317 research outputs found
Semiclassical description of multiphoton processes
We analyze strong field atomic dynamics semiclassically, based on a full
time-dependent description with the Hermann-Kluk propagator. From the
properties of the exact classical trajectories, in particular the accumulation
of action in time, the prominent features of above threshold ionization (ATI)
and higher harmonic generation (HHG) are proven to be interference phenomena.
They are reproduced quantitatively in the semiclassical approximation.
Moreover, the behavior of the action of the classical trajectories supports the
so called strong field approximation which has been devised and postulated for
strong field dynamics.Comment: 10 pages, 11 figure
Evolution of the Red Sequence Giant to Dwarf Ratio in Galaxy Clusters out to z ~ 0.5
We analyze deep g' and r' band data of 97 galaxy clusters imaged with MegaCam
on the Canada-France-Hawaii telescope. We compute the number of luminous
(giant) and faint (dwarf) galaxies using criteria based on the definitions of
de Lucia et al. (2007). Due to excellent image quality and uniformity of the
data and analysis, we probe the giant-to-dwarf ratio (GDR) out to z ~ 0.55.
With X-ray temperature (Tx) information for the majority of our clusters, we
constrain, for the first time, the Tx-corrected giant and dwarf evolution
separately. Our measurements support an evolving GDR over the redshift range
0.05 < z < 0.55. We show that modifying the (g'-r'), m_r' and K-correction used
to define dwarf and giant selection do not alter the conclusion regarding the
presence of evolution. We parameterize the GDR evolution using a linear
function of redshift (GDR = alpha * z + beta) with a best fit slope of alpha =
0.88 +/- 0.15 and normalization beta = 0.44 +/- 0.03. Contrary to claims of a
large intrinsic scatter, we find that the GDR data can be fully accounted for
using observational errors alone. Consistently, we find no evidence for a
correlation between GDR and cluster mass (via Tx or weak lensing). Lastly, the
data suggest that the evolution of the GDR at z < 0.2 is driven primarily by
dry merging of the massive giant galaxies, which when considered with previous
results at higher redshift, suggests a change in the dominant mechanism that
mediates the GDR.Comment: 20 pages, 15 figures. Accepted to MNRA
Galactic cannibalism and CDM density profiles
Using N-body simulations we show that the process of formation of the
brightest cluster galaxy through dissipationless galactic cannibalism can
affect the inner cluster dark matter density profile. In particular, we use as
realistic test case the dynamical evolution of the galaxy cluster C0337-2522 at
redshift z=0.59, hosting in its centre a group of five elliptical galaxies
which are likely to be the progenitor of a central giant elliptical. After the
formation of the brightest cluster galaxy, the inner cluster dark matter
density profile is significantly flatter (logarithmic slope 0.49<beta<0.90)
than the original cusp (beta=1), as a consequence of dynamical friction heating
of the massive galaxies against the diffuse cluster dark matter. In our
simulations we have assumed that the cluster galaxies are made of stars only.
We also show that the presence of galactic dark matter haloes can steepen the
cluster central density profile. We conclude that galactic cannibalism could be
a viable physical mechanism to reconcile - at least at the cluster scale - the
flat dark matter haloes inferred observationally in some galaxy clusters with
the steep haloes predicted by cosmological simulations.Comment: 6 pages with 3 figures. Version accepted for publication in MNRAS.
Longer than first version, with results from additional simulations.
Conclusions unchange
Avaliação da atividade antimicrobiana de extrato aquoso e etanólico de Acanthospermum australe.
As plantas medicinais têm sido amplamente empregadas na terapia de diversas patologias, constituindo parte das ferramentas terapêuticas utilizadas no controle das mais variadas moléstias humanas. A atividade antibacteriana dos extratos aquoso e etanólico de Acanthospermum australe (Loefl.) O. Kuntze foi avaliada frente às bactérias Staphylococcus aureus (ATCC 6538P) e Escherichia coli (ATCC 25922), pelo método de difusão em Agar. Foi observada a inibição de crescimento destes microrganismos por ambos os extratos, nas concentrações testadas. Paralelamente, foi realizada a análise fitoquímica dos extratos aquoso e hidroetanólico para a determinação de compostos fenólicos (taninos, flavonoides, ácidos fenólicos e antraquinonas), alcaloides e compostos terpênicos. Os extratos apresentaram perfis qualitativamente semelhantes, apresentando taninos, flavonoides, ácidos fenólicos e compostos terpênicos
Stars and dark matter in the spiral gravitational lens 2237+0305
We construct a mass model for the spiral lens galaxy 2237+0305, at redshift
z_l=0.04, based on gravitational-lensing constraints, HI rotation, and new
stellar-kinematic information, based on data taken with the ESI spectrograph on
the 10m Keck-II Telescope. High resolution rotation curves and velocity
dispersion profiles along two perpendicular directions, close to the major and
minor axes of the lens galaxy, were obtained by fitting the Mgb-Fe absorption
line region. The stellar rotation curve rises slowly and flattens at r~1.5"
(~1.1 kpc). The velocity dispersion profile is approximately flat. A
combination of photometric, kinematic and lensing information is used to
construct a mass model for the four major mass components of the system -- the
dark matter halo, disc, bulge, and bar. The best-fitting solution has a dark
matter halo with a logarithmic inner density slope of gamma=0.9+/-0.3 for
rho_DM propto r^-gamma, a bulge with M/L_B=6.6+/-0.3 Upsilon_odot, and a disc
with M/L_B =1.2+/-0.3 Upsilon_odot, in agreement with measurements of late-type
spirals. The bulge dominates support in the inner regions where the multiple
images are located and is therefore tightly constrained by the observations.
The disc is sub-maximal and contributes 45+/-11 per cent of the rotational
support of the galaxy at 2.2r_d. The halo mass is (2.0+/-0.6) x 10^12 M_odot,
and the stellar to virial mass ratio is 7.0+/-2.3 per cent, consistent with
typical galaxies of the same mass.Comment: 14 pages, 6 figures, MNRAS, in pres
Inelastic semiclassical Coulomb scattering
We present a semiclassical S-matrix study of inelastic collinear
electron-hydrogen scattering. A simple way to extract all necessary information
from the deflection function alone without having to compute the stability
matrix is described. This includes the determination of the relevant Maslov
indices. Results of singlet and triplet cross sections for excitation and
ionization are reported. The different levels of approximation -- classical,
semiclassical, and uniform semiclassical -- are compared among each other and
to the full quantum result.Comment: 9 figure
The SWELLS Survey. I. A large spectroscopically selected sample of edge-on late-type lens galaxies
The relative contribution of baryons and dark matter to the inner regions of
spiral galaxies provides critical clues to their formation and evolution, but
it is generally difficult to determine. For spiral galaxies that are strong
gravitational lenses, however, the combination of lensing and kinematic
observations can be used to break the disk-halo degeneracy. In turn, such data
constrain fundamental parameters such as i) the mass density profile slope and
axis ratio of the dark matter halo, and by comparison with dark matter-only
numerical simulations the modifications imposed by baryons; ii) the mass in
stars and therefore the overall star formation efficiency, and the amount of
feedback; iii) by comparison with stellar population synthesis models, the
normalization of the stellar initial mass function. In this first paper of a
series, we present a sample of 16 secure, 1 probable, and 6 possible strong
lensing spiral galaxies, for which multi-band high-resolution images and
rotation curves were obtained using the Hubble Space Telescope and Keck-II
Telescope as part of the Sloan WFC Edge-on Late-type Lens Survey (SWELLS). The
sample includes 8 newly discovered secure systems. [abridged] We find that the
SWELLS sample of secure lenses spans a broad range of morphologies (from
lenticular to late-type spiral), spectral types (quantified by Halpha
emission), and bulge to total stellar mass ratio (0.22-0.85), while being
limited to M_*>10^{10.5} M_sun. The SWELLS sample is thus well-suited for
exploring the relationship between dark and luminous matter in a broad range of
galaxies. We find that the deflector galaxies obey the same size-mass relation
as that of a comparison sample of elongated non-lens galaxies selected from the
SDSS survey. We conclude that the SWELLS sample is consistent with being
representative of the overall population of high-mass high-inclination disky
galaxies.Comment: 21 pages, 6 figures, MNRAS, in pres
Dissipational versus Dissipationless Galaxy Formation and the Dark Matter Content of Galaxies
We examine two extreme models for the build-up of the stellar component of
luminous elliptical galaxies. In one case, we assume the build-up of stars is
dissipational, with centrally accreted gas radiating away its orbital and
thermal energy; the dark matter halo will undergo adiabatic contraction and the
central dark matter density profile will steepen. For the second model, we
assume the central galaxy is assembled by a series of dissipationless mergers
of stellar clumps that have formed far from the nascent galaxy. In order to be
accreted, these clumps lose their orbital energy to the dark matter halo via
dynamical friction, thereby heating the central dark matter and smoothing the
dark matter density cusp. The central dark matter density profiles differ
drastically between these models. For the isolated elliptical galaxy, NGC 4494,
the central dark matter densities follow the power-laws r^(-0.2) and r^(-1.7)
for the dissipational and dissipationless models, respectively. By matching the
dissipational and dissipationless models to observations of the stellar
component of elliptical galaxies, we examine the relative contributions of
dissipational and dissipationless mergers to the formation of elliptical
galaxies and look for observational tests that will distinguish between these
models. Comparisons to strong lensing brightest cluster galaxies yield median
M*/L_B ratios of 2.1+/-0.8 and 5.2+/-1.7 at z=0.39 for the dissipational and
dissipationless models, respectively. For NGC 4494, the best-fit dissipational
and dissipationless models have M*/L_B=2.97 and 3.96. Comparisons to expected
stellar mass-to-light ratios from passive evolution and population syntheses
appear to rule out a purely dissipational formation mechanism for the central
stellar regions of giant elliptical galaxies.Comment: 15 pages, 9 figures, accepted to Ap
Disentangling Baryons and Dark Matter in the Spiral Gravitational Lens B1933+503
Measuring the relative mass contributions of luminous and dark matter in
spiral galaxies is important for understanding their formation and evolution.
The combination of a galaxy rotation curve and strong lensing is a powerful way
to break the disk-halo degeneracy that is inherent in each of the methods
individually. We present an analysis of the 10-image radio spiral lens
B1933+503 at z_l=0.755, incorporating (1) new global VLBI observations, (2) new
adaptive-optics assisted K-band imaging, (3) new spectroscopic observations for
the lens galaxy rotation curve and the source redshift. We construct a
three-dimensionally axisymmetric mass distribution with 3 components: an
exponential profile for the disk, a point mass for the bulge, and an NFW
profile for the halo. The mass model is simultaneously fitted to the kinematics
and the lensing data. The NFW halo needs to be oblate with a flattening of
a/c=0.33^{+0.07}_{-0.05} to be consistent with the radio data. This suggests
that baryons are effective at making the halos oblate near the center. The
lensing and kinematics analysis probe the inner ~10 kpc of the galaxy, and we
obtain a lower limit on the halo scale radius of 16 kpc (95% CI). The dark
matter mass fraction inside a sphere with a radius of 2.2 disk scale lengths is
f_{DM,2.2}=0.43^{+0.10}_{-0.09}. The contribution of the disk to the total
circular velocity at 2.2 disk scale lengths is 0.76^{+0.05}_{-0.06}, suggesting
that the disk is marginally submaximal. The stellar mass of the disk from our
modeling is log_{10}(M_{*}/M_{sun}) = 11.06^{+0.09}_{-0.11} assuming that the
cold gas contributes ~20% to the total disk mass. In comparison to the stellar
masses estimated from stellar population synthesis models, the stellar initial
mass function of Chabrier is preferred to that of Salpeter by a probability
factor of 7.2.Comment: 16 pages, 13 figures, minor revisions based on referee's comments,
accepted for publication in Ap
Weak Lensing by Galaxies in Groups and Clusters: I.--Theoretical Expectations
Galaxy-galaxy lensing is rapidly becoming one of the most promising means to
accurately measure the average relation between galaxy properties and halo
mass. In order to obtain a signal of sufficient signal-to-noise, one needs to
stack many lens galaxies according to their property of interest, such as
luminosity or stellar mass. Since such a stack consists of both central and
satellite galaxies, which contribute very different lensing signals, the
resulting shear measurements can be difficult to interpret. In the past,
galaxy-galaxy lensing studies have either completely ignored this problem, have
applied rough isolation criteria in an attempt to preferentially select
`central' galaxies, or have tried to model the contribution of satellites
explicitely. However, if one is able to {\it a priori} split the galaxy
population in central and satellite galaxies, one can measure their lensing
signals separately. This not only allows a much cleaner measurement of the
relation between halo mass and their galaxy populations, but also allows a
direct measurement of the sub-halo masses around satellite galaxies. In this
paper, we use a realistic mock galaxy redshift survey to show that galaxy
groups, properly selected from large galaxy surveys, can be used to accurately
split the galaxy population in centrals and satellites. Stacking the resulting
centrals according to their group mass, estimated from the total group
luminosity, allows a remarkably accurate recovery of the masses and density
profiles of their host haloes. In addition, stacking the corresponding
satellite galaxies according to their projected distance from the group center
yields a lensing signal that can be used to accurate measure the masses of both
sub-haloes and host haloes. (Abridged)Comment: 16 pages, 10 figures, Accepted for publication in MNRA
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