7,867 research outputs found
Quenching Star Formation in the Green Valley: The Mass Flux at Intermediate Redshifts
We have obtained several hundred very deep spectra with DEIMOS/Keck in order
to estimate the galactic mass flux density at intermediate redshifts (0.6 < z < 0.9) from the
”blue cloud” to the red sequence across the so-called ”green valley”, the intermediate region in
the color-magnitude plot between those two populations. We use spectral indices (specifically
D_n (4000) and H_(δ,A)) to determine star formation histories. Together with an independent measurement
of number density of galaxies in each bin of the color-magnitude plot, one can infer
the rate at which galaxies from a given sample are transiting through that bin. Measuring this
value for all magnitude values, studies at lower redshift determined that the mass flux density
in the green valley is comparable to both the mass build-up rate of the red sequence and the
mass loss rate from the blue cloud. We show preliminary results for our intermediate redshift
sample
Gluon saturation and Feynman scaling in leading neutron production
In this paper we extend the color dipole formalism to the study of leading
neutron production in collisions at high energies
and estimate the related observables, which were measured at HERA and may be
analysed in future electron-proton () colliders. In particular, we
calculate the Feynman distribution of leading neutrons, which is
expressed in terms of the pion flux and the photon-pion total cross section. In
the color dipole formalism, the photon-pion cross section is described in terms
of the dipole-pion scattering amplitude, which contains information about the
QCD dynamics at high energies and gluon saturation effects. We consider
different models for the scattering amplitude, which have been used to describe
the inclusive and diffractive HERA data. Moreover, the model dependence of
our predictions with the description of the pion flux is analysed in detail. We
show that the recently released H1 leading neutron spectra can be reproduced
using the color dipole formalism and that these spectra could help us to
observe more clearly gluon saturation effects in future colliders.Comment: 10 pages, 5 figure
Lyman Break Analogs: Constraints on the Formation of Extreme Starbursts at Low and High Redshift
Lyman Break Analogs (LBAs), characterized by high far-UV luminosities and
surface brightnesses as detected by GALEX, are intensely star-forming galaxies
in the low-redshift universe (), with star formation rates reaching
up to 50 times that of the Milky Way. These objects present metallicities,
morphologies and other physical properties similar to higher redshift Lyman
Break Galaxies (LBGs), motivating the detailed study of LBAs as local
laboratories of this high-redshift galaxy population. We present results from
our recent integral-field spectroscopy survey of LBAs with Keck/OSIRIS, which
shows that these galaxies have the same nebular gas kinematic properties as
high-redshift LBGs. We argue that such kinematic studies alone are not an
appropriate diagnostic to rule out merger events as the trigger for the
observed starburst. Comparison between the kinematic analysis and morphological
indices from HST imaging illustrates the difficulties of properly identifying
(minor or major) merger events, with no clear correlation between the results
using either of the two methods. Artificial redshifting of our data indicates
that this problem becomes even worse at high redshift due to surface brightness
dimming and resolution loss. Whether mergers could generate the observed
kinematic properties is strongly dependent on gas fractions in these galaxies.
We present preliminary results of a CARMA survey for LBAs and discuss the
implications of the inferred molecular gas masses for formation models.Comment: To appear in the proceedings of IAU Symposium 277, "Tracing the
Ancestry of Galaxies on the Land of our Ancestors", eds. C. Carignan, K.C.
Freeman, and F. Combe
I am avoiding it! a seniors' perspectives about advertising
The aims are to analyze (i) the relationship between drivers to ad avoidance among senior
viewers and (ii) compare the perceptions about those drivers between TV advertising and
YouTube advertising. Findings reveal that irritation seems to be the crucial factor that lead
consumers to avoid whacking advertisings. A negative attitude toward advertising and
skepticism do not mediate the effect between advertising irritation and avoidance.info:eu-repo/semantics/acceptedVersio
No-horizon theorem for spacetimes with spacelike G1 isometry groups
We consider four-dimensional spacetimes which obey the
Einstein equations , and admit a global spacelike
isometry group. By means of dimensional reduction and local
analyis on the reduced (2+1) spacetime, we obtain a sufficient condition on
which guarantees that cannot contain apparent
horizons. Given any (3+1) spacetime with spacelike translational isometry, the
no-horizon condition can be readily tested without the need for dimensional
reduction. This provides thus a useful and encompassing apparent horizon test
for -symmetric spacetimes. We argue that this adds further evidence
towards the validity of the hoop conjecture, and signals possible violations of
strong cosmic censorship.Comment: 8 pages, LaTeX, uses IOP package; published in Class. Quantum Gra
Different faces of the phantom
The SNe type Ia data admit that the Universe today may be dominated by some
exotic matter with negative pressure violating all energy conditions. Such
exotic matter is called {\it phantom matter} due to the anomalies connected
with violation of the energy conditions. If a phantom matter dominates the
matter content of the universe, it can develop a singularity in a finite future
proper time. Here we show that, under certain conditions, the evolution of
perturbations of this matter may lead to avoidance of this future singularity
(the Big Rip). At the same time, we show that local concentrations of a phantom
field may form, among other regular configurations, black holes with
asymptotically flat static regions, separated by an event horizon from an
expanding, singularity-free, asymptotically de Sitter universe.Comment: 6 pages, presented at IRGAC 2006, Barcelona, 11-15 July 200
Strong curvature singularities in quasispherical asymptotically de Sitter dust collapse
We study the occurrence, visibility, and curvature strength of singularities
in dust-containing Szekeres spacetimes (which possess no Killing vectors) with
a positive cosmological constant. We find that such singularities can be
locally naked, Tipler strong, and develop from a non-zero-measure set of
regular initial data. When examined along timelike geodesics, the singularity's
curvature strength is found to be independent of the initial data.Comment: 16 pages, LaTeX, uses IOP package, 2 eps figures; accepted for
publication in Class. Quantum Gra
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