3,308 research outputs found
AKARI near-infrared spectroscopy of the aromatic and aliphatic hydrocarbon emission features in the galactic superwind of M 82
Aims. We investigate the properties of hydrocarbon grains in the galactic
superwind of M 82. Methods. With AKARI, we performed near-infrared (2.5 - 4.5
um) spectroscopic observations of 34 regions in M 82 including its northern and
southern halos. Results. Many of the spectra show strong emission at 3.3 um due
to polycyclic aromatic hydrocarbons (PAHs) and relatively weak features at 3.4
- 3.6 um due to aliphatic hydrocarbons. In particular, we clearly detect the
PAH 3.3 um emission and the 3.4 - 3.6 um features in halo regions, which are
located at a distance of 2 kpc away from the galactic center. We find that the
ratios of the 3.4 - 3.6 um features to the 3.3 um feature intensity
significantly increase with distance from the galactic center, while the ratios
of the 3.3 um feature to the AKARI 7 um band intensity do not. Conclusions. Our
results clearly confirm the presence of small PAHs even in a harsh environment
of the halo of M 82. The results also reveal that the aliphatic hydrocarbons
emitting the 3.4 - 3.6 um features are unusually abundant in the halo,
suggesting that small carbonaceous grains are produced by shattering of larger
grains in the galactic superwind.Comment: 5 pages, 3 figures, 1 table, accepted for publication in A&
Decaying Sterile Neutrinos as a Heating Source in the Milky Way Center
Recent Chandra and Newton observations indicate that there are
two-temperature components ( 8 keV, 0.8 keV) of the diffuse x-rays
emitted from deep inside the center of Milky Way. We show that this can be
explained by the existence of sterile neutrinos, which decay to emit photons
that can be bound-free absorbed by the isothermal hot gas particles in the
center of Milky Way. This model can account for the two-temperature components
naturally as well as the energy needed to maintain the 8 keV temperature
in the hot gas. The predicted sterile neutrino mass is between 16-18 keV.Comment: Accepted by MNRAS with minor correction
Dynamics aspect of subbarrier fusion reaction in light heavy ion systems
Subbarrier fusion of the 7Li + 12C reaction is studied using an
antisymmetrized molecular dynamics model (AMD) with an after burner, GEMINI. In
AMD, 7Li shows an \alpha + t structure at its ground state and it is
significantly deformed. Simulations are made near the Coulomb barrier energies,
i.e., E_{cm} = 3 - 8 MeV. The total fusion cross section of the AMD + GEMINI
calculations as a function of incident energy is compared to the experimental
results and both are in good agreement at E_{cm} > 3 MeV. The cross section for
the different residue channels of the AMD + GEMINI at E_{cm} = 5 MeV is also
compared to the experimental results.Comment: Talk given by Meirong Huang at the 11th International Conference on
Nucleus-Nucleus Collisions (NN2012), San Antonio, Texas, USA, May 27-June 1,
2012. To appear in the NN2012 Proceedings in Journal of Physics: Conference
Series (JPCS
Chandra detection of diffuse X-ray emission from the globular cluster Terzan 5
Terzan 5, a globular cluster (GC) prominent in mass and population of compact
objects, is searched for diffuse X-ray emission, as proposed by several models.
We analyzed the data of an archival Chandra observation of Terzan 5 to search
for extended diffuse X-ray emission outside the half-mass radius of the GC. We
removed detected point sources from the data to extract spectra from diffuse
regions around Terzan 5. The Galactic background emission was modeled by a
2-temperature thermal component, which is typical for Galactic diffuse
emission.
We detected significant diffuse excess emission above the particle background
level from the whole field-of-view. The surface brightness appears to be peaked
at the GC center and decreases smoothly outwards. After the subtraction of
particle and Galactic background, the excess spectrum of the diffuse emission
between the half-mass radius and 3' can be described by a power-law model with
photon index = 0.90.5 and a surface flux of F =
(1.170.16) 10 erg s cm sr in the 1--7 keV
band. We estimated the contribution from unresolved point sources to the
observed excess to be negligible. The observations suggest that a purely
thermal origin of the emission is less likely than a non-thermal scenario.
However, from simple modeling we cannot identify a clearly preferred scenario.Comment: 6 pages, 4 figures, accepted for publication by A&
Properties of polycyclic aromatic hydrocarbons in local elliptical galaxies revealed by the Infrared Spectrograph on Spitzer
We performed mid-infrared spectroscopic observations of 18 local dusty
elliptical galaxies by using the Infrared Spectrograph (IRS) on board Spitzer.
We have significantly detected polycyclic aromatic hydrocarbon (PAH) features
from 14 out of the 18 galaxies, and thus found that the presence of PAHs is not
rare but rather common in dusty elliptical galaxies. Most of these galaxies
show an unusually weak 7.7 um emission feature relative to 11.3 um and 17 um
emission features. A large fraction of the galaxies also exhibit H2 rotational
line and ionic fine-structure line emissions, which have no significant
correlation with the PAH emissions. The PAH features are well correlated with
the continuum at 35 um, whereas they are not correlated with the continuum at 6
um. We conclude that the PAH emission of the elliptical galaxies is mostly of
interstellar origin rather than of stellar origin, and that the unusual PAH
interband strength ratios are likely to be due to a large fraction of neutral
to ionized PAHs.Comment: 26 pages, 6 figures, accepted for publication in the Ap
AKARI Far-Infrared All Sky Survey
We demonstrate the capability of AKARI for mapping diffuse far-infrared
emission and achieved reliability of all-sky diffuse map. We have conducted an
all-sky survey for more than 94 % of the whole sky during cold phase of AKARI
observation in 2006 Feb. -- 2007 Aug. The survey in far-infrared waveband
covers 50 um -- 180 um with four bands centered at 65 um, 90 um, 140 um, and
160 um and spatial resolution of 3000 -- 4000 (FWHM).This survey has allowed us
to make a revolutionary improvement compared to the IRAS survey that was
conducted in 1983 in both spatial resolution and sensitivity after more than a
quarter of a century. Additionally, it will provide us the first all-sky survey
data with high-spatial resolution beyond 100 um. Considering its extreme
importance of the AKARI far-infrared diffuse emission map, we are now
investigating carefully the quality of the data for possible release of the
archival data. Critical subjects in making image of diffuse emission from
detected signal are the transient response and long-term stability of the
far-infrared detectors. Quantitative evaluation of these characteristics is the
key to achieve sensitivity comparable to or better than that for point sources
(< 20 -- 95 [MJy/sr]). We describe current activities and progress that are
focused on making high quality all-sky survey images of the diffuse
far-infrared emission.Comment: To appear in Proc. Workshop "The Space Infrared Telescope for
Cosmology & Astrophysics: Revealing the Origins of Planets and Galaxies".
Eds. A.M. Heras, B. Swinyard, K. Isaak, and J.R. Goicoeche
Shape Effects of Finite-Size Scaling Functions for Anisotropic Three-Dimensional Ising Models
The finite-size scaling functions for anisotropic three-dimensional Ising
models of size (: anisotropy parameter) are
studied by Monte Carlo simulations. We study the dependence of finite-size
scaling functions of the Binder parameter and the magnetization
distribution function . We have shown that the finite-size scaling
functions for at the critical temperature change from a two-peak
structure to a single-peak one by increasing or decreasing from 1. We also
study the finite-size scaling near the critical temperature of the layered
square-lattice Ising model, when the systems have a large two-dimensional
anisotropy. We have found the three-dimensional and two-dimensional finite-size
scaling behavior depending on the parameter which is fixed; a unified view of
3D and 2D finite-size scaling behavior has been obtained for the anisotropic 3D
Ising models.Comment: 6 pages including 11 eps figures, RevTeX, to appear in J. Phys.
Why NERICA is a successful innovation for African farmers
This paper responds to ‘Funding international agricultural research and the need to be noticed: a case study of NERICA rice’ by Stuart Orr, James Sumberg, Olaf Erenstein and Andreas Oswald, published in this issue of Outlook on Agriculture.
In summary, the article by Orr et al, based on an internal WARDA document written in November 2003 and augmented with results from Internet searches, is outdated and does not seem to be fair, objective or useful. We invite the authors to visit WARDA or any of its partners in Sub-Saharan Africa for evidence of the impact of NERICA varieties or the other improved varieties and technologies that have been developed and disseminated by WARDA in recent years
- …