9,091 research outputs found
Temperature-based metallicity measurements at z=0.8: direct calibration of strong-line diagnostics at intermediate redshift
We present the first direct calibration of strong-line metallicity
diagnostics at significant cosmological distances using a sample at z=0.8 drawn
from the DEEP2 Galaxy Redshift Survey. Oxygen and neon abundances are derived
from measurements of electron temperature and density. We directly compare
various commonly used relations between gas-phase metallicity and strong line
ratios of O, Ne, and H at z=0.8 and z=0. There is no evolution with redshift at
high precision (, ). O, Ne, and H line ratios follow the same
locus at z=0.8 as at z=0 with 0.02 dex evolution and low scatter
(0.04 dex). This suggests little or no evolution in physical
conditions of HII regions at fixed oxygen abundance, in contrast to models
which invoke more extreme properties at high redshifts. We speculate that
offsets observed in the [N II]/H versus [O III]/H diagram at
high redshift are therefore due to [NII] emission, likely as a result of
relatively high N/O abundance. If this is indeed the case, then nitrogen-based
metallicity diagnostics suffer from systematic errors at high redshift. Our
findings indicate that locally calibrated abundance diagnostics based on
alpha-capture elements can be reliably applied at z1 and possibly at
much higher redshifts. This constitutes the first firm basis for the widespread
use of empirical calibrations in high redshift metallicity studies.Comment: 14 pages, 10 figures, accepted to Ap
Keck Spectroscopy of Faint 3 < z < 7 Lyman Break Galaxies: III. The Mean Ultraviolet Spectrum at z=4
We present and discuss the mean rest-frame ultraviolet spectrum for a sample
of 81 Lyman Break Galaxies (LBGs) selected to be B-band dropouts with a mean
redshift of z=3.9 and apparent magnitudes z_AB<26. Most of the individual
spectra are drawn from our ongoing survey in the GOODS fields with the Keck
DEIMOS spectrograph, and we have augmented our sample with published data taken
with FORS2 on the VLT. In general we find similar trends in the spectral
diagnostics to those found in the earlier, more extensive survey of LBGs at z=3
undertaken by Shapley et al (2003). Specifically, we find low-ionization
absorption lines which trace the presence of neutral outflowing gas are weaker
in galaxies with stronger Lyman-alpha emission, bluer UV spectral slopes, lower
stellar masses, lower UV luminosities and smaller half-light radii. This is
consistent with a physical picture whereby star formation drives outflows of
neutral gas which scatters Lyman-alpha and gives rise to strong low-ionization
absorption lines, while increasing the stellar mass, size, metallicity, and
dust content of galaxies. Typical galaxies are thus expected to have stronger
Lyman-alpha emission and weaker low-ionization absorption at earlier times
(higher redshifts). Indeed, our mean spectrum at z=4 shows somewhat weaker
low-ionization absorption lines than at z=3 and available data at higher
redshift indicates a rapid decrease in low-ionization absorption strength with
redshift. We argue that the reduced low-ionization absorption is likely caused
by a decrease in the covering fraction and/or velocity range of outflowing
neutral gas at earlier epochs. Our continuing survey will enable us to extend
these diagnostics more reliably to higher redshift and determine the
implications for the escape fraction of ionizing photons which governs the role
of early galaxies in cosmic reionization. [Abridged]Comment: 17 pages, 12 figures, submitted to ApJ. Comments welcom
The GSFC Mark-2 three band hand-held radiometer
A self-contained, portable, hand-radiometer designed for field usage was constructed and tested. The device, consisting of a hand-held probe containing three sensors and a strap supported electronic module, weighs 4 1/2 kilograms. It is powered by flashlight and transistor radio batteries, utilizes two silicon and one lead sulfide detectors, has three liquid crystal displays, sample and hold radiometric sampling, and its spectral configuration corresponds to LANDSAT-D's thematic mapper bands. The device was designed to support thematic mapper ground-truth data collection efforts and to facilitate 'in situ' ground-based remote sensing studies of natural materials. Prototype instruments were extensively tested under laboratory and field conditions with excellent results
Health information needs, source preferences and engagement behaviours of women with metastatic breast cancer across the care continuum: protocol for a scoping review
INTRODUCTION: The health information needs, information source preferences and engagement behaviours of women with metastatic breast cancer (mBC) depend on personal characteristics such as education level, prior knowledge, clinical complications, comorbidities and where they are in the cancer journey. A thorough understanding of the information behaviours of women living with mBC is essential to the provision of optimal care. A preliminary literature review suggests that there is little research on this topic, but that there may be lessons from a slightly broader literature. This review will identify what is known and what is not known about the health information needs, acquisition and influences of women with mBC across the care continuum. Findings will help to identify research needs and specific areas where in-depth systematic reviews may be feasible, as well as inform evidence-based interventions to address the health information needs of female patients with mBC with different demographics and characteristics and across the mBC journey. METHODS AND ANALYSIS: A scoping review will be performed using the guidelines of Arksey and O'Malley as updated by subsequent authors to systematically search scientific and grey literature for articles in English that discuss the health information needs, source preferences, engagement styles, and associated personal and medical attributes of women ≥18 years living with mBC at different stages of the disease course. A variety of databases (including Cumulative Index to Nursing and Allied Health Literature (CINAHL), PubMed, Excerpta Medica Database (EMBASE), Academic Search Premier, Cochrane Database of Systematic Reviews, PsycINFO, Health Source: Nursing/Academic Edition, and PQDT Open), oncology, patient advocacy and governmental websites will be searched from inception to present day. Research and non-research literature will be included; no study designs will be excluded. The six-stage Arksey and O'Malley scoping review methodological framework involves: (1) identifying the research question; (2) searching for relevant studies; (3) selecting studies; (4) charting the data; (5) collating, summarising and reporting the results; and (6) consulting with stakeholders to inform or validate study findings (optional). Data will be extracted and analysed using a thematic chart and descriptive content analysis. ETHICS AND DISSEMINATION: Being a secondary analysis, this research will not require ethics approval. Results will be disseminated through patient support organisations and websites and publications targeting healthcare professionals, advocates and patients
A Qualitative Study of the Assistive Technology Decision-Making Process in Four Pennsylvania School Districts
The purpose of this study was to gain an understanding of the Assistive Technology decision making process at four regional school districts in Pennsylvania. A qualitative case study research method involving the triangulation of data sources was implemented to collect and analyze data. Through an analysis of the data, three major topics emerged that will be addressed in the body of this paper: (a) the procedure for determining assistive technology needs and the dynamics of the decision-making process, b) the cohesiveness of Special Education and General Education programs, and c) major concerns that impact the delivery of assistive technology services
The OSIRIS Lens-Amplified Survey (OLAS) I: Dynamical Effects of Stellar Feedback in Low Mass Galaxies at z ~ 2
We introduce the OSIRIS Lens-Amplified Survey (OLAS), a kinematic survey of
gravitationally lensed galaxies at cosmic noon taken with Keck adaptive optics.
In this paper we present spatially resolved spectroscopy and nebular emission
kinematic maps for 17 star forming galaxies with stellar masses 8 <
log(/) < 9.8 and redshifts 1.2 < z < 2.3. OLAS is designed to
probe the stellar mass () and specific star formation rate (sSFR) range
where simulations suggest that stellar feedback is most effective at driving
gaseous outflows that create galaxy-wide potential fluctuations which can
generate dark matter cores. We compare our kinematic data with the trend
between sSFR, and H velocity dispersion, , from the
Feedback In Realistic Environments (FIRE) simulations. Our observations reveal
a correlation between sSFR and sigma at fixed that is similar to the
trend predicted by simulations: feedback from star formation drives
star-forming gas and newly formed stars into more dispersion dominated orbits.
The observed magnitude of this effect is in good agreement with the FIRE
simulations, in which feedback alters the central density profiles of low mass
galaxies, converting dark matter cusps into cores over time. Our data support
the scenario that stellar feedback drives gaseous outflows and potential
fluctuations, which in turn drive dark matter core formation in dwarf galaxies.Comment: 9 pages (5 figures) with 9 page appendix (17 figures). Accepted to
Ap
Direct constraints on the dark matter self-interaction cross-section from the merging galaxy cluster 1E0657-56
We compare new maps of the hot gas, dark matter, and galaxies for 1E0657-56,
a cluster with a rare, high-velocity merger occurring nearly in the plane of
the sky. The X-ray observations reveal a bullet-like gas subcluster just
exiting the collision site. A prominent bow shock gives an estimate of the
subcluster velocity, 4500 km/s, which lies mostly in the plane of the sky. The
optical image shows that the gas lags behind the subcluster galaxies. The
weak-lensing mass map reveals a dark matter clump lying ahead of the
collisional gas bullet, but coincident with the effectively collisionless
galaxies. From these observations, one can directly estimate the cross-section
of the dark matter self-interaction. That the dark matter is not fluid-like is
seen directly in the X-ray -- lensing mass overlay; more quantitative limits
can be derived from three simple independent arguments. The most sensitive
constraint, sigma/m<1 cm^2/g, comes from the consistency of the subcluster
mass-to-light ratio with the main cluster (and universal) value, which rules
out a significant mass loss due to dark matter particle collisions. This limit
excludes most of the 0.5-5 cm^2/g interval proposed to explain the flat mass
profiles in galaxies. Our result is only an order-of-magnitude estimate which
involves a number of simplifying, but always conservative, assumptions;
stronger constraints may be derived using hydrodynamic simulations of this
cluster.Comment: Text clarified; some numbers changed slightly for consistency with
final version of the accompanying lensing paper. 6 pages, uses emulateapj.
ApJ in pres
Too Little pH: How Freshwater Acidification Impacts the Abundance of Macrophytes Consumed by Rusty Crayfish
Anthropogenic activities such as the burning of fossil fuels result in increased atmospheric carbon dioxide (CO2) concentration. High levels of atmospheric CO2 cause chemical shifts in the carbon cycle. Changes in the carbon cycle due to increased CO2 levels lead to ocean and freshwater acidification. Freshwater acidification is problematic for species that synthesize their own shells as well as species that use olfaction for decision-making. Rusty crayfish (Faxonius rusticus) were subject to simulated freshwater acidification and fed two types of macrophyte, Chara (Chara braunii) and Myriopyllum (Myriophyllum sibiricum). A series of programming language of R (R Core Team, 2019) indicated that simulated freshwater acidification alters the abundance of macrophytes consumed by rusty crayfish. This study demonstrates that freshwater acidification due to atmospheric levels of CO2 leads to foraging changes in crayfish
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