923 research outputs found
The frequency and properties of young tidal dwarf galaxies in nearby gas-rich groups
We present high-resolution Giant Metrewave Radio Telescope (GMRT) HI
observations and deep Canada-France-Hawaii Telescope (CFHT) optical imaging of
two galaxy groups: NGC 4725/47 and NGC 3166/9. These data are part of a
multi-wavelength unbiased survey of the gas-rich dwarf galaxy populations in
three nearby interacting galaxy groups. The NGC 4725/47 group hosts two tidal
knots and one dIrr. Both tidal knots are located within a prominent HI tidal
tail, appear to have sufficient mass (M_gas~10^8 M_sol) to evolve into
long-lived tidal dwarf galaxies (TDGs) and are fairly young in age. The NGC
3166/9 group contains a TDG candidate, AGC 208457, at least three dIrrs and
four HI knots. Deep CFHT imaging confirms that the optical component of AGC
208457 is bluer -- with a 0.28 mag g-r colour -- and a few Gyr younger than its
purported parent galaxies. Combining the results for these groups with those
from the NGC 871/6/7 group reported earlier, we find that the HI properties,
estimated stellar ages and baryonic content of the gas-rich dwarfs clearly
distinguish tidal features from their classical counterparts. We optimistically
identify four potentially long-lived tidal objects associated to three separate
pairs of interacting galaxies, implying that TDGs are not readily produced
during interaction events as suggested by some recent simulations. The tidal
objects examined in this survey also appear to have a wider variety of
properties than TDGs of similar mass formed in current simulations of
interacting galaxies, which could be the result of pre- or post-formation
environmental influences.Comment: 18 pages, 14 figures, accepted for publication in MNRA
y scaling in electron-nucleus scattering
Data on inclusive electron scattering from A = 4, 12, 27, 56, 197 nuclei at large momentum transfer are presented and analyzed in terms of y scaling. We find that the data do scale for y 1), and we study the convergence of the scaling function with the momentum transfer Q^2 and A
Parametrization of nuclear parton distributions
Optimum nuclear parton distributions are obtained by analyzing available
experimental data on electron and muon deep inelastic scattering (DIS). The
distributions are given at Q^2=1 GeV^2 with a number of parameters, which are
determined by a chi^2 analysis of the data. Valence-quark distributions are
relatively well determined at medium x, but they are slightly dependent on the
assumed parametrization form particularly at small x. Although antiquark
distributions are shadowed at small x, their behavior is not obvious at medium
x from the F_2 data. The gluon distributions could not be restricted well by
the inclusive DIS data; however, the analysis tends to support the gluon
shadowing at small x. We provide analytical expressions and computer
subroutines for calculating the nuclear parton distributions, so that other
researchers could use them for applications to other high-energy nuclear
reactions.Comment: 1+11 pages, LaTeX, amsmath.sty, wrapfig.sty, graphicx.sty, ias.cls,
ias.sty, pramana.sty, pmana10.sty, pbib.sty, times.sty, 9 eps figures.
Invited talk given at the International Symposium on Nuclear Physics, Mumbai,
India, Dec. 18-22, 2000, to be published in proceedings. Complete postscript
file is available at http://www-hs.phys.saga-u.ac.jp Email:
[email protected], [email protected],
[email protected]
A high-precision polarimeter
We have built a polarimeter in order to measure the electron beam
polarization in hall C at JLAB. Using a superconducting solenoid to drive the
pure-iron target foil into saturation, and a symmetrical setup to detect the
Moller electrons in coincidence, we achieve an accuracy of <1%. This sets a new
standard for Moller polarimeters.Comment: 17 pages, 9 figures, submitted to N.I.
Superscaling in inclusive electron-nucleus scattering
We investigate the degree to which the scaling functions derived
from cross sections for inclusive electron-nucleus quasi-elastic scattering
define the same function for different nuclei. In the region where the scaling
variable , we find that this superscaling is experimentally realized
to a high degree.Comment: Corrected previously mislabeled figures and cross references; 9
pages, 4 color figures, using BoxedEPS and REVTeX; email correspondence to
[email protected]
Determination of Matter Surface Distribution of Neutron-rich Nuclei
We demonstrate that the matter density distribution in the surface region is
determined well by the use of the relatively low-intensity beams that become
available at the upcoming radioactive beam facilities. Following the method
used in the analyses of electron scattering, we examine how well the density
distribution is determined in a model-independent way by generating pseudo data
and by carefully applying statistical and systematic error analyses. We also
study how the determination becomes deteriorated in the central region of the
density, as the quality of data decreases. Determination of the density
distributions of neutron-rich nuclei is performed by fixing parameters in the
basis functions to the neighboring stable nuclei. The procedure allows that the
knowledge of the density distributions of stable nuclei assists to strengthen
the determination of their unstable isotopes.Comment: 41 pages, latex, 27 figure
Microscopic calculation of the inclusive electron scattering structure function in O-16
We calculate the charge form factor and the longitudinal structure function
for O and compare with the available experimental data, up to a momentum
transfer of 4 fm. The ground state correlations are generated using the
coupled cluster [exp(S}] method, together with the realistic v-18 NN
interaction and the Urbana IX three-nucleon interaction. Center-of-mass
corrections are dealt with by adding a center-of-mass Hamiltonian to the usual
internal Hamiltonian, and by means of a many-body expansion for the computation
of the observables measured in the center-of-mass system
Ground state correlations and mean-field in O: Part II
We continue the investigations of the O ground state using the
coupled-cluster expansion [] method with realistic nuclear
interaction. In this stage of the project, we take into account the three
nucleon interaction, and examine in some detail the definition of the internal
Hamiltonian, thus trying to correct for the center-of-mass motion. We show that
this may result in a better separation of the internal and center-of-mass
degrees of freedom in the many-body nuclear wave function. The resulting ground
state wave function is used to calculate the "theoretical" charge form factor
and charge density. Using the "theoretical" charge density, we generate the
charge form factor in the DWBA picture, which is then compared with the
available experimental data. The longitudinal response function in inclusive
electron scattering for O is also computed.Comment: 9 pages, 7 figure
Ground State Correlations in 16O and 40Ca
We study the ground state properties of doubly closed shell nuclei O
and Ca in the framework of Correlated Basis Function theory using state
dependent correlations, with central and tensor components. The realistic
Argonne and two-nucleon potentials and three-nucleon
potentials of the Urbana class have been adopted. By means of the Fermi
Hypernetted Chain integral equations, in conjunction with the Single Operator
Chain approximation, we evaluate the ground state energy, one- and two-body
densities and electromagnetic and spin static responses for both nuclei. In
O we compare our results with the available Monte Carlo and Coupled
Cluster ones and find a satisfying agreement. As in the nuclear matter case
with similar interactions and wave functions, the nuclei result under-bound by
2--3 MeV/A.Comment: 33 RevTeX pages + 8 figures, to appear in Phys.Rev.
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