850 research outputs found
XMM-Newton Detects a Hot Gaseous Halo in the Fastest Rotating Spiral Galaxy UGC 12591
We present our XMM-Newton observation of the fastest rotating spiral galaxy
UGC 12591. We detect hot gas halo emission out to 110 kpc from the galaxy
center, and constrain the halo gas mass to be smaller than 3.5e11 solar masses.
We also measure the temperature of the hot gas as T=0.64\pm0.03 keV. Combining
our X-ray constraints and the near-infrared and radio measurements in the
literature, we find a baryon mass fraction of 0.03-0.04 in UGC 12591,
suggesting a missing baryon mass of 75% compared with the cosmological mean
value. Combined with another recent measurement in NGC 1961, the result
strongly argues that the majority of missing baryons in spiral galaxies does
not reside in their hot halos. We also find that UGC 12591 lies significantly
below the baryonic Tully-Fisher relationship. Finally, we find that the baryon
fractions of massive spiral galaxies are similar to those of galaxy groups with
similar masses, indicating that the baryon loss is ultimately controlled by the
gravitational potential well. The cooling radius of this gas halo is small,
similar to NGC 1961, which argues that the majority of stellar mass of this
galaxy is not assembled as a result of cooling of this gas halo.Comment: 20 pages, 8 figures, submitted to Ap
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Associations of Fine Particulate Matter Species with Mortality in the United States: A Multicity Time-Series Analysis
Background: Epidemiological studies have examined the association between PM2.5 and mortality, but uncertainty remains about the seasonal variations in PM2.5-related effects and the relative importance of species. Objectives: We estimated the effects of PM2.5 species on mortality and how infiltration rates may modify the association. Methods: Using city–season specific Poisson regression, we estimated PM2.5 effects on approximately 4.5 million deaths for all causes, cardiovascular disease (CVD), myocardial infarction (MI), stroke, and respiratory diseases in 75 U.S. cities for 2000–2006. We added interaction terms between PM2.5 and monthly average species-to-PM2.5 proportions of individual species to determine the relative toxicity of each species. We combined results across cities using multivariate meta-regression, and controlled for infiltration. Results: We estimated a 1.18% (95% CI: 0.93, 1.44%) increase in all-cause mortality, a 1.03% (95% CI: 0.65, 1.41%) increase in CVD, a 1.22% (95% CI: 0.62, 1.82%) increase in MI, a 1.76% (95% CI: 1.01, 2.52%) increase in stroke, and a 1.71% (95% CI: 1.06, 2.35%) increase in respiratory deaths in association with a 10-μg/m3 increase in 2-day averaged PM2.5 concentration. The associations were largest in the spring. Silicon, calcium, and sulfur were associated with more all-cause mortality, whereas sulfur was related to more respiratory deaths. County-level smoking and alcohol were associated with larger estimated PM2.5 effects. Conclusions: Our study showed an increased risk of mortality associated with PM2.5, which varied with seasons and species. The results suggest that mass alone might not be sufficient to evaluate the health effects of particles. Citation: Dai L, Zanobetti A, Koutrakis P, Schwartz JD. 2014. Associations of fine particulate matter species with mortality in the United States: a multicity time-series analysis. Environ Health Perspect 122:837–842; http://dx.doi.org/10.1289/ehp.130756
On the Baryon Fractions in Clusters and Groups of Galaxies
We present the baryon fractions of 2MASS groups and clusters as a function of
cluster richness using total and gas masses measured from stacked ROSAT X-ray
data and stellar masses estimated from the infrared galaxy catalogs. We detect
X-ray emission even in the outskirts of clusters, beyond r_200 for richness
classes with X-ray temperatures above 1 keV. This enables us to more accurately
determine the total gas mass in these groups and clusters. We find that the
optically selected groups and clusters have flatter temperature profiles and
higher stellar-to-gas mass ratios than the individually studied, X-ray bright
clusters. We also find that the stellar mass in poor groups with temperatures
below 1 keV is comparable to the gas mass in these systems. Combining these
results with individual measurements for clusters, groups, and galaxies from
the literature, we find a break in the baryon fraction at ~1 keV. Above this
temperature, the baryon fraction scales with temperature as f_b \propto
T^0.20\pm0.03. We see significantly smaller baryon fractions below this
temperature, and the baryon fraction of poor groups joins smoothly onto that of
systems with still shallower potential wells such as normal and dwarf galaxies
where the baryon fraction scales with the inferred velocity dispersion as f_b
\propto \sigma^1.6. The small scatter in the baryon fraction at any given
potential well depth favors a universal baryon loss mechanism and a preheating
model for the baryon loss. The scatter is, however, larger for less massive
systems. Finally, we note that although the broken power-law relation can be
inferred from data points in the literature alone, the consistency between the
baryon fractions for poor groups and massive galaxies inspires us to fit the
two categories of objects (galaxies and clusters) with one relation.Comment: 21 pages, 5 figures, ApJ in pres
A radio continuum study of NGC 2082
We present radio continuum observations of NGC 2082 using ASKAP, ATCA and Parkes telescopes from 888 MHz to 9000 MHz. Some 20 arcsec from the centre of this nearby spiral galaxy, we discovered a bright and compact radio source, J054149.24–641813.7, of unknown origin. To constrain the nature of J054149.24–641813.7, we searched for transient events with the Ultra-Wideband Low Parkes receiver, and compare its luminosity and spectral index to various nearby supernova remnants (SNRs), and fast radio burst (FRB) local environments. Its radio spectral index is flat (α = 0.02 ± 0.09), which is unlikely to be either an SNR or pulsar. No transient events were detected with the Parkes telescope over three days of observations, and our calculations show J054149.24–641813.7 is two orders of magnitude less luminous than the persistent radio sources associated with FRB 121102 and 190520B. We find that the probability of finding such a source behind NGC 2082 is P = 1.2%, and conclude that the most likely origin for J054149.24–641813.7 is a background quasar or radio galaxy
The Extended Distribution of Baryons Around Galaxies
We summarize and reanalyze observations bearing upon missing galactic
baryons, where we propose a consistent picture for halo gas in L >~ L*
galaxies. The hot X-ray emitting halos are detected to 50-70 kpc, where
typically, M_hot(<50 kpc) ~ 5E9 Msun, and with density n \propto r^-3/2. When
extrapolated to R200, the gas mass is comparable to the stellar mass, but about
half of the baryons are still missing from the hot phase. If extrapolated to
1.9-3 R200, the baryon to dark matter ratio approaches the cosmic value.
Significantly flatter density profiles are unlikely for R < 50 kpc and they are
disfavored but not ruled out for R > 50 kpc. For the Milky Way, the hot halo
metallicity lies in the range 0.3-1 solar for R < 50 kpc. Planck measurements
of the thermal Sunyaev-Zeldovich effect toward stacked luminous galaxies
(primarily early-type) indicate that most of their baryons are hot, near the
virial temperature, and extend beyond R200. This stacked SZ signal is nearly an
order of magnitude larger than that inferred from the X-ray observations of
individual (mostly spiral) galaxies with M_* > 10^11.3 Msun. This difference
suggests that the hot halo properties are distinct for early and late type
galaxies, possibly due to different evolutionary histories. For the cooler gas
detected in UV absorption line studies, we argue that there are two absorption
populations: extended halos; and disks extending to ~50 kpc, containing most of
this gas, and with masses a few times lower than the stellar masses. Such
extended disks are also seen in 21 cm HI observations and in simulations.Comment: 22 pages, 20 figures, 2 tables, submitted to Ap
A Novel Approach to Interface High-Q Fabry-P\'erot Resonators with Photonic Circuits
The unique benefits of Fabry-P\'erot resonators as frequency-stable reference
cavities and as an efficient interface between atoms and photons make them an
indispensable resource for emerging photonic technologies. To bring these
performance benefits to next-generation communications, computation, and
timekeeping systems, it will be necessary to develop strategies to integrate
compact Fabry-P\'erot resonators with photonic integrated circuits. In this
paper, we demonstrate a novel reflection cancellation circuit that utilizes a
numerically optimized multi-port polarization-splitting grating coupler to
efficiently interface high-finesse Fabry-P\'erot resonators with a silicon
photonic circuit. This circuit interface produces spatial separation of the
incident and reflected waves, as required for on-chip Pound-Drever-Hall
frequency locking, while also suppressing unwanted back reflections from the
Fabry-P\'erot resonator. Using inverse design principles, we design and
fabricate a polarization-splitting grating coupler that achieves 55% coupling
efficiency. This design realizes an insertion loss of 5.8 dB for the circuit
interface and more than 9 dB of back reflection suppression, and we demonstrate
the versatility of this system by using it to interface several reflective
off-chip devices
Construction of New Active Sites: Cu Substitution Enabled Surface Frustrated Lewis Pairs over Calcium Hydroxyapatite for CO Hydrogenation
Calcium hydroxyphosphate, Ca(PO)(OH), is commonly known as hydroxyapatite (HAP). The acidic calcium and basic phosphate/hydroxide sites in HAP can be modified via isomorphous substitution of calcium and/or hydroxide ions to enable a cornucopia of catalyzed reactions. Herein, isomorphic substitution of Ca ions by Cu ions especially at very low levels of exchange created new analogs of molecular surface frustrated Lewis pairs (SFLPs) in CuCa(PO)(OH), thereby boosting its performance metrics in heterogeneous CO photocatalytic hydrogenation. In situ Fourier transform infrared spectroscopy characterization and density functional theory calculations provided fundamental insights into the catalytically active SFLPs defined as proximal Lewis acidic Cu and Lewis basic OH. The photocatalytic pathway proceeds through a formate reaction intermediate, which is generated by the reaction of CO with heterolytically dissociated H on the SFLPs. Given the wealth of information thus uncovered, it is highly likely that this work will spur the further development of similar classes of materials, leading to the advancement and, ultimately, large-scale application of photocatalytic CO reduction technologies
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