and sub-mm loud quasars tend to have dust components that range to hotter temperatures than their less luminous SMG counterparts. In light of these results, we continue to suggest that luminous SMGs may host dust-absorbed quasars that may simultaneously dominate the FIR and hard X-ray backgrounds
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A few StePS forward in unveiling the complexity of galaxy evolution: Light-weighted stellar ages of intermediate-redshift galaxies with WEAVE
Context. The upcoming new generation of optical spectrographs on four-meter-class telescopes, with their huge multiplexing capabilities, excellent spectral resolution, and unprecedented wavelength coverage, will provide invaluable information for reconstructing the history of star formation in individual galaxies up to redshifts of about 0.7.
Aims. We aim at defining simple but robust and meaningful physical parameters that can be used to trace the coexistence of widely diverse stellar components: younger stellar populations superimposed on the bulk of older ones.
Methods. We produced spectra of galaxies closely mimicking data from the forthcoming Stellar Populations at intermediate redshifts Survey (StePS), a survey that uses the WEAVE spectrograph on the William Herschel Telescope. First, we assessed our ability to reliably measure both ultraviolet and optical spectral indices in galaxies of different spectral types for typically expected signal-to-noise ratios. We then analyzed such mock spectra with a Bayesian approach, deriving the probability density function of r- and u-band light-weighted ages as well as of their difference.
Results. We find that the ultraviolet indices significantly narrow the uncertainties in estimating the r- and u-band light-weighted ages and their difference in individual galaxies. These diagnostics, robustly retrievable for large galaxy samples even when observed at moderate signal-to-noise ratios, allow us to identify secondary episodes of star formation up to an age of ~0.1 Gyr for stellar populations older than ~1.5 Gyr, pushing up to an age of ~1 Gyr for stellar populations older than ~5 Gyr.
Conclusions. The difference between r-band and u-band light-weighted ages is shown to be a powerful diagnostic to characterize and constrain extended star-formation histories and the presence of young stellar populations on top of older ones. This parameter can be used to explore the interplay between different galaxy star-formation histories and physical parameters such as galaxy mass, size, morphology, and environment