6,685 research outputs found
Intergalactic Transmission and its Impact on the Ly{\alpha} Line
We study the intergalactic transmission of radiation in the vicinity of the
Ly{\alpha} wavelength. Simulating sightlines through the intergalactic medium
(IGM) in detailed cosmological hydrosimulations, the impact of the IGM on the
shape of the line profile from Ly{\alpha} emitting galaxies at redshifts 2.5 to
6.5 is investigated. In particular we show that taking into account the
correlation of the density and velocity fields of the IGM with the galaxies,
the blue part of the spectrum may be appreciably reduced, even at relatively
low redshifts. This may in some cases provide an alternative to the
often-invoked outflow scenario, although it is concluded that this model is
still a plausible explanation of the many asymmetric Ly{\alpha} profiles
observed. Applying the calculated wavelength dependent transmission to
simulated spectra from Ly{\alpha} emitting galaxies, we derive the fraction of
photons that are lost in the IGM, in addition to what is absorbed internally in
the galaxies due to dust. Moreover, by comparing the calculated transmission of
radiation blueward of the Ly{\alpha} line, the total optical depth to Thomson
scattering of cosmic microwave background, with corresponding observations, we
are able to constrain the epoch when the Universe was reionized to z <~ 8.5.Comment: Substantially extended, ~30 references added, 1.5 page extra (article
style) in particular on the impact of the IGM at z~5.8 and z~6.5, 2 extra
figures, unnecessary fluff cut out, accepted for publication in Ap
Boltzmann equation simulation for a trapped Fermi gas of atoms
The dynamics of an interacting Fermi gas of atoms at sufficiently high
temperatures can be efficiently studied via a numerical simulation of the
Boltzmann equation. In this work we describe in detail the setup we used
recently to study the oscillations of two spin-polarised fermionic clouds in a
trap. We focus here on the evaluation of interparticle interactions. We compare
different ways of choosing the phase space coordinates of a pair of atoms after
a successful collision and demonstrate that the exact microscopic setup has no
influence on the macroscopic outcome
Lyman alpha Resonant Scattering in Young Galaxies - Predictions from Cosmological Simulations
We present results obtained with a 3D, Ly alpha radiative transfer code,
applied to a fully cosmological galaxy formation simulation. The developed
Monte Carlo code is capable of treating an arbitrary distribution of source Ly
alpha emission, neutral hydrogen density, temperature, and peculiar velocity of
the interstellar medium. We investigate the influence of resonant scattering on
the appearance and properties of young galaxies by applying the code to a
simulated "Lyman Break Galaxy" at redshift z = 3.6, and of star formation rate
22 M_sun/yr and total Ly alpha luminosity 2.0 X 10^43 erg/s. It is found that
resonant scattering of Ly alpha radiation can explain that young galaxies
frequently are observed to be more extended on the sky in Ly alpha than in the
optical. Moreover, it is shown that, for the system investigated, due to the
anisotropic escape of the photons, the appearent maximum surface brightness can
differ by a factor of ~15, and the total derived luminosity by a factor of ~4,
depending on the orientation of the system relative to the observer.Comment: Letter updated to match version published in Ap
Feeding behaviour of adult Centropages hamatus (Copepoda, Calanoida): Functional response and selective feeding experiments
The feeding behaviour of adults of the marine calanoid copepod Centropages hamatus was studied in laboratory experiments with ciliates and phytoplankton as food sources. The ingestion rate of algal (flagellates, diatoms) and ciliate prey (oligotrichs) as a function of prey concentration could be described by a Holling type III functional response. with close to zero ingestion rates at concentrations below 5 mu g Cl-1. In general, ingestion of ciliates was higher than ingestion of algae, and maximum feeding rates by adult males reached were half the feeding rates of adult females at prey concentrations exceeding 50 mu g Cl-1. When diatoms and ciliates were offered together C. hamatus (both sexes) fed exclusively on ciliates as long as they contributed with more than 5% to the mixture. This indicates the capability of active prey selection and switching between suspension feeding and ambush predation. Therefore, the feeding behaviour of adult C hamaths can be characterised as omnivorous with a preference for larger motile prey. This implies a trophic level above two, if there is a sufficient abundance of protozoan food available. (C) 2009 Elsevier B.V. All rights reserved
Escape of ionizing radiation from star forming regions in young galaxies
Using results from high-resolution galaxy formation simulations in a standard
Lambda-CDM cosmology and a fully conservative multi-resolution radiative
transfer code around point sources, we compute the energy-dependent escape
fraction of ionizing photons from a large number of star forming regions in two
galaxies at five different redshifts from z=3.8 to 2.39. All escape fractions
show a monotonic decline with time, from (at the Lyman-limit) ~6-10% at z=3.6
to ~1-2% at z=2.39, due to higher gas clumping at lower redshifts. It appears
that increased feedback can lead to higher f_esc at z>3.4 via evacuation of gas
from the vicinity of star forming regions and to lower f_esc at z<2.39 through
accumulation of swept-up shells in denser environments. Our results agree well
with the observational findings of \citet{inoue..06} on redshift evolution of
f_esc in the redshift interval z=2-3.6.Comment: four pages, four figures, submitted to ApJ
- …