997 research outputs found
The Virgo High-Resolution CO Survey. II. Rotation Curves and Dynamical Mass Distributions
Based on a high-resolution CO survey of Virgo spirals with the Nobeyama
Millimeter-wave Array, we determined the dynamical centers using velocity
fields, and derived position-velocity diagrams (PVDs) along the major axes of
the galaxies across their dynamical centers. We applied a new iteration method
to derive rotation curves (RCs), which reproduce the observed PVDs. The
obtained high-accuracy RCs generally show steep rise in the central 100 to 200
pc regions, followed by flat rotation in the disk. We applied a deconvolution
method to calculate the surface-mass density (SMD) using the RCs based on two
extreme assumptions that the mass distribution is either spherical or thin-disk
shaped. Both assumptions give nearly identical results, agreeing with each
other within a factor of two at any radii. The SMD distributions revealed
central massive cores with peak SMD of 10^4 - 10^5 Msun pc^-2 and total mass
within 200 pc radius of the order of about 10^9 Msun Correlation analysis among
the derived parameters show that the central CO-line intensity is positively
correlated with the central SMD, which suggests that the deeper is the
gravitational potential, the higher is the molecular gas concentration in the
nuclei regardless morphological types.Comment: PASJ 2003 in press, Latex 12 pages, 6 figures (Bigger gif/ps figures
available at http://www.ioa.s.u-tokyo.ac.jp/radio/virgo2
The Virgo CO Survey: VI. Gas Dynamics and Star Formation Along the Bar in NGC 4303
We present CO interferometer observations of the barred galaxy NGC 4303
(M61). This galaxy has a gas concentration at the central region and offset
ridges in the bar. Sharp velocity gradients are apparent across the ridges.
Analyses of the CO data and the newborn stellar clusters revealed in HST images
indicate the existence of unresolved molecular clouds with masses of
10^4-6Msun. The observed shear velocity gradient across the ridges is too small
to break up giant molecular clouds. Therefore, the clouds are likely to survive
passage through the ridges. We discuss a cloud orbit model in a bar potential.
The model reproduces the narrow offset ridges and sharp velocity gradients
across the ridges in NGC 4303. We discuss cloud-cloud collisions (and close
interactions) as a possible triggering mechanism for star formation. The
newborn stellar clusters in NGC 4303 are located predominantly at the leading
sides of the offset ridges, where cloud orbits are densely populated and
suggest a high collisional frequency and possibly a high rate of triggered star
formation. Cloud-based dynamics is less dissipative than smooth hydrodynamic
models, possibly extending the timescales of gas dynamical evolution and gas
fueling to central regions in barred galaxies.Comment: 20 pages, 13 figures, 4 tables. PASJ, accepted (Apr. issue), high
resolution version
"http://www.astro.caltech.edu/~koda/paper/n4303/koda_n4303.pdf
Staggered magnetism in LiVO at low temperatures probed by the muon Knight shift
We report on the muon Knight shift measurement in single crystals of LiV2O4.
Contrary to what is anticipated for the heavy-fermion state based on the Kondo
mechanism, the presence of inhomogeneous local magnetic moments is demonstrated
by the broad distribution of the Knight shift at temperatures well below the
presumed "Kondo temperature" ( K). Moreover, a significant
fraction ( %) of the specimen gives rise to a second component which
is virtually non-magnetic. These observations strongly suggest that the
anomalous properties of LiV2O4 originates from frustration of local magnetic
moments.Comment: 11 pages, 5 figures, sbmitted to J. Phys.: Cond. Mat
On the and as Bound States and Approximate Nambu-Goldstone Bosons
We reconsider the two different facets of and mesons as
bound states and approximate Nambu-Goldstone bosons. We address several topics,
including masses, mass splittings between and and between and
, meson wavefunctions, charge radii, and the wavefunction overlap.Comment: 15 pages, late
The HST Cosmos Project: Contribution from the Subaru Telescope
The Cosmic Evolution Survey (COSMOS) is a Hubble Space Telescope (HST)
treasury project.The COSMOS aims to perform a 2 square degree imaging survey of
an equatorial field in (F814W) band, using the Advanced Camera for Surveys
(ACS). Such a wide field survey, combined with ground-based photometric and
spectroscopic data, is essential to understand the interplay between large
scale structure, evolution and formation of galaxies and dark matter. In 2004,
we have obtained high-quality, broad band images of the COSMOS field ( and ) using Suprime-Cam on the Subaru
Telescope, and we have started our new optical multi-band program, COSMOS-21 in
2005. Here, we present a brief summary of the current status of the COSMOS
project together with contributions from the Subaru Telescope. Our future
Subaru program, COSMOS-21, is also discussed briefly.Comment: 4 pages, 3 figures, to appear in the Proceedings of the 6th East
Asian Meeting on Astronomy, JKAS, 39, in pres
Discovery of New Dwarf Galaxy near The Isolated Spiral Galaxy NGC 6503
We report the discovery of a new dwarf galaxy (NGC6503-d1) during the Subaru
extended ultraviolet (XUV) disk survey. It is a likely companion of the spiral
galaxy NGC6503. The resolved images, in B, V, R, i, and Halpha, show an
irregular appearance due to bright stars with underlying, smooth and unresolved
stellar emission. It is classified as the transition type (dIrr/dSph). Its
structural properties are similar to those of the dwarfs in the Local Group,
with a V absolute magnitude ~ -10.5, half-light radius ~400 pc, and central
surface brightness ~25.2. Despite the low stellar surface brightness
environment, one HII region was detected, though its Halpha luminosity is low,
indicating an absence of any appreciable O-stars at the current epoch. The
presence of multiple stellar populations is indicated by the color-magnitude
diagram of ~300 bright resolved stars and the total colors of the dwarf, with
the majority of its total stellar mass ~4x10^6 Msun in an old stellar
population.Comment: Published in ApJL (ApJ, 802, L24). 7 pages, 4 figure
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