39 research outputs found
Orbital fluctuations in the different phases of LaVO3 and YVO3
We investigate the importance of quantum orbital fluctuations in the
orthorhombic and monoclinic phases of the Mott insulators LaVO3 and YVO3.
First, we construct ab-initio material-specific t2g Hubbard models. Then, by
using dynamical mean-field theory, we calculate the spectral matrix as a
function of temperature. Our Hubbard bands and Mott gaps are in very good
agreement with spectroscopy. We show that in orthorhombic LaVO3, quantum
orbital fluctuations are strong and that they are suppressed only in the
monoclinic 140 K phase. In YVO3 the suppression happens already at 300 K. We
show that Jahn-Teller and GdFeO3-type distortions are both crucial in
determining the type of orbital and magnetic order in the low temperature
phases.Comment: 4 pages, 3 figures, final version. To appear in PR
Evidence of Substructure in the Cluster of Galaxies A3558
We investigate the dynamical properties of the cluster of galaxies A3558
(Shapley 8). Studying a region of one square degree ( 3 Mpc) centered
on the cluster cD galaxy, we have obtained a statistically complete photometric
catalog with positions and magnitudes of 1421 galaxies (down to a limiting
magnitude of ). This catalog has been matched to the recent velocity
data obtained by Mazure et al. (1997) and from the literature, yielding a
radial velocity catalog containing 322 galaxies. Our analysis shows that the
position/velocity space distribution of galaxies shows significant
substructure. A central bimodal core detected previously in preliminary studies
is confirmed by using the Adaptive Kernel Technique and Wavelet Analysis. We
show that this central bimodal subtructure is nevertheless composed of a
projected feature, kinematically unrelated to the cluster, plus a group of
galaxies probably in its initial merging phase into a relaxed core. The cD
velocity offset with respect to the average cluster redshift, reported earlier
by several authors, is completely eliminated as a result of our dynamical
analysis. The untangling of the relaxed core component also allows a better,
more reliable determination of the central velocity dispersion, which in turn
eliminates the ``-problem'' for A3558. The cluster also shows a
``preferential'' distribution of subclumps coinciding with the direction of the
major axis position angle of the cD galaxy and of the central X-ray emission
ellipsoidal distribution, in agreement with an anisotropic merger scenario.Comment: 35 pages in latex, 17 figures in Postscript, accepted for publication
in the Astrophysical Journa
Simulations of galactic winds and starbursts in galaxy clusters
We present an investigation of the metal enrichment of the intra-cluster
medium (ICM) by galactic winds and merger-driven starbursts. We use combined
N-body/hydrodynamic simulations with a semi-numerical galaxy formation model.
The mass loss by galactic winds is obtained by calculating transonic solutions
of steady state outflows, driven by thermal, cosmic ray and MHD wave pressure.
The inhomogeneities in the metal distribution caused by these processes are an
ideal tool to reveal the dynamical state of a galaxy cluster. We present
surface brightness, X-ray emission weighted temperature and metal maps of our
model clusters as they would be observed by X-ray telescopes like XMM-Newton.
We show that X-ray weighted metal maps distinguish between pre- or post-merger
galaxy clusters by comparing the metallicity distribution with the
galaxy-density distribution: pre-mergers have a metallicity gap between the
subclusters, post-mergers a high metallicity between subclusters. We apply our
approach to two observed galaxy clusters, Abell 3528 and Abell 3921, to show
whether they are pre- or post-merging systems. The survival time of the
inhomogeneities in the metallicity distribution found in our simulations is up
to several Gyr. We show that galactic winds and merger-driven starbursts enrich
the ICM very efficiently after z=1 in the central (~ 3 Mpc radius) region of a
galaxy cluster.Comment: 18 pages, 25 figures, 2 tables, accepted for publication in A&A, more
technical details added - results are unaffected, high resolution PDF version
is available at http://astro.uibk.ac.at/Kapferer.pd
Valence electronic structure of Mn in undoped and doped lanthanum manganites from relative K x-ray intensity studies
Relative x-ray intensities of in , , and
( = , , and ) systems have been
measured following excitation by 59.54 keV -rays from a 200 mCi
Am point-source. The measured results for the compounds deviate
significantly from the results of pure . Comparison of the experimental
data with the multiconfiguration Dirac-Fock (MCDF) effective atomic model
calculations indicates reasonable agreement with the predictions of ionic model
for the doped {manganites except} that the electron doped
and hole doped compounds
show some small deviations. The results of and deviate
considerably from the predictions of the ionic model. Our measured
ratio of in cannot be explained
as a linear superposition of ratios of for the end
members which is in contrast to the recent proposal by Tyson et al. from their
spectra.Comment: 14 pages, 4 figures. to appear in NIM-B.Please send an e-mail for
figure
Recurrent radio outbursts at the center of the NGC1407 galaxy group
We present deep Giant Metrewave Radio Telescope (GMRT) radio observations at
240, 330 and 610 MHz of the complex radio source at the center of the NGC1407
galaxy group. Previous GMRT observations at 240 MHz revealed faint, diffuse
emission enclosing the central twin-jet radio galaxy. This has been interpreted
as an indication of two possible radio outbursts occurring at different times.
Both the inner double and diffuse component are detected in the new GMRT images
at high levels of significance. Combining the GMRT observations with archival
Very Large Array data at 1.4 and 4.9 GHz, we derive the total spectrum of both
components. The inner double has a spectral index \alpha=0.7, typical for
active, extended radio galaxies, whereas the spectrum of the large-scale
emission is very steep, with \alpha=1.8 between 240 MHz and 1.4 GHz. The
radiative age of the large-scale component is very long, ~300 Myr, compared to
~30 Myr estimated for the central double, confirming that the diffuse component
was generated during a former cycle of activity of the central galaxy. The
current activity have so far released an energy which is nearly one order of
magnitude lower than that associated with the former outburst. The group X-ray
emission in the Chandra and XMM-Newton images and extended radio emission show
a similar swept-back morphology. We speculate that the two structures are both
affected by the motion of the group core, perhaps due to the core sloshing in
response to a recent encounter with the nearby elliptical galaxy NGC1400.Comment: 15 pages, 12 figures and 5 tables. Accepted for publication in Ap
A deep Chandra observation of the poor cluster AWM4 - II. The role of the radio jets in enriching the intra-cluster medium
We use a Chandra observation of the poor cluster AWM4 to map the temperature
and abundance of the intra-cluster medium, so as to examine the influence of
the central radio galaxy on its environment. While the cluster core is
generally enriched to near-solar abundances, we find evidence of super-solar
abundances correlated with the radio jets, extending ~35 kpc from the core of
the central dominant galaxy NGC 6051 along its minor axis. We conclude that the
enriched gas has been transported out of the central galaxy through the action
of the radio source. We estimate the excess mass of iron in the entrained gas
to be ~1.4x10^6 Msol, and find that this can be produced in the core of NGC
6051 within the timescale of the AGN outburst. The energy required to transport
this gas to its current location is ~4.5x10^57 erg, a significant fraction of
the estimated total mechanical energy output of the AGN, though this estimate
is dependent on the degree of enrichment of the uplifted gas. The larger
near-solar abundance region is also compatible with enrichment by metals mixed
outward from NGC 6051 over a much longer timescale.Comment: Accepted for publication in MNRAS, 11 pages, 6 figure
The Photometric Properties of Isolated Early-Type Galaxies
Isolated galaxies are important since they probe the lowest density regimes
inhabited by galaxies. We define a sample of 36 nearby isolated early-type
galaxies for further study. Our isolation criteria require them to have no
comparable-mass neighbours within 2 B-band magnitudes, 0.67 Mpc in the plane of
the sky and 700 km/s in recession velocity. New wide-field optical imaging of
10 isolated galaxies with the Anglo-Australian Telescope confirms their
early-type morphology and relative isolation. We also present imaging of 4
galaxy groups as a control sample. The isolated galaxies are shown to be more
gravitationally isolated than the group galaxies. We find that the isolated
early-type galaxies have a mean effective colour of (B-R)_e = 1.54 +/- 0.14,
similar to their high-density counterparts. They reveal a similar
colour-magnitude relation slope and small intrinsic scatter to cluster
ellipticals. They also follow the Kormendy relation of surface brightness
versus size for luminous cluster galaxies. Such properties suggest that the
isolated galaxies formed at a similar epoch to cluster galaxies, such that the
bulk of their stars are very old. However, our galaxy modelling reveals
evidence for dust lanes, plumes, shells, boxy and disk isophotes in four out of
nine galaxies. Thus at least some isolated galaxies have experienced a recent
merger/accretion event which may have induced a small burst of star formation.
We derive luminosity functions for the isolated galaxies and find a faint slope
of -1.2, which is similar to the `universal' slope found in a wide variety of
environments. We examine the number density distribution of galaxies in the
field of the isolated galaxies.Comment: 16 pages, Latex, 17 figures, 6 tables, MNRAS in pres
A combined low-radio frequency/X-ray study of galaxy groups I. Giant Metrewave Radio Telescope observations at 235 MHz and 610 MHz
We present new Giant Metrewave Radio Telescope observations at 235 MHz and
610 MHz of 18 X-ray bright galaxy groups. These observations are part of an
extended project, presented here and in future papers, which combines
low-frequency radio and X-ray data to investigate the interaction between
central active galactic nuclei (AGN) and the intra-group medium (IGM). The
radio images show a very diverse population of group-central radio sources,
varying widely in size, power, morphology and spectral index. Comparison of the
radio images with Chandra and XMM-Newton X-ray images shows that groups with
significant substructure in the X-ray band and marginal radio emission at >= 1
GHz host low-frequency radio structures that correlate with substructures in
IGM. Radio-filled X-ray cavities, the most evident form of AGN/IGM interaction
in our sample, are found in half of the systems, and are typically associated
with small, low- or mid-power double radio sources. Two systems, NGC5044 and
NGC4636, possess multiple cavities, which are isotropically distributed around
the group center, possibly due to group weather. In other systems the
radio/X-ray correlations are less evident. However, the AGN/IGM interaction can
manifest itself through the effects of the high-pressure medium on the
morphology, spectral properties and evolution of the radio-emitting plasma. In
particular, the IGM can confine fading radio lobes in old/dying radio galaxies
and prevent them from dissipating quickly. Evidence for radio emission produced
by former outbursts that coexist with current activity is found in six groups
of the sample.Comment: Accepted for publication in the Astrophysical Journal Supplement
Series, 26 pages, 18 figures. A version with high-quality figures is
http://www.astro.umd.edu/~simona/giacintucci_hr.pd
Electronic Structure Calculation by First Principles for Strongly Correlated Electron Systems
Recent trends of ab initio studies and progress in methodologies for
electronic structure calculations of strongly correlated electron systems are
discussed. The interest for developing efficient methods is motivated by recent
discoveries and characterizations of strongly correlated electron materials and
by requirements for understanding mechanisms of intriguing phenomena beyond a
single-particle picture. A three-stage scheme is developed as renormalized
multi-scale solvers (RMS) utilizing the hierarchical electronic structure in
the energy space. It provides us with an ab initio downfolding of the global
band structure into low-energy effective models followed by low-energy solvers
for the models. The RMS method is illustrated with examples of several
materials. In particular, we overview cases such as dynamics of semiconductors,
transition metals and its compounds including iron-based superconductors and
perovskite oxides, as well as organic conductors of kappa-ET type.Comment: 44 pages including 38 figures, to appear in J. Phys. Soc. Jpn. as an
invited review pape