143 research outputs found
A Complete Spectroscopic Survey of the Milky Way Satellite Segue 1: The Darkest Galaxy
We present the results of a comprehensive Keck/DEIMOS spectroscopic survey of
the ultra-faint Milky Way satellite galaxy Segue 1. We have obtained velocity
measurements for 98.2% of the stars within 67 pc (10 arcmin, or 2.3 half-light
radii) of the center of Segue 1 that have colors and magnitudes consistent with
membership, down to a magnitude limit of r=21.7. Based on photometric,
kinematic, and metallicity information, we identify 71 stars as probable Segue
1 members, including some as far out as 87 pc. After correcting for the
influence of binary stars using repeated velocity measurements, we determine a
velocity dispersion of 3.7^{+1.4}_{-1.1} km/s, with a corresponding mass within
the half-light radius of 5.8^{+8.2}_{-3.1} x 10^5 Msun. The stellar kinematics
of Segue 1 require very high mass-to-light ratios unless the system is far from
dynamical equilibrium, even if the period distribution of unresolved binary
stars is skewed toward implausibly short periods. With a total luminosity less
than that of a single bright red giant and a V-band mass-to-light ratio of 3400
Msun/Lsun, Segue 1 is the darkest galaxy currently known. We critically
re-examine recent claims that Segue 1 is a tidally disrupting star cluster and
that kinematic samples are contaminated by the Sagittarius stream. The
extremely low metallicities ([Fe/H] < -3) of two Segue 1 stars and the large
metallicity spread among the members demonstrate conclusively that Segue 1 is a
dwarf galaxy, and we find no evidence in favor of tidal effects. We also show
that contamination by the Sagittarius stream has been overestimated. Segue 1
has the highest measured dark matter density of any known galaxy and will
therefore be a prime testing ground for dark matter physics and galaxy
formation on small scales.Comment: 24 pages, 4 tables, 11 figures (10 in color). Submitted for
publication in ApJ. V3 revised according to comments from the refere
A Deeper Look at Leo IV: Star Formation History and Extended Structure
We present MMT/Megacam imaging of the Leo~IV dwarf galaxy in order to
investigate its structure and star formation history, and to search for signs
of association with the recently discovered Leo~V satellite. Based on
parameterized fits, we find that Leo~IV is round, with (at
the 68\% confidence limit) and a half-light radius of pc.
Additionally, we perform a thorough search for extended structures in the plane
of the sky and along the line of sight. We derive our surface brightness
detection limit by implanting fake structures into our catalog with stellar
populations identical to that of Leo~IV. We show that we are sensitive to
stream-like structures with surface brightness mag
arcsec, and at this limit, we find no stellar bridge between Leo IV (out
to a radius of 0.5 kpc) and the recently discovered, nearby satellite Leo
V. Using the color magnitude fitting package StarFISH, we determine that Leo~IV
is consistent with a single age (14 Gyr), single metallicity
() stellar population, although we can not rule out a
significant spread in these value. We derive a luminosity of
. Studying both the spatial distribution and frequency of
Leo~IV's 'blue plume' stars reveals evidence for a young (2 Gyr) stellar
population which makes up 2\% of its stellar mass. This sprinkling of
star formation, only detectable in this deep study, highlights the need for
further imaging of the new Milky Way satellites along with theoretical work on
the expected, detailed properties of these possible 'reionization fossils'.Comment: 26 pages, 14 figures, emulateapj format, ApJ accepted versio
Tidal Signatures in the Faintest Milky Way Satellites: The Detailed Properties of Leo V, Pisces II and Canes Venatici II
We present deep wide-field photometry of three recently discovered faint
Milky Way satellites: Leo V, Pisces II, and Canes Venatici II. Our main goals
are to study the structure and star formation history of these dwarfs; we also
search for signs of tidal disturbance. The three satellites have similar
half-light radii ( pc) but a wide range of ellipticities. Both Leo
V and CVn II show hints of stream-like overdensities at large radii. An
analysis of the satellite color-magnitude diagrams shows that all three objects
are old ( 10 Gyr) and metal-poor ([Fe/H] ), though neither the
models nor the data have sufficient precision to assess when the satellites
formed with respect to cosmic reionization. The lack of an observed younger
stellar population (\la 10 Gyr) possibly sets them apart from the other
satellites at Galactocentric distances \ga 150 kpc. We present a new
compilation of structural data for all Milky Way satellite galaxies and use it
to compare the properties of classical dwarfs to the ultra-faints. The
ellipticity distribution of the two groups is consistent at the
2- level. However, the faintest satellites tend to be more
aligned toward the Galactic center, and those satellites with the highest
ellipticity (\ga 0.4) have orientations () in the range
. This latter
observation is in rough agreement with predictions from simulations of dwarf
galaxies that have lost a significant fraction of their dark matter halos and
are being tidally stripped.Comment: 25 pages, 7 figures, ApJ accepted; version updated to match ApJ
accepte
The Star Formation History and Extended Structure of the Hercules Milky Way Satellite
We present imaging of the recently discovered Hercules Milky Way satellite
and its surrounding regions to study its structure, star formation history and
to thoroughly search for signs of disruption. We robustly determine the
distance, luminosity, size and morphology of Hercules utilizing a bootstrap
approach to characterize our uncertainties. We derive a distance to Hercules of
kpc via a comparison to empirical and theoretical isochrones. As
previous studies have found, Hercules is very elongated, with
and a half light radius of pc. Using
the color magnitude fitting package StarFISH, we determine that Hercules is old
( Gyr) and metal poor (), with a spread in metallicity, in
agreement with previous spectroscopic work. We infer a total absolute magnitude
of . Our innovative search for external Hercules structure both
in the plane of the sky and along the line of sight yields some evidence that
Hercules is embedded in a larger stream of stars. A clear stellar extension is
seen to the Northwest with several additional candidate stellar overdensities
along the position angle of Hercules out to 35' (1.3 kpc). While
the association of any of the individual stellar overdensities with Hercules is
difficult to determine, we do show that the summed color magnitude diagram of
all three is consistent with Hercules' stellar population. Finally, we estimate
that any change in the distance to Hercules across its face is at most 6
kpc; and the data are consistent with Hercules being at the same distance
throughout.Comment: 50 pages, 15 figures, submitted to the Astrophysical Journa
Thymus-Associated Parathyroid Hormone Has Two Cellular Origins with Distinct Endocrine and Immunological Functions
In mammals, parathyroid hormone (PTH) is a key regulator of extracellular calcium and inorganic phosphorus homeostasis. Although the parathyroid glands were thought to be the only source of PTH, extra-parathyroid PTH production in the thymus, which shares a common origin with parathyroids during organogenesis, has been proposed to provide an auxiliary source of PTH, resulting in a higher than expected survival rate for aparathyroid Gcm2−/− mutants. However, the developmental ontogeny and cellular identity of these “thymic” PTH–expressing cells is unknown. We found that the lethality of aparathyroid Gcm2−/− mutants was affected by genetic background without relation to serum PTH levels, suggesting a need to reconsider the physiological function of thymic PTH. We identified two sources of extra-parathyroid PTH in wild-type mice. Incomplete separation of the parathyroid and thymus organs during organogenesis resulted in misplaced, isolated parathyroid cells that were often attached to the thymus; this was the major source of thymic PTH in normal mice. Analysis of thymus and parathyroid organogenesis in human embryos showed a broadly similar result, indicating that these results may provide insight into human parathyroid development. In addition, medullary thymic epithelial cells (mTECs) express PTH in a Gcm2-independent manner that requires TEC differentiation and is consistent with expression as a self-antigen for negative selection. Genetic or surgical removal of the thymus indicated that thymus-derived PTH in Gcm2−/− mutants did not provide auxiliary endocrine function. Our data show conclusively that the thymus does not serve as an auxiliary source of either serum PTH or parathyroid function. We further show that the normal process of parathyroid organogenesis in both mice and humans leads to the generation of multiple small parathyroid clusters in addition to the main parathyroid glands, that are the likely source of physiologically relevant “thymic PTH.
Deep Subaru Hyper Suprime-Cam Observations of Milky Way Satellites Columba I and Triangulum II
Pregnancy and neonatal outcomes of COVID-19: The PAN-COVID study
Objective
To assess perinatal outcomes for pregnancies affected by suspected or confirmed SARS-CoV-2 infection.
Methods
Prospective, web-based registry. Pregnant women were invited to participate if they had suspected or confirmed SARS-CoV-2 infection between 1st January 2020 and 31st March 2021 to assess the impact of infection on maternal and perinatal outcomes including miscarriage, stillbirth, fetal growth restriction, pre-term birth and transmission to the infant.
Results
Between April 2020 and March 2021, the study recruited 8239 participants who had suspected or confirmed SARs-CoV-2 infection episodes in pregnancy between January 2020 and March 2021.
Maternal death affected 14/8197 (0.2%) participants, 176/8187 (2.2%) of participants required ventilatory support. Pre-eclampsia affected 389/8189 (4.8%) participants, eclampsia was reported in 40/ 8024 (0.5%) of all participants.
Stillbirth affected 35/8187 (0.4 %) participants. In participants delivering within 2 weeks of delivery 21/2686 (0.8 %) were affected by stillbirth compared with 8/4596 (0.2 %) delivering ≥ 2 weeks after infection (95 % CI 0.3–1.0). SGA affected 744/7696 (9.3 %) of livebirths, FGR affected 360/8175 (4.4 %) of all pregnancies.
Pre-term birth occurred in 922/8066 (11.5%), the majority of these were indicated pre-term births, 220/7987 (2.8%) participants experienced spontaneous pre-term births. Early neonatal deaths affected 11/8050 livebirths. Of all neonates, 80/7993 (1.0%) tested positive for SARS-CoV-2.
Conclusions
Infection was associated with indicated pre-term birth, most commonly for fetal compromise. The overall proportions of women affected by SGA and FGR were not higher than expected, however there was the proportion affected by stillbirth in participants delivering within 2 weeks of infection was significantly higher than those delivering ≥ 2 weeks after infection. We suggest that clinicians’ threshold for delivery should be low if there are concerns with fetal movements or fetal heart rate monitoring in the time around infection
Effectiveness of a national quality improvement programme to improve survival after emergency abdominal surgery (EPOCH): a stepped-wedge cluster-randomised trial
Background: Emergency abdominal surgery is associated with poor patient outcomes. We studied the effectiveness of a national quality improvement (QI) programme to implement a care pathway to improve survival for these patients. Methods: We did a stepped-wedge cluster-randomised trial of patients aged 40 years or older undergoing emergency open major abdominal surgery. Eligible UK National Health Service (NHS) hospitals (those that had an emergency general surgical service, a substantial volume of emergency abdominal surgery cases, and contributed data to the National Emergency Laparotomy Audit) were organised into 15 geographical clusters and commenced the QI programme in a random order, based on a computer-generated random sequence, over an 85-week period with one geographical cluster commencing the intervention every 5 weeks from the second to the 16th time period. Patients were masked to the study group, but it was not possible to mask hospital staff or investigators. The primary outcome measure was mortality within 90 days of surgery. Analyses were done on an intention-to-treat basis. This study is registered with the ISRCTN registry, number ISRCTN80682973. Findings: Treatment took place between March 3, 2014, and Oct 19, 2015. 22 754 patients were assessed for elegibility. Of 15 873 eligible patients from 93 NHS hospitals, primary outcome data were analysed for 8482 patients in the usual care group and 7374 in the QI group. Eight patients in the usual care group and nine patients in the QI group were not included in the analysis because of missing primary outcome data. The primary outcome of 90-day mortality occurred in 1210 (16%) patients in the QI group compared with 1393 (16%) patients in the usual care group (HR 1·11, 0·96–1·28). Interpretation: No survival benefit was observed from this QI programme to implement a care pathway for patients undergoing emergency abdominal surgery. Future QI programmes should ensure that teams have both the time and resources needed to improve patient care. Funding: National Institute for Health Research Health Services and Delivery Research Programme
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