9,081 research outputs found
Free-free and H42alpha emission from the dusty starburst within NGC 4945 as observed by ALMA
We present observations of the 85.69 GHz continuum emission and H42alpha line
emission from the central 30 arcsec within NGC 4945. Both sources of emission
originate from nearly identical structures that can be modelled as exponential
discs with a scale length of ~2.1 arcsec (or ~40 pc). An analysis of the
spectral energy distribution based on combining these data with archival data
imply that 84% +/- 10% of the 85.69 GHz continuum emission originates from
free-free emission. The electron temperature is 5400 +/- 600 K, which is
comparable to what has been measured near the centre of the Milky Way Galaxy.
The star formation rate (SFR) based on the H42alpha and 85.69 GHz free-free
emission (and using a distance of 3.8 Mpc) is 4.35 +/- 0.25 M/yr. This is
consistent with the SFR from the total infrared flux and with previous
measurements based on recombination line emission, and it is within a factor of
~2 of SFRs derived from radio data. The Spitzer Space Telescope 24 micron data
and Wide-field Infrared Survey Explorer 22 micron data yield SFRs ~10x lower
than the ALMA measurements, most likely because the mid-infrared data are
strongly affected by dust attenuation equivalent to A_V=150. These results
indicate that SFRs based on mid-infrared emission may be highly inaccurate for
dusty, compact circumnuclear starbursts.Comment: 19 pages, 9 figures, accepted for publication in MNRA
ALMA observations of 99 GHz free-free and H40 line emission from star formation in the centre of NGC 253
We present Atacama Large Millimeter/submillimeter Array observations of 99.02
GHz free-free and H40 emission from the centre of the nearby starburst
galaxy NGC 253. We calculate electron temperatures of 3700-4500 K for the
photoionized gas, which agrees with previous measurements. We measure a
photoionizing photon production rate of s and
a star formation rate of M yr within the central
2010 arcsec, which fall within the broad range of measurements from
previous millimetre and radio observations but which are better constrained. We
also demonstrate that the dust opacities are ~3 dex higher than inferred from
previous near-infrared data, which illustrates the benefits of using millimetre
star formation tracers in very dusty sources.Comment: 5 pages, 3 figures, accepted for publication in MNRAS Letter
Senior Programmers: Characteristics of Elderly Users from Stack Overflow
In this paper we presents results of research about elderly users of Stack
Overflow (Question and Answer portal for programmers). They have different
roles, different main activities and different habits. They are an important
part of the community, as they tend to have higher reputation and they like to
share their knowledge. This is a great example of possible way of keeping
elderly people active and helpful for society
The B-Band Luminosity Function of Red and Blue Galaxies up to z=3.5
We have explored the redshift evolution of the luminosity function of red and
blue galaxies up to . This was possible joining a deep I band composite
galaxy sample, which includes the spectroscopic K20 sample and the HDFs
samples, with the deep and samples derived from the
deep NIR images of the Hubble Deep Fields North and South, respectively. About
30% of the sample has spectroscopic redshifts and the remaining fraction
well-calibrated photometric redshifts. This allowed to select and measure
galaxies in the rest-frame blue magnitude up to and to derive the
redshift evolution of the B-band luminosity function of galaxies separated by
their rest-frame color or specific (i.e. per unit mass) star-formation
rate. The class separation was derived from passive evolutionary tracks or from
their observed bimodal distributions. Both distributions appear bimodal at
least up to and the locus of red/early galaxies is clearly identified
up to these high redshifts. Both luminosity and density evolutions are needed
to describe the cosmological behaviour of the red/early and blue/late
populations. The density evolution is greater for the early population with a
decrease by one order of magnitude at with respect to the value at
. The luminosity densities of the early and late type galaxies with
. Indeed while star-forming
galaxies slightly increase or keep constant their luminosity density, "early"
galaxies decrease in their luminosity density by a factor from
to . A comparison with one of the latest versions of
the hierarchical CDM models shows a broad agreement with the observed number
and luminosity density evolutions of both populations.Comment: 41 pages, 14 figures, accepted for publication in Ap
Tests of star formation metrics in the low metallicity galaxy NGC 5253 using ALMA observations of H30 line emission
We use Atacama Large Millimeter/submillimeter Array (ALMA) observations of
H30 (231.90 GHz) emission from the low metallicity dwarf galaxy NGC
5253 to measure the star formation rate (SFR) within the galaxy and to test the
reliability of SFRs derived from other commonly-used metrics. The H30
emission, which originates mainly from the central starburst, yields a
photoionizing photon production rate of (1.90.3)10 s
and an SFR of 0.0870.013 M yr based on conversions that
account for the low metallicity of the galaxy and for stellar rotation. Among
the other star formation metrics we examined, the SFR calculated from the total
infrared flux was statistically equivalent to the values from the H30
data. The SFR based on previously-published versions of the H flux that
were extinction corrected using Pa and Pa lines were lower than
but also statistically similar to the H30 value. The mid-infrared (22
m) flux density and the composite star formation tracer based on H
and mid-infrared emission give SFRs that were significantly higher because the
dust emission appears unusually hot compared to typical spiral galaxies.
Conversely, the 70 and 160 m flux densities yielded SFR lower than the
H30 value, although the SFRs from the 70 m and H30 data
were within 1-2 of each other. While further analysis on a broader
range of galaxies are needed, these results are instructive of the best and
worst methods to use when measuring SFR in low metallicity dwarf galaxies like
NGC 5253.Comment: 14 pages, 5 figures, accepted for publication in MNRA
Distribution of Non-uniform Demagnetization Fields in Paramagnetic Bulk Solids
A general calculation for the distribution of non-uniform demagnetization
fields in paramagnetic bulk solids is described and the fields for various
sample geometries are calculated. Cones, ellipsoids, paraboloids and
hyperboloids with similar sample aspect ratios are considered. Significant
differences in their demagnetization fields are observed. The calculation shows
that the demagnetization field magnitudes decrease along the axis of symmetry
(along ) where an externally applied magnetic field is aligned, and increase
in the vicinity of the lateral surfaces with the largest field values found in
the cone and the narrowest field distributions found in the hyperboloid.
Application is made to the theoretical modeling of the H-NMR spectra of a
single crystal of field-induced superconductor -(BETS)FeCl
with a rectangular sample geometry, providing a good fit to the measured NMR
spectra. This calculation is also applicable to diamagnetic or ferromagnetic
materials in general.Comment: 7 pages, 7 figures, submitted to Physical Review B (Corresponding
author: [email protected]
Using Decision Analysis to Improve Malaria Control Policy Making
Malaria and other vector-borne diseases represent a significant and growing burden in many tropical countries. Successfully addressing these threats will require policies that expand access to and use of existing control methods, such as insecticide-treated bed nets (ITNs) and artemesinin combination therapies (ACTs) for malaria, while weighing the costs and benefits of alternative approaches over time. This paper argues that decision analysis provides a valuable framework for formulating such policies and combating the emergence and re-emergence of malaria and other diseases. We outline five challenges that policy makers and practitioners face in the struggle against malaria, and demonstrate how decision analysis can help to address and overcome these challenges. A prototype decision analysis framework for malaria control in Tanzania is presented, highlighting the key components that a decision support tool should include. Developing and applying such a framework can promote stronger and more effective linkages between research and policy, ultimately helping to reduce the burden of malaria and other vector-borne diseases
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