74 research outputs found
Intrinsic galaxy alignments from the 2SLAQ and SDSS surveys: luminosity and redshift scalings and implications for weak lensing surveys
Correlations between intrinsic shear and the density field on large scales, a potentially important contaminant for cosmic shear surveys, have been robustly detected at low redshifts with bright galaxies in Sloan Digital Sky Survey (SDSS) data. Here we present a more detailed characterization of this effect, which can cause anticorrelations between gravitational lensing shear and intrinsic ellipticity (GI correlations). This measurement uses 36 278 luminous red galaxies (LRGs) from the SDSS spectroscopic sample with 0.15 3σ detections of the effect on large scales (up to 60 h−1 Mpc) for all galaxy subsamples within the SDSS LRG sample; for the 2SLAQ sample, we find a 2σ detection for a bright subsample, and no detection for a fainter subsample. Fitting formulae are provided for the scaling of the GI correlations with luminosity, transverse separation and redshift (for which the 2SLAQ sample, while small, provides crucial constraints due to its longer baseline in redshift). We estimate contamination in the measurement of σ8 for future cosmic shear surveys on the basis of the fitted dependence of GI correlations on galaxy properties. We find contamination to the power spectrum ranging from −1.5 per cent (optimistic) to −33 per cent (pessimistic) for a toy cosmic shear survey using all galaxies to a depth of R= 24 using scales l≈ 500, though the central value of predicted contamination is −6.5 per cent. This corresponds to a bias in σ8 of Δσ8=−0.004 (optimistic), −0.02 (central) or −0.10 (pessimistic). We provide a prescription for inclusion of this error in cosmological parameter estimation codes. The principal uncertainty is in the treatment of the L≤L★ blue galaxies, for which we have no detection of the GI signal, but which could dominate the GI contamination if their GI amplitude is near our upper limits. Characterization of the tidal alignments of these galaxies, especially at redshifts relevant for cosmic shear, should be a high priority for the cosmic shear communit
A longer vernal window: The role of winter coldness and snowpack in driving spring thresholds and lags
Climate change is altering the timing and duration of the vernal window, a period that marks the end of winter and the start of the growing season when rapid transitions in ecosystem energy, water, nutrient, and carbon dynamics take place. Research on this period typically captures only a portion of the ecosystem in transition and focuses largely on the dates by which the system wakes up. Previous work has not addressed lags between transitions that represent delays in energy, water, nutrient, and carbon flows. The objectives of this study were to establish the sequence of physical and biogeochemical transitions and lags during the vernal window period and to understand how climate change may alter them. We synthesized observations from a statewide sensor network in New Hampshire, USA, that concurrently monitored climate, snow, soils, and streams over a three-year period and supplemented these observations with climate reanalysis data, snow data assimilation model output, and satellite spectral data. We found that some of the transitions that occurred within the vernal window were sequential, with air temperatures warming prior to snow melt, which preceded forest canopy closure. Other transitions were simultaneous with one another and had zero-length lags, such as snowpack disappearance, rapid soil warming, and peak stream discharge. We modeled lags as a function of both winter coldness and snow depth, both of which are expected to decline with climate change. Warmer winters with less snow resulted in longer lags and a more protracted vernal window. This lengthening of individual lags and of the entire vernal window carries important consequences for the thermodynamics and biogeochemistry of ecosystems, both during the winter-to-spring transition and throughout the rest of the year
The Morphology of Galaxies in the Baryon Oscillation Spectroscopic Survey
We study the morphology of luminous and massive galaxies at 0.3<z<0.7
targeted in the Baryon Oscillation Spectroscopic Survey (BOSS) using publicly
available Hubble Space Telescope imaging from COSMOS. Our sample (240 objects)
provides a unique opportunity to check the visual morphology of these galaxies
which were targeted based solely on stellar population modelling. We find that
the majority (74+/-6%) possess an early-type morphology (elliptical or S0),
while the remainder have a late-type morphology. This is as expected from the
goals of the BOSS target selection which aimed to predominantly select slowly
evolving galaxies, for use as cosmological probes, while still obtaining a fair
fraction of actively star forming galaxies for galaxy evolution studies. We
show that a colour cut of (g-i)>2.35 selects a sub-sample of BOSS galaxies with
90% early-type morphology - more comparable to the earlier Luminous Red Galaxy
(LRG) samples of SDSS-I/II. The remaining 10% of galaxies above this cut have a
late-type morphology and may be analogous to the "passive spirals" found at
lower redshift. We find that 23+/-4% of the early-type galaxies are unresolved
multiple systems in the SDSS imaging. We estimate that at least 50% of these
are real associations (not projection effects) and may represent a significant
"dry merger" fraction. We study the SDSS pipeline sizes of BOSS galaxies which
we find to be systematically larger (by 40%) than those measured from HST
images, and provide a statistical correction for the difference. These details
of the BOSS galaxies will help users of the data fine-tune their selection
criteria, dependent on their science applications. For example, the main goal
of BOSS is to measure the cosmic distance scale and expansion rate of the
Universe to percent-level precision - a point where systematic effects due to
the details of target selection may become important.Comment: 18 pages, 11 figures; v2 as accepted by MNRA
High Cryptococcal Antigen Titers in Blood Are Predictive of Subclinical Cryptococcal Meningitis Among Human Immunodeficiency Virus-Infected Patients
Background
High mortality rates among asymptomatic cryptococcal antigen (CrAg)–positive patients identified through CrAg screening, despite preemptive fluconazole treatment, may be due to undiagnosed cryptococcal meningitis.
Methods
Symptoms were reviewed in CrAg-positive patients identified by screening 19233 individuals with human immunodeficiency virus infection and CD4 cell counts <100/µL at 17 clinics and 3 hospitals in Johannesburg from September 2012 until September 2015, and at 2 hospitals until June 2016. Cerebrospinal fluid samples from 90 of 254 asymptomatic patients (35%) and 78 of 173 (45%) with headache only were analyzed for cryptococcal meningitis, considered present if Cryptococcus was identified by means of India ink microscopy, culture, or CrAg test. CrAg titers were determined with stored blood samples from 62 of these patients. The associations between blood CrAg titer, concurrent cryptococcal meningitis, and mortality rate were assessed.
Results
Cryptococcal meningitis was confirmed in 34% (95% confidence interval, 25%–43%; 31 of 90) of asymptomatic CrAg-positive patients and 90% (81%–96%; 70 of 78) with headache only. Blood CrAg titer was significantly associated with concurrent cryptococcal meningitis in asymptomatic patients (P 160 (sensitivity, 88.2%; specificity, 82.1%); the odds ratio for concurrent cryptococcal meningitis was 34.5 (95% confidence interval, 8.3–143.1; P < .001).
Conclusions
About a third of asymptomatic CrAg-positive patients have concurrent cryptococcal meningitis. More effective clinical assessment strategies and antifungal regimens are required for CrAg-positive patients, including investigation for cryptococcal meningitis irrespective of symptoms. Where it is not possible to perform lumbar punctures in all CrAg-positive patients, blood CrAg titers should be used to target those most at risk of cryptococcal meningitis
CANDELS: The progenitors of compact quiescent galaxies at z~2
We combine high-resolution HST/WFC3 images with multi-wavelength photometry
to track the evolution of structure and activity of massive (log(M*) > 10)
galaxies at redshifts z = 1.4 - 3 in two fields of the Cosmic Assembly
Near-infrared Deep Extragalactic Legacy Survey (CANDELS). We detect compact,
star-forming galaxies (cSFGs) whose number densities, masses, sizes, and star
formation rates qualify them as likely progenitors of compact, quiescent,
massive galaxies (cQGs) at z = 1.5 - 3. At z > 2 most cSFGs have specific
star-formation rates (sSFR = 10^-9 yr^-1) half that of typical, massive SFGs at
the same epoch, and host X-ray luminous AGN 30 times (~30%) more frequently.
These properties suggest that cSFGs are formed by gas-rich processes (mergers
or disk-instabilities) that induce a compact starburst and feed an AGN, which,
in turn, quench the star formation on dynamical timescales (few 10^8 yr). The
cSFGs are continuously being formed at z = 2 - 3 and fade to cQGs by z = 1.5.
After this epoch, cSFGs are rare, thereby truncating the formation of new cQGs.
Meanwhile, down to z = 1, existing cQGs continue to enlarge to match local QGs
in size, while less-gas-rich mergers and other secular mechanisms shepherd
(larger) SFGs as later arrivals to the red sequence. In summary, we propose two
evolutionary scenarios of QG formation: an early (z > 2), fast-formation path
of rapidly-quenched cSFGs that evolve into cQGs that later enlarge within the
quiescent phase, and a slow, late-arrival (z < 2) path for SFGs to form QGs
without passing through a compact state.Comment: Submitted to the Astrophysical Journal Letters, 6 pages, 4 figure
The Eighth Data Release of the Sloan Digital Sky Survey: First Data from SDSS-III
The Sloan Digital Sky Survey (SDSS) started a new phase in August 2008, with
new instrumentation and new surveys focused on Galactic structure and chemical
evolution, measurements of the baryon oscillation feature in the clustering of
galaxies and the quasar Ly alpha forest, and a radial velocity search for
planets around ~8000 stars. This paper describes the first data release of
SDSS-III (and the eighth counting from the beginning of the SDSS). The release
includes five-band imaging of roughly 5200 deg^2 in the Southern Galactic Cap,
bringing the total footprint of the SDSS imaging to 14,555 deg^2, or over a
third of the Celestial Sphere. All the imaging data have been reprocessed with
an improved sky-subtraction algorithm and a final, self-consistent photometric
recalibration and flat-field determination. This release also includes all data
from the second phase of the Sloan Extension for Galactic Understanding and
Evolution (SEGUE-2), consisting of spectroscopy of approximately 118,000 stars
at both high and low Galactic latitudes. All the more than half a million
stellar spectra obtained with the SDSS spectrograph have been reprocessed
through an improved stellar parameters pipeline, which has better determination
of metallicity for high metallicity stars.Comment: Astrophysical Journal Supplements, in press (minor updates from
submitted version
The Ninth Data Release of the Sloan Digital Sky Survey: First Spectroscopic Data from the SDSS-III Baryon Oscillation Spectroscopic Survey
The Sloan Digital Sky Survey III (SDSS-III) presents the first spectroscopic
data from the Baryon Oscillation Spectroscopic Survey (BOSS). This ninth data
release (DR9) of the SDSS project includes 535,995 new galaxy spectra (median
z=0.52), 102,100 new quasar spectra (median z=2.32), and 90,897 new stellar
spectra, along with the data presented in previous data releases. These spectra
were obtained with the new BOSS spectrograph and were taken between 2009
December and 2011 July. In addition, the stellar parameters pipeline, which
determines radial velocities, surface temperatures, surface gravities, and
metallicities of stars, has been updated and refined with improvements in
temperature estimates for stars with T_eff<5000 K and in metallicity estimates
for stars with [Fe/H]>-0.5. DR9 includes new stellar parameters for all stars
presented in DR8, including stars from SDSS-I and II, as well as those observed
as part of the SDSS-III Sloan Extension for Galactic Understanding and
Exploration-2 (SEGUE-2).
The astrometry error introduced in the DR8 imaging catalogs has been
corrected in the DR9 data products. The next data release for SDSS-III will be
in Summer 2013, which will present the first data from the Apache Point
Observatory Galactic Evolution Experiment (APOGEE) along with another year of
data from BOSS, followed by the final SDSS-III data release in December 2014.Comment: 9 figures; 2 tables. Submitted to ApJS. DR9 is available at
http://www.sdss3.org/dr
The Baryon Oscillation Spectroscopic Survey of SDSS-III
The Baryon Oscillation Spectroscopic Survey (BOSS) is designed to measure the
scale of baryon acoustic oscillations (BAO) in the clustering of matter over a
larger volume than the combined efforts of all previous spectroscopic surveys
of large scale structure. BOSS uses 1.5 million luminous galaxies as faint as
i=19.9 over 10,000 square degrees to measure BAO to redshifts z<0.7.
Observations of neutral hydrogen in the Lyman alpha forest in more than 150,000
quasar spectra (g<22) will constrain BAO over the redshift range 2.15<z<3.5.
Early results from BOSS include the first detection of the large-scale
three-dimensional clustering of the Lyman alpha forest and a strong detection
from the Data Release 9 data set of the BAO in the clustering of massive
galaxies at an effective redshift z = 0.57. We project that BOSS will yield
measurements of the angular diameter distance D_A to an accuracy of 1.0% at
redshifts z=0.3 and z=0.57 and measurements of H(z) to 1.8% and 1.7% at the
same redshifts. Forecasts for Lyman alpha forest constraints predict a
measurement of an overall dilation factor that scales the highly degenerate
D_A(z) and H^{-1}(z) parameters to an accuracy of 1.9% at z~2.5 when the survey
is complete. Here, we provide an overview of the selection of spectroscopic
targets, planning of observations, and analysis of data and data quality of
BOSS.Comment: 49 pages, 16 figures, accepted by A
Intrinsic galaxy alignments from the 2SLAQ and SDSS surveys: luminosity and redshift scalings and implications for weak lensing surveys
Correlations between intrinsic shear and the density field on large scales, a
potentially important contaminant for cosmic shear surveys, have been robustly
detected at low redshifts with bright galaxies in SDSS data. Here we present a
more detailed characterization of this effect, which can cause
anti-correlations between gravitational lensing shear and intrinsic ellipticity
(GI correlations). This measurement uses 36278 Luminous Red Galaxies (LRGs)
from the SDSS spectroscopic sample with 0.15<z<0.35, split by redshift and
luminosity; 7758 LRGs from the 2SLAQ Survey at 0.4<z<0.8; and a variety of
other SDSS samples from previous, related work. We find >3sigma detections of
the effect for all galaxy subsamples within the SDSS LRG sample; for the 2SLAQ
sample, we find a 2sigma detection for a bright subsample, and no detection for
a fainter subsample. Fitting formulae are provided for the scaling of the GI
correlations with luminosity, transverse separation, and redshift. We estimate
contamination in the measurement of sigma_8 for future cosmic shear surveys on
the basis of the fitted dependence of GI correlations on galaxy properties. We
find contamination to the power spectrum ranging from -1.5 (optimistic) to -33
per cent (pessimistic) for a toy cosmic shear survey using all galaxies to a
depth of R=24 using scales l~500. This corresponds to a bias in sigma_8 of
Delta sigma_8=-0.004 (optimistic), -0.02 (central), or -0.10 (pessimistic). We
provide a prescription for inclusion of this error in cosmological parameter
estimation codes. The principal uncertainty is in the treatment of the L<=L*
blue galaxies. Characterization of the tidal alignments of these galaxies,
especially at redshifts relevant for cosmic shear, should be a high priority
for the cosmic shear community. (Abridged)Comment: Matches MNRAS accepted version. Extended/updated data tables and
expanded comparison to theor
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