1,191 research outputs found
High-Velocity Molecular Gas in the Galactic Center Radio Lobe
We point out a possible association of high-velocity molecular gas with the
Galactic Center Radio Lobe (GCL). A molecular spur in the eastern GCL ridge is
receding at \Vlsr \sim +100 \kms, and the western spur approaching at \Vlsr
\sim -150 \kms, suggesting a high-velocity rotation of the GCL. We study the
kinematics of the GCL based on these molecular line data.Comment: To appear in ApJ. Letters, Plain TeX, Figures on reques
Orbital Decay and Tidal Disruption of a Star Cluster: Analytical Calculation
The orbital decay and tidal disruption of a star cluster in a galaxy is
studied in an analytical manner. Owing to dynamical friction, the star cluster
spirals in toward the center of the galaxy. Simultaneously, the galactic tidal
field strips stars from the outskirts of the star cluster. Under an assumption
that the star cluster undergoes a self-similar evolution, we obtain the
condition and timescale for the star cluster to reach the galaxy center before
its disruption. The result is used to discuss the fate of so-called
intermediate-mass black holes with >10^3 M(sun) found recently in young star
clusters of starburst galaxies and also the mass function of globular clusters
in galaxies.Comment: 12 pages, 1 PS file for 2 figures, to appear in The Astrophysical
Journa
Noncommutative Deformation of Spinor Zero Mode and ADHM Construction
A method to construct noncommutative instantons as deformations from
commutative instantons was provided in arXiv:0805.3373. Using this
noncommutative deformed instanton, we investigate the spinor zero modes of the
Dirac operator in a noncommutative instanton background on noncommutative R^4,
and we modify the index of the Dirac operator on the noncommutative space
slightly and show that the number of the zero mode of the Dirac operator is
preserved under the noncommutative deformation. We prove the existence of the
Green's function associated with instantons on noncommutative R^4, as a smooth
deformation of the commutative case. The feature of the zero modes of the Dirac
operator and the Green's function derives noncommutative ADHM equations which
coincide with the ones introduced by Nekrasov and Schwarz. We show a one-to-one
correspondence between the instantons on noncommutative R^4 and ADHM data. An
example of a noncommutative instanton and a spinor zero mode are also given.Comment: 34 pages, no figures, v3: an appendix and some definitions
added,typos correcte
Runaway Merging of Black Holes: Analytical Constraint on the Timescale
Following the discovery of a black hole (BH) with a mass of 10^3-10^6 M(sun)
in a starburst galaxy M82, we study formation of such a BH via successive
merging of stellar-mass BHs within a star cluster. The merging has a runaway
characteristic. This is because massive BHs sink into the cluster core and have
a high number density, and because the merging probability is higher for more
massive BHs. We use the Smoluchowski equation to study analytically the
evolution of the BH mass distribution. Under favorable conditions, which are
expected for some star clusters in starburst galaxies, the timescale of the
runaway merging is at most of order 10^7 yr. This is short enough to account
for the presence of a BH heavier than 10^3 M(sun) in an ongoing starburst
region.Comment: 10 pages, no figures, to appear in The Astrophysical Journal
(Letters
Iteration Method to Derive Exact Rotation Curves from Position-Velocity Diagrams of Spiral Galaxies
We present an iteration method to derive exact rotation curves (RC) of spiral
galaxies from observed position-velocity diagrams (PVD), which comprises the
following procedure. An initial rotation curve, RC0, is adopted from an
observed PV diagram (PV0), obtained by any simple method such as the
peak-intensity method. Using this rotation curve and an observed radial
distribution of intensity (emissivity), we construct a simulated PV diagram
(PV1). The difference between a rotation curve obtained from this PV1 and the
original RC (e.g., difference between peak-intensity velocities) is used to
correct the initial RC to obtain a corrected rotation curve, RC1. This RC1 is
used to calculated another PVD (PV2) using the observed intensity distribution,
and to obtain the second iterated RC (RC2). This iteration is repeated until
PV converges to PV0, so that the differences between PV and PV0 becomes
minimum. Finally RC is adopted as the most reliable rotation curve. We apply
this method to some observed PVDs of nearby galaxies, and show that the
iteration successfully converges to give reliable rotation curves. We show that
the method is powerful to detect central massive objects.Comment: To appear in ApJ.Letters, 5 pages Latex with 4 figure
Effect of the spin-orbit interaction and the electron phonon coupling on the electronic state in a silicon vacancy
The electronic state around a single vacancy in silicon crystal is
investigated by using the Green's function approach. The triply degenerate
charge states are found to be widely extended and account for extremely large
elastic softening at low temperature as observed in recent ultrasonic
experiments. When we include the LS coupling on each Si
atom, the 6-fold spin-orbital degeneracy for the state with the valence
+1 and spin 1/2 splits into doublet groundstates and
quartet excited states with a reduced excited energy of . We also consider the effect of couplings between electrons and
Jahn-Teller phonons in the dangling bonds within the second order perturbation
and find that the groundstate becomes quartet which is responsible
for the magnetic-field suppression of the softening in B-doped silicon.Comment: 4 pages, 2 figure
Scalability of spin FPGA: A Reconfigurable Architecture based on spin MOSFET
Scalability of Field Programmable Gate Array (FPGA) using spin MOSFET (spin
FPGA) with magnetocurrent (MC) ratio in the range of 100% to 1000% is discussed
for the first time. Area and speed of million-gate spin FPGA are numerically
benchmarked with CMOS FPGA for 22nm, 32nm and 45nm technologies including 20%
transistor size variation. We show that area is reduced and speed is increased
in spin FPGA owing to the nonvolatile memory function of spin MOSFET.Comment: 3 pages, 7 figure
VLBI study of water maser emission in the Seyfert 2 galaxy NGC5793. I: Imaging blueshifted emission and the parsec-scale jet
We present the first result of VLBI observations of the blueshifted water
maser emission from the type 2 Seyfert galaxy NGC5793, which we combine with
new and previous VLBI observations of continuum emission at 1.7, 5.0, 8.4, 15,
and 22 GHz. Maser emission was detected earlier in single-dish observations and
found to have both red- and blueshifted features relative to the systemic
velocity. We could image only the blueshifted emission, which is located 3.6 pc
southwest of the 22 GHz continuum peak. The blueshifted emission was found to
originate in two clusters that are separated by 0.7 milliarcsecond (0.16 pc).
No compact continuum emission was found within 3.6 pc of the maser spot. A
compact continuum source showing a marginally inverted spectrum between 1.7 and
5.0 GHz was found 4.2 pc southwest of the maser position. The spectral turnover
might be due to synchrotron self-absorption caused by a shock in the jet owing
to collision with dense gas, or it might be due to free-free absorption in an
ionized screen possibly the inner part of a disk, foreground to the jet.
The water maser may be part of a maser disk. If so, it would be rotating in
the opposite sense to the highly inclined galactic disk observed in CO
emission. We estimate a binding mass within 1 pc of the presumed nucleus to be
on the order of 10^7 Msun. Alternatively, the maser emission could result from
the amplification of a radio jet by foreground circumnuclear molecular gas. In
this case, the high blueshift of the maser emission might mean that the masing
region is moving outward away from the molecular gas surrounding an active
nucleus.Comment: 20 pages, 6 figures, to appear in ApJ, Oct. 200
Effect of exchange interaction on fidelity of quantum state transfer from a photon qubit to an electron-spin qubit
We analyzed the fidelity of the quantum state transfer (QST) from a
photon-polarization qubit to an electron-spin-polarization qubit in a
semiconductor quantum dot, with special attention to the exchange interaction
between the electron and the simultaneously created hole. In order to realize a
high-fidelity QST we had to separate the electron and hole as soon as possible,
since the electron-hole exchange interaction modifies the orientation of the
electron spin. Thus, we propose a double-dot structure to separate the electron
and hole quickly, and show that the fidelity of the QST can reach as high as
0.996 if the resonant tunneling condition is satisfied.Comment: 5 pages, 4 figures, to be published in Phys. Rev. B Rapid
Communication
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