4,757 research outputs found
The Universality of the Fundamental Plane of E and S0 Galaxies. Spectroscopic data
We present here central velocity dispersion measurements for 325 early-type
galaxies in eight clusters and groups of galaxies, including new observations
for 212 galaxies. The clusters and groups are the A262, A1367, Coma (A1656),
A2634, Cancer and Pegasus clusters, and the NGC 383 and NGC 507 groups. The new
measurements were derived from medium dispersion spectra, that cover 600 A
centered on the Mg Ib triplet at lambda ~ 5175. Velocity dispersions were
measured using the Tonry & Davis cross-correlation method, with a typical
accuracy of 6%. A detailed comparison with other data sources is made.Comment: 12 pages, 5 tables, 3 figures, to appear in AJ. Note that tables 2
and 3 are in separate files, as they should be printed in landscape forma
The Fundamental Plane of Gravitational Lens Galaxies and The Evolution of Early-Type Galaxies in Low Density Environments
Most gravitational lenses are early-type galaxies in relatively low density
environments -- a ``field'' rather than a ``cluster'' population. We show that
field early-type galaxies with 0 < z < 1, as represented by the lens galaxies,
lie on the same fundamental plane as those in rich clusters at similar
redshifts. We then use the fundamental plane to measure the combined
evolutionary and K-corrections for early-type galaxies in the V, I and H bands.
Only for passively evolving stellar populations formed at z > 2 (H_0=65 km/s
Mpc, Omega_0=0.3, Lambda_0=0.7) can the lens galaxies be matched to the local
fundamental plane. The high formation epoch and the lack of significant
differences between the field and cluster populations contradict many current
models of the formation history of early-type galaxies. Lens galaxy colors and
the fundamental plane provide good photometric redshift estimates with an
empirical accuracy of -0.03 +/- 0.11 for the 17 lenses with known redshifts. A
mass model dominated by dark matter is more consistent with the data than
either an isotropic or radially anisotropic constant M/L mass model, and a
radially anisotropic model is better than an isotropic model.Comment: 36 pages, 9 figures, 6 tables. ApJ in press. Final version contains
more observational dat
Influence of intrinsic decoherence on nonclassical properties of the output of a Bose-Einstein condensate
We investigate nonclassical properties of the output of a Bose-Einstein
condensate in Milburn's model of intrinsic decoherence. It is shown that the
squeezing property of the atom laser is suppressed due to decoherence.
Nevertheless, if some very special conditions were satisfied, the squeezing
properties of atom laser could be robust against the decoherence.Comment: 17 pages, 5 figures, Late
Quantum and classical thermal correlations in the XY spin-1/2 chain
We investigate pairwise quantum correlation as measured by the quantum
discord as well as its classical counterpart in the thermodynamic limit of
anisotropic XY spin-1/2 chains in a transverse magnetic field for both zero and
finite temperatures. Analytical expressions for both classical and quantum
correlations are obtained for spin pairs at any distance. In the case of zero
temperature, it is shown that the quantum discord for spin pairs farther than
second-neighbors is able to characterize a quantum phase transition, even
though pairwise entanglement is absent for such distances. For finite
temperatures, we show that quantum correlations can be increased with
temperature in the presence of a magnetic field. Moreover, in the XX limit, the
thermal quantum discord is found to be dominant over classical correlation
while the opposite scenario takes place for the transverse field Ising model
limit
Relation between metallicities and spectral energy distributions of Herbig Ae/Be stars. A potential link with planet formation
(Abridged) The stellar metallicity, [M/H], may have important implications
for planet formation. In particular, Kama et al. proposed that the deficit of
refractory elements in the surfaces of some Herbig Ae/Be stars (HAeBes) may be
linked to the presence of disk cavities likely caused by Jovian planets that
trap the metal-rich content. This work aims to provide a robust test on the
previous proposal by analyzing the largest sample of HAeBes with homogeneously
derived [M/H] values, stellar, and circumstellar properties. [M/H] values of 67
HAeBes were derived based on observed spectra and Kurucz synthetic models.
Statistical analyses were carried out aiming to test the potential relation
between [M/H] and the group I sources from the spectral energy distribution
(SED) classification by Meeus et al., associated to the presence of cavities
potentially carved by giant planets. Our study robustly confirms that group I
sources tend to have a lower [M/H] than that of group II HAeBes. A similar
analysis involving SED-based transitional disks does not reveal such a
relation, indicating that not all processes capable of creating dust holes have
an effect on the stellar abundances. We also show that the observed [M/H]
differences are not driven by environmental effects. Finally, group I sources
tend to have stronger (sub-) mm continuum emission presumably related to the
presence of giant planets. Indeed, literature results indicate that disk
substructures probably associated to their presence are up to ten times more
frequent in group I HAeBes. We provide indirect evidences suggesting that giant
planets are more frequent around group I/low [M/H] stars than around the rest
of the HAeBes. However, the direct test requires multiple detections of forming
planets in their disks, so far limited to the candidate around the metal
depleted ([M/H] = -0.35 +- 0.25) group I HAeBe star AB Aur.Comment: 16 pages, 10 figures, 2 tables. Accepted in A&
Probing the evolution of early-type cluster galaxies through chemical enrichment
A simple chemical enrichment model for cluster early-type galaxies is
described in which the mechanisms considered in the evolutionary model are
infall of primordial gas, outflows and a possible variation in the star
formation efficiency. We find that - within the framework of our models - only
outflows can generate a suitable range of metallicities. The chemical
enrichment tracks can be combined with the latest population synthesis models
to simulate clusters over a wide redshift range, for a set of toy models. The
color-magnitude relation of local clusters is used as a constraint, fixing the
correlation between absolute luminosity and ejected fraction of gas from
outflows. It is found that the correlations between color or mass-to-light
ratios and absolute luminosity are degenerate with respect to most of the input
parameters. However, a significant change between monolithic and hierarchical
models is predicted for redshifts z\simgt 1. The comparison between predicted
and observed mass-to-light ratios yield an approximate linear bias between
total and stellar masses: in
early-type galaxies. If we assume that outflows constitute the driving
mechanism for the colors observed in cluster early type galaxies, the
metallicity of the intracluster medium (ICM) can be linked to outflows. The
color-magnitude constraint requires faint galaxies to eject 85%
of their gas, which means that most of the metals in the ICM may have
originated in these dwarf galaxies.Comment: Accepted for publication in ApJ. Uses emulateapj.sty. 12 pages with
10 embedded EPS figure
The Stellar Population Histories of Early-Type Galaxies. II. Controlling Parameters of the Stellar Populations
We analyze single-stellar-population (SSP) equivalent parameters for 50 local
elliptical galaxies as a function of their structural parameters. These
galaxies fill a two-dimensional plane in the four-dimensional space of [Z/H],
log t, log , and [E/Fe]. SSP age and velocity dispersion can be taken
as the two independent parameters that specify a galaxy's location in this
``hyperplane.'' The hyperplane can be decomposed into two sub-relations: (1) a
``Z-plane,'' in which [Z/H] is a linear function of log and log t; and
(2) a relation between [E/Fe] and in which [E/Fe] is larger in
high- galaxies. Cluster and field ellipticals follow the same
hyperplane, but their (,t) distributions within it differ. Nearly all
cluster galaxies are old; the field ellipticals span a large range in SSP age.
The tight Mg-- relations of these ellipticals can be understood as
two-dimensional projections of the metallicity hyperplane showing it edge-on;
the tightness of these relations does not necessarily imply a narrow range of
ages at fixed . The relation between [E/Fe] and is consistent
with a higher effective yield of Type II SNe elements at higher . The
Z-plane is harder to explain and may be a powerful clue to star formation in
elliptical galaxies if it proves to be general. Present data favor a
``frosting'' model in which low apparent SSP ages are produced by adding a
small frosting of younger stars to an older base population. If the frosting
abundances are close to or slightly greater than the base population, simple
two-component models run along lines of constant in the Z-plane, as
required. This favors star formation from well-mixed pre-enriched gas rather
than unmixed low-metallicity gas from an accreted object. (Abridged)Comment: To be published in the June 2000 issue of the Astronomical Journal.
28 pages, 13 figures, uses emulateap
Reef Coral Reproduction in the Eastern Pacific: Costa Rica, PanamĂĄ, and the GalĂĄpagos Islands (Ecuador). VI. Agariciidae, Pavona clavus
The reproductive ecology of the zooxanthellate reef coral Pavona clavus was investigated at several sites in Costa Rica, Panama, and the Galapagos Islands (Ecuador) over the period 1985â2009. Pavona clavus displayed stable gonochorism as only five hermaphrodites were found in 590 samples. At four of five locations, sex ratios were skewed toward female dominance; however, at Saboga Island (Panama) male colonies predominated. In Panama, sexual maturity was observed in an estimated eight year old female colony, and several colonies of 10â20 years of age demonstrated gametogenesis. Sexual activity was observed at all study sites, but gamete development occurred in only 14â31% of colonies sampled sporadically. Seasonality of gametogenic activity occurred predominantly during the warm/wet season, June to August, at mainland sites (Cano Island, Costa Rica, and Gulfs of Chiriqui and Panama, Panama). This pattern was repeated in the Galapagos Islands, but mainly from March to May when seasonally high sea temperatures and rainfall prevailed there. Histological sampling and field observations indicated that spawning was centered around the full moon, most frequently on lunar day 17, and near sunset (1,800 h). Mean fecundity (mature ova cm-2 live tissue) estimates were significantly different for two sites and ranged from ~1,780 (Saboga Island, Gulf of Panama, seasonally upwelling) to ~4,280 (Uva Is, Gulf of Chiriqui, nonupwelling). Assuming three annual spawning events colony-1 (August, September, October), extrapolation of minimum and maximum fecundities yield 5,340 and 12,840 ova cm-2 year-1. Seasonal, lunar, and diel spawning patterns in nine zooxanthellate species at Uva Island indicate asynchronous coral community spawning
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