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

Cu-spin dynamics in the overdoped regime of La_2-x_Sr_x_Cu_1-y_Zn_y_O_4_ probed by muon spin relaxation

Muon-spin-relaxation measurements have been performed for the partially Zn-substituted La_2-x_Sr_x_Cu_1-y_Zn_y_O_4_ with y=0-0.10 in the overdoped regime up to x=0.30. In the 3 % Zn-substituted samples up to x=0.27, exponential-like depolarization of muon spins has been observed at low temperatures, indicating Zn-induced slowing-down of the Cu-spin fluctuations. The depolarization rate decreases with increasing x and almost no fast depolarization of muon spins has been observed for x=0.30 where superconductivity disappears. The present results suggest that the dynamical stripe correlations exist in the whole superconducting regime of La_2-x_Sr_x_CuO_4_ and that there is no quantum critical point at x~0.19.Comment: 6 pages, 5 figure

Staggered magnetism in LiV2_2O4_4 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" ($T^*\simeq 30$ K). Moreover, a significant fraction ($\simeq10$ %) 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

Molecular clouds and clumps in the Boston University-Five College Radio Astronomy Observatory Galactic Ring Survey

The Boston University-Five College Radio Astronomy Observatory (BU-FCRAO) Galactic Ring Survey (GRS) of 13 CO (1-0) emission covers Galactic longitudes 18 deg < l < 55.7 deg and Galactic latitudes |b| <= 1 deg. Using the SEQUOIA array on the FCRAO 14m telescope, the GRS fully sampled the 13 CO Galactic emission (46 arcsec angular resolution on a 22 arcsec grid) and achieved a spectral resolution of 0.21 km/s. Because the GRS uses 13 CO, an optically thin tracer, rather than 12 CO, an optically thick tracer, the GRS allows a much better determination of column density and also a cleaner separation of velocity components along a line of sight. With this homogeneous, fully-sampled survey of 13 CO, emission, we have identified 829 molecular clouds and 6124 clumps throughout the inner Galaxy using the CLUMPFIND algorithm. Here we present details of the catalog and a preliminary analysis of the properties of the molecular clouds and their clumps. Moreover, we compare clouds inside and outside of the 5 kpc ring and find that clouds within the ring typically have warmer temperatures, higher column densities, larger areas, and more clumps compared to clouds located outside the ring. This is expected if these clouds are actively forming stars. This catalog provides a useful tool for the study of molecular clouds and their embedded young stellar objects.Comment: 29 pages. ApJ in pres

On the π\pi and KK as qqˉq \bar q Bound States and Approximate Nambu-Goldstone Bosons

We reconsider the two different facets of $\pi$ and $K$ mesons as $q \bar q$ bound states and approximate Nambu-Goldstone bosons. We address several topics, including masses, mass splittings between $\pi$ and $\rho$ and between $K$ and $K^*$, meson wavefunctions, charge radii, and the $K-\pi$ wavefunction overlap.Comment: 15 pages, late

Post-starburst Tidal Tails in the Archetypical Ultra Luminous Infrared Galaxy Arp 220

We present our new deep optical imaging and long-slit spectroscopy for Arp 220 that is the archetypical ULIRG in the local universe. Our sensitive Ha imaging has newly revealed large-scale, Ha absorption, i.e., post-starburst regions in this merger; one is found in the eastern superbubble and the other is in the two tidal tails that are clearly reveled in our deep optical imaging. The size of Ha absorption region in the eastern bubble is 5 kpc x 7.5 kpc and the observed Ha equivalent widths are ~2 A +- 0.2 A. The sizes of the northern and southern Ha-absorption tidal tails are ~5 kpc x 10 kpc and ~6 kpc x 20 kpc, respectively. The observed Ha equivalent widths range from 4 A to 7 A. In order to explain the presence of the two post-starburst tails, we suggest a possible multiple-merger scenario for Arp 220 in which two post-starburst disk-like structures merged into one, and then caused the two tails. This favors that Arp 220 is a multiple merging system composed of four or more galaxies, arising from a compact group of galaxies. Taking our new results into account, we discuss a star formation history in the last 1 Gyr in Arp 220.Comment: 6 pages, 7 figures, Accepted for publication in the Astrophysical Journa