12,539 research outputs found
The Interplay of Cluster and Galaxy Evolution
We review here the interplay of cluster and galaxy evolution. As a case
study, we consider the Butcher-Oemler effect and propose that it is the result
of the changing rate of cluster merger events in a hierarchical universe. This
case study highlights the need for new catalogs of clusters and groups that
possess quantified morphologies. We present such a sample here, namely the
Sloan Digital Sky Survey (SDSS) C4 Catalog, which has been objectively-selected
from the SDSS spectroscopic galaxy sample. We outline here the C4 algorithm and
present first results based on the SDSS Early Data Release, including an X-ray
luminosity-velocity dispersion (L_x-sigma) scaling relationship (as a function
of cluster morphology), and the density-SFR relation of galaxies within C4
clusters (Gomez et al. 2003). We also discuss the merger of Coma and the
NGC4839 group, and its effect on the galaxy populations in these systems. We
finish with a brief discussion of a new sample of Hdelta-selected galaxies
(i.e., k+a, post--starburst galaxies) obtained from the SDSS spectroscopic
survey.Comment: Invited review at the JENAM 2002 Workshop on "Galaxy Evolution in
Groups and Clusters", Porto, Sep 5-7 2002, eds. Lobo, Serote-Roos and
Biviano, Kluwer in pres
Polarized Parton Densities
In this talk we summarize main results of a recent determination of the
polarized deeply inelastic parton distributions to NLO from the world data. In
the analysis the LO and NLO parton densities and their statistical
errors were derived and parameterized. The strong coupling constant
is determined Comparisons of the
low moments of the parton densities with recent lattice results are given. A
detailed error-analysis of the gluon density is performed.Comment: 3 pages LATEX, 1 style file, 1 eps file, to appear in the Proceedings
of PANIC '02, Osaka, Ocrober 200
Chemical Analysis of a Diffuse Cloud along a Line of Sight Toward W51: Molecular Fraction and Cosmic-Ray Ionization Rate
Absorption lines from the molecules OH+, H2O+, and H3+ have been observed in
a diffuse molecular cloud along a line of sight near W51 IRS2. We present the
first chemical analysis that combines the information provided by all three of
these species. Together, OH+ and H2O+ are used to determine the molecular
hydrogen fraction in the outskirts of the observed cloud, as well as the
cosmic-ray ionization rate of atomic hydrogen. H3+ is used to infer the
cosmic-ray ionization rate of H2 in the molecular interior of the cloud, which
we find to be zeta_2=(4.8+-3.4)x10^-16 per second. Combining the results from
all three species we find an efficiency factor---defined as the ratio of the
formation rate of OH+ to the cosmic-ray ionization rate of H---of
epsilon=0.07+-0.04, much lower than predicted by chemical models. This is an
important step in the future use of OH+ and H2O+ on their own as tracers of the
cosmic-ray ionization rate.Comment: 21 pages, 1 figure, 4 table
MgII Absorption Lines in z=2.974 Damped Lyman-alpha System toward Gravitationally Lensed QSO APM 08279+5255: Detection of Small-scale Structure in MgII Absorbing Clouds
1.02-1.16 micron spectra (R ~ 7,000) of the gravitationally lensed QSO APM
08279+5255 at z_em=3.911 were obtained during the commissioning run of IRCS,
the 1-5 micron near-infrared camera and spectrograph for the Subaru 8.2 m
Telescope. Strong MgII doublet at 2976,2800 angstrom and FeII (2600 angstrom),
FeII (2587 angstrom) absorption lines at z_abs=2.974 were clearly detected in
the rest-frame UV spectra, confirming the presence of a damped Lyman-alpha
system at the redshift as suggested by Petitjean et al. Also MgI (2853
angstrom) absorption line is probably detected. An analysis of the absorption
lines including velocity decomposition was performed. This is a first detailed
study of MgII absorption system at high redshift (z > 2.5) where the MgII
doublet shifts into the near-infrared in the observer's frame.
The spectra of the lensed QSO pair A and B with 0.38 arcsec separation were
resolved in some exposure frames under excellent seeing condition. We extracted
the MgII doublet spectra of A and B separately. Although three velocity
components (v ~ -28, +5, +45 km/s) are known to exist in this MgII system
(Petitjean et al.), the v ~ +45 km/s absorption line was not detected toward
source B, showing that the +45 km/s MgII cloud lies only in the line of sight
to the source A. Our results suggests that the size of the MgII absorbing
clouds is as small as 200 pc, which corresponds to the separation of A and B at
the redshift of the absorber. This is the first direct detection of the
small-scale structure of MgII clouds at high-redshift, confirming the estimated
cloud sizes from photoionization model by Churchill and Charlton.Comment: ApJ in press (Vol.569, 20 April 2002 issue
Green's function of fully anharmonic lattice vibration
Motivated by the discovery of superconductivity in beta-pyrochlore oxides, we
study property of rattling motion coupled with conduction electrons. We derive
the general expression of the Green's function of fully anharmonic lattice
vibration within the accuracy of the second order perturbation of electron-ion
interaction by introducing self-energy, vertex-correction, and normalization
factor for each transition. Using the expression, we discuss the characteristic
properties of the spectral function in the entire range from weakly anharmonic
potential to double-well case, and calculate NMR relaxation rate due to the two
phonon Raman process
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