1,238 research outputs found
Kinematic Properties and Dark Matter Fraction of Virgo Dwarf Early-Type Galaxies
What happens to dwarf galaxies as they enter the cluster potential well is
one of the main unknowns in studies of galaxy evolution. Several evidence
suggests that late-type galaxies enter the cluster and are transformed to dwarf
early-type galaxies (dEs). We study the Virgo cluster to understand which
mechanisms are involved in this transformation. We find that the dEs in the
outer parts of Virgo have rotation curves with shapes and amplitudes similar to
late-type galaxies of the same luminosity. These dEs are rotationally
supported, have disky isophotes, and younger ages than those dEs in the center
of Virgo, which are pressure supported, often have boxy isophotes and are
older. Ram pressure stripping, thus, explains the properties of the dEs located
in the outskirts of Virgo. However, the dEs in the central cluster regions,
which have lost their angular momentum, must have suffered a more violent
transformation. A combination of ram pressure stripping and harassment is not
enough to remove the rotation and the spiral/disky structures of these
galaxies. We find that on the the Faber-Jackson and the Fundamental Plane
relations dEs deviate from the trends of massive elliptical galaxies towards
the position of dark matter dominated systems such as the dwarf spheroidal
satellites of the Milky Way and M31. Both, rotationally and pressure supported
dEs, however, populate the same region in these diagrams. This indicates that
dEs have a non-negligible dark matter fraction within their half light radius.Comment: Proceeding of the XXVIII IAU General Assembly, Special Session 3:
Galaxy Evolution through Secular Processes. Edts: R. Buta and D. Pfennige
The tilt of the Fundamental Plane of Early-type galaxies: wavelength dependence
The photometric parameters R_e and mu_e of 74 early-type (E+S0+S0a) galaxies
in the Coma cluster are derived for the first time in the near IR H band. These
are used, coupled with measurements of the central velocity dispersion found in
the literature, to determine the H band Fundamental Plane (FP) relation of this
cluster. The same procedure is applied to previously available photometric data
in the B, V, r, I, and K bands, to perform a multi-wavelength study of the FP.
Because systematic uncertainties in the value of the FP parameters are
introduced both by the choice of the fitting algorithm, and by the presence of
statistical biases connected with the sample selection procedure, we emphasize
the importance of deriving the FP parameters in the six photometric bands using
an identical fitting algorithm, and appropriate corrections to eliminate the
effects of sample incompleteness. We find that the FP mu_e coefficient is
stable with wavelength, while the sigma coefficient increases significantly
with increasing wavelength, in agreement with an earlier result presented by
Pahre & Djorgovski. The slope of the FP relation, although changing with
wavelength, never approaches the virial theorem expectation. We also find that
the magnitude of the slope change can be entirely explained by the presence of
the well known relation between color and magnitude among early-type galaxies.
We conclude that the tilt of the Fundamental Plane is significant, and must be
due to some form of broken homology among early-type galaxies, while its
wavelength dependence derives from whatever mechanism (currently the preferred
one is the existence of a mass-metal content sequence) produces the
color-magnitude relation in those galaxies.Comment: 8 pages, 7 figures, 6 tables; table 3 should be printed in landscape
mode, and inserted into the text. Accepted for publication in MNRA
The GALEX Ultraviolet Virgo Cluster Survey (GUViCS). II. Constraints on star formation in ram-pressure stripped gas
Context: Several galaxies in the Virgo cluster are known to have large HI gas
tails related to a recent ram-pressure stripping event. The Virgo cluster has
been extensively observed at 1539 A in the far-ultraviolet for the GALEX
Ultraviolet Virgo Cluster Survey (GUViCS), and in the optical for the Next
Generation Virgo Survey (NGVS), allowing a study of the stellar emission
potentially associated with the gas tails of 8 cluster members. On the
theoretical side, models of ram-pressure stripping events have started to
include the physics of star formation. Aim: We aim to provide quantitative
constraints on the amount of star formation taking place in the ram-pressure
stripped gas, mainly on the basis of the far-UV emission found in the GUViCS
images in relation with the gas content of the tails. Methods: We have
performed three comparisons of the young stars emission with the gas column
density: visual, pixel-by-pixel and global. We have compared our results to
other observational and theoretical studies. Results: We find that the level of
star formation taking place in the gas stripped from galaxies by ram-pressure
is low with respect to the available amount of gas. Star formation is lower by
at least a factor 10 compared to the predictions of the Schmidt Law as
determined in regular spiral galaxy disks. It is also lower than measured in
dwarfs galaxies and the outer regions of spirals, and than predicted by some
numerical simulations. We provide constraints on the star formation efficiency
in the ram-pressure stripped gas tails, and compare these with current models.Comment: Accepted in A&A, 17 pages (including the appendix and "on-line"
figures of the paper
A semiquantitative approach to the impurity-band-related transport properties of GaMnAs nanolayers
We investigate the spin-polarized transport of GaMnAs nanolayers in which a
ferromagnetic order exists below a certain transition temperature. Our
calculation for the self-averaged resistivity takes into account the existence
of an impurity band determining the extended ("metallic" transport) or
localized (hopping by thermal excitation) nature of the states at and near the
Fermi level. Magnetic order and resistivity are inter-related due to the
influence of the spin polarization of the impurity band and the effect of the
Zeeman splitting on the mobility edge. We obtain, for a given range of Mn
concentration and carrier density, a "metallic" behavior in which the transport
by extended carriers dominates at low temperature, and is dominated by the
thermally excited localized carriers near and above the transition temperature.
This gives rise to a conspicuous hump of the resistivity which has been
experimentally observed and brings light onto the relationship between
transport and magnetic properties of this material
Formation and evolution of dwarf early-type galaxies in the Virgo cluster II. Kinematic Scaling Relations
We place our sample of 18 Virgo dwarf early-type galaxies (dEs) on the V-K -
velocity dispersion, Faber-Jackson, and Fundamental Plane (FP) scaling
relations for massive early-type galaxies (Es). We use a generalized velocity
dispersion, which includes rotation, to be able to compare the location of both
rotationally and pressure supported dEs with those of early and late-type
galaxies. We find that dEs seem to bend the Faber-Jackson relation of Es to
lower velocity dispersions, being the link between Es and dwarf spheroidal
galaxies (dSphs). Regarding the FP relation, we find that dEs are significantly
offset with respect to massive hot stellar systems, and re-casting the FP into
the so-called kappa-space suggests that this offset is related to dEs having a
total mass-to-light ratio higher than Es but still significantly lower than
dSph galaxies. Given a stellar mass-to-light ratio based on the measured line
indices of dEs, the FP offset allows us to infer that the dark matter fraction
within the half light radii of dEs is on average >~ 42% (uncertainties of 17%
in the K band and 20% in the V band), fully consistent with an independent
estimate in an earlier paper in this series. We also find that dEs in the
size-luminosity relation in the near-infrared, like in the optical, are offset
from early-type galaxies, but seem to be consistent with late-type galaxies. We
thus conclude that the scaling relations show that dEs are different from Es,
and that they further strengthen our previous findings that dEs are closer to
and likely formed from late-type galaxies.Comment: 14 pages, 9 figures, 2 appendixes. Accepted for publication in A&
Effects of Microvibrations and Their Damping on the Evolution of Pinot Noir Wine during Bottle Storage.
(c) The Author/sEnvironmental conditions such as vibrations, temperature, and exposure to light can lower the quality of bottled wine, causing great economic and image losses for wineries. Even under optimal storage conditions, environmental microvibrations can be a constant source of energy transfer to the stored bottles, and little is known about their effects over time. In this study, the effects of microvibrations on a fine Pinot noir wine were evaluated over a storage period of one year under controlled conditions and compared with those obtained using natural magnetic levitation as a damping technique to reduce the power transmitted by the vibrations. The wines were subjected to the treatments according to the following experimental set-up: (A) wines not exposed to microvibrations, but to natural magnetic levitation; (B) wines placed on a shelf in contact with the floor, and exposed to microvibrations; (C) controls, a shelf in direct contact with the floor, without the application of microvibrations; (D) wines on a shelf with natural magnetic levitation and exposed to microvibrations. Phenolic and volatile compounds were not significantly different between treatments, which is in line with the reduced energy stress applied. In contrast, the storage time significantly influenced these chemical profiles. Through the sensory analysis performed after 0 and 12 months of storage, it was possible to distinguish the wines, as the overall quality improved, especially for the microvibration-treated samples. After 12 months of storage: (a) the overall sensory quality improved for all wines compared to the samples at T0; (b) the damping of microvibrations reduced the rate of wine evolution; (c) treatment with microvibration up to 6 months was useful for improving the quality of wine not yet ready for the market. Therefore, modulation of wine evolution can be achieved by applying a combination of microvibrations and their damping, depending on the enological objective.Published onlin
On the nature of the spin-polarized hole states in a quasi-two-dimensional GaMnAs ferromagnetic layer
A self-consistent calculation of the density of states and the spectral
density function is performed in a two-dimensional spin-polarized hole system
based on a multiple-scattering approximation. Using parameters corresponding to
GaMnAs thin layers, a wide range of Mn concentrations and hole densities have
been explored to understand the nature, localized or extended, of the
spin-polarized holes at the Fermi level for several values of the average
magnetization of the Mn ystem. We show that, for a certain interval of Mn and
hole densities, an increase on the magnetic order of the Mn ions come together
with a change of the nature of the states at the Fermi level. This fact
provides a delocalization of spin-polarized extended states anti-aligned to the
average Mn magnetization, and a higher spin-polarization of the hole gas. These
results are consistent with the occurrence of ferromagnetism with relatively
high transition temperatures observed in some thin film samples and
multilayered structures of this material.Comment: 3 page
Effects of transport conditions on the stability and sensory quality of wines
The quality of wine can be affected by several factors after bottling: temperature changes, shipment time, type and amount of mechanical stress (vibrations) and environmental conditions, such as light exposure and relative humidity. The effects of delivery using different packaging systems (boxes, bottles, containers) and the impacts of mode of shipment (car, truck, airplane and cargo ship) are reviewed, along with compositional markers, the reactions leading to off-odours and/or off-flavours and the approaches to monitoring transportation conditions (temperature, relative humidity and type and entity of vibration) and their impacts on the sensory profile of the wine. Temperature fluctuations are more prevalent during the transport of wine over land than by sea, and may lead to a decrease in the fresh, fruity and floral aromas of the wine and to premature aging due to the ‘pump’ effect (repeated expansion and contraction cycles). Trans-shipment phases should be reduced to a minimum, especially in hot climates. Vibrations, even for a short period of time (15 days), can alter the overall quality of the product.Publishe
Hole spin polarization in GaAlAs:Mn structures
A self-consistent calculation of the electronic properties of GaAlAs:Mn
magnetic semiconductor quantum well structures is performed including the
Hartree term and the sp-d exchange interaction with the Mn magnetic moments.
The spin polarization density is obtained for several structure configurations.
Available experimental results are compared with theory.Comment: 4 page
Formation and evolution of dwarf early-type galaxies in the Virgo cluster I. Internal kinematics
We present new medium resolution kinematic data for a sample of 21 dwarf
early-type galaxies (dEs) mainly in the Virgo cluster, obtained with the WHT
and INT telescopes at the Roque de los Muchachos Observatory (La Palma, Spain).
These data are used to study the origin of the dwarf elliptical galaxy
population inhabiting clusters. We confirm that dEs are not dark matter
dominated galaxies, at least up to the half-light radius. We also find that the
observed galaxies in the outer parts of the cluster are mostly rotationally
supported systems with disky morphological shapes. Rotationally supported dEs
have rotation curves similar to those of star forming galaxies of similar
luminosity and follow the Tully-Fisher relation. This is expected if dE
galaxies are the descendant of low luminosity star forming systems which
recently entered the cluster environment and lost their gas due to a ram
pressure stripping event, quenching their star formation activity and
transforming into quiescent systems, but conserving their angular momentum.Comment: 24 pages, 15 figures and 7 tables. Replaced to match the journal
versio
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