271 research outputs found
Very large array H53α and H92α line observations of the central region of NGC 253
We present new VLA observations toward NGC 253 of the recombination line H53α (43 GHz) at an angular resolution of 1".5 × 1".0. The free-free emission at 43 GHz is estimated to be ~140 mJy, implying a star formation rate of 2 M⊙ yr-1 in the nuclear region of this starburst galaxy. A reanalysis is made for previously reported H92α observations carried out with angular resolution of 1".5 × 1".0 and 0".36 × 0".21. Based on the line and continuum emission models used for the 1".5 × 1".0 angular resolution observations, the RRLs H53α and H92α are tracers of the high-density (~105 cm-3) and low-density (~103 cm-3) thermally ionized gas components in NGC 253, respectively. The velocity fields observed in the H53α and H92α lines (1".5 × 1".0) are consistent. The velocity gradient in the central ~18 pc of the NE component, as observed in both the H53α and H92α lines, is in the opposite direction to the velocity gradient determined from the CO observations. The enclosed virial mass, as deduced from the H53α velocity gradient over the NE component, is ~5 × 106 M⊙ in the central ~18 pc region. The H92α line observations at high angular resolution (0".36 × 0".21) reveal a larger velocity gradient, along a P.A. ~ -45° on the NE component, of ~110 km s-1 arcsec-1. The dynamical mass estimated using the high angular resolution H92α data (~7 × 106 M⊙) supports the existence of an accreted massive object in the nuclear region of NGC 253
VLA H53alpha observations of the central region of the Super Star Cluster Galaxy NGC 5253
We present observations in the H53alpha line and radio continuum at 43 GHz
carried out with the VLA in the D array (2'' angular resolution) toward the
starburst galaxy NGC 5253. VLA archival data have been reprocessed to produce a
uniform set of 2, 1.3 and 0.7 cm high angular (0.''2 X 0.''1) radio continuum
images. The RRL H53alpha, a previously reported measurement of the H92alpha RRL
flux density and the reprocessed high angular resolution radio continuum flux
densities have been modeled using a collection of HII regions. Based on the
models, the ionized gas in the nuclear source has an electron density of ~6 X
10^4 cm^-3 and an volume filling factor of 0.05. A Lyman continuum photon
production rate of 2 X 10^52 s^-1 is necessary to sustain the ionization in the
nuclear region. The number of required O7 stars in the central 1.5 pc of the
supernebula is ~ 2000. The H53alpha velocity gradient 10 km s^-1 arcsec^-1)
implies a dynamical mass of ~3X10^5 Msun; this mass suggests the supernebula is
confined by gravity.Comment: Accepted in Astrophysical Journal 7 figure
Valence Bond States: Link models
An isotropic anti-ferromagnetic quantum state on a square lattice is
characterized by symmetry arguments only. By construction, this quantum state
is the result of an underlying valence bond structure without breaking any
symmetry in the lattice or spin spaces. A detailed analysis of the correlations
of the quantum state is given (using a mapping to a 2D classical statistical
model and methods in field theory like mapping to the non-linear sigma model or
bosonization techniques) as well as the results of numerical treatments
(regarding exact diagonalization and variational methods). Finally, the
physical relevance of the model is motivated. A comparison of the model to
known anti-ferromagnetic Mott-Hubbard insulators is given by means of the
two-point equal-time correlation function obtained i) numerically from the
suggested state and ii) experimentally from neutron scattering on cuprates in
the anti-ferromagnetic insulator phase.Comment: 20 pages, 15 figures; added references, corrected some typos, new
sections. Published versio
VLA H53alpha radio recombination line observations of the ultraluminous infrared galaxy Arp 220
We present high angular resolution (0.7'') observations made with the Very
Large Array (VLA) of the radio recombination line (RRL) H53alpha and radio
continuum emission at 43 GHz from the ultraluminous infrared galaxy (ULIRG) Arp
220. The 43 GHz continuum emission shows a compact structure (~2'') with two
peaks separated by ~1'', the East (E) and West (W) components, that correspond
to each galactic nucleus of the merger. The spectral indices for both the E and
W components, using radio continuum images at 8.3 and 43 GHz are typical of
synchrotron emission (alpha ~ -1.0). Our 43 GHz continuum and H53alpha line
observations confirm the flux densities predicted by the models proposed by
Anantharamaiah et al. This agreement with the models implies the presence of
high-density (~ 100,000 cm^-3) compact HII regions (~ 0.1 pc) in Arp 220. The
integrated H53alpha line emission is stronger toward the non-thermal radio
continuum peaks, which are also coincident with the peaks of molecular emission
of the H2CO. The coincidence between the integrated H53alpha and the H2CO maser
line emission suggests that the recent star forming regions, traced by the high
density gas, are located mainly in regions that are close to the two radio
continuum peaks. A velocity gradient of ~ 0.30 km/s/pc in the H53alpha RRL is
observed toward the E component and a second velocity gradient of ~ 0.15
km/s/pc is detected toward the W component. The orientations of these velocity
gradients are in agreement with previous CO, HI and OH observations. The
kinematics of the high-density ionized gas traced by the H53alpha line are
consistent with two counter rotating disks as suggested by the CO and HI
observations.Comment: The original version was published in the ApJ,633,198,2005. This new
version is submitted with the corrected velocity scal
VLA H53alpha and H92alpha line observations of the central region of NGC 253
We present new Very Large Array (VLA) observations toward NGC 253 of the
recombination line H53alpha (43 GHz) at an angular resolution of 1.''5 X 1.''0.
The free-free emission at 43 GHz is estimated to be ~100 mJy, implying a star
formation rate of ~1.3 Msun/yr in the nuclear region of this starburst galaxy.
A reanalysis is made for previously reported H92alpha observations carried out
with angular resolution of 1.''5 X 1.''0 and 0.''36 X 0.''21. Based on the line
and continuum emission models used for the 1.''5 X 1.''0 angular resolution
observations, the RRLs H53alpha and H92alpha are tracers of the high-density
(~10^5 cm-3) and low-density (~10^3 cm^-3) thermally ionized gas components in
NGC 253, respectively. The velocity fields observed in the H53alpha and
H92alpha lines 1.''5 X 1.''0) are consistent. The velocity gradient in the
central ~18 pc of the NE component, as observed in both the H53alpha and
H92alpha lines, is in the opposite direction to the velocity gradient
determined from the CO observations. The enclosed virial mass, as deduced from
the H53alpha velocity gradient over the NE component, is ~5 X 10^6 Msun in the
central ~18 pc region. The H92alpha line observations at high angular
resolution (0.''36 X 0.''21) reveal a larger velocity gradient, along a P.A. ~
-45 deg on the NE component, of ~110 km/s/arcsec. The dynamical mass estimated
using the high angular resolution H92alpha data (~7 X 10^6 Msun) supports the
existence of an accreted massive object in the nuclear region of NGC 253.Comment: Accepted for publication in Ap
Phylogenetic history demonstrates two different lineages of dengue type 1 virus in Colombia
Background: Dengue Fever is one of the most important viral re-emergent diseases affecting about 50 million people around the world especially in tropical and sub-tropical countries. In Colombia, the virus was first detected in the earliest 70′s when the disease became a major public health concern. Since then, all four serotypes of the virus have been reported. Although most of the huge outbreaks reported in this country have involved dengue virus serotype 1 (DENV-1), there are not studies about its origin, genetic diversity and distribution. Results: We used 224 bp corresponding to the carboxyl terminus of envelope (E) gene from 74 Colombian isolates in order to reconstruct phylogenetic relationships and to estimate time divergences. Analyzed DENV-1 Colombian isolates belonged to the formerly defined genotype V. Only one virus isolate was clasified in the genotype I, likely representing a sole introduction that did not spread. The oldest strains were closely related to those detected for the first time in America in 1977 from the Caribbean and were detected for two years until their disappearance about six years later. Around 1987, a split up generated 2 lineages that have been evolving separately, although not major aminoacid changes in the analyzed region were found. Conclusion: DENV-1 has been circulating since 1978 in Colombia. Yet, the phylogenetic relationships between strains isolated along the covered period of time suggests that viral strains detected in some years, although belonging to the same genotype V, have different recent origins corresponding to multiple re-introduction events of viral strains that were circulating in neighbor countries. Viral strains used in the present study did not form a monophyletic group, which is evidence of a polyphyletic origin. We report the rapid spread patterns and high evolution rate of the different DENV-1 lineages
Production properties of K*(892) vector mesons and their spin alignment as measured in the NOMAD experiment
First measurements of K*(892) mesons production properties and their spin
alignment in nu_mu charged current (CC) and neutral current (NC) interactions
are presented. The analysis of the full data sample of the NOMAD experiment is
performed in different kinematic regions. For K*+ and K*- mesons produced in
nu_mu CC interactions and decaying into K0 pi+/- we have found the following
yields per event: (2.6 +/- 0.2 (stat.) +/- 0.2 (syst.))% and (1.6 +/- 0.1
(stat.) +/- 0.1 (syst.))% respectively, while for the K*+ and K*- mesons
produced in nu NC interactions the corresponding yields per event are: (2.5 +/-
0.3 (stat.) +/- 0.3 (syst.))% and (1.0 +/- 0.3 (stat.) +/- 0.2 (syst.))%. The
results obtained for the rho00 parameter, 0.40 +/- 0.06 (stat) +/- 0.03 (syst)
and 0.28 +/- 0.07 (stat) +/- 0.03 (syst) for K*+ and K*- produced in nu_mu CC
interactions, are compared to theoretical predictions tuned on LEP measurements
in e+e- annihilation at the Z0 pole. For K*+ mesons produced in nu NC
interactions the measured rho00 parameter is 0.66 +/- 0.10 (stat) +/- 0.05
(syst).Comment: 20 p
Search for nu(mu)-->nu(e) Oscillations in the NOMAD Experiment
We present the results of a search for nu(mu)-->nu(e) oscillations in the
NOMAD experiment at CERN. The experiment looked for the appearance of nu(e) in
a predominantly nu(mu) wide-band neutrino beam at the CERN SPS. No evidence for
oscillations was found. The 90% confidence limits obtained are delta m^2 < 0.4
eV^2 for maximal mixing and sin^2(2theta) < 1.4x10^{-3} for large delta m^2.
This result excludes the LSND allowed region of oscillation parameters with
delta m^2 > 10 eV^2.Comment: 19 pages, 8 figures. Submitted to Phys. Lett.
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