144 research outputs found
Dust Abundance Variations in the Magellanic Clouds: Probing the Lifecycle of Metals with All-Sky Surveys
Observations and modeling suggest that the dust abundance (gas-to-dust ratio,
G/D) depends on (surface) density. The variations of the G/D provide
constraints on the timescales for the different processes involved in the
lifecycle of metals in galaxies. Recent G/D measurements based on Herschel data
suggest a factor 5---10 decrease in the dust abundance between the dense and
diffuse interstellar medium (ISM) in the Magellanic Clouds. However, the
relative nature of the Herschel measurements precludes definitive conclusions
on the magnitude of those variations. We investigate the variations of the dust
abundance in the LMC and SMC using all-sky far-infrared surveys, which do not
suffer from the limitations of Herschel on their zero-point calibration. We
stack the dust spectral energy distribution (SED) at 100, 350, 550, and 850
microns from IRAS and Planck in intervals of gas surface density, model the
stacked SEDs to derive the dust surface density, and constrain the relation
between G/D and gas surface density in the range 10---100 \Msu pc on
80 pc scales. We find that G/D decreases by factors of 3 (from 1500 to
500) in the LMC and 7 (from 1.5 to 2000) in the SMC between the
diffuse and dense ISM. The surface density dependence of G/D is consistent with
elemental depletions and with simple modeling of the accretion of gas-phase
metals onto dust grains. This result has important implications for the
sub-grid modeling of galaxy evolution, and for the calibration of dust-based
gas mass estimates, both locally and at high-redshift.Comment: 20 pages, 14 figure
Serendipity observations of far infrared cirrus emission in the Spitzer Infrared Nearby Galaxies Survey: Analysis of far-infrared correlations
We present an analysis of far-infrared dust emission from diffuse cirrus
clouds. This study is based on serendipitous observations at 160 microns at
high galactic latitude with the Multiband Imaging Photometer (MIPS) onboard the
Spitzer Space Telescope by the Spitzer Infrared Nearby Galaxies Survey (SINGS).
These observations are complemented with IRIS data at 100 and 60 microns and
constitute one of the most sensitive and unbiased samples of far infrared
observations at small scale of diffuse interstellar clouds. Outside regions
dominated by the cosmic infrared background fluctuations, we observe a
substantial scatter in the 160/100 colors from cirrus emission. We compared the
160/100 color variations to 60/100 colors in the same fields and find a trend
of decreasing 60/100 with increasing 160/100. This trend can not be accounted
for by current dust models by changing solely the interstellar radiation field.
It requires a significant change of dust properties such as grain size
distribution or emissivity or a mixing of clouds in different physical
conditions along the line of sight. These variations are important as a
potential confusing foreground for extragalactic studies.Comment: 25 pages, 7 figures, 2 tables, accepted to Ap
Extinction map of the Small Magellanic Cloud based on SIRIUS and 6X 2MASS point source catalogs
In this paper, we present the first extinction map of the Small Magellanic Cloud (SMC) constructed using the color excess at near-infrared wavelengths. Using a new technique named "X percentile method", which we developed recently to measure the color excess of dark clouds embedded within a star distribution, we have derived an E(J – H) map based on the SIRIUS and 6X Two Micron All Sky Survey (2MASS) star catalogs. Several dark clouds are detected in the map derived from the SIRIUS star catalog, which is deeper than the 6X 2MASS catalog. We have compared the E(J – H) map with a model calculation in order to infer the locations of the clouds along the line of sight, and found that many of them are likely to be located in or elongated toward the far side of the SMC. Most of the dark clouds found in the E(J – H) map have counterparts in the CO clouds detected by Mizuno et al. with the NANTEN telescope. A comparison of the E(J – H) map with the virial mass derived from the CO data indicates that the dust-to-gas ratio in the SMC varies in the range A_V /N_H = 1-2 × 10^(–22) mag H^-1 cm^2 with a mean value of ~1.5 × 10^(–22) mag H^-1 cm^2. If the virial mass underestimates the true cloud mass by a factor of ~2, as recently suggested by Bot et al., the mean value would decrease to ~8×10^(–23) mag H^-1 cm^2, in good agreement with the value reported by Gordon et al., 7.59 × 10^(–23) mag H^-1 cm^2
The Spitzer Survey of the Small Magellanic Cloud: FIR Emission and Cold Gas in the SMC
We present new far infrared maps of the Small Magellanic Cloud (SMC) at 24,
70, and 160 microns obtained as part of the Spitzer Survey of the Small
Magellanic Cloud (S3MC,Bolatto et al. 2006). These maps cover most of the
active star formation in the SMC Bar and the more quiescent Wing. We combine
our maps with literature data to derive the dust surface density across the
SMC. We find a total dust mass of Mdust = 3 10^5 Msun, implying a
dust-to-hydrogen ratio over the region studied of log D/H = -2.86, or 1-to-700,
which includes H_2. Assuming the dust to trace the total gas column, we derive
H_2 surface densities across the SMC. We find a total H_2 mass M_H2 = 3.2 10^7
Msun in a distribution similar to that of the CO, but more extended. We compare
profiles of CO and H_2 around six molecular peaks and find that on average H_2
is more extended than CO by a factor of \sim 1.3. The implied CO-to-H_2
conversion factor over the whole SMC is XCO = 13 +/- 1 10^21 cm^-2 (K km/s)^-1.
Over the volume occupied by CO we find a lower conversion factor, XCO = 6 +/- 1
10^21 cm^-2 (K km/s)^-1, which is still a few times larger than that found
using virial mass methods. The molecular peaks have H_2 surface densities
\Sigma_H2 \approx 180 +/- 30 Msun pc^-2, similar to those in Milky Way GMCs,
and correspondingly low extinctions, A_V \sim 1 - 2 mag. To reconcile these
measurements with predictions by the theory of photoionization-regulated star
formation, which requires A_V \sim 6, the GMCs must be \sim 3 times smaller
than our 46 pc resolution element. We find that for a given hydrostatic gas
pressure, the SMC has a 2 - 3 times lower ratio of molecular to atomic gas than
spiral galaxies. Combined with the lower mean densities in the SMC this may
explain why this galaxy has only 10% of its gas in the molecular phase.Comment: 24 pages, 16 figures, accepted by ApJ. A version with nice figures is
available at http://celestial.berkeley.edu/spitzer/publications
The Relationship Between Molecular Gas, HI, and Star Formation in the Low-Mass, Low-Metallicity Magellanic Clouds
The Magellanic Clouds provide the only laboratory to study the effect of
metallicity and galaxy mass on molecular gas and star formation at high (~20
pc) resolution. We use the dust emission from HERITAGE Herschel data to map the
molecular gas in the Magellanic Clouds, avoiding the known biases of CO
emission as a tracer of H. Using our dust-based molecular gas estimates,
we find molecular gas depletion times of ~0.4 Gyr in the LMC and ~0.6 SMC at 1
kpc scales. These depletion times fall within the range found for normal disk
galaxies, but are shorter than the average value, which could be due to recent
bursts in star formation. We find no evidence for a strong intrinsic dependence
of the molecular gas depletion time on metallicity. We study the relationship
between gas and star formation rate across a range in size scales from 20 pc to
~1 kpc, including how the scatter in molecular gas depletion time changes with
size scale, and discuss the physical mechanisms driving the relationships. We
compare the metallicity-dependent star formation models of Ostriker, McKee, and
Leroy (2010) and Krumholz (2013) to our observations and find that they both
predict the trend in the data, suggesting that the inclusion of a diffuse
neutral medium is important at lower metallicity.Comment: 24 pages, 14 figures, accepted for publication in ApJ. FITS files of
the dust-based estimates of the H2 column densities for the LMC and SMC
(shown in Figures 2 and 3) will be available online through Ap
Determinants of the clinical course of musculoskeletal complaints in general practice: design of a cohort study
BACKGROUND: Musculoskeletal complaints are frequent and have large consequences for public health. Information about the prognosis after presentation in general practice is far from complete. Knowledge about determinants of the clinical course of musculoskeletal complaints is essential for management decisions and to inform patients about their prognosis. The purpose of this study is to provide information about the prognosis of musculoskeletal complaints other than low back pain by studying the course of these complaints in general practice and to identify determinants of this course. METHODS: Patients of 18 years and older, who present in general practice with a new episode of a musculoskeletal complaint of the neck, shoulder, elbow, wrist, hand, arm, hip, knee, ankle or foot, are recruited by their general practitioner (GP). Participants will receive complaint-specific questionnaires by mail at baseline and after 3, 6, 12 and 18 months. The following putative determinants of the course of the complaints will be investigated: sociodemographic characteristics, characteristics of the complaint, psychosocial job characteristics, physical workload, physical activity during leisure time, pain coping, mood, kinesiophobia, social support, optimism. The primary outcomes are perceived recovery, pain, functional status, sick leave and overall quality of life
Resource use and costs of type 2 diabetes patients receiving managed or protocolized primary care:A controlled clinical trial
Background: The increasing prevalence of diabetes is associated with increased health care use and costs. Innovations to improve the quality of care, manage the increasing demand for health care and control the growth of health care costs are needed. The aim of this study is to evaluate the care process and costs of managed, protocolized and usual care for type 2 diabetes patients from a societal perspective. Methods. In two distinct regions of the Netherlands, both managed and protocolized diabetes care were implemented. Managed care was characterized by centralized organization, coordination, responsibility and centralized annual assessment. Protocolized care had a partly centralized organizational structure. Usual care was characterized by a decentralized organizational structure. Using a quasi-experimental control group pretest-posttest design, the care process (guideline adherence) and costs were compared between managed (n = 253), protocolized (n = 197), and usual care (n = 333). We made a distinction between direct health care costs, direct non-health care costs and indirect costs. Multivariate regression models were used to estimate differences in costs adjusted for confounding factors. Because of the skewed distribution of the costs, bootstrapping methods (5000 replications) with a bias-corrected and accelerated approach were used to estimate 95% confidence intervals (CI) around the differences in costs. Results: Compared to usual and protocolized care, in managed care more patients were treated according to diabetes guidelines. Secondary health care use was higher in patients under usual care compared to managed and protocolized care. Compared to usual care, direct costs were significantly lower in managed care (-1.181 (95% CI: -2.597 to -334)) while indirect costs were higher (758 (95% CI: -353 to 2.701), although not significant. Direct, indirect and total costs were lower in protocolized care compared to usual care (though not significantly). Conclusions: Compared to usual care, managed care was significantly associated with better process in terms of diabetes care, fewer secondary care consultations and lower health care costs. The same trends were seen for protocolized care, however they were not statistically significant. Trial registration. Current Controlled trials: ISRCTN66124817. © 2014 van der Heijden et al.; licensee BioMed Central Ltd
The Quest for the Missing Dust: II -- Two Orders of Magnitude of Evolution in the Dust-to-Gas Ratio Resolved Within Local Group Galaxies
We explore evolution in the dust-to-gas ratio with density within four
well-resolved Local Group galaxies - the LMC, SMC, M31, and M33. We do this
using new maps, which restore extended emission that was
missed by previous reductions. This improved data allows us to
probe the dust-to-gas ratio across 2.5 orders of magnitude in ISM surface
density. We find significant evolution in the dust-to-gas ratio, with
dust-to-gas varying with density within each galaxy by up to a factor 22.4. We
explore several possible reasons for this, and our favored explanation is dust
grain growth in denser regions of ISM. We find that the evolution of the
dust-to-gas ratio with ISM surface density is very similar between M31 and M33,
despite their large differences in mass, metallicity, and star formation rate;
conversely, we find M33 and the LMC to have very different dust-to-gas
evolution profiles, despite their close similarity in those properties. Our
dust-to-gas ratios address previous disagreement between UV- and FIR-based
dust-to-gas estimates for the Magellanic Clouds, removing the disagreement for
the LMC, and considerably reducing it for the SMC - with our new dust-to-gas
measurements being factors of 2.4 and 2.0 greater than the previous
far-infrared estimates, respectively. We also observe that the dust-to-gas
ratio appears to fall at the highest densities for the LMC, M31, and M33; this
is unlikely to be an actual physical phenomenon, and we posit that it may be
due to a combined effect of dark gas, and changing dust mass opacity.Comment: Accepted for publication in the Astrophysical Journa
Molecular hydrogen emission in the interstellar medium of the Large Magellanic Cloud
We present the detection and analysis of molecular hydrogen emission toward
ten interstellar regions in the Large Magellanic Cloud. We examined
low-resolution infrared spectral maps of twelve regions obtained with the
Spitzer infrared spectrograph (IRS). The pure rotational 0--0 transitions of
H at 28.2 and 17.1 are detected in the IRS spectra for ten
regions. The higher level transitions are mostly upper limit measurements
except for three regions, where a 3 detection threshold is achieved for
lines at 12.2 and 8.6. The excitation diagrams of the detected
H transitions are used to determine the warm H gas column density and
temperature. The single-temperature fits through the lower transition lines
give temperatures in the range . The bulk of the excited H
gas is found at these temperatures and contributes 5-17% to the total gas
mass. We find a tight correlation of the H surface brightness with
polycyclic aromatic hydrocarbon and total infrared emission, which is a clear
indication of photo-electric heating in photodissociation regions. We find the
excitation of H by this process is equally efficient in both atomic and
molecular dominated regions. We also present the correlation of the warm H
physical conditions with dust properties. The warm H mass fraction and
excitation temperature show positive correlations with the average starlight
intensity, again supporting H excitation in photodissociation regions.Comment: Accepted for publication in MNRA
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