919 research outputs found
Metal Transport to the Gaseous Outskirts of Galaxies
We present a search for outlying H II regions in the extended gaseous outskirts of nearby ( D < 40 Mpc) galaxies and subsequent multi-slit spectroscopy used to obtain the H II region nebular oxygen abundances. The galaxies in our sample have extended H I disks and/or interaction-related H I features that extend well beyond their primary stellar components. We report oxygen abundance gradients out to 2.5 times the optical radius for these galaxies which span a range of morphologies and masses. We analyze the underlying stellar and neutral H I gas distributions in the vicinity of the H II regions to understand the physical processes that give rise to the observed metal distributions in galaxies. These measurements, for the first time, convincingly show flat abundance distributions out to large radii in a wide variety of systems and have broad implications for galaxy chemodynamical evolution.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90754/1/0004-637X_735_2_71.pd
Effect of Testing and Treatment on Emergency Department Length of Stay Using a National Database
Objectives: Testing and treatment are essential aspects of the delivery of emergency care. Recognition of the effects of these activities on emergency department (ED) length of stay (LOS) has implications for administrators planning efficient operations, providers, and patients regarding expectations for length of visit; researchers in creating better models to predict LOS; and policy‐makers concerned about ED crowding. Methods: A secondary analysis was performed using years 2006 through 2008 of the National Hospital Ambulatory Medical Care Survey (NHAMCS), a nationwide study of ED services. In univariate and bivariate analyses, the authors assessed ED LOS and frequency of testing (blood test, urinalysis, electrocardiogram [ECG], radiograph, ultrasound, computed tomography [CT], or magnetic resonance imaging [MRI]) and treatment (providing a medication or performance of a procedure) according to disposition (discharged or admitted status). Two sets of multivariable models were developed to assess the contribution of testing and treatment to LOS, also stratified by disposition. The first was a series of logistic regression models to provide an overview of how testing and treatment activity affects three dichotomized LOS cutoffs at 2, 4, and 6 hours. The second was a generalized linear model (GLM) with a log‐link function and gamma distribution to fit skewed LOS data, which provided time costs associated with tests and treatment. Results: Among 360 million weighted ED visits included in this analysis, 227 million (63%) involved testing, 304 million (85%) involved treatment, and 201 million (56%) involved both. Overall, visits with any testing were associated with longer LOS (median = 196 minutes; interquartile range [IQR] = 125 to 305 minutes) than those with any treatment (median = 159 minutes; IQR = 91 to 262 minutes). This difference was more pronounced among discharged patients than admitted patients. Obtaining a test was associated with an adjusted odds ratio (OR) of 2.29 (95% confidence interval [CI] = 1.86 to 2.83) for experiencing a more than 4‐hour LOS, while performing a treatment had no effect (adjusted OR = 0.84; 95% CI = 0.68 to 1.03). The most time‐costly testing modalities included blood test (adjusted marginal effects on LOS = +72 minutes; 95% CI = 66 to 78 minutes), MRI (+64 minutes; 95% CI = 36 to 93 minutes), CT (+59 minutes; 95% CI = 54 to 65 minutes), and ultrasound (US; +56 minutes; 95% CI = 45 to 67 minutes). Treatment time costs were less substantial: performing a procedure (+24 minutes; 95% CI = 20 to 28 minutes) and providing a medication (+15 minutes; 95% CI = 8 to 21 minutes). Conclusions: Testing and less substantially treatment were associated with prolonged LOS in the ED, particularly for blood testing and advanced imaging. This knowledge may better direct efforts at streamlining delivery of care for the most time‐costly diagnostic modalities or suggest areas for future research into improving processes of care. Developing systems to improve efficient utilization of these services in the ED may improve patient and provider satisfaction. Such practice improvements could then be examined to determine their effects on ED crowding.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/92123/1/j.1553-2712.2012.01353.x.pd
On the Escape of Ionizing Radiation from Starbursts
Far-ultraviolet spectra obtained with show that the strong
1036 interstellar absorption-line is essentially black in five of
the UV-brightest local starburst galaxies. Since the opacity of the neutral ISM
below the Lyman-edge will be significantly larger than in the line, these
data provide strong constraints on the escape of ionizing radiation from these
starbursts. Interpreted as a a uniform absorbing slab, the implied optical
depth at the Lyman edge is huge (). Alternatively, the areal
covering factor of opaque material is typically 94%. Thus, the fraction
of ionizing stellar photons that escape the ISM of each galaxy is small: our
conservative estimates typically yield . Inclusion of
extinction due to dust will further decrease . An analogous analysis
of the rest-UV spectrum of the star-forming galaxy at =2.7
leads to similar constraints on . These new results agree with the
constraints provided by direct observations below the Lyman edge in a few other
local starbursts. However, they differ from the recently reported properties of
star-forming galaxies at 3. We assess the idea that the strong
galactic winds seen in many powerful starbursts clear channels through their
neutral ISM. We show empirically that such outflows may be a necessary - but
not sufficient - part of the process for creating a relatively porous ISM. We
note that observations will soon document the cosmic evolution in the
contribution of star-forming galaxies to the metagalactic ionizing background,
with important implications for the evolution of the IGM.Comment: 17 pages; ApJ, in pres
The Metal-Enriched Outer Disk of NGC 2915
We present optical emission-line spectra for outlying HII regions in the
extended neutral gas disk surrounding the blue compact dwarf galaxy NGC 2915.
Using a combination of strong-line R23 and direct oxygen abundance
measurements, we report a flat, possibly increasing, metallicity gradient out
to 1.2 times the Holmberg radius. We find the outer-disk of NGC 2915 to be
enriched to a metallicity of 0.4 Z_solar. An analysis of the metal yields shows
that the outer disk of NGC 2915 is overabundant for its gas fraction, while the
central star-foming core is similarly under-abundant for its gas fraction. Star
formation rates derived from very deep ~14 ks GALEX FUV exposures indicate that
the low-level of star formation observed at large radii is not sufficient to
have produced the measured oxygen abundances at these galactocentric distances.
We consider 3 plausible mechanisms that may explain the metal-enriched outer
gaseous disk of NGC 2915: radial redistribution of centrally generated metals,
strong galactic winds with subsequent fallback, and galaxy accretion. Our
results have implications for the physical origin of the mass-metallicity
relation for gas-rich dwarf galaxies.Comment: 11 pages, 4 figures, accepted to ApJ April 8th, 201
Isolated OB Associations in Stripped HI Gas Clouds
HST ACS/HRC images in UV (F250W), V (F555W), and I (F814W) resolve three
isolated OB associations that lie up to 30 kpc from the stellar disk of the S0
galaxy NGC 1533. Previous narrow-band Halpha imaging and optical spectroscopy
showed these objects as unresolved intergalactic HII regions having Halpha
luminosities consistent with single early-type O stars. These young stars lie
in stripped HI gas with column densities ranging from 1.5 - 2.5 * 10^20 cm^-2
and velocity dispersions near 30 km s^-1. Using the HST broadband colors and
magnitudes along with previously-determined Halpha luminosities, we place
limits on the masses and ages of each association, considering the importance
of stochastic effects for faint (M_V >-8) stellar populations. The upper limits
to their stellar masses range from 600 M_sun to 7000 M_sun, and ages range from
2 - 6 Myrs. This analysis includes an updated calculation of the conversion
factor between the ionizing luminosity and the total number of main sequence O
stars contained within an HII region. The photometric properties and sizes of
the isolated associations and other objects in the HRC fields are consistent
with those of Galactic stellar associations, open clusters and/or single O and
B stars. We interpret the age-size sequence of associations and clustered field
objects as an indication that these isolated associations are most likely
rapidly dispersing. Furthermore, we consider the possibility that these
isolated associations represent the first generation of stars in the HI ring
surrounding NGC 1533. This work suggests star formation in the unique
environment of a galaxy's outermost gaseous regions proceeds similarly to that
within the Galactic disk and that star formation in tidal debris may be
responsible for building up a younger halo component.Comment: 21 pages, 9 figures, 6 tables; accepted for publication in Ap
The Rich Globular Cluster System of Abell 1689 and the Radial Dependence of the Globular Cluster Formation Efficiency
We study the rich globular cluster (GC) system in the center of the massive
cluster of galaxies Abell 1689 (z=0.18), one of the most powerful gravitational
lenses known. With 28 HST/ACS orbits in the F814W bandpass, we reach magnitude
I_814=29 with >90% completeness and sample the brightest ~5% of the GC system.
Assuming the well-known Gaussian form of the GC luminosity function (GCLF), we
estimate a total population of N(GC_total) = 162,850 GCs within a projected
radius of 400kpc. As many as half may comprise an intracluster component. Even
with the sizable uncertainties, which mainly result from the uncertain GCLF
parameters, this is by far the largest GC system studied to date. The specific
frequency S_N is high, but not uncommon for central galaxies in massive
clusters, rising from S_N~5 near the center to ~12 at large radii. Passive
galaxy fading would increase S_N by ~20% at z=0. We construct the radial mass
profiles of the GCs, stars, intracluster gas, and lensing-derived total mass,
and we compare the mass fractions as a function of radius. The estimated mass
in GCs, M(GC_total)=3.9x10^10 Msun, is comparable to ~80% of the total stellar
mass of the Milky Way. The shape of the GC mass profile appears intermediate
between those of the stellar light and total cluster mass. Despite the extreme
nature of this system, the ratios of the GC mass to the baryonic and total
masses, and thus the GC formation efficiency, are typical of those in other
rich clusters when comparing at the same physical radii. The GC formation
efficiency is not constant, but varies with radius, in a manner that appears
similar for different clusters; we speculate on the reasons for this similarity
in profile.Comment: 13 pages, 11 figures; accepted for publication in Ap
Evaluation of medical professionals' knowledge about Q fever.
Aims: evaluate the medical professionals’ knowledge about Q fever, seeking integrative contributions to public health that may favor the formulation of policies and the development of strategies based on a One Health approach. Methods: this is a cross-sectional and quantitative study with data collection through a structured questionnaire applied face-to-face to physicians from various clinical specialties working at the three levels of health care in Brazil. The questionnaire consisted of 25 questions, seven of which were specific to assessing knowledge about Q fever. Univariate and multivariate logistic regression analyses were conducted to assess whether the variables medical specialty, level of health care in which they work, age range and gender were associated with a correct answer to at least one specific question about Q fever. Results: among the 254 physicians included, 236 (92.9%) were unaware of Q fever. Only three (16.6%) of the 18 who correctly answered at least one specific question about the disease had a score of more than 50%. The highest rates of correct answers for at least one question (p < 0.0001) occurred among the medical specialties most related to clinical signs and symptoms or the differential diagnosis of Q fever and among males. It is highlighted that 85.8% of physicians consider Q fever a neglected and underreported disease in Brazil. Additionally, all physicians responded that they were not aware of the One Health approach. Conclusions: the almost total lack of knowledge among medical professionals regarding Q fever reinforces the need for greater disclosure for this zoonosis with a One Health approach in Medical Schools, in Residency Programs and for physicians in general. In addition, the inclusion of Q fever in the national list of notifiable diseases becomes relevant, allowing a better understanding of its epidemiological situation in Brazil. Finally, effective public health actions must be carried out to avoid underdiagnosis and the development of severe cases of the disease
Outlying HII Regions in HI-Selected Galaxies
We present results from the first systematic search for outlying HII regions,
as part of a sample of 96 emission-line point sources (referred to as ELdots -
emission-line dots) derived from the NOAO Survey for Ionization in Neutral Gas
Galaxies (SINGG). Our automated ELdot-finder searches SINGG narrow-band and
continuum images for high equivalent width point sources outside the optical
radius of the target galaxy (> 2 X r25 in the R-band). Follow-up longslit
spectroscopy and deep GALEX images (exposure time > 1000 s) distinguish
outlying HII regions from background galaxies whose strong emission lines
([OIII], Hbeta or [OII]) have been redshifted into the SINGG bandpass. We find
that these deep GALEX images can serve as a substitute for spectroscopic
follow-up because outlying HII regions separate cleanly from background
galaxies in color-color space. We identify seven SINGG systems with outlying
massive star formation that span a large range in Halpha luminosities
corresponding to a few O stars in the most nearby cases, and unresolved dwarf
satellite companion galaxies in the most distant cases. Six of these seven
systems feature galaxies with nearby companions or interacting galaxies.
Furthermore, our results indicate that some outlying HII regions are linked to
the extended-UV disks discovered by GALEX, representing emission from the most
massive O stars among a more abundant population of lower mass (or older) star
clusters. The overall frequency of outlying HII regions in this sample of
gas-rich galaxies is 8 - 11% when we correct for background emission-line
galaxy contamination (~75% of ELdots).Comment: 20 pages, 14 Figures, Accepted by A
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