343 research outputs found
Revision of the Selection Function of the Optical Redshift Survey using the Sloan Digital Sky Survey Early Data Release: Toward an Accurate Estimate of Source Number Density of Ultra-High Energy Cosmic Rays
If Ultra-High Energy Cosmic Rays (UHECRs) are originated from nearby
galaxies, modeling of the distribution of nearby galaxies is important to an
accurate estimate the source number density of UHECRs. We investigate
uncertainty of the selection function of the Optical Redshift Survey (ORS),
which we used to construct a source model of UHECRs. The investigation is based
on a comparison of numbe counts of ORS galaxies with those of the spectroscopic
sample of the Sloan Digital Sky Survey (SDSS) Early Data Release (EDR). We
carefully count galaxies in the same absolute magnitude bin from the two
samples. We find a slight systematic overestimate of the ORS counts outside
5000 km s by about a factor of 2. We revise the selection function of
the ORS assuming that the SDSS counts are correct. Our revision is based on the
absorption given in the ORS catalog as well as that computed from Schlegel et
al. (1998), which is systematically larger than the former by
mag in the region of low absorption. It is found that introduction of Schlegel
et al.'s absorption changes one of the parameters of the ORS selection function
by more than 10%. The revision should be taken into account in the future
analysis of the source number density of UHECRs based on the ORS. Using the
revised selection function, we determine the global structure of the Local
Supercluster (LSC) with a source model of UHECRs, that is, a number-density
model consisting of a uniform spherical halo and an exponential disk. We find
that the revision is insignificant in terms of the structure of the LSC.
However, the revised selection function will be useful to other studies such as
peculiar velocity and correlation function.Comment: 22 pages, 13 figures. accepted for publication in PAS
31P-NMR and muSR Studies of Filled Skutterudite Compound SmFe4P12: Evidence for Heavy Fermion Behavior with Ferromagnetic Ground State
The 31P-NMR (nuclear magnetic resonance) and muSR (muon spin relaxation)
measurements on the filled skutterudite system SmFe4P12 have been carried out.
The temperature T dependence of the 31P-NMR spectra indicates the existence of
the crystalline electric field effect splitting of the Sm3+$ (J = 5/2)
multiplet into a ground state and an excited state of about 70 K. The
spin-lattice relaxation rate 1/T1 shows the typical behavior of the Kondo
system, i.e., 1/T1 is nearly T independent above 30 K, and varies in proportion
to T (the Korringa behavior, 1/T1 \propto T) between 7.5 K and 30 K. The T
dependence deviated from the Korringa behavior below 7 K, which is independent
of T in the applied magnetic field of 1 kOe, and suppressed strongly in higher
fields. The behavior is explained as 1/T1is determined by ferromagnetic
fluctuations of the uncovered Sm3+ magnetic moments by conduction electrons.
The muSR measurements in zero field show the appearance of a static internal
field associated with the ferromagnetic order below 1.6 K.Comment: 6 pages, 9 figures, to be published in J. Phys. Soc. Jpn. 75 (2006
Interstellar Gas and X-rays toward the Young Supernova Remnant RCW 86; Pursuit of the Origin of the Thermal and Non-Thermal X-ray
We have analyzed the atomic and molecular gas using the 21 cm HI and 2.6/1.3
mm CO emissions toward the young supernova remnant (SNR) RCW 86 in order to
identify the interstellar medium with which the shock waves of the SNR
interact. We have found an HI intensity depression in the velocity range
between and km s toward the SNR, suggesting a cavity in the
interstellar medium. The HI cavity coincides with the thermal and non-thermal
emitting X-ray shell. The thermal X-rays are coincident with the edge of the HI
distribution, which indicates a strong density gradient, while the non-thermal
X-rays are found toward the less dense, inner part of the HI cavity. The most
significant non-thermal X-rays are seen toward the southwestern part of the
shell where the HI gas traces the dense and cold component. We also identified
CO clouds which are likely interacting with the SNR shock waves in the same
velocity range as the HI, although the CO clouds are distributed only in a
limited part of the SNR shell. The most massive cloud is located in the
southeastern part of the shell, showing detailed correspondence with the
thermal X-rays. These CO clouds show an enhanced CO = 2-1/1-0 intensity
ratio, suggesting heating/compression by the shock front. We interpret that the
shock-cloud interaction enhances non-thermal X-rays in the southwest and the
thermal X-rays are emitted by the shock-heated gas of density 10-100 cm.
Moreover, we can clearly see an HI envelope around the CO cloud, suggesting
that the progenitor had a weaker wind than the massive progenitor of the
core-collapse SNR RX J1713.73949. It seems likely that the progenitor of RCW
86 was a system consisting of a white dwarf and a low-mass star with
low-velocity accretion winds.Comment: 19 pages, 15 figures, 4 tables, accepted for publication in Journal
of High Energy Astrophysics (JHEAp
Discovery of possible molecular counterparts to the infrared Double Helix Nebula in the Galactic center
We have discovered two molecular features at radial velocities of -35 km/s
and 0 km/s toward the infrared Double Helix Nebula (DHN) in the Galactic center
with NANTEN2. The two features show good spatial correspondence with the DHN.
We have also found two elongated molecular ridges at these two velocities
distributed vertically to the Galactic plane over 0.8 degree. The two ridges
are linked by broad features in velocity and are likely connected physically
with each other. The ratio between the 12CO J=2-1 and J=1-0 transitions is 0.8
in the ridges which is larger than the average value 0.5 in the foreground gas,
suggesting the two ridges are in the Galactic center. An examination of the K
band extinction reveals a good coincidence with the CO 0 km/s ridge and is
consistent with a distance of 8 +/-2 kpc. We discuss the possibility that the
DHN was created by a magnetic phenomenon incorporating torsional Alfv\'en waves
launched from the circumnuclear disk (Morris, Uchida & Do 2006) and present a
first estimate of the mass and energy involved in the DHN.Comment: 32 pages, 23 figures, Accepted by Ap
Low-Temperature Structure of the Quarter-Filled Ladder Compound alpha'-NaV2O5
The low-temperature (LT) superstructure of -NaVO was
determined by synchrotron radiation x-ray diffraction. Below the phase
transition temperature associated with atomic displacement and charge ordering
at 34K, we observed the Bragg peak splittings, which evidence that the LT
structure is monoclinic. It was determined that the LT structure is
with the space group where and
represent the high temperature orthorhombic unit cell. The valence estimation
of V ions according to the bond valence sum method shows that the V sites are
clearly separated into two groups of V and V with a
charge ordering pattern. This LT structure is consistent with resonant x-ray
and NMR measurements, and strikingly contrasts to the LT structure previously
reported, which includes V sites.Comment: 4 pages, 3 figures, 1 tabl
Magnetic Susceptibility for
We examine experimental magnetic susceptibility for
CaVO by fitting with fitting function .
The function is a power series of 1/T and the lowest order
term is fixed as , where is the Curie constant as determined by the
experimental -value (g=1.96). Fitting parameters are , and
expansion coefficients except for the first one in .
We determine and as 0.73 and 0 for an
experimental sample. We interpret as the volume fraction of
CaVO in the sample and as the susceptibility for the
pure CaVO. The result of means that the sample includes
nonmagnetic components. This interpretation consists with the result of a
perturbation theory and a neutron scattering experiment.Comment: 4pages, 4figure
Temperature and Density Distribution in the Molecular Gas Toward Westerlund 2: Further Evidence for Physical Association
Furukawa et al. 2009 reported the existence of a large mass of molecular gas
associated with the super star cluster Westerlund 2 and the surrounding HII
region RCW49, based on a strong morphological correspondence between NANTEN2
12CO(J=2-1) emission and Spitzer IRAC images of the HII region. We here present
temperature and density distributions in the associated molecular gas at 3.5 pc
resolution, as derived from an LVG analysis of the 12CO(J=2-1), 12CO(J=1-0) and
13CO(J=2-1) transitions. The kinetic temperature is as high as 60-150 K within
a projected distance of 5-10 pc from Westerlund 2 and decreases to as low as 10
K away from the cluster. The high temperature provides robust verification that
the molecular gas is indeed physically associated with the HII region,
supporting Furukawa et al.'s conclusion. The derived temperature is also
roughly consistent with theoretical calculations of photo dissociation regions
(PDRs), while the low spatial resolution of the present study does not warrant
a more detailed comparison with PDR models. We suggest that the molecular
clouds presented here will serve as an ideal laboratory to test theories on
PDRs in future higher resolution studies.Comment: 23 pages, 5 figures, accepted for publication in Ap
Ab initio evaluation of the charge-ordering in
We report {\it ab initio} calculations of the charge ordering in
using large configurations interaction methods on
embedded fragments. Our major result is that the electrons of the
bridging oxygen of the rungs present a very strong magnetic character and
should thus be explicitly considered in any relevant effective model. The most
striking consequence of this result is that the spin and charge ordering differ
substantially, as differ the experimental results depending on whether they are
sensitive to the spin or charge density.Comment: 4 page
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